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Anthropogenic alterations of fluvial sediment supply to the San Pedro Littoral Cell of California
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Anthropogenic alterations of fluvial sediment supply to the San Pedro Littoral Cell of California
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INFORMATION TO USERS This manuscript has been reproduced from the microfilm master. UM I films the text directly from the original or copy submitted. Thus, some thesis and dissertation copies are in typewriter face, while others may be from any type of computer printer. The quality of this reproduction is dependent upon the quality of the copy submitted. Broken or indistinct print, colored or poor quality illustrations and photographs, print bleedthrough, substandard margins, and improper alignment can adversely affect reproduction. In the unlikely event that the author did not send U M I a complete manuscript and there are missing pages, these w ill be noted. Also, if unauthorized copyright material had to be removed, a note w ill indicate the deletion. Oversize materials (e.g., maps, drawings, charts) are reproduced by sectioning the original, beginning at the upper left-hand comer and continuing from left to right in equal sections with small overlaps. Photographs included in the original manuscript have been reproduced xerographically in this copy. Higher quality 6” x 9" black and white photographic prints are available for any photographs or illustrations appearing in this copy for an additional charge. Contact U M I directly to order. ProQuest Information and Learning 300 North Zeeb Road, Ann Arbor. M l 48106-1346 USA 800-521-0600 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ANTHROPOGENIC ALTERATIONS OF FLUVIAL SEDIMENT SUPPLY TO THE SAN PEDRO LITTORAL CELL OF CALIFORNIA by Kamron Michele Barron A Thesis Presented to the FACULTY OF THE GRADUATE SCHOOL UNIVERSITY OF SOUTHERN CALIFORNIA In Partial Fulfillment of the Requirements for the Degree MASTER OF ARTS (GEOGRAPHY) August 2001 Copyright 2001 Kamron Michele Barron R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. UMI Number: 1409577 _ ___ _( g > UMI UMI Microform 1409577 Copyright 2002 by ProQuest Information and Learning Company. All rights reserved. This microform edition is protected against unauthorized copying under Title 17, United States Code. ProQuest Information and Learning Company 300 North Zeeb Road P.O. Box 1346 Ann Arbor, Ml 48106-1346 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. UNIVERSITY O F S O U T H E R N CALIFO RN IA THE GRADUATE SCHOOL UNIVERSITY RARK LOS ANGELES. CALIFORNIA S0007 This thesis, written by Kamron Michele Barron_______________ _____ under the direction of h J Z J L Thesis Committee, and approved by all its members, has been pre sented to and accepted by the Dean of The Graduate School, in partial fulfillment of the requirements for the degree of Master of Arts C m s Date AujKs tm7J_2001___ THESIS COMMITTEE t R eproduced with perm ission of the copyright owner. Further reproduction prohibited without permission. Acknowledgements I would like to gratefully acknowledge the ideas and encouragement of Dr. Doug Sherman during the course o f this work. I would also like to thank Dr. Bemie Bauer and Dr. Rod McKenzie for their input in the final stages of this thesis. Additionally, the support of Kim Sterrett at the California Department of Boating and Waterways helped make this possible. Several representatives from the United States Army Corps of Engineers, Los Angeles County Department of Public Works and the California Division of Mines and Geology made significant contributions in the form of data and details. Without their involvement and willingness to discuss issues in depth, I would not have been able to successfully complete the goals of this thesis. I am grateful for the continuous support provided by other faculty, staff and students in the Department of Geography. And, I would especially like to thank my family who has encouraged me throughout this process. R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table of Contents Acknowledgements..........................................................................................................i i List of Figures and Tables.............................................................................................. iv Chapter 1: Introduction.....................................................................................................1 Chapter 2: Conceptual Background............................................................................... 12 Chapter 3: Regional Background................................................................................... 30 Chapter 4: Data Sources and Analysis...........................................................................72 Chapter 5: Results........................................................................................................... 81 Chapter 6: Conclusion..................................................................................................103 Works Cited................................................................................................................. 111 Appendices...................................................................................................................120 iii R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. List of Figures and Tables Figure 1-1: Impact of dams on sediment supply to beaches......................................... 4 Figure 1-2: The Los Angeles, San Gabriel and Santa Ana rivers are inputs to the San Pedro Cell........................................................................................... 5 Figure 1-3: Breakwaters, groins and other coastal structures influence littoral transport of sand on this Ventura County shoreline.......... 8 Figure 1-4: Computer-generated image o f the results of a simulated beach nourishment project............................................................................................10 Figure 2-1: La Tuna Canyon Debris Basin, built by L.A. County Flood Control District in 1955, shown in winter 2000............................................................ 21 Figure 2-2: The spillway of Hansen Dam, completed by the U.S. Army Corps of Engineers in 1940...............................................................................................22 Figure 3-1: Features of the Los Angeles Basin............................................................ 32 Figure 3-2: A 1917 view of Los Angeles..................................................................... 35 Figure 3-3: Los Angeles County Department of Public Works Dams.......................47 Figure 3-4: Seven United States Army Corps of Engineers structures...................... 49 Figure 3-5: Construction of dams in the Los Angeles River and San Gabriel River watersheds...............................................................................................50 Figure 3-6: Construction of debris basins in the Los Angeles River and San Gabriel river watersheds....................................................................................51 Figure 3-7: Los Angeles County Department of Public Works Debris Basins......... 53 Figure 3-8: Sand and gravel mining in the San Gabriel Fan in Irwindale..................59 Figure 3-9: Production-consumption regions in the Los Angeles area...................... 61 Figure 3-10: The Consumnes River near Sacramento is one of a handful of free-flowing rivers in California...................................................................... 63 Figure 3-11: The San Gabriel River is one of several heavily altered Southern California rivers................................................................................ 64 Figure 3-12: Orange County beaches downcoast of the Los Angeles and San Gabriel rivers.....................................................................................................68 Figure 5-1: LACDPW dam capacity in comparison to sediment deposition............83 Figure 5-2: Maximum debris capacity of basins in the LA and SG watersheds........87 Figure 5-3: Debris deposition in basins in the LAR and SGR watersheds................89 Figure 5-4: Total amount o f debris production by year recorded for individual basins’ maximum event in the LAR and SGR watersheds............................. 92 Figure 5-5: Total impact of maximum debris events in the LA and SG watersheds..94 Figure 5-6: PCC aggregate reserves and consumption by P-C region....................... 97 Figure 5-7: Aggregate production in Los Angeles County from 1960 to 1992....... 98 Table 2-1: Components of a sediment budget............................................................. 16 Table 3-1: Dam and debris basin construction by decade.......................................... 54 Table 3-2: Distribution of dams and debris basins in the LAR and SGR watersheds......................................................................................................... 56 iv permission of the copyright owner. Further reproduction prohibited without permission. Chapter I—Introduction Beaches exemplify a cultural and visual identity for the Southern California region. They provide aesthetic benefits to the state’s coastal communities; however, their influence is not restricted to the narrow stretch of sandy shore. Beaches are a financial boon to coastal cities and beyond, provide critical habitat for species ranging from worms to sea lions and are also often linked to the lifestyle of the region. Beach tourism and recreation bring dollars that are vital to the regional, state and federal economies. California’s shoreline, 1,067 miles in length (and longer when embayments and offshore islands are included), generated $14 billion dollars in direct revenue in 1998 (King, 1999). That is about $13 million dollars per year for every mile of shoreline. With sand beaches attracting larger crowds than cliffs and gravel beaches, this dollar value can be considered much higher for sand beaches. There are about 700 miles of sand beaches in California (Inman, 1980), translating to about $20 million in direct revenue per mile of beach. When the indirect and induced benefits of beach-related spending are calculated, the total contribution to the national economy is $73 billion (King, 1999). With the economies of many locales dependent on coastal recreation and tourism, there are many jobs at stake. California beaches provided more than 883,000 jobs for people across the United States in 1998 (King, 1999), and 3l /i R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. percent of all jobs in California—approximately 500,000—are supported by coastal tourism (Eichblatt, 1998). Beyond the economic factors, California’s beaches provide valuable habitat for many species of plants and animals. Sand beaches provide habitat for burrowing animals— like crabs, shellfish and worms—and other organisms inhabit the drier upper beach (Bird, 1996). A number of other animals rely upon these beach inhabitants for their meals and are thus dependent on the coastal ecosystem. Birds, like endangered brown pelicans and least terns, gather on cliffs and marshes in Southern California (USACE, 1972). Some birds in the region rely almost exclusively on sand beaches, including snowy plovers and willets (USACE, 1972). Large mammals, such as harbor seals and the California sea lion, may also visit local beaches (USACE, 1972). The beach is also a cultural commodity, an integral part o f the state’s image (Sherman, 1997). It is a backdrop for movies and other entertainment media such as Baywatch, and this coastal imagery is disseminated to the rest of the world. To residents, the beach is part of the vacation circuit. Nine out of 10 California residents visit the state’s beaches each year, and total attendance is greater than at Disneyland, Disneyworld and all of the national parks combined (Eichblatt, 1998). Beaches are a destination for sunbathers, fishermen, boaters, swimmers and surfers. All contribute to this cultural identity. R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. Meanwhile, California’s beaches are disappearing. Of the 1,067 miles of shoreline in the state, about 925 miles are eroding (Eichblatt, 1998), leaving the state’s most visible and valuable physical asset in a vulnerable situation. There is little question as to the importance of the beach to the livelihood o f California. However, the state lacks a comprehensive policy to deal with its coastal problems, particularly erosion (Griggs, 1998). There are three basic options immediately available to counter risks of shoreline erosion—remove or relocate threatened structures, nourish the beach or armor the shoreline (Griggs, 1998). These responses are often reactionary, more often than not relying upon structures like groins, seawalls and rock revetments to protect valuable coastal property (Moore, 1998). State residents are caught in a predicament of which few are aware. Development adjacent to the shoreline and in the coastal plain is prevalent and popular, but requires alterations to the environment to make such habitation possible. These modifications—including adjustments to the river, land and coastline—have intruded heavily upon a natural system that transports sediment to the beach and down the coast. The same things attracting people to the coast— the views, sandy beaches and the natural scenery—are the same things being threatened by development. In many regions, the dominant sources of beach sand are the rivers and streams that erode and entrain sediment for delivery to the coast. However, early settlers were in need of a reliable supply of water and were unable to cope with 3 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. the unpredictable nature o f river flooding. Their settlements were often in the risk-prone floodplains, attractive due to the fertile soils, which prompted the establishment of extensive water-regulating structures early on. The construction of dams often accompanied the arrival of human settlers and the structures were subsequently followed by the modification of sediment transport in these rivers, as seen in Figure 1-1. Source: Bird (1996) Figure 1-1: Impact of dams on sediment supply to beaches This thesis will address how human activities and structures associated with the urbanization of Los Angeles County, including dams, debris basins (sediment-retaining basins) and sand mining, have directly or indirectly impacted fluvial san d supply d istributed along co ast 1 . Without Dam dim inished ‘luviai sand supoly resu lts in beach ero sio n 2. With Dam R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. the availability of beach sand by rivers. The extensive development has nearly eliminated the supply o f beach sand by the region’s two primary rivers, the Los Angeles and San Gabriel. Other small streams exist in the region, but these mainly drain urban areas and carry little or no sediment. The Los Angeles and San Gabriel rivers originate in the Santa Monica and San Gabriel mountains and transport sediment to the San Pedro Littoral Cell (Figure 1-2). This coastal cell extends from the Palos Verdes Peninsula to the Newport Submarine Canyon and these two rivers (along with a third, Orange County’s Santa Ana River) were the primary sediment sources. Today, natural sand sources are limited and, increasingly, non-natural sources, including beach nourishment, are relied upon to maintain the beaches in the San Pedro Littoral Cell. LOS ANGELES SAN PEDRO CELL Ne*»pon\ CanyorK (Adapted from Inman. 1980) Figure 1-2: The Los Angeles, San Gabriel and Santa Ana rivers (whose outlets are represented by arrows) are inputs to the San Pedro Littoral Cell 5 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. Other studies have examined littoral cells in California (and elsewhere) and have determined the components of their sediment budgets that quantitatively explain the sources and sinks of sand in littoral cells. Studies related to the San Pedro Cell and Los Angeles region, however, have been limited in scope and certainty. Portions o f the area’s sediment budget have been studied with varying degrees of success (Brownlie and Taylor, 1981; Flick, 1993); this thesis will summarize the previous findings and quantify the extent of impact by inland structures and activities on the sediment supply. This will be accomplished by using agency-compiled data documenting sand entrapment or removal in the region’s dams, debris basins and sand mining operations. Data and interviews with agency officials were obtained from the United States Army Corps of Engineers, the Los Angeles County Department of Public Works and the California Division of Mines and Geology. The purpose of this thesis is to gain a better understanding of the impact of extensive and rapid urbanization on the reduction of sand supplies available for transport to the coastline. Using a sediment budget approach to examine contributions to the San Pedro Littoral Cell will allow quantification of the scope of sediment transport interruption induced by dams, debris basins and sand mining. There are, of course, other sediment-affecting modifications of the Los Angeles region that are not as easily quantified and whose impact is often indirect. Chief among these, the paving over o f many square miles of pervious 6 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. soil throughout the region has led to a greater peak in the region’s hydrograph (Mount, 1995). This is expressed as a larger and a more rapid arrival of floodwaters as water cannot be absorbed or slowed by permeable ground (Mount, 1995). This increased surface flow would typically increase the transport of sediment. However, the paving of surfaces prevents the erosion of surface materials, reducing the amount o f sediment available for transport. The paving of the riverbed itself, known as channelization, has removed the baseflow component of the river system, thwarted the natural tendency of a river to modify its channel and prevented the bank-river exchange o f sediments that would normally occur. However, these alterations of the fluvial environment are usually preceded by the structures (dams and debris basins) directly interfering with the transport of sediment that can be quantified through empirical observation. Throughout California, dams are a contentious issue due to their impact on fisheries and sediment transport. There are more than 1,400 dams in the state, ranging from large structures involved in water delivery to others used for flood control or recreation, all of which combine to make the state the site of the largest water-engineering project in the world (Mount, 1995). Much of the need for these structures was brought about by the tremendous 20lh century growth of California’s population—from 1.5 million to more than 34 million (Mount, 1995). An unexpected consequence of this population and construction growth has been the near-obliteration of sand-supplying mechanisms associated with rivers and streams. This has resulted in lower rates of sand delivery to the coast. 7 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. As urbanization has spread at an epidemic rate in many areas o f California, the need for construction materials and protection for hillside housing from debris flows has led to an even greater depletion of sand resources and deliveries. The general response to shoreline erosion has been to add more structures—groins, jetties, revetments, and seawalls—to the coastline to salvage sand supplies and protect coastal property (Komar, 1996). These are often used alone or in combination with one another to help maintain the eroding shoreline and prevent further retreat. An example of this can be seen in Figure 1-3. These methods often have adverse effect. Seawalls, for example, can lead to the depletion of the beaches that front them, while groins and breakwaters interrupt longshore transport and initiate downshore erosion (Bird, 1996). Approximately 12 percent, or 130 miles, of California’s coast has been armored with such structures (Griggs, 1998), predominantly within the Southern California region. (Noble Consultants) Figure 1-3: Breakwaters, groins and other coastal structures influence littoral transport of sand on this Ventura County shoreline 8 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. Nourishment of beaches with offshore, harbor or inland sand supplies has become a popular alternative to the hard-stabilization methods described above. The photos in Figure 1-4 simulate the outcome of beach nourishment to gamer support for a regional nourishment project in San Diego. Between 1919 and 1978 there were approximately 600 nourishment projects along the California coast (Bird, 1996). The 30 years prior to 1978 comprise the period during which much of the construction along the California coast occurred (Griggs, 1998), so the full impact of beach erosion and the need to counter it has been seen to a greater degree during more recent times. Los Angeles County added 3 million cubic yards of sand to its beaches between 1981 and 1997 (Fischer, 1998). Between 1940 and 1990, the shoreline from Sunset Beach to Newport Beach has received nearly 400,000 cubic yards of sand each year (Flick, 1993). This “soft” method o f beach recovery, also known as replenishment or restoration, can be effective with careful planning and regular maintenance in certain situations, but oftentimes it can be a large expense that only results in a temporary relief to the erosion problem (Bird, 1996). As beaches are nourished, depending upon the material type and the wave and shoreline characteristics, much of the sand may be quickly washed offshore or downshore (Bird, 1996). 9 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. (SANDAG) Figure 1-4: Computer-generated image of the results of a simulated beach nourishment project The combined impact of all of these structures and the development of California has led to a number of chronic shoreline erosion problems that pose “a substantial threat to property, coastally dependent economic enterprise, and aspects of coastal ecosystems” (Sherman, 1997, 550). As of the mid-1980s, 86 percent of the state’s 1,067 miles of coastline was undergoing erosion, and more than 11 percent of that erosion was deemed very critical (Griggs and Savoy, 1985). As the state is dependent—economically, environmentally and 10 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. aesthetically—upon its shoreline resources, it is imperative for the coastal erosion problem to be addressed and mitigated. The current state of the problem and the human response to it can be seen as unsustainable. The solution to one problem often leads to the creation of a new one, especially when non-natural structures are involved. The primary tool that should be employed in evaluating remedial actions is to explore the natural and altered sediment-transporting conditions (Komar, 1996). By quantitatively assessing sources and sinks of sand, as well as the extent of human alterations of these, more knowledgeable insight into potential solutions will be available (Komar, 1996). R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. Chapter II—Conceptual Background The term sand refers to a size of material that ranges in diameter from 0.0625 millimeters to 2 millimeters (USACE, 1984a; Bird, 1996; Komar, 1998). Sand particles are typically single-mineral grains, unlike gravel and larger material that are often multi-mineral rock fragments (USACE, 1984a). Weathering of rocks can occur through chemical (decomposition of minerals) and physical (disintegration and/or dislodgement) processes, although chemical weathering is usually the dominant factor in California (Mount, 1995). Through these processes, which usually are linked, rocks, gravel, sand and fine sediment are gradually broken down from larger materials (Mount, 1995). The potential for particle decomposition and disintegration is dependent on a number of characteristics, especially the composition of the parent material and the degree o f stress being placed on it. Materials are made more vulnerable to erosion, the process of carrying away the material, as these processes occur (Mount, 1995). Sand is of particular importance in the composition o f beaches, which are distinguished as the accumulation of unconsolidated materials extending from the mean low-tide line to a physiographic change of surface (Komar, 1998). Sand is the most likely sediment size to be transported to and remain on the beach. Rocks and gravel are often incapable of being transported to beach sites by rivers during normal flow, while finer sediments on beaches are usually quickly entrained by waves or are carried directly offshore while suspended in the fluvial discharge. 12 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. While sand may appear ordinary, in actuality it is a dynamic entity influenced by a number of factors. It often is the primary component on the beach. However, the processes that deliver it to and remove it from the beach as well as the geographic boundaries influencing its placement are less apparent. These processes and boundaries, however, are responsible for the status of a beach, whether it is experiencing growth, remaining stable or undergoing erosion. Littoral Cells Along the U.S. West Coast, sand on the beach moves in a direction dictated by nearshore circulation, a general northwest-to-southeast or north-to- south direction along most of the coastline. (This is reversed for a short distance in San Diego County.) There are, however, physical obstructions that prevent a continuous transfer of sediments in these directions. Along most coastlines, littoral cells can be defined by these interruptions that can include headlands and submarine canyons. Littoral cells are coastal compartments that include a source o f beach sand and an eventual sink for beach sand, which can be related to these large-scale geographic features that exist on the coastline (Inman and Frautschy, 1966; Komar, 1996; Komar, 1998). Inman and Frautschy (1966) developed the concept of a littoral cell along the Southern California coast. Distinct cells were recognized in this region 13 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. (shown in Appendix I), including the Santa Barbara Cell, Santa Monica Cell, San Pedro Cell, Oceanside Cell and the Silver Strand Cell (Inman, 1980). There is little or no interaction between these cells (Inman, 1980; Best and Griggs, 1991), although sub-cells can also be observed within these cells as determined by the location of inputs, outputs, coastline configurations and man-made structures (Komar, 1996). For example, the San Pedro Cell begins below the headlands of the Palos Verdes Peninsula and concludes at the Newport Submarine Canyon. There are smaller sub-cells created by jetties associated with the development of the San Pedro and Long Beach harbors as well as groins and breakwaters on many of the downcoast beaches. This is common in many coastal regions in close proximity to development. The Oceanside Cell, for example, had at least six identifiable sub-cells by the mid-1980s with several related to man-made structures (USACE, 1984b). Sediment Budget Within each littoral cell there are defined boundaries that contain the cell’s own inputs, transport rates and losses to sinks (Inman, 1980). The concept that explains the existence o f a beach and the related processes that form it is encompassed in the idea of a sediment budget (Bowen and Inman, 1966). It applies the principle of conservation of mass to beach sediments, which asserts “the time rate of change of sand within the system is dependent upon the rate at 14 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. which sand is brought into the system versus the rate at which sand leaves the system” (Komar, 1998, 66). This may be expressed simply as: Credits-Debits=Beach Accretion or Erosion In this expression, if credits (sediment sources) are greater than debits (sediment sinks), then the beaches will accrete. If the credits are less than the debits, then the beach will erode. If the credit and debit terms are equal to one another, then the beach will remain stable, or is said to be in a state of equilibrium. Examples of sources and sinks of sediment are included in Table 2-1. The sediment budget should reflect, to a reasonable degree of accuracy, what is being viewed visually in terms of accretion or erosion of sand on the beach (Bowen and Inman, 1966; Komar, 1996; Komar, 1998). If a sediment budget predicts erosion, then erosion should be seen at the site being examined, and vice versa for accretion. If there is a divergence from the quantitative assessment to the visual observations, a red flag is raised, indicating that another process could be taking place that was not previously known or expected (Komar, 1996). Sources and sinks are further defined by the extent of the area where they occur (USACE, 1984a). Point sources or sinks (such as tidal inlets) occur in a limited area, while line sources or sinks (like wind transport of sand) affect an extended segment (USACE, 1984a). R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. Sources Sinks Balance Longshore Transport In Longshore Transport Out Beach Erosion Onshore Transport Offshore Transport OR Wind Transport Onto Wind Transport Away Beach Accretion River Transport Submarine Canyon Deposition Sea-Cliff Erosion Mining Biogenous Deposition Hydrogenous Deposition Beach Nourishment Table 2*1: Components of a Sediment Budget Sources of sand to a beach vary greatly and are dependent upon the characteristics of the surrounding land. The most common natural sand sources include river transport, sea-cliff erosion and longshore transport (USACE, 1984a; Komar, 1998), while offshore-to-onshore transport, wind transport, hydrogenous (sediments derived from chemical synthesis) and biogenous (sediments derived from marine organisms, usually shells) deposition can also occur and add to the beach (Komar, 1998). The sediment budget concept also allows for consideration of anthropogenic sources, primarily beach nourishment, which is capable of contributing large volumes o f sediment to a beach (Komar, 1996; Komar, 1998). Considering the California coastline in its entirety, supplies of beach sand are typically derived from cliff and bluff retreat and fluvial sediment sources (Griggs, 1987a; Griggs, 1987b). Cliffs and bluffs are less common in Southern California and are often developed, as is the case in San Diego County, where cliffs and bluffs must be stabilized to protect homes that are atop them. Rivers and streams are thus the primary natural suppliers of beach sand to the Southern California coastline (Griggs, 1987). 16 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. In general, the fluvial transport of sand to the beach is dependent upon the geologic material within the catchment, the slope, the intensity of precipitation and runoff, the effects of earthquakes and volcanic eruptions, as well as the vegetative cover (Bird, 1996). Steep slopes, for example, allow for easy transport of material, while earthquakes and volcanic eruptions may provide a large amount of loose material that can be eroded and conveyed by the river. Slopes lacking vegetation have significantly faster runoff rates and greater discharges compared to slopes that have a vegetative cover that interrupts, retards and recycles rainfall (Bird, 1996). These and additional factors affect the amount and type of sediment delivered. If a river is a dominant sediment provider, the beach will reflect the composition of the inland material being carried by the waterway. Large rivers, which account for most of the volume o f sediment delivered to the world’s oceans, actually provide very little sand (USACE, 1984a), while more than half of the material carried by smaller rivers passing through sandy drainage areas may be sand sized (Chow, 1964). There is, in fact, a fluvial sediment budget that is similar in concept to the littoral cell sediment budget in that there are sources and sinks of sediment supply along rivers and streams. Sources include the weathering and erosion of upland materials, the entrainment of bed materials and a number of human-generated sediment supplies. Sinks include deposition in the channel, deposition in the floodplain and a number of man- made sinks, such as dams and debris basins that trap sediment. Therefore, fluvial 17 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. transport of sediment is dependent on a great number of characteristics that determine its eventual sediment yield. Sea-cliff erosion depends upon the geologic material type as well as the erosive forces, in this case, the waves and current (Bird, 1996). Some of the more typical rock types being eroded include sedimentary rocks and chalk cliffs, which often produce shingle beaches (Bird, 1996). Attrition of sea cliffs will continue as long as the eroded material is moved from the site, either by being transferred downshore or offshore (Bird, 1996). Longshore transport o f sediment, with a net direction parallel to the shoreline (US ACE, 1984a), occurs as a result of waves and longshore currents (Komar, 1996). Sediment transferred by this means occurs as either bedload or suspended load transport (USACE, 1984a) and is most effective in areas where the shoreline is open and free from headlands and other natural or man-made obstacles (Komar, 1996). There can be gains and losses expected due to other processes that occur independent of littoral transport, including wind transport. Losses within a littoral cell are most often related to longshore transport out of an area, offshore transport (including deposition in submarine canyons) and wind transport shoreward (Komar, 1998). Other factors include human generated losses such as sand mining in the nearshore region (Komar, 1998). R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. Littoral System Variations Changes o f sediment supply or other conditions within littoral systems can occur naturally, for example, in cases of drought when river discharges to the ocean decrease, or, frequently, as a result of man-made circumstances. With development increasingly focused on the shoreline and the coastal plains, the extent to which humans interfere with natural coastal processes has increased. Most directly, shore protection structures built on the shoreline cause immediate interruptions in the normal flow of sand. A small groin could reduce the amount of sand carried by littoral transport. This man-made protrusion, along with those of jetties and piers, can obstruct the path of sand, sometimes cutting off downcoast beaches from nourishment or directing the sand offshore. Looking beyond the coastal processes involved in the littoral system reveals the great influence inland fluvial processes have on sediment transport, a large credit to many littoral cells. A littoral sediment budget can be entirely altered following the construction of a dam or other structure on a sediment- delivering river as well as by other activities in the river’s watershed (Komar, 1998). While this situation is not directly a credit or debit in terms of the littoral cell’s sediment budget, it does reduce the size of one of its primary credits. This can greatly influence the eventual balance of a littoral cell. Structures affecting the sediment delivery of Southern California’s rivers include check dams, debris basins, flood control and water conservation dams, sand and gravel mining and channelization. These developments have increased 19 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. and become necessary with the ever-growing population and urbanization of the region. While these structures may have accomplished their intended goal, the repercussions of the modifications, including the entrapment o f beach sand, were not fully recognized or were deemed of less concern than the larger purpose of the structure (Brownlie and Taylor, 1981; Fall, 1981; Taylor, 1981). Check dams are small structures with heights of about three to five meters that are used in conjunction with each other to decrease the amount of large debris descending small streams and channels (Brown and Taylor, 1982). A variety of materials have been used to construct them, including loose rocks, combinations of wire and rocks, and concrete (Ferrell et al., 1959). Their use became significant in the mid-1800s in mountainous European countries where erosion and debris production is a concern (Ferrell et al., 1959). Placed deep in mountainous terrain, check dams trap large debris and reduce the gradient of the channel while allowing water and finer sediments to pass through (Brown and Taylor, 1982). There are typically several check dam structures throughout a mountainous watershed with debris basins and/or dams at the mouths of the canyons (Ferrell et al., 1959). Their impact is usually only temporary as clearing them is not a design feature and they are only capable of containing 102 to 103 cubic meters of material (Brown and Taylor, 1982). Debris basins are much larger structures constructed of concrete or earthen fill that can collect 104 to 105 cubic meters of debris (Brown and Taylor, 1982). Like the check dams, debris basins allow the through-flow of water and 20 R eproduced with perm ission of the copyright owner. Further reproduction prohibited without permission. fine sediment (Brown and Taylor, 1982). These structures, like La Tuna Canyon Debris Basin shown in Figure 2-1, are typically located near the mouths of small streams and channels (Brown and Taylor, 1982). As urbanization has spread into alluvial fans and floodplains, the construction o f debris basins has become necessary for property protection, catching debris flows as they descend canyons in the vicinity of development (Brown and Taylor, 1982). To ensure that the capacity of these structures can contain the flows, which resemble mudflows, they are periodically emptied so that their full capacity is available for the next debris flow event (Brown and Taylor, 1982). Figure 2-1: La Tuna Canyon Debris Basin, built by L.A. County Flood Control District in 1955, shown in winter 2000 Dams have been constructed for flood control, water conservation, storage, hydropower and recreational purposes. A compromise between flood control and water conservation has to be negotiated so that both goals can be reached (Brown and Taylor, 1982). Hansen Dam, shown in Figure 2-2, is an example. A portion of 21 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. the reservoir’s capacity has to be available to handle any envisaged flood event (Brown and Taylor, 1982). Though this diminishes its water conservation function, it serves to protect developed areas from flooding. While water is released periodically, particularly during seasons of heavy rain, usually only the fine sediments, contained in the washload, are transported (Brown and Taylor, 1982). This leaves any large debris and sediment that is too heavy to be transported to settle at the bottom of the retention structure after water has been drained (Brown and Taylor, 1982). Figure 2-2: The spillway of Hansen Dam, completed by the U.S. Army Corps of Engineers in 1940 Sand and gravel mining has been a popular practice for more than a century in Southern California (Gumprecht, 2000) and can take a variety of forms (Brown and Taylor, 1982; Sandecki, 1989). River sediments make ideal construction aggregate because the bedload is physically abraded and naturally graded, sorted and rounded (Sandecki, 1989). There are many methods of mining, including safe-yield mining (removing annual aggradation), streambed 22 R eproduced with perm ission of the copyright owner. Further reproduction prohibited without permission. skimming (removing individual gravel bars), instream pit mining (excavation from an active channel bed) and floodplain and terrace pit mining (Sandecki, 1989). To varying degrees, these operations directly remove sediment that has been deposited in and around river systems, an alteration which can cause additional modifications o f sediment transport by changing channel configurations or by trapping additional sediment in mining pits during flows (Sandecki, 1989). Channelization, the replacement of natural riverbeds and levees with concrete, reduces the unpredictability of rivers and their efforts to maintain equilibrium (Mount, 1995). This type of structure physically restrains the river in a fixed bed, leaving no opportunity to meander or make other adjustments to its channel (Mount, 1995). The natural exchange o f sediments through deposition and erosion between the river and its channel has been greatly altered as the channel bed materials are no longer free to be transported and vegetation is no longer abundant along the river’s banks to trap sediment or reduce the speed o f flow. Sediment budgets can quantitatively reflect the composition of littoral systems under natural conditions and subsequent to alterations. This is especially useful in the analysis of fluvial contributions to the budget and the changes that may occur due to river modifications, including dams and other structures. Sediment budgets are often the conceptual method used to examine such human interference (Komar, 1998). 23 R eproduced with perm ission of the copyright owner. Further reproduction prohibited without permission. Applying Sediment Budget and Littoral Cell Concepts Several examples of utilizing sediment budgets to reflect natural and man-made conditions exist. In Bowen and Inman’s (1966) study, quantitative estimates of the supply and loss of beach sands and rates of sediment transport for the Santa Barbara Littoral Cell were examined so that a budget of beach sand could be derived for the area. The regional characteristics of this cell, including climate, wave and currents, existing beaches and drainage basins, were examined. Upon identifying the major credits and debits to sediment budgets in general, Bowen and Inman (1966) analyzed those that directly affected the Santa Barbara Littoral Cell— longshore transport, onshore-offshore transport, wind transport, river transport, cliff erosion, submarine canyon deposition and mining. Many of these budget characteristics had been greatly affected by human alterations to the littoral cell, including the building of major dams on its primary sediment-delivering rivers (Bowen and Inman, 1966). Bowen and Inman (1966) maintained that using the sediment budget concept in studying such processes in littoral cells could allow the estimation of poorly defined sediment transport components based on those that have been more accurately determined. Qualitative aspects of cells and the processes occurring within them were fairly well understood, but quantitative knowledge was and is lacking (Bowen and Inman, 1966). This budget concept provided an 24 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. opportunity to employ knowledge about things that were understood—using such resources as maps, surveys, and climatic and wave conditions—to gather knowledge about things that required further comprehension (Bowen and Inman, 1966). It has become a concept upon which many studies exploring littoral processes have been based. Other studies that have employed littoral cell and sediment budget concepts are numerous. Examples can be found in Shih and Komar’s (1994) examination of sea cliff erosion impacts on the Lincoln City Littoral Cell in Oregon, Morelock’s (1987) study of biogenous contributions to western Puerto Rico’s sand budget, the Corps o f Engineers’ (1984b) examination of San Diego County’s littoral cells, Chesser and Peterson’s (1987) efforts to define and examine components of littoral cells and sub-cells in the Pacific Northwest, Best and Grigg’s (1991) sediment budget and boundary analysis of the Santa Cruz Littoral Cell, Grigg’s (1987b) examination o f the dredging of harbors based on their locations within a littoral cell, Osbome and Yeh’s (1991) analysis of grain shapes and coastal processes in the Oceanside Littoral Cell and its sub-cells and Galster and Schwartz’s (1990) research on the impact of dams and a shoreline structure on the sand budget of Ediz Hook in Washington. These are but a few examples of an even greater and broader extent of literature using littoral cell and sediment budget concepts in their methodologies. Komar (1996) undertook a study that reviewed the 30-year-old notion of a sediment budget and examined its quantitative evaluations and implementations 25 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. in various studies within those years. He found that the sediment budget concept has many uses that can infer characteristics of a littoral cell, but it does have some disadvantages (Komar, 1996). It is often difficult, and sometimes impossible, to quantify all o f the variables of a littoral cell as well as to achieve a balance between the numbers and what is observed (Komar, 1996). “But even then, undertaking the exercise can be fruitful, as it allows one to recognize that the construction of a dam on a river hundreds of kilometers away may ultimately have a destructive impact on the beach{.. .}”(Komar, 1996, 25). The methods of quantitatively assessing the credits and debits within a littoral cell differ in the studies based upon the components of the budget that are being examined. The use o f USGS gauging station data is among the most common ways to determine the sand input of rivers (Komar, 1996). Bowen and Inman (1966) recommended these gauging stations as a means of gathering data to apply to the Einstein Bed Load Formula, which can estimate rates of sediment transport at the bed-level of a river, including those that are sand-sized. A sediment rating curve relates sediment discharge to water discharge for a given stream (Graf, 1984; Morris and Fan, 1998), and was used when Best and Griggs (1991) developed a sediment budget for the Santa Cruz Littoral Cell. For rivers with comprehensive data sets, this is the most direct and reliable technique for determining river contributions (Komar, 1996). Many rivers, however, had stream-gauging stations installed only after alterations of the waterway took place. As a result, there is not a complete dataset 26 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. representing the waterway in natural conditions. In these cases, studies can use engineering formulae—involving river discharge, bed stress and flow power calculations (Graf, 1984) or rainfall data, drainage basin size and vegetative cover data (Morris and Fan, 1998)—to approximate river sediment contributions. These calculations are useful only in providing estimates, which do not always accurately reflect the actual events occurring. While equations are useful in gathering information that cannot be derived through observation or records, equations cannot account for all events or activities that could have occurred. They can only incorporate the variables that are known and understood. Whether river gauging stations or engineering formulae are used to derive sediment budget figures, the amount of material estimated to be acquired through means such as river transport must be amended to account for only the material that is of the right quality to remain on the beach (Komar, 1996). For example, fine sediment does not usually remain on the beach for very long (Komar, 1996) and would thus not play a crucial role in the actual sediment budget process. The Santa Cruz Littoral Cell study (Best and Griggs, 1991) analyzed existing sand on the beach to determine the appropriate grain size suitable for that area. The total volume of sediment estimated to be originating from the rivers was then adjusted to include only sand grain sizes that were found on that beach. 27 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. Utilization of the Sediment Budget Concept Using sediment budgets to examine what is transpiring in a coastal environment is a useful instrument in coastal management and in terms of understanding sediment passage along the coast (Best and Griggs, 1991). It should be the first step in investigating the causes and impacts of erosion (Komar, 1996). Determining solutions to erosion would often be the primary goal of employing a budget investigation, but the process can also advance knowledge o f the coastal region by organizing what is understood and where gaps still exist (Komar, 1996). It is important to recognize that a “complete sediment budget can only be achieved through an evolving process, building upon judicious interpretation of data as the data base is steadily increased and thus continuously curtailing the degree of freedom for untested hypotheses” (Dolan et al., 1987, 1303). This lends credence to the importance of individual, even small, contributions to the exploration of sediment budget components. Utilizing the sediment budget and littoral cell concepts in this examination of the Los Angeles region allows the study of some components of a larger process without requiring the complete explanation of all that is occurring. In this case, it permits an investigation o f the sediment transport interruption of inland structures and activities in Los Angeles and an examination of their role in the sediment budget of the San Pedro Littoral Cell and does not necessitate an assessment of other cell characteristics, such as wind transport or sea-cliff 28 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. erosion. The information gathered in this research can be applied then to other studies of the region in an attempt to identify the cause or scope of beach erosion and allow for the examination of potential solutions. R eproduced with perm ission of the copyright owner. Further reproduction prohibited without permission. Chapter III—Regional Background In Los Angeles the mountains verge upon the Pacific Ocean and, as a result, climate, landforms, soil and vegetation change drastically in a relatively small area. The particular combination of physical traits that formed the area created a distinctive, multifaceted environment. From a watershed perspective, there is a rather quick descent of runoff from the highest reaches of the surrounding Santa Monica and San Gabriel mountains through the local waterways and to the ocean. The Los Angeles River drops from 1,500 feet (457 meters) to sea level in 51 miles (82 kilometers) (LACDPW, 1999c) and, thus, has an average slope of 0.0056 (0.56%) over this distance. The San Gabriel River watershed drops from 10,000 feet (3,048 meters) to sea level in 37 miles (59.5 kilometers) (LACDPW, 1999c) and has an average slope of 0.051 (5.1%). The Mississippi River, in comparison, drops from 1,500 feet (457 meters) to sea level in 1,500 miles (933 kilometers)—30 times the distance it takes the Los Angeles River to do the same—(LACDPW, 1999c) and it has an average slope of 0.00019 (0.019%). The short traveling distance and steep gradient of the Los Angeles and San Gabriel rivers, however, would be an easy journey for water and the sediment they carry, especially during times of heavy flow, if not for the development that stands between the mountains and the ocean destination. Hundreds of structures protecting development not only reduce flood risks but also hinder the natural delivery of sediment to the beaches. Additionally, mining operations have 30 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. made use of sand and gravel from old riverbeds, alluvial fans and behind dams by removing the material for use in building the structures and streets that occupy the floodplain as well as constructing the dams that protect it. Examining the cause and effect o f the changes in one geographic area, in this case Los Angeles, will identify how development has transformed a once-natural system into one where tampering with nature is seen as the norm, or is not recognized at all. This may set the stage for recognizing the pros and cons of the current system and identifying new ways o f making what we have work. Two leading proposals heard within the Southern California region include decommissioning dams—ones said to have outlived their usefulness—or finding a way for Los Angeles’ trapped sand resources to be put to their most beneficial use, which could include nourishing local beaches with material dredged from nearby structures. Inland Characteristics Geologic Conditions Greater Los Angeles is circled by a series of mountain ranges, “youthful geomorphic terrain” (Fall, 1981), most of which were uplifted approximately 1 million years ago during the mid-Pleistocene era (Gumprecht, 1999). To the northwest are the Santa Monica Mountains and to the northeast are the San Gabriel Mountains, both part of the east-west trending Transverse Range (beginning about 65 million years ago during the Tertiary period) (Fall, 1981; Gumprecht, 1999). 31 R eproduced with perm ission of the copyright owner. Further reproduction prohibited without permission. Smaller mountain ranges and hills, including the Puente Hills, Santa Ana Mountains and the Palos Verdes Hills, exist to the east and to the south (as seen in Figure 3-1). However, the Santa Monica Mountains and especially the San Gabriel Mountains have the greatest influence on the rivers passing through the region. Los Angeles County S m 1 1 ilnn I W ■^M ountains Glendale Santa Monica Mount; Puente Los. X , A ngelrav. R iver < Ballons? CreelT Santa Monica Bay an r G abriel R iver mg Beach Santana lA n a ™ Mountain: Palos Verde: Hills Figure 3-1: Features of the Los Angeles Basin During the period that the northern ranges were growing in relief, much of the basin area in southern Los Angeles County was located below sea level (Brownlie and Taylor, 1981). The waters extended inland as far as Pasadena and Pomona (Troxel, 1954). In fact, both the Los Angeles Basin and the Ventura Basin to the north were deep marine troughs (Woodford et al., 1954), and their seas were 32 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. connected (Troxel, 1954). The Transverse Ranges, including the Santa Monica and San Gabriel mountains, were structurally weak and became more vulnerable as they grew higher during this time, allowing waterways to erode easily and wash away material (Gumprecht, 1999). The coastal plain was developed by the discharge of this mountain sediment, filling up the area connecting the mountains and Palos Verdes Peninsula (Gumprecht, 1999), which was, at that time, an island (Troxel, 1954). Within their floodplains, instead of circumventing the developing hills and mountains, the Los Angeles River cut down through the Dominguez Hills (Sharp, 1954; Brownlie and Taylor, 1981) and the San Gabriel River cut down through the Puente Hills (Sharp, 1954) so they could remain on virtually direct paths to the sea. In Los Angeles, the mountainous terrain is precipitous (Bigger, 1959). Topographic features include steep, V-shaped canyons with slopes that are commonly 70 percent or greater (LACDPW, 1991). Rainfall loosens sediment through kinetic energy, the water fills the pores in the soil and, when the precipitation rate exceeds the infiltration rate (expressed in the Hortonian flow model), the sediment is carried as sheetwash (Mount, 1995). This is then deposited as an alluvial accumulation where the slopes meet the valley flow. “An apron of large alluvial fans is a prominent” characteristic of the “oversteepened south front of the San Gabriel Mountains” (Bailey and Jahns, 1954, 85). Alluvial fans are deposits of sediment on the plains that are supplied by debris flows and channel flows derived from mountain-front catchments (Cooke, 1984). 33 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. Climate trends in the Southern California region contribute greatly to the extreme flood characteristics of the area. The region periodically experiences torrential rains during relatively short spans of time (Bigger, 1959). The ground quickly becomes saturated and can no longer absorb any subsequent rain. With steep slopes and minimal vegetative cover, especially in fire-scarred areas, the water quickly descends the mountainsides and canyons, discharging in great amounts and speeds (Bigger, 1959). Much of this water is “is heavily laden with silt, sand, and fine gravel, accumulating more such debris as it rushes through the erodible foothill and upper valley areas, and even the plains” (Bigger, 1959, 7). There are five major drainage areas in Los Angeles County: Ballona Creek Basin, Los Angeles River Basin and San Gabriel River Basin, as well as the Santa Clara River Basin and Antelope Valley to the north (LACDPW, 1991). River discharge in pre-urbanized Los Angeles was concentrated predominantly within the Los Angeles and San Gabriel Rivers, shown in Figure 3-2. These are the largest waterways that traverse the Los Angeles Basin and exit within county boundaries. While both were erratic—often changing courses, overflowing their banks, converging with one another or conveying water only seasonally—they delivered enough sand to fill the Los Angeles Basin and to the lagoons, bays and, during flooding, to the shoreline (Brownlie and Taylor, 1981). 34 permission of the copyright owner. Further reproduction prohibited without permission. o c LEGENO rv "s. M ountains and B ills P rin c ip a l Rlvar Channals ( P a tte rn Indicates ap p ro x la ate v ld th in uneonflned re a c h sa ) C oastal Lagoons and Inland Marahea V NSwoori ^ B o y Figure 3-2: A 1917 View of Los Angeles Source: Brown and Taylor (1982) The Los Angeles River The Los Angeles River, with a length of just more than 50 miles (90 km) along its main stem, originates in the Santa Monica Mountains (and the northern Santa Susanna Mountains), that border the western and southern portions of the San 35 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. Fernando Valley (Brownlie and Taylor, 1981). In the San Fernando Valley, the river exists almost entirely below the surface as an underground reservoir with a capacity o f about 3.2 million acre-feet (Gumprecht, 1999). The soil in the Los Angeles region was very porous and would often result in the complete infiltration of the river’s flow (Reagan, 1915). Several smaller creeks—the Tujunga, Pacoima and others— descend the western San Gabriel Mountains to join with the greater river during times of flooding. More often, however, these sank into the pervious surface to contribute to the underground reservoir (Brownlie and Taylor, 1981). The mountains that nearly surround this valley contribute greatly to orographic precipitation, blocking winter storms and extracting moisture from them (LACDPW, 1991). The San Gabriel Mountains—reaching approximately 7,000 feet in this area, twice the height of neighboring ranges—are instrumental in generating precipitation (Gumprecht, 1999). The average annual rainfall is 28 inches in the mountains and 14 inches on the coastal plain (LACDPW, 1999c). The Los Angeles River exits the San Fernando Valley through a small passage known as the Glendale Narrows, located between Glendale and Los Angeles (Figure 3-1). The mountains on either side of the river converge toward the southern valley, leaving only a narrow passage that is a few hundred yards wide near Elysian Park (Gumprecht, 1999). An impermeable bedrock layer just below the surface of the Glendale Narrows forces the river to rise to the surface in order to pass through the constricted passageway (Brownlie and Taylor, 1981). 36 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. Beyond Glendale Narrows, the route of the Los Angeles River varied historically (Reagan, 1915; Brownlie and Taylor, 1981; Gumprecht, 1999). The broad coastal plain provided numerous courses to the ocean that could be reached by traveling west or by going a slightly longer route to the south of the Palos Verdes Peninsula. Prior to 1825, the Los Angeles River, traveling the path of what is now Ballona Creek into Santa Monica Bay, emptied on Los Angeles’ western shoreline (Reagan, 1915; Woodford etal., 1954; Herron, 1980; Brownlie and Taylor, 1981; Brown and Taylor, 1982; Flick, 1993; Leidersdorf et al., 1994; Wiegel, 1994; Gumprecht, 1999; Gumprecht, 2000). Flooding during 1825 forced the river’s change in course that sent water flowing south toward San Pedro (Brownlie and Taylor, 1981). The course has remained southward since that time with two exceptions—when floods occurred in 1862 and 1884 the river again sent some of its flows to the west (Brownlie and Taylor, 1981). While its general direction has remained almost constant for 175 years, the Los Angeles River has taken numerous paths across the coastal plain in its southerly journey (Reagan, 1915; Brownlie and Taylor, 1981; Gumprecht, 1999). Its proximity to the San Gabriel River has resulted in a number of encounters between the two, exchanging of channels, and the fluctuation of their outlets to the Pacific Ocean (Reagan, 1915). Exchanges have occurred on a regular basis via the Rio Hondo, a 20-mile (32 km) long stream derived from the San Gabriel River, which connects to the Los Angeles River just northeast of Compton (Brownlie and Taylor, 1981). Even then, the precise location of their exits varied. Floodwaters often caused the Los 37 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. Angeles River to fan out between San Pedro and Long Beach and, occasionally, the water would become “clogged” along the south and west sides of Dominguez Hills, creating a slough (Reagan, 1915). The Los Angeles River’s frequent channel fluctuations are a result of its highly variable flow patterns and intensities as well as dense vegetation that impeded its path (Reagan, 1915). The sediment carried by the Los Angeles River is provided predominantly by the erosion of mountainsides near its point of origin in the San Fernando Valley region. Its upland catchment is approximately 850 square kilometers (about 328.2 square miles) where heights range from 900 to 2,100 meters (2,952 to 6,888 feet) (Brownlie and Taylor, 1981). Steep grades contribute significantly to the river’s ability to erode and carry sediment with slopes of its upland tributaries measured to be 0.04 (Brownlie and Taylor, 1981). The river’s slope in the San Fernando Valley is 0.006 and in the coastal plains, 0.003, and this valley and plains combine for an area of 1,250 square kilometers (482.6 square miles) (Brownlie and Taylor, 1981). The flatter slopes in the Los Angeles River’s lower reaches caused a great amount of sediment deposition to occur along the coastal plain. However, during times of flooding, the river would carry its sediment to the shoreline, depositing sand on the beaches below San Pedro and along its littoral cell path southward along the Orange County coast to the Newport Submarine Canyon, the cell’s sink. In the Southern California region, large floods result from episodic storm events that occur at regular intervals (Inman and Jenkins, 1999). Interchanging dry and wet periods occur every few decades, but strong El Nino events and severe 38 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. storms arrive every three to seven years during these wet periods (Inman and Jenkins, 1999). The single 1969 flood year, for example, exceeded the total transport of most rivers in Southern California during the preceding 25-year dry period (Inman and Jenkins, 1999). Besides 1969, other major floods occurred on the Los Angeles River in 1825, 1861-62, 1867-68, 1884, 1889,1914, 1934 and 1938 (Reagan, 1915; Cooke, 1984; Gumprecht, 1999; Gumprecht, 2000). There were other episodes of flooding, but not all were of significant impact. Cooke (1984) asserts that the most important 20th - century events were in 1914,1934,1938,1969 and 1978. The Los Angeles River was known to increase its flow 3,000-fold in a single 24-hour period, accelerating local erosion and sedimentation rates tremendously (Davis, 1998). The San Gabriel River While there is less documentation for the San Gabriel River—perhaps due to its less-proximate location in relation to early Los Angeles development—much of the story is the same. Brownlie and Taylor (1981) argue that the Los Angeles and San Gabriel rivers can be discussed collectively since their basins are connected naturally, their information and data are complementary and their periods and extent of human development parallel one another. The San Gabriel River drains the central segment of the San Gabriel Mountains that reach heights of almost 3,000 meters (9,840 feet) (Brownlie and Taylor, 1981). This mountainous area, comprising rugged topography with steep, 39 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. narrow canyons, accounts for approximately one-third of the river’s total drainage area o f 1,663 square kilometers (642 square miles), while the San Gabriel Valley and coastal plain account for the remaining two-thirds (Brownlie and Taylor, 1981). Two branches o f the San Gabriel River, one arriving from the east and the other from the west (Figure 3-2), join 14 kilometers (8.7 miles) above San Gabriel Canyon to form the river, which then descends for 25 kilometers (15.5 miles) in a southwesterly direction through the San Gabriel Valley (Brownlie and Taylor, 1981). The San Gabriel River passes through Whittier Narrows, which— like Glendale Narrows for the Los Angeles River—was the only passage available for the river to reach the coastal plain (Brownlie and Taylor, 1981). The San Gabriel River, like other rivers in the Southern California region, is heavily influenced by episodic weather, and is thus prone to flooding and heavy sediment transport during wet periods (Inman and Jenkins, 1999). The great height of the San Gabriel Mountains to the north is especially effective in generating rainfall. The steep slopes, combined with an erosive surface, produce a great amount of sediment that is transported by the San Gabriel River. The ability o f the river to reach the shoreline with this sediment is subject to the same type of constraints that restrict the flow of the Los Angeles River. High flows, during large storm events in wet years, produce conditions that allow sediment to be deposited on the shoreline (Inman and Jenkins, 1999). In the case of the San Gabriel River, its mouth was usually located at Alamitos Bay, although fluctuations occurred occasionally (Brownlie and Taylor, 1981; Moffatt and Nichol Engineers, 1984). 40 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. Coastal Characteristics Initially, the Los Angeles and San Gabriel rivers crossed the Los Angeles coastal plain and delivered sediment to two of the five littoral cells in Southern California that are seen in Appendix 1. The Santa Monica Littoral Cell on the western boundary of Los Angeles, stretches from just south of Pt. Dume to the Redondo Submarine Canyon near Palos Verdes Peninsula (Flick, 1993; Leidersdorf et al., 1994). It received sediment from the Los Angeles River until 1825 when a flood sent its waters flowing south (Flick, 1993; Leidersdorf et al., 1994). Since that time sources of natural sediment transport to the Santa Monica Littoral Cell have been few. The relatively insignificant Ballona Creek (see Figure 3-1), which primarily contains urban runoff, serves as the main natural contributor of beach sand to this cell today (Flick, 1993; Leidersdorf et al., 1994). The lack o f a major source of fluvial sediment would have caused the beaches of the Santa Monica Cell to narrow, but human intervention has led to artificial replenishment that has widened the beaches for recreational and protective benefits (Leidersdorf et al., 1994; Dean, 1999). The San Pedro Cell has received sediment inputs from the San Gabriel River throughout its recent geological history and has received waters from the Los Angeles River almost regularly since 1825. The combined natural sediment yield of these rivers is approximated to be about 600,000 cubic meters (about 784,000 cubic yards) annually (Brownlie and Taylor, 1981). A third river, the Santa Ana River of 41 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. Orange County, joins these two as the primary natural contributors of beach sand to this cell (Flick, 1993). Long Beach City Beach and Belmont Shore exist between the mouths o f the Los Angeles and San Gabriel rivers in Los Angeles County. Immediately downcoast o f the San Gabriel River’s outlet are Orange County’s beaches, including Seal Beach, Surfside Beach, Sunset Beach, Huntington Beach and Newport Beach. And, when political boundaries do not follow the boundaries of physical processes in an area, the activities of one jurisdiction affect the resources of another. The sediment delivery of two rivers in Los Angeles County, or the lack thereof, greatly affects the availability of sand supplies to beaches in Orange County. Of the material that is capable of transport, there is a minimum grain size— termed the littoral cutoff diameter—for material that will remain within the active zone of littoral transport for any considerable amount of time (Best and Griggs, 1991). Seal Beach, just downcoast of the mouths of the Los Angeles and San Gabriel rivers, has grain sizes ranging from 0.06 to 0.11 millimeters on the deeper, flatter portions of both its groin-separated west and east segments (Moffat & Nichol Engineers, 1985). The beach’s steeper portions, above the mean sea level, consist of sands ranging from 0.12 to 0.6 millimeters (Moffat & Nichol Engineers, 1985). Thus, the sediment matching these sizes (0.06 to 0.6 millimeters) within the dams and debris basins or removed through mining could have potentially contributed to local beaches had they reached the shoreline. This is fairly consistent with a previous 42 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. study that found that sands on the Southern California coast vary in size from 0.1 to 0.6 millimeters (Emery, 1960). Human Development The Los Angeles region changed hands several times during the 19th century, from Spain, to Mexico, and, in 1848, to the United States. While settlers were slow in coming at this time, modifications of the river occurred early and grew exponentially with the population booms that occurred in the coming years. With very limited local water resources there were immediate concerns about sources of water to supply the growing town. Early alterations made to the river, some of which had obvious impacts on the sediment supply, included the continuous siphoning of river water, the only surface water supply in the region until Owens River water was brought via an aqueduct in 1913 (Gumprecht, 2000). With agriculture the dominant economic activity, zanjas, irrigation ditches, were built for the conveyance of water to ranches (Workman, 1935). This, added to the demands of the tremendous population that arrived, drained the river and its underground flow dry by the early 1900s (Gumprecht, 2000). With its water drained, the Los Angeles River no longer resembled a river and nearby residents no longer perceived it as one (Gumprecht, 2000). The empty channel, which had railroad tracks running down both sides of its banks, was put to many uses, in particular as a dumping ground, other than the one for which it was 43 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. naturally intended (Gumprecht, 2000). Many Angelenos supported a measure to convert the river into the city’s sewer system, but city engineers realized that the river’s paltry flow could do little in carrying the sewage away efficiently (Gumprecht, 2000). In addition to becoming a de facto dump for the city, the Los Angeles River’s dry riverbed became a primary mining ground. In 1907, between 1,000 and 1,200 truckloads of sand and gravel were being removed from the bed each day (Gumprecht, 2000). Bridges were barely able to support the stress placed on them by the continuous transport of these heavy materials (Gumprecht, 2000). As Los Angeles’ population continued to grow, the city began to occupy more land, much of it within the immediate floodplain of the Los Angeles River. Ignoring warnings from those who had experienced the region’s catastrophic floods (Gumprecht, 2000), agriculture, industries and homes were established in the foothills at canyon mouths and along low riverbanks (Bigger, 1959). Some cities were even built within abandoned channels of the Los Angeles River. Periods of time between floods are sometimes long, whereas memory of man is short. Lands which historically have been seriously menaced were purchased by those—especially newcomers—who thought that the climate of Los Angeles was all sunshine and warmth (Bigger, 1959, 3). The Los Angeles and San Gabriel rivers did not behave like many o f the rivers in the Midwest—to the region’s newcomers, sudden, catastrophic flooding on such apparently insignificant rivers seemed unimaginable (Gumprecht, 2000). 44 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. Large floods, surprising many of the new residents of Los Angeles, occurred in 1884, 1886,1889 and 1890 (Gumprecht, 2000). The population, numbering about 100,000 in 1890 had, by 1914, grown to about 700,000 (Bigger, 1959). During this quarter-decade period the rivers displayed little risk for flooding, and the region experienced tremendous economic expansion (Bigger, 1959). The lack of preparation and foresight stimulated calls for flood protection (Bigger, 1959). Heavy rains in 1911 led to the commissioning o f regional flood hazard reports that were completed in time for the 1914 storm season (Bigger, 1959; Cooke, 1984). When floods hit in 1914, causing $10 million in damage (Bigger, 1959), a flood control program to reduce the flood hazards was initiated (Cooke, 1984). By then, property values had skyrocketed, populations had increased several times over and protecting people’s property had become a great concern (Cooke, 1984). As population and development continued to expand, the risk to life and property also increased. While flooding in 1914 and 1916 did not claim any lives, according to reports of the time, those in 1934 and 1938 killed 40 and 59, respectively (Bigger, 1959). Damage resulting from these four floods was $10 million, $4 million, $5 million and $62 million, respectively (Bigger, 1959). “Realiz{ing} that the water has a combined power for good and evil,” (Reagan, 1917,5) was a primary consideration in the taming of the Los Angeles, Rio Hondo and San Gabriel rivers, according to James W. Reagan, chief engineer of the Los Angeles County Flood Control District (1917). There was great debate concerning approaches to controlling flood hazards as well as meeting the equally 45 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. important goal of water conservation. As Reagan stated, “ {t}he works.. .are proposed almost entirely upon such a class o f conservation as should nearly remove the necessity of flood control, and they will be, for the most part of lasting and permanent construction” (Reagan, 1924,6). However, many initial plans of the LACFCD were abandoned due to the complexities of the Los Angeles region. Traditional damming was made difficult due to the lack of appropriate reservoir sites, unstable foundations, the seismic instability of the region that could rupture masonry dams, rockslides that made construction difficult, structural size limitations that made containment of large floods and debris loads complicated and the possibility that debris would almost immediately inundate the structures (Bigger, 1959). A flood control philosophy and guide that stemmed from the 1914 flood experience directed the early efforts toward containing flood flows and conserving water (of importance due to the region’s lack of local water supplies) (Bigger, 1959). A 1924 report to the LACFCD Board of Supervisors by Reagan suggested that the surface of the area’s pumping water was falling, attributed to fluctuating rainfall and the increasing prevalence o f wells (Reagan, 1924). This dwindling water level threatened supplies at a time when these and those of the Owens Valley were the only water sources for the growing population of Los Angeles. Early conservation and flood control actions included the building of several small dams, many small check dams to reduce debris from canyons and some improvements to the channels themselves (Bigger, 1959). However, many of these efforts were slowed or 46 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. abandoned due to risks, economic disputes, differences of opinion and the lack o f data upon which to base decisions (Bigger, 19S9). 1: P a c o im a 2 : B lg T u Ju n g a 3 : D evil’s G a le 4 : E a to n W ash 5: S a n ta A n ita 6 : C o g sw ell 7: S a w p lt 8 : S a n G a b rie l 9: M o rris 10: B ig D a lto n 11: P u d d ln g sto n e D tv en io 12: S a n D int 13: L iv e O a 14: T h o m p s o n C t w C T ! 15: P u d d in g sto Los Angeles County San Gabriel Mountains ca Mount L o s A ngeles River Ballona Creek Santa Monica Bay jjjfcSanta ‘ a ountain: Figure 3-3: Los Angeles County Department of Public Works Dams Between 1927 and 1931, a detailed flood control plan that proposed a number of reservoirs, spreading grounds and debris basins was developed (Bigger, 1959). It was amended in 1935 and 1938 and resulted in a plan that focused on reducing hazards in the upstream portions of the Los Angeles River and San Gabriel River watersheds (Bigger, 1959). Between 1920 and 1939 the Los Angeles Flood Control District (LACFCD) completed 15 dams, shown in Figure 3-3 (LACDPW, 1999b). 47 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. The smallest, Puddingstone Diversion, has a capacity of 342,027 cubic yards of water; the largest, San Gabriel Dam, has a capacity of more than 86 million cubic yards. The total capacity of the 15 dams exceeds 223 million cubic yards (LACDPW, 1999b). Appendix II is an inventory of these 15 dams and their attributes. Federal aid was requested and the downstream plans for the region became the center of the United States Army Corps of Engineers’ (USACE) responsibilities in the area. This included major dam, debris basin and extensive channel improvement projects that would reduce risks to the metropolitan area (Bigger, 1959). The Corps took over the flood control program between 1935 and 1959 after the local LACFCD program “had proven incapable of satisfactorily limiting the flood hazard in a rapidly growing metropolis” (Gumprecht, 2000,1-2). A devastating flood in 1934, the first one of its size in two decades, was the impetus of the federal government’s efforts to reduce flood hazards in Los Angeles (Cooke, 1984) and served the dual purpose of alleviating unemployment (Cooke, 1984; Davis, 1998). A flood just four years later claimed a record 87 lives and seemed to justify flood control efforts (Cooke, 1984; Davis, 1998). Many of the 16 debris basins that existed at the time were filled during this flooding and the reservoirs also trapped a significant amount of sediment, which helped prevent serious damage (Cooke, 1984). The construction of structures in the region continued and seven Corps dams, shown in Figure 3-4, were completed during the 1940s and the 1950s. This marked a definite end to proposals by urban designers/planners, Frederick Law Olmsted, Jr. and Harlan Bartholomew, who saw limiting human encroachment into the rivers’ 48 R eproduced with perm ission of the copyright owner. Further reproduction prohibited without permission. floodplains through land-use planning as a method to limit damage caused by floods (Davis, 1998). Their proposition asserted that “it was cheaper to keep property away from floodplains through hazard zoning than to keep floods away from property through vast public works” (Davis, 1998,70). Los Angeles County San G a b r ie lV H L M ountains lica Mountai JrSaatM Fe littier Narrows] Ballons? CreelT Angeles's. / River , ( \ Santa Monica Bay Santa [ountain: Figure 3-4: Seven United States Army Corps of Engineers Dams The seven USACE structures, though large, are located downstream of the debris basins and dams constructed by the LACFCD. Much o f the sediment is, thus, removed from the system prior to reaching these structures (Brown and Taylor, 1982). Any sediment found in these structures is removed—sometimes by 49 R eproduced with perm ission of the copyright owner. Further reproduction prohibited without permission. construction companies who pay to mine it (Casey, 2001)—when they are drained each year. The catchment behind Hansen Dam, shown in Figure 2-2, has been mined for aggregate (Bahner, 2001; Casey, 2001). The history of dam construction, shown in Figure 3-5, reflects a trend of building during a relatively short 40-year time span in the early half of the century. The columns indicate the number of structures that were constructed during individual years, whereas the thick line reflects the total number of dams that exist at any point of Los Angeles’ history. The patterns of construction also describe the potential escalation of sediment transport interruption in the region. As more structures were built the amount of uncontrolled drainage area decreased and more sediment could potentially be trapped in the structures instead of being carried through the Los Angeles Basin to the ocean. • • r.i..-.;v?. .v. - v : ■"& .• Number Built in Individual Years Total Number in Existence Figure 3-5: Construction of dams in the Los Angeles River and San Gabriel River watersheds 50 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. The construction of debris basins, graphed in Figure 3*6, has been uninterrupted since the onset of flood control efforts by both the LACFCD and USACE (LACDPW, 1999a). There were 115 debris basins constructed as o f 1997, and their locations are shown in Figure 3-7. A complete listing of these debris basins and their attributes is listed in Appendix m and more detailed maps are in Appendix IV. There are evident correlations between large flood events and the construction of debris basins throughout the Los Angeles region. The most notable years o f flooding and debris flows since debris basin construction initiated in the 1920s include 1934- 35,1968 and 1978. As seen in Figure 3-6, these years were often met with reactionary construction of debris basins. Peaks in construction occur in 1935, from 1968-70 and in the early 1980s (though this was to a lesser degree than in prior years, but is a peak in comparison to the years that follow). (A C '3 5 a ffl 3 o i- Number Built in Individual Years Total Number in Existence <0 (0(0 O B g to Figure 3-6: Construction of debris basins in the Los Angeles River and San Gabriel River watersheds 51 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. Considerably smaller than most dams, these debris basins were built with the purpose of containing the debris flows that occur frequently in the mountains surrounding Los Angeles. Debris flows—mudflows of large boulders, mud and sediments—occur in areas that are plagued by fires, have chaparral or desert-like vegetation, experience heavy and sudden rains and have steep slopes (McPhee, 1989). The relationship between fire and chaparral (fire-prone vegetation native to Southern California) is of particular importance in generating these events since the burning o f chaparral leaves an impenetrable film in the soil that accelerates surface runoff. Debris flows descend these burned mountainsides, enveloping homes and posing a risk to humans and property in this region. The basins provide some risk reduction by capturing much of the flow before it can reach developed areas. 52 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. Los Angeles River , 'aan Gabriel River ) /Downtown Los Angeles = debris basin Figure 3-7: Los Angeles County Department of Public Works Debris Basins The relationship between building the two primary structure types shows that there was an initial focus on the construction of dams and later, debris basins. This trend, shown in Table 3-1, is in some ways tied to early experiences with the sedimentation behind dams, especially Santa Anita Dam, that occurred following 53 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. fires in the dams’ watersheds. Debris basins were built to reduce the sediment yield of the mountain channels and burned areas that preceded the dams. N um ber o f N ew Dams Constructed Total N um ber o f D am s N um ber o f N ew D ebris B asins C onstructed Total N um ber o f D ebris Basins 1920-29 10 10 2 2 1930-39 5 15 14 16 1940-49 5 20 5 21 1950-59 2 22 22 43 1960-69 0 22 20 63 1970-79 0 22 31 94 1980-89 0 22 10 104 1990-97 0 22 2 106 Table 3-1: Dam and Debris Basin Construction by Decade Several methods, including flat rates of capacity per square kilometer of drainage area, were employed in determining the design features of debris basins during the early years of their construction. Since 1959, however, the design of individual debris basins has been contingent upon the features of the area in which construction is to take place and their potential for sediment production based on debris-production curves (Cooke, 1984). Five Debris Potential Area (DPA) zones have been established in Los Angeles County (see Appendix V) based upon geologic, topographic, vegetative and rainfall characteristics (LACDPW 1993). Using the Debris Production (DP) curve (refer to Appendix VI) produced by the 54 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. Department of Public Works, the debris production rate can be determined by comparing the established DPA zone to the size of the drainage area. Debris production is the rate at which sediment passes a particular point and is dependent on geology, soil type, intensity of rainfall, vegetative cover, runoff and watershed slope (LACDPW, 1993). Total debris production, or the Design Debris Event (DDE) that a basin is designed to capture, is then determined by multiplying the debris production rate by the drainage area (LACDPW, 1993). Further adjustments are made to this equation if there is development or other features in the watershed, such as the existence of more than one DPA zone (LACDPW, 1993). When construction of a retaining structure is being considered, the DPA zone is compared to its total sediment production to determine the appropriate type of structure. This could range from a debris basin (for areas with considerable risk for damage) or an elevated or desilting inlet (for areas with little risk) (LACDPW, 1993). These inlets are small, modified versions of debris basins and never exceed a capacity of 19,999 cubic yards for elevated inlets and 4,999 cubic yards for desilting inlets. There are more than 100 of these debris-retaining inlets in Los Angeles County, but their impact is minimal and this is the reason no records are maintained for them (Bohlander, 2001). Some basins were downgraded from debris basin (high-risk) status to that of an inlet, because they did not produce significant (or any) debris (Bohlander, 2001). Debris basins are allowed to accumulate sediment up to 25 percent of their volume in watersheds that have not burned in the preceding four- to five-year period, and up to 5 percent o f their volume in recently burned watersheds (Bohlander, 2001). 55 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. In late 2000, outlet towers located within each debris basin were marked with a 5 and 25 percent line to make calculating debris volume easier and to avoid delays in recognizing debris basins that are in need of clearing (Bohlander, 2001). The distribution of structures in the two watersheds shows that almost 60 percent of the dams are located in the San Gabriel River watershed while more than 86 percent of debris basins are located in the Los Angeles River watershed. These are referred to in Table 3-2. The Department of Public Works built all but six dams in the San Gabriel River watershed, while the focus was placed on debris basins in the Los Angeles River watershed. The United States Army Corps of Engineers built four dams on the San Gabriel River and three on the Los Angeles River. W atershed N um ber o f D am s N um ber o f D ebris Basins Percentage o f Dam s P ercentage o f D ebris Basins Los Angeles River 9 85 40.9% 80.2% San Gabriel River 13 21 59.1% 19.8% Table 3-2: Distribution of dams and debris basins in the Los Angeles River and San Gabriel River watersheds The structures in the San Gabriel River watershed are larger than those in the Los Angeles River watershed. Debris basin capacities average about 84,790 cubic yards in the San Gabriel River watershed and approximately 68,391 cubic yards, almost 20 percent smaller, in the Los Angeles River watershed. Each basin controls approximately the same size drainage area—an average of 0.52 and 0.57 square miles for the Los Angeles River watershed and the San Gabriel River watershed respectively. 56 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. The placement of the structures within the region also reflects a geographic pattern. Debris basins in the region are usually located deep within mountainous areas in close proximity to the areas where debris is produced. The 15 dams built by the Department of Public Works in the San Gabriel Mountains are also typically situated close to the mountains and below the debris basins. Most dams built by the U.S. Army Corps of Engineers, however, were constructed at a greater distance from the mountains and often within the coastal floodplain. A focus had been placed on improvements, including dams and channelization, in the floodplains at the point that the federal government began managing the flood control system. Sand mining has reduced the sediment content of the Los Angeles Basin. Gumprecht (1999) asserts that the primary use of Los Angeles’ rivers today is for sand and gravel mining. Since local sand and gravel production reflects local demand (Kolker, 1982), Los Angeles has had to support its persistent rate of expansion by providing the physical resources necessary to meet the needs o f the growing region. Data received by Kolker (1982) from the Southern California Rock Products Association indicated that 68 percent of the sand and gravel mined in Los Angeles between 1930 and 1969 was used in the construction of freeways, dams and other public structures. Mining in Los Angeles County was the greatest in the state during 1986 in terms of production quantity, nearly doubling the production o f the second county, Alameda (Sandecki, 1989). As of the last decennial report produced by the California Division of Mines and Geology (CDMG) in 1994, amounts of portland 57 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. cement concrete (PCC) aggregate removed by large-scale mining operations in Los Angeles County are on the order of about 28 million tons (about 21.4 million cubic yards) each year, a figure that has shown an increasing, though erratic, trend through the last several decades (Miller, 1994). If consumption increased to the present at the same rate as it did between 1982 and 1994, Los Angeles could be consuming as much as 30.5 million tons (about 23.3 million cubic yards) of PCC aggregate each year. There are several types of sand and gravel mining activities, including aggregate for PCC, asphaltic concrete and base material, in Los Angeles County. All require varying material compositions and are used for different purposes. Portland cement concrete (PCC) aggregate is comprised of approximately 50 percent sand and 50 percent gravel (Miller, 2001) and is used to construct homes, buildings, dams, sewers and docks (Evans et al., 1979). Asphaltic concrete, the dark, top layer of roads, is composed of very little sand (Miller, 2001). Base material is the foundational layer of roads and buildings and contains approximately 50 percent sand-sized sediment (Miller, 2001). Asphaltic concrete and base materials are made from artificially sized and broken aggregates, usually “crushed rock” (Evans et al., 1979). These rough surfaces are more cohesive in their mixtures and strengthen the product (Evans et al., 1979). However, PCC aggregate is in need of naturally smooth, round particles (Evans et al., 1979), such as might be found in sediment exposed to water erosion in rivers. Under natural conditions, the rivers would have been capable of carrying much of 58 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. the sand materials used in PCC aggregate to local beaches. Asphaltic concrete and base material aggregate are made from rocks (crushed) that are often too heavy to be moved by a flowing river. This demonstrates that PCC aggregate is of primary importance in assessing the impact of the mining industry on supplies of natural sand. CDMG maintains records of the production of PCC, but does not quantify the production of asphaltic concrete or base material (Miller, 2001). Sediment is being removed from four main sources in the Southern California region: (1) streambeds, (2) floodplains and terraces, (3) alluvial fans and (4) bedrock (Kolker, 1982). In Los Angeles County no mining is occurring in active streambeds (Miller, 2001). Terraces also do not provide a great amount of sand and gravel in Los Angeles (Kolker, 1982). However, alluvial fans, including the Tujunga Fan, near Hansen Dam, and the San Gabriel Fan (shown in Figure 3-8) in Irwindaie (Kolker, 1982; Miller, 2001), have been mined. Bedrock mining has occurred in Los Angeles in the Montebello and Palos Verdes hills (Kolker, 1982). Figure 3-8: Sand and gravel mining in the San Gabriel Fan in Irwindaie R eproduced with perm ission of the copyright owner. Further reproduction prohibited without permission. As of 1994, 16 PCC mines existed in Los Angeles County (Miller, 1994), but a controversial mining project in Soledad Canyon near Santa Clarita, which would extract 78 million tons of sand and gravel, received federal approval in August 2000 after a decade-long battle (Risling, 2000). This project still must undergo a number o f legal procedures and obtain local approval before being put into operation (Miller, 2001). However, a protest, primarily of homeowners from Soledad Canyon, erupted as the item was discussed at a Los Angeles Board of Supervisors meeting in January 2001 and has created tremendous pressure to halt the project. CDMG has divided Los Angeles County into seven PCC aggregate production-consumption (P-C) regions (Figure 3-9) that are reviewed every decade. The most recent report was issued in 1994. The reason for classifying the region in this manner stems from the local focus o f the sand and gravel mining industry. There are large costs involved in transporting aggregate material, so local production is preferable for local demands. Monitoring individual P-C regions makes it possible to identify trends, including the rate of development and population growth in these areas, in the production and use of aggregate materials within specific geographic regions. 60 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. R Q S A y u N D 2 2 > * - ROGERS .5 2 '--5 K R A M f n PALW3ALE REGION S A U G t J S - *E¥«8Afcfc R E G I O N ACTON /A LY C R M i r n r R E G l o w A N F E R N A N D V A L L E V P = * C R E G I O N / S A N q A C L A R E M O N T - U P L A N D P - C R E G I O N BRIE !V A L L P - - G . B E G 1 Q O R A N G E C O U N T Y TEMESCAL VALLEY P-C^REGfONl Source: Miller (1994) Figure 3-9: Production-consumption regions in the Los Angeles area (the central area is the San Gabriel Mountains where production and consumption do not occur) Only four of seven local P-C regions—San Fernando Valley, San Gabriel Valley, Saugus-Newhall and Palmdale— are located entirely within the boundaries of Los Angeles County. The Claremont-Upland P-C Region straddles San Bernardino County where all of its production occurs. The Orange-County-Temescal Valley P-C Region contains only a small area in southern Los Angeles County. The Simi P-C Region includes two small pockets of land on the western boundary of Los Angeles County bordering Ventura County. The four found entirely within Los Angeles County as well as the Claremont-Upland P-C Region were assessed in the 1994 61 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. report, but for purposes of studying Los Angeles County only the data for the first four will be considered in this thesis. These four serve the bulk of the aggregate needs within the county (LACDRP, 1999). Resources, reserves and consumption are the key terms that are analyzed within these P-C regions. Resources are aggregate deposits that are technologically and economically available. Reserves are aggregate deposits that are owned or maintained by a mining company and are authorized for extraction through a valid permit. Consumption is the amount of aggregate produced and used (Miller, 1994). Impacts on Natural Sediment Supply The consequences of these cumulative activities on beaches in Southern California have been tremendous. California’s coastal streams produce between 70 and 85 percent of beach-size sediment, which means that the state’s beaches are dependent on this supply (Griggs, 1987a). However, the difference between heavily developed and relatively undeveloped areas illustrates varying impacts on beach sand supplies. The only two free-flowing rivers in the state are located in Northern California. Taken as a group, the relatively unobstructed northern California streams today discharge about 80 percent of the state’s beach sand, with the heavily altered southern California streams producing the remaining 20 percent (Griggs, 1987, 1825). Besides fewer obstructions, the natural conditions in Northern California increase the likelihood of sediment contributions to the shoreline. The coastal area has erosive R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. rocks, steep slopes and significant rainfall that result in a great amount o f erosion and stream sediment discharge (Bird and Schwartz, 1985). Figures 3-10 and 3-11 reflect two extremes—the unobstructed Consumnes River in Northern California and the concrete channel of Los Angeles’ San Gabriel River. Figure 3-10: The Consumnes River near Sacramento is one of a handful of free-flowing rivers in California 63 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 3-11: The San Gabriel River is one of several heavily altered Southern California rivers In Southern California, the primary problem in the reduction of beach sand is the greatly reduced bedload o f rivers (Griggs, 1987a). The bedload consists of materials that are too heavy to be transported within the flow of the stream as suspended load or wash load, and is instead transported through intermittent motion that involves short periods of transport and longer periods of no motion (Mount, 1995). The disrupted, non-continuous flow of rivers in Los Angeles, caused by the frequent structural interruptions, reduces the transport of bedload (Griggs, 1987a). 64 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. The last significant supply of beach sand to the San Pedro Littoral Cell occurred during the 1938 flood (Herron, 1980). Approximately 200,000 cubic meters (about 261,000 cubic yards) of sand from the Los Angeles and San Gabriel rivers reached the shoreline each year by the early 1980s (Brownlie and Taylor, 1981). With few additions to the flood and debris control system since then, it can be expected that approximately the same amount arrives today. When this sediment is carried into the ocean by the Los Angeles and San Gabriel rivers, it is trapped within a harbor complex of jetties and breakwaters that prevents the transport of this material to beaches in the San Pedro Littoral Cell (Herron 1980). Sand and sediment delivered from the Los Angeles River, which discharges in the middle of the Los Angeles-Long Beach Harbor, clogs the harbor and causes dredging problems (Flick, 1993). “ {F}rom the viewpoint of harbor maintenance, it is an advantage that the sand yield from at least this river has been so greatly reduced” (Flick, 1993, 10). The San Gabriel River provides some sand to the Long Beach strand within the harbor and to Seal Beach, immediately to the south, but the sand shortages have been felt south of this area stretching from Sunset Beach to Newport Beach (Flick, 1993). A beach nourishment program that uses Sunset Beach as its feeder site contributes approximately 300,000 cubic meters (about 392,000 cubic yards) of sand each year to maintain the heavily used and developed beaches in this area (Flick, 1993). 65 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. Strategies and Solutions In Southern California, the response to sediment transport problems and the resulting erosion has been to adjust the shoreline environment. Groins, revetments, seawalls and other forms of “hard” solutions are common efforts to combat shoreline erosion, the attrition of the coastline. Efforts to prevent beach erosion—the diminishment of a beach as opposed to the coastline in general—has typically involved great amounts of replenishment, a “soft” solution, as well as groins designed to decrease littoral transport off o f a beach. A combination of flood control structures, navigation projects and shoreline structures have affected Southern California’s natural beaches. In the late 1930s, soon after flood control structures—predominantly dams—began impacting sediment transport, needs began arising for the construction of jetties, breakwaters and other structures along the shore for purposes of improving harbors and for the protection of beaches that were experiencing erosion (USACE, 1986). Between the mouths of the Los Angeles and San Gabriel rivers, a four-mile section of shoreline, which already faced reduced sediment supply due to alterations of the river, was cut off from the Los Angeles River by the 1943 construction of a navigational breakwater (USACE, 1986). Most of the beach disappeared and remained that way until 1948-49 when the river’s delta and the Long Beach Marina were dredged to rebuild the beach (USACE, 1986). The breakwater was extended and it eliminated serious wave action that had induced littoral drift (USACE, 1986). The beach erosion problem in this section o f shoreline was apparently solved, but the 66 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. reduced passage o f water has resulted in almost no cleansing action and this has left the bottom murky (USACE, 1986). The beaches downcoast from the mouth of the San Gabriel River (shown in Figure 3-12) have suffered tremendously as efforts have been made just to retain the sand on the beaches. The reduction of sediment was a result of flood control mechanisms on the San Gabriel River (USACE, 1986), but responses to this dwindling supply caused further problems. Seal Beach, immediately downcoast of San Gabriel’s outlet, built a groin, cutting off sand supply to beaches farther down the coast, at its easternmost point in 1939 (USACE, 1986). Other groins were added to compartmentalize the beach and further control littoral drift. However, Surfside, Sunset, Huntington and Newport beaches were then left without a source of sediment. Additionally, the U.S. Naval Weapons Station made changes to Anaheim Bay, which separated Seal Beach from Surfside and the other beaches (USACE, 1986). The long jetties that defined the entrance to the bay made littoral drift impossible and increased erosion by exacerbating wave action (USACE, 1986). 67 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. LONG 3EACH •J.5 Naval Waapona Siabcn h u n tin g to;, _ n 3SACI' S i.-rfsice 3«ach H u rtT ifw jlo n M j r c c r Source: US ACE (1986) Figure 3-12: Orange County beaches downcoast of the Los Angeles and San Gabriel rivers. Newport Beach, the last beach in the San Pedro Littoral Cell, is southeast of Huntington Harbor To rectify the situation, Surfside became a “feeder beach” to those further down in the littoral cell (US ACE, 1986). Dredging of sand from between the navy jetties and, occasionally, offshore areas provides a source of nourishment for this beach. Eventually, littoral drift carries it downcoast (USACE, 1986). A number of groin fields and other stabilizing structures have been erected on some of these beaches, including Newport (USACE, 1986). 68 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. Beaches along Los Angeles’ western boundary—though not nourished by the Los Angeles River since 1825 other than a handful of floods later in the 19th century—have experienced some beach erosion, but they are naturally narrow (Flick, 1993). Groins and other shoreline structures protect these beaches and development along much of the coastline. Large infrastructure projects in Southern California, including the construction of the Hyperion Sewage Treatment Plant and the Los Angeles International Airport, led to beach replenishment primarily in the Santa Monica Littoral Cell, which stretches along Los Angeles’ western border. The benefits of these large-scale construction projects, which were mostly the remnants of development during the post-World War II era (Dean, 1999), have gradually decreased with the passing of time. Other sites rely upon sand made available through artificial means like harbor construction/dredging [such as in Marina del Rey (Dean, 1999)], sand transfers from offshore to onshore [as is included in a plan for San Diego Regional Beach Sand Project (SANDAG, 2001)] and through other procedures like harbor by-passing (such as at Ventura Harbor). The maintenance required for such sand management efforts is expensive and recurring. To return eroding beaches to a system requiring less maintenance would entail looking at the causes of the problem rather than just addressing its effects. In this case, urbanization and its impact upon natural fluvial sediment transport need to be examined for potential methods of resolving the conflicting needs of the Southern California region. 69 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. One possible solution proposed by some in the region involves the decommissioning and removal of dams. Many dams have collected large quantities of sand, thus compromising their ability to handle floodwaters or serve water conservation purposes, the reason many were built. Matilija Dam in Ventura County is among those being recommended for demolition due to its tendency to accumulate sediment that reduces its ability to trap floodwaters or conserve water. Increasingly, advocates for fish runs and spawning grounds have been supporting measures to remove these structures to open up streams for fisheries. Matilija Dam, for example, is located along a stretch of stream that could potentially be revived for native steelhead trout (Polakovic, 1998). Combined with the fact that it is near capacity with 6 million cubic yards of sediment that has rendered it useless (LAT, 2000), the Matilija Dam is under increased scrutiny. The costs to destroy the structure and concern that the removal procedure would destroy the remaining steelhead trout population have plagued the proposal (Polakovic, 1998). The process of dismantling could take from two to 25 years and cost between $22 million and $180 million, depending on the method used (Booth, 2000). Similar problems exist in other areas where dam removal is being supported, and many of these difficulties involve managing the sediment itself. On the Elwha River in Washington, the removal of several dams will cost between $60 million and $200 million to ensure that sediment is removed in a manner that does not negatively affect the salmon population (Collier etal., 1996). 70 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. With many alternatives, including dam removal, unfeasible, the possibility still exists of reviving Southern California beaches by transporting sediment recovered from basin and dam cleanouts to the beaches that they would have naturally nourished. Dozens of inland debris disposal sites in Los Angeles County have been used and are currently in use for the storage of material removed from local structures (Kolker, 1982; Soriano, 1999). These sites are typically located in canyons, which construction companies occasionally visit to remove material suitable for construction purposes (Soriano, 1999). There have been attempts to make best use of this material, including a nourishment project near Malibu, but enormous costs to transport the material have been a significant obstacle (Bohlander, 2001). As a result, much of this sediment remains unused. Sediment in the disposal sites and the material currently located in the structures are a vast resource that could be examined as a means of nourishing the starved beaches of Southern California. 71 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. Chapter IV—Data Sources and Analysis Development of river-altering structures in the Los Angeles region commenced decades ago. As this research explores the changes in sediment yields of the Los Angeles and San Gabriel rivers from their natural state to current times, it is compulsory that the historical context of these alterations be established. The data necessary to recognize these changes must be obtained from the agencies that have built and monitored these structures. This analysis assumes that the data collected by these agencies are accurate. It does not contradict findings of other studies and would have had to severely undercount the sediment deposition in order to have reached a different conclusion. Additionally, it is necessary to supplement this quantitative information with qualitative details from representatives of the agencies to explain ambiguous trends as well as provide background information explaining history and reasons for occurrences. Data There are several agencies responsible for the creation of the structures and activities that affect sediment yield in the region. Chief among them are the United States Army Corps of Engineers, the Los Angeles County Flood Control District (whose responsibilities are now contained in the Los Angeles County Department of Public Works) and the California Division of Mines and Geology (a division o f the California Resources Agency). 72 R eproduced with perm ission of the copyright owner. Further reproduction prohibited without permission. LACDPW’s 15 dams, shown in Figure 3-3, are located in the San Gabriel Mountains and were built prior to the 1940s. The agency has maintained detailed records of debris removal from these structures since the time of their completion. The available data include measurements of volumes of sediment deposited, the amount removed, and the capacity of each structure. The set of data obtained provides information through the 1996-1997 storm season. This was the most up-to- date data available when this thesis was undertaken. More data was found since then, but it could not be confirmed what span of time the data covered, so it was not used. Additionally, it was beneficial to use the data through 1996-1997 since it matched the time span covered by data for the LACDPW debris basins. The Corps of Engineers has not maintained regular records of the sediment content and removal of their seven structures, shown in Figure 3-4, although annual debris deposition has been calculated for their three largest dams in this region. These data, provided by Bahner (2001), have been determined unofficially within the agency and have not been released in report form. However, these data are the best available at this time. The impact of these structures is minimal in comparison to the LACDPW dams and debris basins located farther upstream, closer to the origin of the sediment. Also, some of the sediment found in the USACE dams, in particular Santa Fe and Whittier Narrows dams, has been sluiced from upstream LACFCD dams in San Gabriel Canyon (San Gabriel and Morris dams) (Wood, 2001) and has already been quantified by surveys monitoring these structures. Counting this sediment deposition would be duplicating what has already been quantified once. 73 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. The debris basins, numbering 115 in 1997 (there are now 116), have been monitored by the Flood Control District and the Department o f Public Works, though some were also built by USACE, CalTrans, the United States Forest Service and other local, state and federal agencies (LACDPW, 1999a). Maps o f the debris basins are shown in Figure 3-7 and in Appendix IV. Most of the debris basins (106) are located in the Los Angeles River and San Gabriel River watersheds. The others (nine) are located in the watersheds of the Santa Clara River, Ballona Creek and Santa Monica Bay, and are excluded from this study. The Santa Clara River flows through Ventura County (although its watershed extends into Los Angeles County), which is why it was excluded. Those in the Ballona Creek and Santa Monica Bay watersheds were eliminated since they produce little sediment and are not located on a significant river that would have transported sediment. Records have been maintained for all of the debris basins in Los Angeles County since they were constructed. There are extensive data for each structure, consisting o f detailed information about the annual and total deposition of sediment, seasons of maximum deposition, design debris event, structural capacity, basin dimensions, years of use, drainage area, latitude/longitude coordinates, closest cities, waterways receiving its waters, upstream canyons and watercourses and Debris Production Area (DP A) zones. The records run from the construction of each structure through the conclusion o f the 1996-1997 storm season, which was the most up-to-date at the time this thesis was initiated. Newer debris basin data, through the 1999-2000 storm season, has recently been made available, but it does not include all 74 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. of the categories of information that the older one does. This newer source was only available after data analysis of the older data was complete and, additionally, it would only provide three more years of data to the decades o f data already available. Using the newer data would not have changed the overall findings of this thesis and would have actually provided fewer details than the older data set. One debris basin, which is not included in this thesis, was added in the Los Angeles River watershed in 1998. There had not been any depositional data recorded for it by 2000, so its inclusion would not have made any significant impact. The California Division of Mines and Geology (CDMG) releases decennial reports of portland cement concrete aggregate (also referred to as construction aggregate) mining for Southern California counties. The most recent report for Los Angeles County was issued in 1994 and examines the PCC aggregate reserves, resources and consumption. These variables are discussed in terms of the seven production-consumption districts located within Los Angeles County, shown in Figure 3-9. These agency-derived data will serve as the primary source of information about the sediment impacts caused by these structures and activities. The data collected by these agencies are consistent temporally and in terms of procedures according to structure types (except for the dams, which has two sources), reducing the number of difficulties posed by comparing and combining data of different origins. 75 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. Secondary Data In addition to agency data, there are a number of reports and articles that offer complementary information and observations on the history of the structures as well as sediment deposition and removal in the region. These will be used as points o f comparison and to validate prior knowledge on the subject of sediment transport interruptions in the region. Reports by Pasadena’s Environmental Quality Lab, which were completed in the early 1980s, include a great amount of information ranging from the geological history o f the region to the individual sedimentation trends of some structures. Brownlie and Taylor (1981) examine a number of records and available data to make calculations of natural sand transport by the Los Angeles and San Gabriel rivers. My findings will be applied to their calculations of natural and altered sand yields by the two rivers. Data and observations from Inman and Jenkins (1999) are used in the analysis of the impact of large storm events in the production of sand and sediment. The size and years of maximum debris production events for debris basins and dams are compared to the findings produced by Inman and Jenkins (1999). Some literature about local sand mining, including Beeby et al. (1999), also provides data about more recent occurrences in sand mining that are not available in the older, 1994 CDMG report. Some articles were also useful in examining the changes caused by human alterations on the two rivers and also provide quantifications of characteristics o f the 76 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. San Pedro Littoral Cell. Flick (1993) examines changes within this cell and relies upon Brownlie and Taylor’s (1981) estimates of natural sediment yield o f the rivers in determining the changes to the cell’s sand sources. Interviews Quantitative data provide one view of events. Questions of causation that may include policy decisions and natural or man-made occurrences are often difficult to asses using quantitative data alone. Interviewing or consulting officials who have direct involvement in decisions and are knowledgeable about events that have occurred will fill in many gaps and may explain some inconsistencies or trends. Additionally, such officials can identify the direction an agency will take in the future and provide insight on any anticipated changes prior to the changes being observed in the data. Several representatives from the three primary agencies—the United States Army Corps of Engineers, the Los Angeles County Department of Public Works, and the California Division of Mines and Geology—have been contacted for purposes of providing additional information. Agency officials include Andrew Kadib (coastal studies manager), Kerry Casey (hydraulic engineer) and Chris D. Bahner (hydraulic engineer) of USACE; Michael Bohlander (head o f hydraulic engineering section), Patricia Wood (hydraulic engineer, dams) and Loreto Soriano (debris basins) of LACDPW; and Russell V. Miller (senior geologist) of CDMG. 77 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. Each of these officials was referred to me by someone within their agency or was contacted because of their known expertise in the subject area. There was no set o f established questions for the interviews. They were conducted to answer questions specific to the respective agencies and the data that had been provided. For example, LACDPW employees were asked about the destination of sediment removed from their dams and debris basins. Each subject was contacted and interviewed on the telephone though some communication also transpired via mail and e-mail. During several of the longer telephone interviews, a tape recorder was used to document the details of the conversation. Analysis The primary data used for this research, obtained from the three agencies, were examined using Microsoft Excel software to graph the temporal and spatial patterns of sediment deposition and/or removal. Many o f the agencies used different measurement units, including acre-feet (USACE) and tons (CDMG), to record the data, so they first had to be converted to cubic yards, which was selected as the primary unit of measurement. One acre-foot is equal to 1,613.333 cubic yards, and so the data provided in acre-feet by USACE was converted by multiplying it by 1,613.333 cubic yards. The conversion from tons, a weight measurement, to cubic yards, a measure of volume, is much more difficult. The conversion can vary according to the grain diameter and porosity of the material. Approximately 97 78 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. pounds is equal to one cubic foot of aggregate (Bahner, 2001). Wright et al. (1954) confirms this conversion, stating that one cubic foot is equal to about 100 pounds for sand and gravel. One ton o f sand and gravel, using the Bahner’s (2001) conversion, is therefore equal to about 0.764 cubic yards. Each ton of aggregate measured by CDMG was multiplied by 0.764 to obtain the measurement in cubic yards. Following the conversion o f these measurements, the dams, debris basins and sand mining were then investigated in terms of their sediment deposition or removal patterns in the Los Angeles region. These structures and activities were examined and compared in terms of their physical size and the scope of their sediment entrapment or removal. The capacity, basin size, debris deposition and calculated maximum debris events were examined for the Department of Public Works’ 15 dams located in the San Gabriel Mountains. The capacity, basin size, years of existence, debris deposition and maximum debris events were looked at for the 106 debris basins that are located in the Los Angeles River and San Gabriel River watersheds. For both the LACDPW dams and debris basins, these characteristics were delineated in terms of both the total for the region and individual structures as well as trends on the watershed level. PCC aggregate mining was examined according to the production-consumption (P-C) regions defined by the California Division of Mines and Geology. The four P-C regions located entirely within Los Angeles County’s boundaries were examined in terms of resources, reserves and actual consumption. 79 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. The size of sediment deposited in dams and debris basins or removed in sand mining operations was also examined. This is important in the context that only certain sizes are compatible with the beaches that might be naturally nourished. The sediment sizes ideal for beach sand material can be determined by looking at the sizes that exist on the local beaches. In this case, the sediment sizes found at Seal Beach (shown in Figure 3-12), located downcoast of the Los Angeles River mouth and immediately below the mouth of the San Gabriel River, were considered representative of sediment sizes that would be suitable for beaches within the San Pedro Littoral Cell. The size data were obtained from a study done by Moffat & Nichol, Engineers (198S). The size of sediments found in dams and debris basins or those that are mined are examined for compatibility with those found on local beaches. 80 R eproduced with perm ission of the copyright owner. Further reproduction prohibited without permission. Chapter V—Results The structural interruption o f sediment transport within the watersheds of the Los Angeles and San Gabriel rivers and sand mining within Los Angeles County has been substantial. In terms of the interruption of sediment transport within the region’s waterways—which would naturally carry this sediment to local beaches— the Los Angeles County Department o f Public Works’ dams have had a significant influence. Annually, an average of about 2,242,000 cubic yards of sediment are deposited behind these 15 dams (LACDPW, 1999b). Based on the three U.S. Army Corps of Engineers’ (USACE) dams (Santa Fe, Whittier Narrows and Hansen dams) that have available data and which are the largest structures constructed by USACE in this region, the average annual deposition is a total of 727 acre-feet (about 1,173,000 cubic yards) for these three structures (Bahner, 2001). The annual sediment deposition in the 106 debris basins located in the Los Angeles River and San Gabriel River watersheds is, on average, 332,000 cubic yards (LACDPW, 1999a). By far, sand mining impacts the greatest amount o f sediment within Los Angeles County, with an average 21.4 million ton (approximately 16.35 million cubic yards) annual production rate for portland cement concrete aggregate that has been maintained through recent decades (Miller, 1994). 81 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. Dams The Los Angeles County Department of Public Works (LACDPW) built 15 dams in the San Gabriel Mountains—six within the Los Angeles River watershed and nine in the San Gabriel River watershed. The histories of these structures have been documented in spreadsheet form since their creation by the department (LACDPW, 1999b). Refer to Appendix II for a list o f these dams and their attributes. Construction commenced with Devil’s Gate Dam in 1920 and concluded with San Gabriel Dam in 1939. This 20-year period saw the creation of more than 223 million cubic yards of capacity to trap water and sediment over a drainage area totaling 481 square miles. The range of sizes, including both capacity and drainage area, varies greatly among the dams. The youngest and largest, San Gabriel, has more than 86 million cubic yards of capacity, and the smallest, Puddingstone Diversion, has just more than a 342,000-cubic-yard capacity. San Gabriel also has the largest drainage area with 203 square miles (about two-fifths of the total) and Live Oak has the smallest with 2 square miles. All of these dams are located in the San Gabriel River watershed. Characteristics of the other dams are documented in Appendix II. 82 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. 250,000,000 | 100,000,000 O > u 1 150,000,000 200, 000,000 50,000,000 0 ■Original Dam Capacity □ Sediment Deposited Los Angeles River Watershed San Gabriel River Watershed Figure 5-1: LACDPW dam capacity in comparison to sediment deposition Sediment amounting to about 65 percent o f the capacity of these dams, or just more than 144 million cubic yards (34.5 million cubic yards in the Los Angeles River watershed and 109.5 million cubic yards in the San Gabriel River watershed), has been deposited over the dams’ lifetimes. The dam capacity and sediment deposition were totaled using data from LACDPW distinguished on a watershed basis in Figure 5-1. As o f 1997, more than 42 million cubic yards of sediment remained in storage behind these dams, while just more than 101 million cubic yards had been removed. The data do not reflect the years and amount of maximum deposition, but that is important in the context of the extreme floods that cause a great increase in sediment transport (Inman and Jenkins, 1999). In the case of the debris basins, about one-fourth of the sediment deposited in the Los Angeles region arrived in these basins during a single maximum-debris-producing season, which can vary from basin to basin. It is more appropriate to compare these dams to the debris basins in 83 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. their respective watersheds, because their watersheds would reflect similar flooding and debris production characteristics. Approximately 37 percent of the sediment arriving in San Gabriel River watershed’s debris basins was derived during a single, maximum-debris-producing season. By applying this percentage to the total amount of deposition in the nine Department of Public Works dams within this same watershed, about 40.8 million cubic yards of sediment would have arrived during their maximum-debris-producing season. The remaining 68.8 million cubic yards would then have arrived during more typical conditions. The average amount deposited behind one of these dams during a year of normal conditions is about 123,000 cubic yards of sediment, while average deposition during an anomalous year (the year o f maximum debris production) would be, on average, 4.5 million cubic yards per dam. In the Los Angeles River watershed, 23.1 percent of sediment deposited in debris basins was attributable to single maximum events. This translates to nearly 8 million cubic yards of sediment for the six DPW dams in this watershed. The additional 26.5 million cubic yards would have been deposited during years of more normal deposition. The average amount arriving in one of these dams during a normal year would be approximately 66,000 cubic yards, while more than 1.3 million cubic yards would be deposited in a single dam during a flood season. Without separating the larger-than-normal events from the typical debris production histories of these dams, the overall average debris production for all 15 dams is 2,241,648 cubic yards annually. Each dam thus receives approximately 84 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. 150,000 cubic yards of debris each year. This is just more than 4,660 cubic yards of sediment per square mile drainage area. The United States Army Corps of Engineers has several structures in the Los Angeles region. There are three dams (one, Lopez, is occasionally referred to as a debris basin) in the Los Angeles River watershed and four in the San Gabriel River watershed, although two of these are located just within the Orange County border. Records have not been maintained through the history of these structures, but recent unpublished analyses have calculated annual debris deposition in the three largest dams. Lopez, Sepulveda and Hansen dams are located in the Los Angeles River watershed. Of the seven USACE dams, these three are in the middle in terms of size, with two larger and two smaller in the San Gabriel River watershed. Hansen is the largest o f the trio and an estimated 272 acre-feet (about 440,000 cubic yards) of sediment are deposited in it each year (Bahner, 2001). No recent annual deposition estimates exist for the other structures. Sepulveda Dam, which has a zero allocation for sediment deposition (meaning it was not planned/intended to store any sediment), had a total of 141 acre-feet (about 230,000 cubic yards) of sediment deposited between 1944 and 1961 (Bahner, 2001). This amount is small compared to deposition in other dams. The San Gabriel River watershed contains the two largest dams, Santa Fe and Whittier Narrows, and the relatively small Brea and Fullerton dams in Orange County. Santa Fe Dam is the farthest north, just below the San Gabriel Mountains, 85 R eproduced with perm ission of the copyright owner. Further reproduction prohibited without permission. and is followed by Whittier Narrows Dam that diverts water to either the San Gabriel River channel or the Rio Hondo (which connects a short distance later to the Los Angeles River). Brea and Fullerton dams provide flood control on tributaries of the San Gabriel River just outside Los Angeles County. Estimates of annual debris deposition exist for both Santa Fe and Whittier Narrows dams. Santa Fe receives approximately 125 acre-feet (about 200,000 cubic yards) of sediment annually, while Whittier Narrows collects 330 acre-feet (about 530,000 cubic yards) each year (Bahner, 2001). Some of the sediment in these two dams may have been sluiced downstream from LACDPW’s two upstream dams (San Gabriel and Morris dams) in San Gabriel Canyon in accordance with the San Gabriel Canyon Sediment Management Plan participated in by LACDPW and USACE (Wood, 2001). The combined debris deposition of Hansen, Santa Fe and Whittier Narrows dams is 727 acre-feet (1,173,000 cubic yards) annually. The amount for all seven dams would not be grossly larger than this figure since the three dams accounted for are the largest in terms of capacity. Some of the finer sediment in the USACE structures may be transported downstream when the structures are drained each year in preparation for floods (Bahner, 2001). Surveys are done regularly to determine the depletion of sediment allocation in each of the structures and, if sediment removal is necessary, options for removing the sediment are examined (Bahner, 2001). Some of the structures, particularly Hansen Dam, are mined on occasion by companies with the purpose of using the sand and gravel for construction (Bahner, 2001; Casey, 2001). 86 R eproduced with perm ission of the copyright owner. Further reproduction prohibited without permission. Debris Basins The Los Angeles County Department of Public Works, which is charged with the maintenance o f many of Los Angeles’ flood control facilities, also supplied the data (LACDPW, 1999a) that was examined to draw conclusions about the scope of sediment interruption caused by debris basins. O f the 115 debris basins that had been constructed and utilized in Los Angeles County by the end of the 1996-1997 storm season, 85 of them released waters to the Los Angeles River and 21 released waters to the San Gabriel River. Of the remaining nine basins, one released waters to Ballona Creek, six to Santa Clara River (in neighboring Ventura County), and two to Santa Monica Bay. To maintain focus on the two primary waterways responsible for the largest amount of sediment transport in the focus region, only the 106 debris basins associated with the Los Angeles and San Gabriel rivers will be examined. u E 3 o C & U M IB V S' « o> E 3 E x 7.000.000 6.000.000 5.000.000 4.000.000 3.000.000 2.000.000 1,000,000 0 90.000 | 80.000 g + 70,000 e 60.000 50.000 « - S 40.000 g -£ 30.000 « 20.000 » 10,000 g 0 < Los Angeles River Watershed San Gabriel River Watershed ■ Maximum Debris Capacity of All Basins □Average Maximum Debris Capacity Of A Single Basin Figure 5-2: Maximum capacity of basins in the Los Angeles River and San Gabriel River watersheds 87 R eproduced with perm ission of the copyright owner. Further reproduction prohibited without permission. Figure 5-2 illustrates the capacity differences according to watershed. The combined capacity o f the 85 debris basins in the Los Angeles River watershed totals 5,813,250 cubic yards, while the total for the San Gabriel River is 1,780,600 cubic yards. Although the capacity of the basins is larger in the Los Angeles River watershed, the capacity of individual basins in the San Gabriel River is, on average, larger. The average capacity of a single basin is about 68,000 cubic yards for the Los Angeles River and 85,000 cubic yards for the San Gabriel River. The basins of the Los Angeles River were designed to contain debris events averaging about 61,000 cubic yards, and those of the San Gabriel River were designed for just less than 64.000 cubic yard events on average. The debris basins in the Los Angeles River watershed have existed for several decades longer than those in the San Gabriel River watershed. The combined number o f storm seasons that the 85 debris basins of the Los Angeles River have gone through total 3,091 seasons (or years), which averages about 30 seasons per basin. Those in the San Gabriel River watershed add up to 620 seasons, or an average of 15 seasons per basin. In 1997, Los Angeles’ youngest was two years old and its oldest was 70. San Gabriel’s youngest was 12 years old and its oldest was 45. The amount of sediment that structures have trapped directly relates to the capacity and length of time these basins have existed. The basins in the Los Angeles River watershed have trapped a total o f about 11,752,000 cubic yards of sediment, as shown in Figure 5-3. Those in the San Gabriel River watershed have accumulated 2.555.000 cubic yards. The great incongruity in sediment deposition between the two 88 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. watersheds can be attributed to the difference in the number of basins in each, as well as the relative youth of the basins in the vicinity of the San Gabriel River. Looking at the average total for individual basins corrects for the uneven distribution of basins, although it does not adjust for the age differences. Los Angeles River averages about 143,000 cubic yards of sediment deposition per basin; San Gabriel River averages 122,000 cubic yards per basin. In terms of drainage area, about 6,000 cubic yards of sediment is deposited annually per square mile in the Los Angeles River watershed. Approximately 5,600 cubic yards of sediment is deposited annually per square mile of drainage area in the San Gabriel watershed, so sediment production is quite similar. Figure 5-3: Debris deposition in basins in the Los Angeles River and San Gabriel River watersheds Adjusting basin depositions in both watersheds for the number of years they have existed as well as for the uneven distribution finds that deposition trends are relatively similar in the two watersheds. The basins of the Los Angeles River Debris Deposition e 14.000.000 12.000.000 10,000,000 8,000,000 6,000,000 4.000.000 2.000.000 160,000— 140,000 § 120.000 2 g 100.000 o c u 80.000 « o 60.000 ° S 40.000 20.000 « 0 0 < Los Angeles River Watershed San Gabriel River Watershed ■Total Debris Deposited In All Basins □Average Debris Deposited In A Single Basin 89 R eproduced with perm ission of the copyright owner. Further reproduction prohibited without permission. watershed average about 3,200 cubic yards o f sediment annually. Those of the San Gabriel River watershed average nearly 3,400 cubic yards annually. This difference is probably within the range of measurement error. The combined 106 debris basins o f these two watersheds have an average o f almost 332,000 cubic yards of debris deposited in them annually. An average for each individual basin is thus nearly 3,300 cubic yards of debris annually. As a number of studies (including an in-depth examination in Inman and Jenkins 1999) have indicated, large flooding incidents are responsible for sediment production that is considerably larger than average sediment yields. The LACDPW data provides information—amounts and years—for maximum debris production events for each debris basin. These maximum debris production events are closely associated with the large flooding events identified as peak episodes during wet periods by Inman and Jenkins (1999). Their study stated that this region experienced a dry period from 1944 to 1968 that was followed by a wet period from 1969 to 1995. Within the wet period, there were strong El Nifio events every three to seven years that caused large runoffs as well as sediment yields (Inman and Jenkins, 1999). Sediment yield increased with the number of dry or low-flow years that preceded a wet-year event due to the build-up of sediment within the watersheds (Inman and Jenkins, 1999). Most importantly, transport of sand-sized sediment, as opposed to clay or silt, escalated as streamflow increased (Inman and Jenkins, 1999), which would indicate that these events were important in terms o f beach nourishment. 90 perm ission of the copyright owner. Further reproduction prohibited without permission. The Inman and Jenkins (1999) report examined 20 Southern California rivers on an individual basis, including the Los Angeles and San Gabriel rivers. The Los Angeles River was noted to have its highest flux/yield of suspended sediment in 1969, 1983 and 1978, respectively, all during the wet period (Inman and Jenkins, 1999). Examination of debris deposition in debris basins reveals that two of these years had similarly high levels of activity. The 1983 storm year may not have had significant sediment yield since it followed closely behind the 1978 storm that would have flushed much of the available sediment. Overall trends were recorded and available for 99 of the 106 debris basins that had a recorded maximum debris event and associated year. Most of the debris basins that lacked information about their maximum event did not have any data available (they were too new) or there were not any significant debris inflows that warranted a designation as a maximum event. Details of these records can be located in Appendix III. 91 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. u u u u i i i u u o i & d i i i i d i N ' J s a a c B O O O U a > < 0 N U > O B - ‘ « ' J O U a > < O t O < J I C D - * & - > 4 O C a > Debris Season I Size of Debris Events in LAR Watershed Size of Debris Events in SGR Watershed Figure 5-4: Total amount of debris production by year recorded for individual basins’ maximum event in the Los Angeles River and San Gabriel River watersheds Maximum event deposition trends are shown in Figure 5-4. This figure shows the combined debris production for the maximum events recorded for each debris basin. There is one maximum event per basin and the deposition amounts were summed when they occurred in the same season. There are small peaks during the late 1930s when more than 350,000 cubic yards of sediment were deposited. This event was a large one compared to the number of debris basins that existed during that time. There were only 16 debris basins and this time period was the maximum for most of them throughout their 60-plus year histories. There are also noticeable peaks during the 1968-69 season (a maximum for 10 debris basins; 546,400 cubic yards deposited) and the 1977-78 season (a maximum for 27 debris basins; 829,855 cubic yards deposited), which continued into the 1979-80 and 1980-81 seasons. A 92 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. small peak also occurred in the early 1990s and more than 300,000 cubic yards o f sediment was deposited between late 1991 and early 1995. In terms of the quantity of debris production, 1978, 1969 and 1938 had the greatest sediment production, respectively. Two of these three years matched maximum suspended sediment flux/yield years identified by Inman and Jenkins (1999). It is important to note that debris was produced throughout the 1960s, as shown in the graph, which was prior to the 1969 onset of the wet period that was identified by Inman and Jenkins (1999). Inman and Jenkins (1999) found that the highest flux/yield of suspended sediment on the San Gabriel River occurred in 1983, 1980 and 1969, respectively, all during the region’s calculated wet period (that was determined by using the Hurst method). Of the 21 debris basins in the San Gabriel River watershed, 18 of them reported a maximum debris deposition event and associated year. For half of these, the 1968-69 debris season resulted in the greatest amount of sediment deposition, totaling 912,900 cubic yards. This could be considered a “first flush” event, which removed sediment that had accumulated for decades during the dry period (Inman and Jenkins, 1999). Flood events after this flood would have less available sediment to transport. The remaining nine maximum debris events were primarily spread from late 1977 to early 1982. In terms o f the size of the events, 1969 had the largest, followed by 1981 and 1980. Once again, two of the three matched Inman and Jenkins’ (1999) maximum suspended sediment flux/yield years for the San Gabriel River. It is presumed that while 1983 had significant suspended sediment yield for the river that most of the debris that could have been transported to the debris basins 93 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. during that year had already been transported and deposited during the preceding years of significant flow. Unlike the Los Angeles River watershed, there were no recorded maximum debris production events during the dry period defined by Inman and Jenkins (1999). 3,000.000 2,000,000 1,500,000 1,000,000 500,000 60,000 50,000 ! 40,000 - 30,000 I 20.000 10,000 I Los Angeles River San Gabriel River Watershed Watershed B Total Of Maxim um Debris Events For All Basins □Average Maximum Debris Event For A Single B asin Figure 5-5: Total impact of maximum debris events in the Los Angeles River and San Gabriel River watersheds Although the data reflecting the highest flux/yield of suspended sediment and the maximum debris-producing events of debris basins did not match perfectly, there is an evident correlation that reflects the role of these abnormal events in the regional production and transport of sediment. Separating this maximum event from the total deposition amount for each basin provides a more accurate representation of sediment deposition during “normal” years. Figure 5-5 illustrates the vast differences in maximum debris events in the Los Angeles River and San Gabriel River 94 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. watersheds. O f the approximate 11,752,000 cubic yards of sediment deposited in the basins o f the Los Angeles River watershed, 2,719,000 cubic yards (or about 34,000 cubic yards per basin) were derived during the basins’ maximum production year. This means 23.1 percent of deposited sediment was produced during the maximum year. O f the nearly 2,555,000 cubic yards deposited in the basin of the San Gabriel River watershed, 1,604,000 cubic yards (or about 53,000 cubic yards per basin) were deposited during the non-maximum years. On average, the Los Angeles River’s debris basins receive slightly more sediment during a normal year than do those in the San Gabriel River watershed. A normal seasonal deposition for a single basin is about 2,500 cubic yards in the Los Angeles River watershed and nearly 2,400 cubic yards in the San Gabriel River watershed. These numbers are about 6.7 and 4.5 percent, respectively, of what occurs during a maximum event in these watersheds. The two watersheds have combined for a total of almost 14,307,000 cubic yards of deposition, of which more than 10,637,000 cubic yards—about three- quarters—have been deposited during normal, non-maximum years. On average, a year of maximum deposition leaves about 37,000 cubic yards in a basin and normal deposition is about 2,500 cubic yards annually. Sand Mining Sand mining data for Los Angeles County are based upon reports by Miller (1994). County resources amounted to approximately 11.9 billion tons (almost 9.1 95 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. billion cubic yards) of aggregate in 1994. Most of these resources are located in the Saugus-Newhall P-C Region (Figure 3-9) where there exists approximately 7.4 billion tons (about 5.65 billion cubic yards) of available aggregate. The Palmdale and San Gabriel Valley P-C regions have 1.8 and 1.6 billion tons (about 1.4 billion and 1.2 billion cubic yards) respectively. Palmdale, though not within the proximity of the Los Angeles and San Gabriel rivers, may be an important source o f aggregate for construction in the Los Angeles Basin in the future since nearby aggregate sources are being reduced. San Fernando Valley has the smallest available resources with only 259 million tons (almost 200 million cubic yards), almost 30 times less than Saugus-Newhall’s supply. A small amount of resources, about 800 million tons (about 611 million cubic yards), exist in the other P-C regions that overlap into Los Angeles County. Only about 6 percent, or about 749 million tons (about 572 million cubic yards), o f these aggregate resources were set aside for mining as o f 1994. The San Gabriel Valley P-C Region has the greatest amount set aside for mining with 334 million tons (about 255 million cubic yards), approximately one-fifth of its resources. The Palmdale and Saugus-Newhall P-C regions’ reserves are 207 and 158 million tons (about 158 and 121 million cubic yards) respectively. Data regarding aggregate production in the San Fernando Valley P-C Region were withheld for confidentiality reasons (Miller, 1994), because there are only two mining operations in the region and publishing an exact number would reveal one’s production amount, an industry secret, to its rival business (Miller, 2001). There are multiple mining 96 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. operations in the other P-C regions, so this is not an issue. Production has been estimated to be between 20 and 80 million tons (15.3 and 61.1 million cubic yards) and is referred to as being about 50 million tons (38.2 million cubic yards) (LACDRP, 1999). The reserves and consumption (which is interchangeable with the term production) within these P-C regions are shown in Figure 5-6. 350 « T 300 c c o 250 200 5 150 2 100 o > < 50 0 o T J C i f c C Q C/3 ¥ ^ O n c > ( 9 CO 3 2 “ I w z £ a T J E a CL □ Aggregate Reserves (Million Tons) 11994 Estimated Annual Consumption (Million Tons/Year) Production-Consumption Region Figure 5-6: PCC Aggregate reserves and consumption by production-consumption region Annual consumption of aggregate in Los Angeles County was nearly 4 percent o f its reserves in 1994, or about 28 million tons (about 21.4 million cubic yards) in that year. More than half of this, 16 million tons (about 12.2 million cubic yards), was used and produced in the San Gabriel Valley P-C Region. Palmdale P-C Region consumed 3 million tons (about 2.3 million cubic yards) and Saugus-Newhall P-C Region about 2 million tons (about 1.5 million cubic yards). San Fernando Valley P-C Region, which has the lowest quantity of both resources and reserves, 97 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. used about 8 million tons (about 6.1 million cubic yards) in 1994. With this rate of consumption, this region is expected to exhaust its reserves by 2001 (LACDRP, 1999). It is ideal for these P-C regions to maintain a 20-year supply of aggregate at all times (LACDRP, 1999), though reserves at aggregate sites serving metropolitan Los Angeles will be depleted in 20 years or less (Beeby et al., 1999). The reason for the lack of supplies in the San Fernando region is due to the unexpected growth in the population and economy that was not accurately projected in earlier calculations (LACDRP, 1999). As a result, this region will have to rely on supplies in the San Gabriel Valley and Saugus-Newhall P-C regions (LACDRP, 1999). Urbanization has spread throughout the region, which will make the siting of these large mines more difficult. Alternate sources of aggregate may have to be sought in the future. ^ 45 ,0 0 0 ,0 0 0 I 40 ,0 0 0 ,0 0 0 t 35 ,000 ,0 00 5 30 ,000 ,0 00 | 25 ,000 ,0 00 | 20,000,000 6 15 ,000,000 5 10,000,000 | 5,0 00,00 0 CO CO CD CO CO oo o o c o o o n o o n o Production Year Figure 5-7: Aggregate production in Los Angeles County from 1960 to 1992 98 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. Miller’s (1994) report examined aggregate consumption between 1960 and 1992, which is recorded in Figure 5-7. It only extends to 1992, not 1994, because data for 1993 was not available. In total, approximately 705 million tons (nearly 540 million cubic yards) of aggregate were consumed during this three-decade period, averaging 21.4 million tons (approximately 16.35 million cubic yards) annually during this period. The start and conclusion of this time period ranged from 5.8 million tons (about 4.4 million cubic yards) of aggregate produced in 1960 to 24.4 million tons (18.6 million cubic yards) in 1992. The height of aggregate production took place in the late 1980s with the greatest amount generated in 1988 at a rate of 40.7 million tons (almost 31.1 million cubic yards). A steady decline occurred after that point with a drastic dip in production of more than 12 million tons (almost 9.2 million cubic yards) between 1990 and 1991. As of 1994, the most recent year with data, the consumption rate was larger—about 28 million tons (about 21.4 million cubic yards) annually. An updated report is expected in approximately 2004, but in the interim new figures have not been calculated for PCC aggregate production in Los Angeles County (Miller, 2001). However, Los Angeles County remains as the greatest aggregate producer in the state (Miller, 2001). The combined counties o f Ventura, Los Angeles and Orange produce and use more PCC aggregate than any other U.S. metropolitan area with a combined 35 million tons (more than 26.7 million cubic yards) in 1997 (Beeby et al., 1999). This was not broken down by individual counties, so the most recent data for Los Angeles County is 1994. 99 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. Sediment Sizes and Availability for Transport Not all of the sediment that has been deposited in dams and debris basins or removed from mining sites is o f a size that would remain on beaches for any length of time. A Los Angeles County Flood Control District study examined the debris quality of its structures to determine whether there was any potential for the deposited sediment to be used for construction aggregate (LACFCD, 1959). A copy of the LACFCD report is no longer available, but it found that between 48 and 74 percent of the sediment deposited behind debris basins was sand-sized (Chambers Group, 1992). There are no known studies done in more recent years regarding the quality of the debris found in LACDPW’s structures (Bohlander, 2001; Wood, 2001). Applying these 1959 sand-percentage figures to the 14,306,928 cubic yards that have been deposited in these debris basins, between about 6.9 million and 10.6 million cubic yards of this material is sand-sized material. Applying these same percentage calculations to the LACDPW dams means that between 49 and 75.5 million cubic yards of sand-sized material have been removed from these structures and between 20 and 31 million cubic yards of sand-sized material is being stored. The seven dams maintained by the U.S. Army Corps of Engineers contain primarily very fine-grained sediment due to their location below many other sediment-trapping structures, though some, like Hansen Dam, may contain larger 100 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. sediments (Bahner, 2001). According to agency representatives, there are no known studies done on the composition o f the sediment that has been trapped and/or removed horn these dams. Portland cement concrete aggregate is half sand and half gravel (Miller, 2001). The 1994 annual rate o f production and consumption of this material was about 28 million tons (about 21.4 million cubic yards), so about 14 million tons (approximately 10.7 million cubic yards) of this was sand. Between 1960 and 1992, 705 million tons (nearly 539 million cubic yards) o f this aggregate was produced and used, of which 352.5 million tons (about 269 million cubic yards) would have been sand. Since none of the mining taking place in Los Angeles County is occurring in active riverbeds, it would be unlikely that any of this material would be available for transport to the beach (Miller, 2001). However, inactive channels and floodplains, including in the Tujunga Wash (in the Los Angeles River watershed) where mining operations are located, have reactivated during heavy storms (Bull and Scott, 1974). Although it is unlikely to recur, this could happen to the other mines that are in the vicinity of an active stream. The most important human impacts, therefore, are the dams and debris basins maintained by the Los Angeles County Department o f Public Works. Using the findings of the Los Angeles County Flood Control District’s 1959 study (Chambers Group, 1992), between 56 and 86 million cubic yards of sand has been deposited in these structures. This is a large amount of sand, which would be enough to create a 101 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. beach about 15 to 20 miles long and 100 yards wide. The sheer size indicates the significance of these structures as sediment traps. R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. Chapter VI—Conclusion The scope of sediment entrapment and removal in Los Angeles County due to man-made interference is substantial. Structures, including dams and debris basins, play significant roles in modifying the natural sediment delivery system in the region. Under natural conditions, beaches in Southern California relied predominantly on rivers and streams to provide sand nourishment (Griggs, 1987a), but the abundance of structures has interrupted the sand delivery process (Norris, 1964; Brownlie and Taylor, 1981; Griggs, 1989; Inman, 1989; Flick, 1993; Wiegel, 1994; Griggs, 1998). The extent to which beaches have been deprived of sand from these rivers has been difficult to quantify because alterations were made on these waterways prior to any measurement o f natural sediment delivery rates. This thesis has assessed the amount of sediment that is currently trapped or has been removed from the 106 debris basins and 15 Department of Public Works dams in the Los Angeles River and San Gabriel River watersheds. Estimated annual debris deposition was also examined for several of the large U.S. Army Corps of Engineers dams located in these two watersheds. And, lastly, the production of Portland cement concrete aggregate (construction aggregate) through sand and gravel mining was analyzed for the county. Each of these factors—the dams, debris basins and mining—has a potential for disrupting sediment transport. This was determined by examining individual deposition and/or removal patterns. Data were obtained from the agencies 103 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. responsible for monitoring these structures and industries. Additionally, interviews were conducted with representatives of these agencies, which included the United States Army Corps of Engineers, the Los Angeles County Department of Public Works and the California Division o f Mines and Geology. They provided information about the removal of dredged sediment, plans for the dredging of the sediment in the future, policies or plans that affect the draining of dams or the dredging of debris basins, etc. Annually, an average o f about 332,000 cubic yards o f sediment are deposited in the 106 debris basins of the Los Angeles River and San Gabriel River watersheds (LACDPW, 1999a). If the amount of sand-sized material ranged between 48 and 74 percent, as found by the Los Angeles County Flood Control District in 1959 (Chambers Group, 1992), the amount of sand trapped in debris basins would range between about 160,000 and 245,000 cubic yards each year. The LACDPW’s dams receive an average of 2,242,000 cubic yards of sediment every year, based upon the combined data regarding accumulated and removed sediment (LACDPW, 1999b). Again, using the LACFCD’s 1959 findings (Chambers Group, 1992), between 1,076,000 cubic yards and 1,660,000 cubic yards o f sediment annually deposited within these 15 dams could be sand-sized material. The sediment impoundment or removal attributable to the U.S. Army Corps of Engineers’ seven dams is relatively minor and the mining o f portland cement concrete aggregate is inconsequential in comparison to that o f LACDPW’s structures. The LACDPW structures are located in or in close proximity to the upper 104 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. reaches of the Los Angeles and San Gabriel rivers where the sediment originates. They are usually the first to encounter the sediment and are effective in trapping it (Miller, 2001), negating the influence of the many downstream structures and activities located in or near the coastal plain. The Corps of Engineers’ dams are located downstream of many LACDPW structures (dams and debris basins) that capture most sediment. In several o f the dams below San Gabriel Canyon, the sediment that is trapped in the structures has been released from upstream LACDPW dams where its measurements have already been quantified (Wood, 2001). What little sediment reaches the Corps o f Engineers structures is usually fine sediment unsuitable for beaches with occasional exceptions (Bahner, 2001). Hansen Dam, for example, receives some larger material that is occasionally mined and Lopez Dam/Debris Basin is small and requires dredging every 10 to 15 years to recover its capacity (Bahner, 2001.) However, the seven Corps structures are drained each year to vacate space for flood preparation and during this draining some finer sediments are transported in this water to the ocean (Bahner, 2001). Although the mining of aggregate for construction purposes may appear intrusive upon the fluvial environment and related sediment transport, it is not, in fact, significant in that context. There is no mining occurring in any active streambeds in Los Angeles County, thus making this aggregate unavailable for transport to beaches (Miller, 2001). Though the rivers at one time created the alluvial fans, including the Tujunga and San Gabriel fans, that serve as the primary source of 105 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. aggregate for mining in Los Angeles, there is little likelihood that this material would become accessible for transport by water (Miller, 2001). There has been at least one case where an inactive channel in Los Angeles has become reactivated when mining was occurring in it (Bull and Scott, 1974), but these events are rare. Mining areas are, however, a large consumer of sand and other material. O f the 28 million tons (about 21.4 million cubic yards) of portland cement concrete aggregate produced and consumed each year by 1994 (Miller, 1994), approximately half (about 10.7 million cubic yards) is sand-sized material. The average PCC aggregate consumption between 1960 and 1992 was 21.4 million tons (approximately 16.35 million cubic yards) (Miller, 1994), so about 10.7 million tons (8.2 million cubic yards) of sand were consumed each year during that time period for use in the production of portland cement concrete. While the amounts of sediments involved in aggregate mining are great, none of this would be available for transport unless a channel was to become reactivated or if it were to be artificially transported to beaches. The combined impact of the debris basins and LACDPW dams is an obstruction of almost 2,574,000 cubic yards o f sediment annually of which approximately 1,236,000 to 1,905,000 cubic yards is sand based on LACDPW deposition records (LACDPW, 1999a; LACDPW, 1999b) and the 1959 LACFCD debris quality study (Chambers Group, 1992). Excluding the amount of sediment deposited during each dam and debris basin’s maximum year, which is usually a significant portion of its total deposition, there are nearly 1,766,000 cubic yards of 106 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. sediment deposited behind dams and debris basins during a normal, non-maximum year on average. Between 848,000 and 1,307,000 cubic yards of this material would be sand sized using the LACFCD percentages. There is some degree of error in these values, but the amount is unknown since there may be inconsistencies in the methods used in calculating and recording sediment deposition since the time the structures were constructed. However, the methods would have had to undercount the total sediment deposition of the structures by about 58 percent in order to contradict other research findings and change the results of this thesis. The fluvial sources of sand, which were the greatest sand source in the San Pedro Littoral Cell’s sediment budget under natural conditions, are vital to the maintenance of the cell’s beaches. The individual processes occurring inland as part o f the fluvial sediment budget determine how much sand is eventually delivered as a source or “credit” to the littoral cell. Brownlie and Taylor (1981) estimated that the combined sand yield of the Los Angeles and San Gabriel rivers under natural conditions was approximately 600,000 cubic meters (about 784,000 cubic yards) annually. It is important to note that this figure would vary dramatically due to extreme flood events that would increase the sediment transport rates of rivers by enormous amounts (Inman and Jenkins, 1999). For less-urbanized rivers draining the Transverse Ranges during the 1969 flood, for example, the amount transported exceeded the sum of their average annual transport during the preceding 25-year dry period by a factor of 31 (Inman and Jenkins, 1999). These large events would diverge from an assigned average annual sand yield to a significant degree. For 107 R eproduced with perm ission of the copyright owner. Further reproduction prohibited without permission. planning and policy purposes, however, it is necessary to consider the average annual sediment transport rate of rivers. In recent years the actual annual sand yield of the combined Los Angeles and San Gabriel rivers has been 200,000 cubic meters (about 261,000 cubic yards), which is one-third of its estimated natural sand yield (Brownlie and Taylor, 1981). This means 400,000 cubic meters (about 523,000 cubic yards) o f sand that would normally make it to the San Pedro Littoral Cell beaches have become trapped inland each year. If Brownlie and Taylor’s (1981) measurements were indeed true, between 713.000 and 1,382,000 cubic yards of sand trapped annually (between 325,000 and 784.000 cubic yards of sand using the average that excluded maximum-year depositions) would have been deposited in the floodplain of the Los Angeles Basin, formerly a marine trough that was built-up through fluvial sediment deposition. This floodplain deposition would have increased the slope at the base of the mountains over time, which would have increased the sediment transport of the rivers. Also, some sediment would have been deposited in lowlands during flooding that covered large areas of the region. The other 523,000 cubic yards of sediment trapped annually would have made it to the beach. To put this in perspective of efforts to counter the erosion occurring in this cell, there is an average of 300,000 cubic meters (about 392,000 cubic yards) of sand placed on beaches each year between Sunset Beach and Newport Beach (refer to Figure 3-12) (Flick, 1993). The amount of sand nourishment necessary to maintain all of the beaches in this cell is similar to the amount currently withheld from the beaches due to inland obstructions. 108 R eproduced with perm ission of the copyright owner. Further reproduction prohibited without permission. The reduction in fluvial sand has resulted in an overall decrease in available sources within the sediment budget of the San Pedro Littoral Cell. There is very limited information about the natural conditions o f beaches within this cell, including whether they were naturally wide and accreting or naturally narrow. Inman (1954) states that most beaches in Southern California were naturally narrow, but includes in a list of naturally wide beaches Newport Beach, which is at the conclusion of the San Pedro Littoral Cell. While there is little known about the condition of many of the beaches in this cell prior to the onset of river alterations, it is expected that the average annual sediment contributions by rivers may have been minor and may have allowed erosion within the cell. However, large flood events would have greatly enhanced the beaches, perhaps maintaining their size during years of lesser sand yields that would have otherwise resulted in their disappearance. The natural transport of this sand along the beaches o f this littoral cell would be nearly impossible to accomplish today even if the dams and debris basins were removed. A number of jetties, groins and other structures have divided the San Pedro Littoral Cell into sub-cells, including massive harbor complexes that separate the mouths of the Los Angeles and San Gabriel rivers from the rest of the cell. This would prevent the transport of any sand delivered by rivers to continue through what would have been the cell’s natural littoral cell cycle, which included transport down the coast of Orange County and an exit at Newport Submarine Canyon. Artificial transport of the sand to the beaches seems to be the only viable option remaining. LACDPW would like to find a use for the trapped material 109 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. (Bohlander, 2001), which is normally discarded at sediment placement sites or in landfills (Soriano, 1999). Some material has been released through two of the dams in San Gabriel Canyon (Wood, 2001) and, in the past, some sediment was removed from debris basins and placed on beaches near Malibu (Bohlander, 2001). However, large-scale efforts to utilize the removed sediment have been hindered by the tremendous costs involved in transporting material removed from behind structures as well as roads that are unsuitable for frequent, heavy truck traffic (Bohlander, 2001). Some coastal communities spend millions of dollars importing sand or acquiring it from offshore areas. At the same time, agencies spend millions of dollars dredging sediment from behind debris and flood control structures. It appears that efforts are being duplicated and the financial expenses are being undertaken twice. A joint system needs to be established to permit trapped sediment, which is unwelcome in these inland areas, to be transported to coastal regions to nourish eroding beaches and to where it should have been delivered under natural conditions. The correlation between the two is clear, as is the solution. 110 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. Works Cited Bahner, Chris D. Hydrology and Hydraulics Section, United States Army Corps of Engineers, Los Angeles District. Telephone and e-mail communication. 29 Jan. 2001. Bailey, Thomas L., and Richard H. Jahns. “Ch. 6 Geology of the Transverse Range Province, Southern California.” Comp, by California Division of Mines. Geology of Southern California. Chapter U: Geology of the Natural Provinces. Bulletin 170. San Francisco: Division of Mines, Department of Natural Resources, 1954. Beeby, David J., Russell V. Miller, Robert L. Hill, and Robert E. Grunwald. Aggregate Resources in the Los Angeles Metropolitan Area. Miscellaneous Map No. 010. Sacramento: California Department of Conservation, Division of Mines and Geology, 1999. Best, T.C., and Gary B. Griggs. “A Sediment Budget for the Santa Cruz Littoral Cell, California.” From Shoreline to Abvss. Spec, issue of SEPM, No. 46 (1991): 35-50. Bigger, Richard. Flood Control in Metropolitan Los Angeles. Los Angeles: University o f California Press, 1959. Bird, Eric C. F. Beach Management. New York: John Wiley & Sons, 1996. Bohlander, Michael. Hydrologic Engineering Section, Los Angeles County Department of Public Works. Telephone communication. 23 Jan. 2001. Booth, William. “Restoring Rivers—At a High Price.” Washington Post. 10 Dec. 2000: A03. Bowen, A.J., and Douglas L. Inman. Budget of Littoral Sands in the Vicinity of Point Arguello. California. U.S. Army Coastal Engineering Research Technical Memorandum, No. 19,1966. Bray, Malcolm J., David J. Carter, and Janet M. Hooke. “Littoral Cell Definition and Budgets for Central Southern England.” Journal of Coastal Research. 11 (1995): 381-400. I ll R eproduced with perm ission of the copyright owner. Further reproduction prohibited without permission. Brown HI, William M., and Brent D. Taylor. 1982. “Part D: Special Inland Studies, Inland Control Structures.” Sediment Management for Southern California Mountains. Coastal Plains and Shoreline. EQL Report No. 17D. Pasadena, CA: California Institute of Technology, 1982.1-26. Brownlie, William R., and Brent D. Taylor. “Part C: Coastal Sediment Delivery by Major Rivers in Southern California.” Sediment Management for Southern California Mountains. Coastal Plains and Shoreline. EQL Report No. 17C. Pasadena, CA: California Institute o f Technology, 1981. Bull, William B., and Kevin M. Scott. “Impact of Mining Gravel from Urban Stream Beds in the Southwestern United States.” Geology. 2 (1974): 171-174. Casey, Kerry. Hydraulic Engineer, Hydrology & Hydraulics Branch, United States Army Corps of Engineers, Los Angeles District. Telephone Communication. 19 Jan. 2001. Chambers Group, Inc. Final Environmental Impact Report/Environmental Assessment for the BEACON Beach Nourishment Demonstration Project. SCH No. 91011072. Irvine, CA: Chambers Group, Inc., 1992. Chesser, Steve A., and Curt D. Peterson. “Littoral Cells of the Pacific Northwest Coast.” Coastal Sediments *87. New York: American Society of Civil Engineers, 1987.1346-1360. Chow, Ven Te. Handbook of Applied Hydrology: A Compendium of Water- Resources Technology. New York: McGraw-Hill, 1964. Collier, Michael, Robert H. Webb, and John C. Schmidt. Dams and Rivers: Primer on the Downstream Effects of Dams. USGS Circular 1126. Tucson, Ariz.: United States Geological Survey, 1996. Cooke, R.U. Geomorpholoeical Hazards in Los Angeles. London: George Allen and Unwin Ltd, 1984. Davis, Mike. Ecology of Fear. New York: Henry Holt and Company, Inc, 1998. Dean, Cornelia. Against the Tide: The Battle for America’s Beaches. New York: Columbia University Press, 1999. Department o f Navigation and Oceanic Development, California State Resources Agency. Shore Protection in California. N.p., n.p., n.d. 112 R eproduced with perm ission of the copyright owner. Further reproduction prohibited without permission. Dolan, Thomas J., Pamela G. Castens, Choule J. Sonu, and Anders K. Egense. “Review of Sediment Budget Methodology: Oceanside Littoral Cell, California.” Coastal Sediments ’87. New York: American Society of Civil Engineers, 1987.1289-1304. Eichblatt, Robert E. “Cal-Coast.” Ed. Lesley Ewing and Douglas Sherman. California’s Coastal Natural Hazards. Los Angeles: University of Southern California Sea Grant Program, 1998. Emery, Kenneth 0. The Sea off Southern California: A Modem Habitat of Petroleum. New York: Wiley, 1960. Evans, James R., Thomas P. Anderson, Michael W. Manson, Randall L. Maud, William B. Clark, and Donald L. Fife. Aggregates in the Greater Los Angeles Area. California. Special Report 139. Sacramento, CA: California Division of Mines and Geology, 1979. Fall, Edward W. “Part A: Regional Geological History.” Sediment Management for Southern California Mountains. Coastal Plains and Shoreline. EQL Report No. 17A.Pasadena, CA: California Institute of Technology, 1981. Ferrell, William R., W.R. Barr, K.D. Matthews, R. Nagel, and J.S. Angus. Report on Debris Reduction Studies for Mountain Watersheds. Los Angeles: Los Angeles County Flood Control District, 1959. Fischer, David W. “Coastal Hazards in Southern California: Los Angeles and Orange County City Responses.” Ed. Lesley Ewing and Douglas Sherman. California’s Coastal Natural Hazards. Los Angeles: University of Southern California Sea Grant Program, 1998. Flick, Reinhard E. “The Myth and Reality of Southern California Beaches.” Shore and Beach. 61 (1993): 3-13. Galster, Richard W., and Maurice L. Schwartz. “Ediz Hook—A Case History of Coastal Erosion and Rehabilitation.” Spec, issue of Journal of Coastal Research 6 (1990): 103-113. Graf, Walter Hans. Hydraulics of Sediment Transport. Highlands Ranch, Colorado: Water Resources Publications, LLC, 1984. Griggs, Gary B. “The Production, Transport, and Delivery o f Coarse-Grained Sediment by California’s Coastal Streams.” Coastal Sediments ’87. New York: American Society of Civil Engineers, 1987a. 1825-1838. 113 R eproduced with perm ission of the copyright owner. Further reproduction prohibited without permission. — . “Littoral Cells and Harbor Dredging Along the California Coast.” Environmental Geology. 10 (1987b): 7-20. — . “California’s Coastal Hazards.” Critical Problems Relating to the Quality o f California’s Coastal Zone. Background Papers for a Workshop: 12-13 January 1989. San Francisco: California Academy of Sciences, 1989. — . “California Needs a Coastal Hazards Policy.” California Coast & Ocean (1998): 30-33. Griggs, Gary B., and Lauret Savoy, ed. Living with the California Coast. Durham, N.C.: Duke University Press, 1985. Gumprecht, Blake. The Los Angeles River. Baltimore, Maryland: The Johns Hopkins University Press, 1999. — . “Who Killed the Los Angeles River?.” Forthcoming in Land of Sunshine: The Environmental History of Greater Los Angeles. Ed. William Deverell and Greg Hise. Pittsburgh: University of Pittsburgh Press, 2000. <http://geograDhv.ou.edu/research/killed.html>. Herron, William J. “Artificial Beaches in Southern California.” Shore and Beach (1980): 3-12. Inman, Douglas L. “Ch. 4. Beach and Nearshore Processes Along the Southern California Coast.” Comp. California Division of Mines. Geology of Southern California. Ch. V: Geomorphologv. Bulletin 170. San Francisco: Division of Mines, Department of Natural Resources, 1954. — . Summary Report o f Man’s Impact on the California Coastline. Sacramento, CA: California Department of Boating and Waterways, 1980. — . “Dammed Rivers and Eroded Coasts.” Critical Problems Relating to the Quality of California’s Coastal Zone. Background Papers for a Workshop. January 12-13. 1989. San Francisco: California Academy of Sciences, 1989. Inman, Douglas L., and J.D. Frautschy. “Littoral Processes and the Development of Shorelines.” Proceedings of the Coastal Engineering Specialty Conference. Santa Barbara. CA. Santa Barbara, CA: American Society o f Civil Engineers, 1966. 511-536. 114 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. Inman, Douglas L., and Scott A. Jenkins. “Climate Change and the Episodicity of Sediment Flux o f Small California Rivers.” The Journal of Geology 107 (1999): 251-270. King, Philip. The Fiscal Impact of Beaches. San Francisco: Public Research Institute, San Francisco State University, 1999. Kolker, Oded C. “Part D: Special Inland Studies, Inland Artificial Sediment Movements.” Sediment Management for Southern California Mountains. Coastal Plains and Shoreline. Pasadena, CA: California Institute of Technology, 1982. 27-49. Komar, Paul D. “The Budget of Littoral Sediments Concepts and Applications." Shore and Beach 64 (1996): 18-26. — . Beach Processes and Sedimentation. 2n d ed. Upper Saddle River, NJ: Prentice-Hall, Inc., 1998. Leidersdorf, Craig B., Ricky C. Hollar, and Gregory Woodell. “Human Intervention with the Beaches of Santa Monica Bay, California.” Shore and Beach (1994): 29-38. Los Angeles County Department of Public Works. Los Angeles Countv Department of Public Works Hydrology Manual. CD-ROM. Los Angeles: LACDPW, 1991. — . Los Angeles County Department of Public Works Sedimentation Manual. CD-ROM. Los Angeles: LACDPW, 1993. — . Debris Basins and Structures Alone Streams/Channels. Data as of 1996-97 Storm Season. Los Angeles: LACDPW, 1999a. — . Sediment Removal History for Department of Public Works Dams. Los Angeles: LACDPW, 1999b. — . Flood Control Fact Sheet. Los Angeles: LACDPW, 1999c. — . 1996-1997 Hvdroloeic Report. Los Angeles: LACDPW, 1999d. <http://dpw.co.la.us/hwc/report/9697>. Los Angeles County Department of Regional Planning. Soledad Canyon Sand and Gravel Mining Project Draft Environmental Impact Report. Project #91165. State Clearinghouse No. 9111106. Los Angeles: LACDRP, February 1999. 115 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. Los Angeles County Flood Control District. San Gabriel Reservoir—Debris Quality Study. Los Angeles: LACFCD, 1959. Los Angeles Times. “River Group Demands Removal of Matiiija Dam.” 11 Apr. 2000: B4. McPhee, John. The Control of Nature. New York: The Noonday Press, 1989. Miller, Russell V. Update o f Mineral Land Classification of Portland Cement Concrete Aggregate. Part II--Los Angeles County. Sacramento: California Department of Conservation, Division of Mines and Geology, 1994. — . Senior Geologist, California Division of Mines and Geology, Department of Conservation. Telephone Communication. 18 Jan. 2001. Moffatt & Nichol, Engineers. The Winterization o f Seal Beach. Long Beach, CA: Moffat & Nichol, Engineers, 1984. — . Preliminary Economic Study for the Seal Beach Groin. Long Beach, CA: Moffat & Nichol, Engineers, 1985. Moore, Jon T. “Let’s Mimic Mother Nature Instead.” California Coast and Ocean (1998): 34-36. Morelock, Jack. “Beach Sand Budget for Western Puerto Rico.” Coastal Sediments ’87. New York: American Society of Civil Engineers, 1987. 1333-1345. Morris, Gregory L., and Jiahua Fan. Reservoir Sedimentation Handbook: Design and Management of Dams. Reservoirs, and Watersheds for Sustainable Use. New York: McGraw-Hill, 1998. Mount, Jeffrey F. California Rivers and Streams: The Conflict between Fluvial Process and Land Use. Los Angeles: University of California Press, 1995. Noble Consultants. Civil/Harbor Engineering Design: Breakwaters. Jetties, and Groins. Irvine, CA: Noble Consultants, n.d. <http://www.nobleconsultants.com/breakwaters.htm>. Norris, Robert M. “Dams and Beach-Sand Supply in Southern California.” Ed. Robert L. Miller. Papers in Marine Geology. Shepard Commemorative Volume. New York: The Macmillan Company, 1964. 116 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. Osborne, Robert H., and Chia-Chen Yeh. “Fourier Grain-Shape Analysis of Coastal and Inner Continental-Shelf Sand Samples: Oceanside Littoral Cell, Southern Orange and San Diego Counties, Southern California.” From Shoreline to Abvss. Spec, issue o fSEPM 46 (1991): 35-50. Polakovic, Gary. “Imperiled Steelhead Caught in Dam Plans.” Los Angeles Times. 6 Dec. 1998: B3+. Reagan, James W. A Report on Floods. River Phenomena, and Rainfall in the Los Angeles Region. Los Angeles: University of California, Los Angeles, 1915. — . Report of J.W. Reagan Upon the Control of Flood Waters in this District bv Correction of Rivers. Diversion and Care of Washes. Building of Dikes and Dams. Protecting Public Highways. Private Property and Los Angeles and Long Beach Harbors. January 2. 1917. Los Angeles: Los Angeles County Flood Control District, 1917. — . Report of J.W. Reagan Upon the Control of Flood Waters in this District bv Correction of Rivers. Diversion and Care of Washes. Building of Dikes and Dams. Protecting Public Highways. Private Property and Los Angeles and Long Beach Harbors. April 1.1924. Los Angeles: Los Angeles County Flood Control District, 1924. Risling, Greg. “U.S. Agency OKs Santa Clarita Gravel Mining.” Los Angeles Times. 3 Aug. 2000: Bl. SANDAG. How to Save a Beach: A Practical Guide for the San Diego Region and an Invitation to Help. San Diego, CA: San Diego Association of Governments, n.d. Sandecki, Michael. “Aggregate Mining in River Systems.” California Geology 44 (1989): 88-94. Sharp, Robert P. “ 1. Some Physiographic Aspects of Southern California. Geology o f Southern California.” Comp, by Geology of Southern California Chapter IV: Geomorphologv. Bulletin 170. San Francisco: Division of Mines, Department o f Natural Resources, 1954. Sherman, Douglas J. “Human Impacts on California’s Coastal Sediment Supply.” California and the World Ocean *97: Taking a Look at California’s Ocean Resources: An Agenda for the Future. Vol. 1. Reston, Virginia: American Society of Civil Engineers, 1997. 117 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. Shih, Shyuer-Ming, and Paul D. Komar. “Sediments, Beach Morphology and Sea Cliff Erosion within an Oregon Coast Littoral Cell.” Journal of Coastal Research. 10(1994): 144-157. Soriano, Loreto. Los Angeles County Department of Public Works. Telephone communication. Sept. 1999. Taylor, Brent D. “Part B: Inland Sediment Movements by Natural Processes.” Sediment Management for Southern California Mountains. Coastal Plains and Shoreline. EQL Report No. 17B. Pasadena, CA: California Institute of Technology, 1981. Troxel, Bennie W. “Geologic Guide No. 3: Los Angeles Basin.” Comp, by Geology of Southern California. Bulletin 170. San Francisco: Division of Mines, Department of Natural Resources, 1954. United States Army Corps of Engineers. Preliminary Draft Environmental Statement. Los Angeles-Long Beach Harbors. Los Angeles: U.S. Army Engineer District, 1972. — . Shore Protection Manual. 2 vols. Vicksburg, Miss.: U.S. Army Engineer Waterways Experiment Station Coastal Engineering Research Center, 1984a. — . Los Angeles District. Coast of California Storm and Tidal Waves Study: Geomorphology Framework Report. Dana Point to the Mexican Border. Ref. No. CCSTWS 84-4. Los Angeles: United States Army Corps of Engineers, 1984b. — . — . Oral History of Coastal Engineering Activities in Southern California 1930-1981. Los Angeles: US ACE, 1986. — . — . “Los Angeles District Project Information V2.” <http://www.spl.usace.armv.mil/resreg/htdocs/proiect v2.html> Wiegel, Robert L. “Ocean Beach Nourishment on the USA Pacific Coast.” Shore and Beach. 62 (1994): 11-36. Wood, Patricia. Hydraulic/Water Conservation Division, Los Angeles County Department of Public Works. Telephone and mail communication. 6 Feb. 2001. 118 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. Woodford, A.O., J.E. Schoellhamer, J.G. Vedder and R.F. Yerkes. “Ch. 5 Geology of the Los Angeles Basin.” Comp, by Geology of Southern California. Chanter II: Geology of the Natural Provinces. Bulletin 170. San Francisco: Division of Mines, Department o f Natural Resources, 1954. Workman, Boyle. The City that Grew. Los Angeles: The Southland Publishing Co., 1935. Wright, Lauren A., Charles W. Chesterman, and L.A. Norman Jr. “7. Occurrence and Use of Nonmetallic Commodities in Southern California.” Comp, by Geology of Southern California. Chapter VIII: Mineral Deposits and the Mineral Industry. Bulletin 170. San Francisco: Division of Mines, Department o f Natural Resources, 1954. 119 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission o f th e copyright owner. Further reproduction prohibited without permission. Appendix I Southern California Littoral Cells SANTA B A n sA n A CONCEPTION SANTA BARBARA CE LL \ —_ J c< 1 "wn •. Wit. C «r" X ft} V » « < l *3 ■ i —= U i b e KILOMETERS LITTORAL CELL \* « * I I S o fx lftia d w i I f . _______ fteUyCoo*' ("siJBU ARJN E B A SIN ) M O N IC A — v - - - ‘C ’ ^ v ? T i > i N y V jb Y B A S I N / ^ N ... * “ S A N ( A Khun ’ Sonia Barbara I f \ ^ ! ' Sot n> (p o i I r C x SANTA MONICA CELL M 1 0 3 ANSEl E* SAN PEDRO CELL BASIN OCEANSIDE CELL Y C A TALIN A ' B A S IN \ \ • ^ V'* San CtetiHK I w e g o U N 01 ECO \ SILVER S IR , \ T ' v : I . s t .c o w l — I v ■ . c ' -O to o ( I n m a n 1 9 8 0 ) Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. Appendix II Dams Maintained by the Los Angeles County Department of Public Works Dam Year Completed Drainage Area Original Capacity1 Total Accumulated Sediment1 Total Sediment Removed1 Sediment in Storage1 Watershed Bis Dalton 1929 5 1,698,836 1,205,149 1,020,292 184,857 San Gabriel River Big Tuiunga 1931 82 10,067,179 13,967,237 13,253,051 714,816 Los Angeles River Cogswell 1934 22 19,840,732 7,029,097 2,687,146 4,341,951 San Gabriel River Devil’s Gate 1920 32 7,422,931 8,416,976 5.731,458 2.685,518 Los Angeles River Eaton Wash 1937 12 1,542,347 3,621,597 3,468,831 152,766 Los Angeles River Live Oak 1922 2 403,332 400,657 392,073 8,584 San Gabriel River Morris 1934 8 52,110,559 14,130,297 935,047 13,195,250 San Gabriel River Pacoima 1929 28 9,776,780 6,560,725 2,242,529 4,318,196 Los Angeles River Puddingstone 1928 33 28,068,715 1,710,129 6,453 1,703,676 San Gabriel River Puddingstone Div. 1928 20 342,027 1,370,341 1,355,419 14,922 San Gabriel River San Dimas 1922 16 2,516,800 3,872,061 3,867,428 4,633 San Gabriel River San Gabriel 1939 203 86,061,653 47,365,839 32,943,471 14,422,368 San Gabriel River Santa Anita 1927 11 1,524,600 33,247,590 33,015,802 231,788 Los Angeles River Sawpit 1927 3 767,945 711,638 598,705 112,933 Los Angeles River Thompson Creek 1928 4 926,051 475,123 408,172 66,951 San Gabriel River Total 481 223,070,487 144,084,456 101,925377 42.158379 Basin Average 32 14371.366 9,605,630 6,795,058 2 3 1 0 3 7 2 Percentage of Total Dam Capacity 61.8% 45.7% 18.9% (LACDPW 1999b) 1 M easured in square m iles. 2 M easured in cubic yards. Reproduced with permission o f th e copyright owner. Further reproduction prohibited without permission. Appendix III Debris Basins Maintained by the Los Angeles County Department of Public Works in the Los Angeles River and San Gabriel River Watersheds Debris Basin Year Completed Drainage Area i Capacity1 Debris Deposited1 Maximum Debris Event2 Maximum Debris Season Watershed Aliso 1970 2.77 41,700 243,717 52,206 1994-95 Los Angeles Arbor Dell 1971 0.11 12,400 1,481 800 1979-80 Los Angeles Auburn 1954 0.19 37,700 104,406 2,428 1961-62 Los Angeles Bailey 1945 0.6 128,800 291,811 5,612 1979-80 Los Angeles Beatty 1970 0.27 43,000 14,061 7,600 1979-80 San Gabriel Big Dalton 1959 2.94 517,800 859,003 296,700 1968-69 San Gabriel Bicbriar 1971 0.02 2,600 4,140 866 1992-93 Los Angeles Blanchard 1968 0.47 74,500 78,368 36,600 1977-78 Los Angeles Blue Gum 1968 0.19 39,600 41,619 19,100 1977-78 Los Angeles Brace 1971 0.29 30,300 41,755 12,000 1977-78 Los Angeles Bracemar 1971 0.01 700 671 283 1980-81 Los Angeles Bradbury 1954 0.68 89,800 274,144 70,200 1968-69 San Gabriel Brand 1935 1.04 166,000 276,813 53,100 1977-78 Los Angeles Buena Vista 1985 0.1 21,800 440 400 1992-93 San Gabriel Carriage House 1970 0.03 6,100 7,846 3,400 1979-80 Los Angeles Carter 1954 0.12 14,500 42,831 12,600 1979-80 Los Angeles Cassara 1976 0.21 36,700 29,687 16,800 1977-78 Los Angeles Chamberlain 1974 0.04 4,700 910 300 1974-75 Los Angeles Chandler 1995 0.16 20,300 (3 ) d> (!) " ....... Los Angeles Childs 1963 0.3 50,400 46.518 10.700 1980-81 Los Angeles Cloud Creek 1972 0.01 5,100 4,232 1,800 1977-78 Los Angeles Cooks 195! 0.58 51,900 174,821 61,200 1977-78 Los Angeles 1 M easured in square m iles. 2 M easured in cubic yards. (3 > D ata unavailable. N J N > Reproduced with permission o f th e copyright owner. Further reproduction prohibited without permission. Cooks M-l A 1975 33,700 (4 ) ---------- (4 )---------- (4) Los Angeles Crestview 1983 0.03 5,900 (5 ) '(JT" ..... 4 5 ) San Gabriel Deer 1954 0.59 56,600 171,511 44,200 1968-69 Los Angeles Denivelle 1976 0.18 7,900 9,837 5,500 1977-78 Los Angeles Devonwood 1981 0.05 10,800 6,584 5,800 1993-94 Los Angeles Dry Canyon - South Fork 1978 0.49 7,900 8,968 5,300 1979-80 Los Angeles Dunsmuir 1935 0.84 102,700 380,728 86,200 1977-78 Los Angeles Eagle 1936 0.48 63,100 200,078 41,700 1937-38 Los Angeles Elmwood 1964 0.31 61,100 56,061 16,100 1980-81 Los Angeles Emerald-East 1964 0.32 13,600 16,294 1,800 1985-86 San Gabriel Englewild 1961 0.44 40,600 87,450 60,200 1968-69 San Gabriel Fair Oaks 1935 0.21 23,800 116,240 15,700 1935-36 Los Angeles Fern 1935 0.31 43,400 188,352 23,900 1968-69 Los Angeles Fieldbrook 1974 0.35 2,800 2,254 500 1991-92 San Gabriel Golf Club Drive 1970 0.99 14,700 34,893 11,600 1979-80 Los Angeles Gordon 1973 0.18 32,600 5,604 3,800 1977-78 San Gabriel Gould 1947 0.36 52,800 122,273 18,000 1965-66 Los Angeles Gould Upper 1976 0.18 52,300 39,179 11,177 1991-92 Los Angeles Halls 1935 0.83 89,400 612,877 102,100 1937-38 Los Angeles Harrow 1958 0.43 68,000 78,347 63,400 1968-69 San Gabriel Haven Way 1991 0.13 38,200 (5) (!)' (!) Los Angeles Hay 1936 0.2 36,700 74,352 18,200 1937-38 Los Angeles Hillcrest 1962 0.35 57,800 52,649 11,700 1964-65 Los Angeles Hog 1969 0.32 42,500 10,534 3,900 1977-78 Los Angeles Hook East 1968 0.13 22,300 46,609 40,200 1968-69 San Gabriel Hook West 1970 0.17 21,600 7,268 3,600 1979-80 San Gabriel Inverness 1982 0.03 3,300 498 252 1982-83 Los Angeles Irving Drive 1974 0.03 1,200 1,746 600 1980-81 Los Angeles Kinneloa-East 1964 0.2 35,800 108,102 36,366 1993-94 Los Angeles (4 > D ata co m b in ed w ith C o o k s D eb ris B asin. < s > N o significant debris inflow s recorded. N > u > Reproduced with permission o f th e copyright owner. Further reproduction prohibited without permission. Kinneloa-West 1966 0.19 35,000 141,622 34,754 1993-94 Los Angeles La Tuna 1955 5.34 495,300 652,523 172,100 1977-78 Los Angeles Lannan 1954 0.25 41,400 84,767 18,200 1969-70 Los Angeles Las Flores 1935 0.45 55,600 239,060 36,000 1937-38 Los Angeles Las Lomas 1983 0.07 17,900 615 (51 (5) San Gabriel Limekiln 1968 3.72 171,600 348,858 42,300 1965-66 Los Angeles Lincoln 1935 0.5 38,400 139,793 28,400 1968-69 Los Angeles Linda Vista 1970 0.37 3,200 14,389 3,400 1977-78 Los Angeles Little Dalton 1959 3.31 660,500 928,373 337,800 1968-69 San Gabriel Maddock 1954 0.26 45,000 57,134 16,200 1980-81 San Gabriel May No. 1 1953 0.7 64,000 233,384 45,800 1968-69 Los Angeles May No. 2 1953 0.09 13,400 28,016 6,200 1966-67 Los Angeles Monument 1981 0.11 6,800 2,767 2,600 1981-82 San Gabriel Morgan 1964 0.6 79,100 30,841 12,900 1968-69 San Gabriel Mountbatten 1983 0.01 1,400 110 1 5 ) (5) Los Angeles Mull 1973 0.15 12,500 2,426 1,100 1979-80 San Gabriel Mullally 1974 0.34 9,400 65,706 24,400 1977-78 Los Angeles Oak 1975 0.05 12,000 13,267 6,900 1977-78 Los Angeles Oakxlade 1974 0.06 7,250 1,657 1,200 1977-78 Los Angeles Oakmont View Drive 1984 0.02 3,400 621 221 1991-92 Los Angeles Oliver 1989 0.18 32,100 31,980 16,255 1977-78 Los Angeles Pickens 1935 1.5 125,100 731,007 140,600 1977-78 Los Angeles Pinelawn 1973 0.02 3,200 5,509 1,200 1976-77 Los Angeles Rowley 1953 0.21 43,100 79,235 13,000 1977-78 Los Angeles Rowley (Upper) 1976 0.31 28,800 51,805 31,900 1977-78 Los Angeles Rubio 1943 1.26 148,000 345,798 133,000 1979-80 Los Angeles Ruby (Lower) 1955 0.28 28,600 21,032 8,300 1968-69 Los Angeles Santa Anita 1959 1.7 394,600 755,383 132,000 1961-62 Los Angeles Sawpit 1954 2.82 635,700 700,497 232,200 1968-69 Los Angeles Scholl 1945 0.66 9,300 20,072 3,500 1968-69 Los Angeles < s > N o significant deb ris inflow s recorded. 4 ^ Reproduced with permission o f th e copyright owner. Further reproduction prohibited without permission. Schoolhouse 1962 0.28 67,700 34,491 21,600 1962-63 Los Angeles Schwartz 1976 0.25 45,400 49,859 21,600 1977-78 Los Angeles Shields 1937 0.06 34,800 133,930 7,800 1937-38 Los Angeles Shields (Upper) 1976 0.21 40,400 43,247 16,900 1977-78 Los Angeles Sierra Madre Dam 1927 2.39 136,400 374,822 95,200 1968-69 Los Angeles Sierra Madre Villa 1957 1.46 402,300 774,422 171,775 1993-94 Los Angeles Snover 1936 0.21 24,800 109,960 19,300 1938-39 Los Angeles Sombrero 1969 1.06 87,900 14,355 3,300 1977-78 Los Angeles Spinks 1958 0.44 56,000 68,322 15,600 1968-69 San Gabriel Starfall 1973 0.13 14,900 29,123 14,200 1977-78 Los Angeles Stetson 1969 0.29 41,300 22,052 1,500 1977-78 Los Angeles Stongh 1940 1.65 180,600 162,119 44,100 1964-65 Los Angeles Sturtevant 1967 0.03 1,400 1,378 500 1977-78 Los Angeles Sunnyside 1970 0.02 3,400 4,164 1,621 1993-94 Los Angeles Sunset (Lower) 1963 0.45 158,900 143,580 20,200 1980-81 Los Angeles Sunset (Upper) 1928 0.44 15,900 149,680 27,000 1964-65 Los Angeles Sunset Canyon - Deer 1982 0.21 5,000 4,192 3,400 1982-83 Los Angeles Turnbull 1952 0.99 21,600 72,492 15,900 1968-69 San Gabriel Verdueo 1935 9.4 131,000 827,992 105,400 1937-38 Los Angeles Ward 1956 0.12 26,400 52,671 17,800 1977-78 Los Angeles West Ravine 1935 0.25 44,900 172,444 29,900 1937-38 Los Angeles Westridge 1974 0.02 1,400 294 (!) (!) San Gabriel Wilson 1962 2.58 313,100 216,134 55,500 1968-69 Los Angeles Winery 1968 0.18 29,200 27,215 9,400 1968-69 Los Angeles Zachau 1956 0.35 48,000 111,181 48,100 1977-78 Los Angeles Total 69.31 7.593.850 14.306.928 3.669.576 Averaee 0.65 71,640 138,902 36,696 % of Total Basin Capacity 188.4% 48.3% (5 > N o significant debris inflow s recorded. N > U l Appendix IV West Los Angeles County Debris Basins (LACDPW 1999d) R eproduced with perm ission of the copyright owner. Further reproduction prohibited without permission. Central Los Angeles County Debris Basins A •*- ( L A C D P W I 9 9 9 d ) 127 R eproduced with permission of the copyright owner. Further reproduction prohibited without permission. Eastern Los Angeles County Debris Basins • • • V a • ;x ■+(LACDPW I999d) 128 R eproduced with perm ission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission o f th e copyright owner. Further reproduction prohibited without permission. Appendix VI Los Angeles County Department of Public Works’ Debris Production Curve for the Los Angeles Basin iSiliSiglihsiiHnilm ■ ■•IfM M M IliiN M nilM III MMllitillUl I'O IIU ■ IMtlil M i •••■••*« I M M IH U IIU IIII ■ ■■■••vnM iiuniitiiiiiiiH iaiiiuiiiniiim iiK i ■ ■ ■ • ■ B M a i i i u i i t i i a t t i S i a t i i i t t i l i i i i m l ' i i M i i ■■■BaiBtiiiuiiitiiiiM hiiiiaiiiiniBHiiuuimtci iocooo ■ ■ ■ •a a a a a a iiiiiiiiiiiiiiih M ia iiiu iiiin iin nnm ■ ■ ■ ■ a a a a a a ii m i n i m u m m u HiiiHiiH'ti nu u • • • • a a a a i m i i i i i t m m i i i M i M i i t i i w r •' u r n ...... ■ J i t t i l i n n I t l H»tl»IMMil ltiilu • IMIIIiniUIBH......f'"- ••• * t M l 1 1 1 1 1 1 M I t lilt! L I I ■ ii iitm ti niitai ill ........ « ■ ■•aiaiiH I I I I I I I I I t J iH iii I S « i I I I ! M U 1 1 I I i M i t a t u 1 9 DRAINAGE AREA IN SQUARE MILES Los A n g eles County D e p o flm e m o l Public w o r n DEBRIS PRODUCTION RATES lo r L os A n g e e s B oiin (LACDPW 1993)
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Barron, Kamron Michele
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Anthropogenic alterations of fluvial sediment supply to the San Pedro Littoral Cell of California
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Geography
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environmental sciences,Geography,OAI-PMH Harvest,Physical geography
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Sherman, Douglas J. (
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