University of Southern California Dissertations and Theses

Shelf Sediment Transport System

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Shelf Sediment Transport System

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Content S H E L F SE D IM EN T TR A N SPO R T SYSTEM
by
J a m e s W esley V ern o n
A D is s e rta tio n P r e s e n te d to the
FA C U L T Y OF THE GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN C A LIFO RN IA
In P a r t i a l F u lfillm e n t of the
R e q u ire m e n ts fo r the D e g ree
DOCTOR OF PHILOSOPHY
(Geology)
J a n u a ry 1966
UNIVERSITY O F SOUTHERN CALIFORNIA
TH E GRADUATE S C H O O L
U N IV ER SITY PA RK
LOS A N G ELE S, C A L IF O R N IA 9 0 0 0 7
This dissertation, written by
.................... J.am es„W e.sley. Ve_r£on......................
under the direction of his Dissertation Com
mittee, and approved by all its members, has
been presented to and accepted by the Graduate
School, in partial fulfillment of requirements
for the degree of
D O C T O R OF P H I L O S O P H Y
Dean
D ate.....slaimar.y.*..1.9.6.6...
DISSERTATION COMMITTEE
Chairman
PLLASL liOTL:
Figure pages are not original copy.
They tend to curl. Filmed in the best
way possible.
University Microfilms , Inc.
CONTENTS
Page
LIST O F IL L U ST R A T IO N S .......................................................................... iv
A B S T R A C T ........................................................................................................... 1
IN T R O D U C T IO N ............................................................................................. 2
G e n e ra l s t a t e m e n t ................................................................................ 2
P r e v io u s s t u d i e s ................................................................................... 3
P h ilo so p h y of a p p r o a c h ...................................................................... 7
A c k n o w le d g m e n ts ................................................................................... 9
M E T H O D S ........................................................................................................... 11
T r a c e r sand and d y e in g ...................................................................... 11
D iving o p e r a tio n s ................................................................................... 14
T r a c e r sand re le a s e an d sam ple p o s i t i o n i n g ....................... 14
S a m p l i n g .................................................................................................... 20
U n d e rw ate r p h o t o g r a p h y .................................................................. 25
W ave and c u r r e n t m e a s u r e m e n ts ............................................... 32
L a b o r a t o r y .................................... 41
CH ARA CTERISTICS OF T E S T A R E A S ............................................... 43
San D ie g o .................................................................................................... 43
S a n ta C atalin a I s l a n d ......................................................................... 43
San P e d ro B a y .......................................................................................... 47
HYDRODYNAMIC S E T T I N G ...................................................................... 48
W a v e -in d u c e d s u r g e ............................................................................. 48
B o tto m s l o p e ............................................................................................. 50
ii
P ag e
The null point c o n c e p t......................................................................... 52
PA T T E R N S OF TR A C ER SAND D I S P E R S I O N .............................. 53
H o r i z o n t a l ................................................................................................. 53
O n s h o r e ............................................................................................. 53
N e u t r a l ............................................................................................. 64
O f f s h o r e ............................................................................................. 72
L o n g s h o r e ....................................................................................... 77
O b s t r u c t i o n s ................................................................................... 78
V e r t i c a l ....................................................................................................... 90
ANALYSIS OF DISPERSION P A T T E R N S ....................................... . 101
O n sh o re/o ffsh o re and o ffsh o re /o n sh o re r a t i o s .................... 101
R ates of t r a c e r san d m i g r a t i o n ..................................................... 107
V o lu m etric c a l c u l a t i o n s ................................................................... 113
SAND TRA N SPORT S Y S T E M ................................................................... 118
SIL T AND C L A Y -S IZ E P A R T IC L E TR A N SPO R T SYSTEM . . 124
C O N C L U S IO N S ................................................................................................. 131
R E F E R E N C E S .................................................................................................... 134
iii
LIST OF ILLU STRA TIO N S
F ig u re Page
1. G rain siz e d is trib u tio n c u rv e s of t r a c e r sands u s e d . . . 13
2. M ethod of placing dyed san d on bottom f o r sm all,
s h o r t- te r m t e s t ................................................................................ 16
3. T r a c e r sand on b o tto m at s t a r t of lo n g -te rm t e s t ............. 19
4. M ethod of m e a s u rin g b e a rin g and d is ta n c e to r e l e a s e
p o in t during s a m p l i n g ................................................................... 22
5. M a rk e r stak es u s e d to c o n tro l lo c atio n of sa m p le s .. . . 24
6. G re a s e d c a rd m e th o d fo r c o lle c tio n of su rfa ce la y e r
of s a n d .................................................................................................... 27
7. M ethod of opening sand rip p le s to o b tain sam p les fro m
the i n t e r i o r .......................................................................................... 29
8. C o llectio n of sa m p le at c r e s t of rip p le f o r size a n a ly s is 31
9. T r a c e r sand s c a tte r e d on the s e a bed by w ater
m o v e m e n t s .......................................................................................... 34
10. T im e - la p s e c a m e r a pho to g rap h in g san d r i p p l e s ................. 36
11. M ethod of m e a s u rin g sand rip p le d i m e n s i o n s ................... 38
12. M ethod by which c u r r e n t v e lo city along bottom w a s
m e a s u r e d w ith n e u tra lly -b u o y a n t d r o g u e ........................ 40
13. L o catio n of sand t r a c e r t e s t s , s o u th e rn C alifo rn ia c o a st 45
14. T est D. Iso p leth s showing t r a c e r san d m ig ra tio n in
d ire c tio n of w ave a d v a n c e ........................................................ 55
iv
F ig u re P ag e
15. T e s ts G and H p e r f o r m e d c o n c u rre n tly th a t show ed
sa n d m ig ra tio n in d ire c tio n of w ave a d v a n c e ................. 57
16. T e s ts M and N show ing d iffe re n tia l r a te s of t r a c e r sand
tr a n s p o r t a t w a te r depths of 12 and 35 f e e t .................... 59
17. T r a c e r te s t at S ilv e r S tran d b e a c h ........................................... 63
18. T e s t Y, n e u tra l and o n sh o re p a tte rn s of t r a c e r sand
d is tr i b u t i o n .......................................................................................... 66
19. T e s t W showing n e u tra l tr a n s p o r t p a t t e r n ............................... 68
20. T e s t T, an ex am p le of n e u tra l d is trib u tio n p a tte r n . . . . 70
21. T e s t U, an ex am p le of o ffsh o re m ig ra tio n of t r a c e r san d 74
22. T e s t Q show ing effects of sand rip p le s on t r a c e r sand
t r a n s p o r t ............................................................................................. 76
23. T e s t O. W ave and c u r r e n t e ffe c ts on sand m ig ra tio n . . 80
24. T e s t S. E ffe cts of c u r r e n t, w av es, and bottom slope on
t r a c e r san d m i g r a t i o n ................................................................... 82
25. A balone point fro m the a ir , site of T e s t A ................ 85
26. T e s t E . E ffect of ro c k o b stac le on san d m ig r a tio n . . . . 87
27. T e s t A. Sand m ig r a tio n n e a r a ro c k y h e a d l a n d ................... 89
28. T e s t Y. V e rtic a l d is p e r s io n of t r a c e r san d in sand
r i p p l e s .................................................................................................... 93
29. T e s t W. V e rtic a l d is p e r s io n of t r a c e r san d in sand
r i p p l e s .................................................................................................... 95
30. C u rv e s show ing dep letio n of t r a c e r san d at r e le a s e
p o in t d u rin g a p e rio d of 6 m o n th s (T e st Y ) .................... 97
31. C u rv e s show ing depletion of t r a c e r sand at the r e le a s e
p o in t d u rin g a p e rio d of 4 m onths (T e s t W ) .................... 99
v
F ig u re P ag e
32. O n sh o re/o ffsh o re ra tio s of t r a c e r san d m ig ra tio n
r e la te d to w a te r depths (wave h e ig h ts 2.5 fe e t) . . . . 104
33. R atios of o n sh o re and o ffsh o re m ig r a tio n d is ta n c e s
r e la te d to w a te r depths (wave h e ig h ts 0.75 fe e t) . . . . 106
34. T r a c e r san d m ig ra tio n r a te s r e la te d to w a te r depths
(wave h eig h t 1.5 f e e t ) ................................................................... 109
35. T r a c e r san d m ig ra tio n r a te s r e la te d to w a te r depths
(wave h eig h ts 2.5 f e e t ) ............................................................... I l l
36. M ig ra tio n ra te s of v e ry fine (0.10 m m ) t r a c e r san d
r e la te d to w a te r depths (wave h e ig h t 2.0 f e e t ) ............. 115
37. D ia g ra m m a tic p ro file show ing c o a s ta l sand c ir c u la tio n . 120
38. D ia g ra m m a tic p la n view of c o a sta l san d c irc u la tio n . . . 122
39. T u rb id w a te r n e a r c o a st w ith c le a r w a te r o ffsh o re . . . . 126
40. T u rb id shallow w a te r and its re la tio n s h ip to tu rb id
bottom w a te r o f f s h o r e ................................................................... 129
vi
A BSTRA CT
The o b se rv a tio n and m e a s u r e m e n t of flu o re s c e n t t r a c e r sand
m o v e m e n t on the s e a flo o r u n d e r fu ll- s c a le s e a conditions have o u t
lin ed m a jo r e le m e n ts of the se d im e n t tr a n s p o r t sy ste m o p e ra tiv e above
w ave b a se . M uch of th is p ic tu re h ad not h e re to fo re been defined in the
field.
O sc illa to ry su rg e acco m p an y in g su rfa c e w aves d riv e s the s y s
tem im p a rtin g m o v e m e n t to se d im e n t p re d o m in a n tly in the d ire c tio n of
w ave advance. S ed im en t is tr a n s p o r te d fro m c o a sta l s o u rc e s in p r e
d ictab le p a tte rn s w hich a re dependent m a in ly on su rg e v e lo c ity and d i
re c tio n , o th er c u r r e n ts , s e d im e n t g ra in size, and bottom slo p e. S ed i
m e n t m o v em en t p a tte rn s c a u se d by su rg e a re d is to rte d by th e c u rre n ts
of o th e r o rig in s.
A null lin e e x ists fo r a given se d im e n t siz e , w ave c h a r a c te r and
bottom slope. S edim ent s h o re w a rd of the null line m ig r a te s onshore;
se d im e n t se a w a rd of the null line m ig r a te s to w a rd w ave b a se . S ed i
m e n t m oves o n sh o re w ith in c re a s in g v elo city in shoaling w a te r, u lti
m a te ly e n terin g the s u r f - s w a s h lo n g sh o re d rift w hich in tu r n is lo cally
d e fle cte d o ffsh o re by rip c u r r e n ts o r ro c k y h ead lan d s. E v en tu ally s e d i
m e n t shifted o ffsh o re is ag ain re w o rk e d in the o n sh o re se d im e n t m o v e
m e n t induced by w ave su rg e.
S edim ent m oving in tr a c tio n and s a lta tio n is lo s t fro m the s y s
tem e ith e r w hen tra p p e d in s u b m a rin e canyons o r during p e rio d s of
la rg e w aves w hen se d im e n t is tr a n s p o r te d beyond the re a c h of n o rm a l
w av es. S edim ent kept in s u sp e n sio n by w a v e-in d u ced su rg e fo rm s a
dense tu rb id la y e r at the bottom which, as w ave e n e rg y d e c r e a s e s ,
flow s slow ly down the sea bed and beyond wave b a se into d e e p e r w a te r.
1
INTRODUCTION
G e n era l S ta te m e n t
A b a sic concept of geology is th at se d im e n t d e riv e d fro m lan d
m a s s e s is tr a n s p o r te d to s ite s of d e p o sitio n in the ocean. S tr e a m s v i s
ibly lo ad ed w ith se d im e n t d is c h a rg e into the ocean. E v id en ce of the
tr a n s p o r t and so rtin g of th is se d im e n t is d e te c te d in th e co m p o sitio n
and te x tu ra l p a tte r n s in b e a c h e s and on the s e a flo o r. Im p licit in the
o b se rv a tio n s is the e x iste n c e of p r o c e s s e s and m e c h a n is m s d e riv in g
th e ir e n e rg y fro m m oving w a te r w hich m o re o r le s s s y s te m a tic a lly
s o r ts and t r a n s p o r ts the se d im e n t to s ite s of d ep o sitio n . O b se rv a tio n s
of a n c ie n t s e d im e n ts show th at at su c h site s g r e a t th ic k n e ss e s of s tr a ta
m a y a cc u m u la te .
S tudies to define the paths an d p r o c e s s e s by w hich se d im e n t
m o v e s fro m its point of e n try into the o cean to its final point of d e p o s i
tio n and b u r ia l can be g ro u p e d on the b a s is of the m a jo r to p o g rap h ic
fe a tu re s c o m m o n to m o s t c o a sts: b e a c h e s, sh e lv e s, slo p es, su b m a rin e
canyons, o ffsh o re b a sin s and deep s e a flo o rs.
In g e n e ra l, know ledge of tr a n s p o r t p r o c e s s e s in the o cean is d e
finitive to a d e g re e w hich is in v e rs e ly p ro p o rtio n a l to th e depth of the
o v erly in g w a te r . A cco rd in g ly , c o n sid e ra b le p r o g r e s s h a s b een m a d e
to w a rd u n d e rsta n d in g p r o c e s s e s p e c u lia r to b e a c h e s, and re c e n t in v e s
tig a tio n s of su b m a rin e canyons have outlined in convincing d e tail the
p r o c e s s e s in th e ir h e ad s and to a l e s s e r d e g re e the p r o c e s s e s in th e ir
2
d e e p e r p o rtio n s. But, t r a n s p o r t m o d e s on the slope, in b a sin s , and the
deep se a fo r the m o s t p a r t have d efied d ir e c t o b s e rv a tio n and id eas
about th em have b e e n in f e r r e d fro m shape an d co m p o sitio n of m o d e rn
se d im e n t a c c u m u la tio n s an d an alo g o u s a n cie n t se d im e n t seq u e n c es.
T h e re re m a in s , th en , the sh e lf w h e re a c o n sid e ra b le body of d ata e x ists
re g a rd in g the co m p o sitio n and d is trib u tio n of sed im en t. T h e o re tic a l
m o d e ls of se d im e n t tr a n s p o r t, su p p o rte d by a n a ly s is of the p h y sic s of
w a te r m o tio n s and e n tra in e d sed im en t, have b een dev elo p ed to ex p lain
known se d im e n t d is trib u tio n p a tte rn s and to p r e d ic t d ire c tio n and ra te
of s e d im e n t tr a n s p o r t along the s e a bed. The r e s u lts of a few te s ts d e
sig n ed to tr a c e s e d im e n t m o v e m e n t on the sh elf have b een p u b lish ed ,
w hich, to g e th e r w ith th e o re tic a l c o n s id e ra tio n s , su p p o rt the id ea of s y s
te m a tic , p re d ic ta b le se d im e n t m o v e m e n ts on the sh elf and e m p h a s iz e
the n eed fo r field stu d ie s a im e d at outlining the p a tte r n of th o s e m o v e
m e n ts . It is the m a in o b jectiv e of the p r e s e n t study to p ro v id e the
n e e d e d fie ld o b se rv a tio n s to d e te rm in e the d ire c tio n s and r a te s of
m o v e m e n t of shelf se d im e n t. T h ese d ata m a y then be u sed to outline
the m a s t e r tr a n s p o r t sy ste m . The p rin c ip a l field tech n iq u e em p lo y ed
w a s to r e le a s e s a n d ta g g ed w ith a d istin c tiv e flu o re s c e n t dye and th e n
tr a c e its m o v e m e n t. M o st of the o b s e rv a tio n s have b een m a d e using
SCUBA-
P r e v io u s Studies
The d ire c tio n of sa n d m o v e m e n t on b e a c h e s is a fu n ctio n of the
angle of w ave ap p ro ach . W hen w a v es ap p ro a ch the c o a s t fro m a d i r e c
tio n o th er th an p e rp e n d ic u la r, sand is m o v ed along the sh o re in a z ig zag
c o u rs e in the d ire c tio n of th e lo n g sh o re com ponent of the s a v e s . The
r a te of m o v e m e n t h as b een e s tim a te d by co m p u tatio n s b a se d on m e a s
u re d e ro s io n and a c c re tio n of the b e a c h e s at key p o ints along the co ast.
C o m p arab le r a te s have b een deduced fro m a n a ly se s of t r a c e r san d
m o v em en ts on b e ac h e s in re s p o n s e to a w ide v a rie ty of wave c h a r a c
t e r is tic s , d ire c tio n s of w ave a p p ro ach , and san d te x tu ra l p a r a m e te r s
(Ingle, in p r e s s ) . S easo n al ch an g es of san d d is trib u tio n a re f a ir ly w ell
known, the b e a c h e s p ro g ra d e in s u m m e r and ero d e d u rin g the w in ter;
changes a re re fle c te d in d e p o sitio n of san d outside the s u rf in w in te r
and e ro s io n th e re d u rin g the s u m m e r.
A long the so u th e rn C alifo rn ia C o ast su b m a rin e canyons h ead
n e a r the s tra n d at s e v e r a l p o in ts. Sand is tra p p e d in the h ead s of th ese
canyons and in te rm itte n tly m o v es down the canyon into deep w a te r, and
is p e rm a n e n tly re m o v e d fro m the n e a r s h o re -b e a c h se d im e n t re g im e
(Dill, 1964).
Both th e o re tic a l and fie ld in v e stig atio n s have b een em p lo y ed to
a s s e s s the d ire c tio n s and r a te s of s e d im e n t m ig ra tio n on the shelf. The
th e o re tic a l stu d ie s have a tte m p te d to define the p h y sics of tra n s p o rtin g
m ix e d fluids and so lid s w hen m oving w a te r d is tu rb s so lid p a r tic le s on
the s e a bed. E a c h a tte m p t is b a se d on a ssu m p tio n s re g a rd in g the b e
h a v io r and d is trib u tio n of se d im e n t g ra in s on the s e a bed, and w a te r
m o tio n s p re s e n t.
T h ese stu d ie s and u n d e rw a te r o b se rv a tio n s point to su rg e , in
duced by p r o g r e s s iv e s u rfa c e w av es, a s the s tro n g e s t fo rc e a v ailab le to
m ove se d im e n t on m o s t of the shelf. T hey a ls o show th at su rfa c e
w av es a re acc o m p a n ied by a net d rift of w a te r in the d ire c tio n of w ave
p ro p ag atio n . G re a te s t w a te r t r a n s p o r t is at the su rfa c e and sig n ifican t
w a te r m o tio n and tr a n s p o r t p re v a il to a depth equal to about o n e -h a lf
th e d e e p -w a te r wave len g th of the su rfa c e w a v e s. O b serv ed and th e o
r e tic a l su rg e v e lo c itie s a re adequate to s tir bottom sed im en t and thus
a ffe ct tr a n s p o r t. On g e n tly -slo p in g s e a beds (le s s than about 3°)
Bagnold (1947) e s tim a te d that s e d im e n t w ill be tr a n s p o r te d in th e d ir e c
tio n of wave advance at a p p ro x im a te ly o n e -th ird the r a te of w a te r d rift.
T h e o re tic a l m o d e ls of sh elf sed im en t t r a n s p o r t a re dependent
upon the v a lid ity of a ssu m p tio n s w h ich are n e c e s s a r ily open to q u estio n
b e c a u se few of the a s s u m e d p a r a m e te r s have b e en m e a s u re d . F o r e x
a m p le, su rg e velocity acco m p an y in g w aves and the th re s h o ld tr a n s p o r t
v e lo c itie s of sed im en ts a r e not know n. F u r th e r m o r e , w a v e-in d u ce d
su rg e is o sc illa to ry , p ro d u cin g undefined p a r tic le conditions of m o v e
m e n t, r e s t an d b u ria l fo r unknown p e rio d s .
The a p p ro a ch an d re s u lt of the p r e s e n t study w e re m a in ly q u a li
ta tiv e but d a ta obtained w e re of su fficien t v o lu m e to achieve w ith c o n
s id e ra b le c e r ta in ty the p r im a r y o b jectiv e of outlining the p a tte r n s of
se d im e n t m o v e m e n t s e a w a r d of th e su rf. M a jo r co n clusions re a c h e d in
th is study a r e not d ep en d en t on the w o rk of o th e rs but a r e b a se d on the
r a t h e r s p e c ia l data o b tain ed and, th e re fo re , d e ta ile d c o m p a r is o n w ith
the s e v e ra l th e o re tic a l m o d els and fr a g m e n ta r y field m e a s u r e m e n ts of
o th e rs lack s in s tru c tiv e p u rp o se. A cco rd in g ly , d is c u s s io n of p r i o r
s tu d ie s is b rie f.
In r e c e n t p u b licatio n s p r i o r w o rk w ith t r a c e r s h as been t h o r
oughly re v ie w e d and ex ten siv e b ib lio g ra p h ie s c o m p ile d w hich d e a l a l
m o s t e x c lu siv e ly w ith th e use of t r a c e r s on b e a c h e s. A rev iew by G al
v in (1964) of the th e o ry and use of t r a c e r s in se d im e n t tr a n s p o r t
stu d ies e v a lu a te s p u b lish e d d a ta on t r a c e r use fro m w hich he concluded:
" T r a c e r s h av e b een p r a c tic a lly u seful to the c o a s ta l e n g in e e r in stu d ies
of shoaling, and they a r e beco m in g p r a c tic a lly u se fu l in stu d ie s of the
n et d ire c tio n , but not ra te , of litto r a l d rif t m o v e m e n t." A s im ila r but
m o re e x ten d ed re v ie w w as a ls o m ad e by A jbulatov, et a l. (1961).
P u b lish e d d a ta re p o rtin g r e s u lts of t r a c e r san d r e le a s e s s e a
w a rd of the su rf a r e few. One te s t u sin g ir r a d ia te d q u a rtz sand, r e
le a s e d in w a te r 10 fe e t deep off S crip p s Beach, r e s u lte d in p r e d o m i
nantly s h o re w a rd m o v e m e n t of the t r a c e r (Inm an, 1959). Ingle (in
p r e s s ) r e le a s e d flu o re s c e n t t r a c e r san d in a s im ila r situ a tio n and o n
sh o re t r a n s p o r t of the sand a lso o c c u r re d . B ritis h in v e s tig a to rs have
p u b lish ed r e s u lts of a flu o r e s c e n t t r a c e r study w hich had as its lim ite d
p u rp o se d is c o v e ry of the lo cal so u rc e of sand cau sin g a san d b an k to m i
g ra te (Jo lliffe, 1963). He stated :
The p rin c ip a l fa c t w hich e m e r g e d fr o m the use of t r a c e r w as the
la rg e d e g re e of d is p e rs io n . The w o rk d e s c rib e d above h a s d e m o n
s tr a te d th a t in the a r e a of L ow estoft h a rb o u r, san d m o v e m e n ts a re
c o n sid e ra b le and v e r y com plex; th at th e re is an exchange of m a t e r i
al b e tw ee n o ffsh o re banks and a d jac e n t b e ac h e s, and b etw een the o ff
sh o re banks th e m s e lv e s ; and th at s tro n g tid al c u r r e n ts a r e i n s t r u
m e n ta l in cau sin g la rg e c o a stw ise m o v e m e n ts of sand. M edium to
heavy sw e ll m ay have c o n trib u te d to s h o re w a rd d is p e r s io n of m a t e
ria l.
In o ther w o rd s , no w e ll-d e fin e d p a tte rn s of se d im e n t m o v e m e n t w e re
d isc o v e re d .
D ata on s c a tte r e d field te s ts of san d m o v e m e n ts a re too m e a g e r
to be sy n th e s iz e d in t e r m s of r a te s and d ire c tio n of m ig r a tio n w ith r e
sp ect to w a te r m o tio n s o r to develop a sch e m e of se d im e n t c irc u la tio n
w hich h as g e n e ra l ap p licatio n to shelf se d im e n ts.
P h ilo so p h y of A p p ro ach
S pecific and g e n e ra l a p p ro a c h e s to the p ro b le m w e re c o n sid e re d .
The f o r m e r w ould a tte m p t to define the re g im e n of indigenous san d
m o v e m e n t in a sp ecific a re a . The la tte r w ould be to d e te rm in e p a t
te r n s of s e d im e n t m o v e m e n t in s e v e r a l a r e a s and re la te th em to s e d i
m e n t and h y d ro g ra p h ic p a r a m e te r s w ith the ex p ec ta tio n th at p rin c ip le s
and m e c h a n is m s of m o v e m e n t having g e n e r a l ap p lic ab ility w ould
e m e r g e . The g e n e ra l a p p ro a c h w as p r im a r i ly p u rs u e d in th is study.
H ow ever, th e g e n e ra l a p p ro a c h h a s a re g io n a l affinity w ith the so u th ern
C alifo rn ia c o a s ta l se d im e n t re g im e n , in the se n s e th a t se le c tio n of a
su itab le t r a c e r sand and p o sitio n s of r e le a s e w e re b a se d on the known
cy cle of n e a r s h o r e se d im e n ta tio n of th a t a r e a .
S electio n of t r a c e r sand w as b a se d on c o n sid e ra tio n s of the
known sequence of se d im e n ta tio n ev en ts along the so u th e rn C alifo rn ia
c o a s t and the d e s ir a b ility of sim p lify in g a co m p lex p ro b le m by e l i m i
nating v a ria b le s w h e re p o ssib le .
M o st se d im e n t e n te r s the so u th e rn C alifo rn ia c o a s ta l w a te r s in
" slu g s" of p o o rly s o rte d se d im e n t ran g in g in g ra in siz e fro m c lay to
b o u ld e rs. T h e se " s lu g s " a re fro m s tr e a m s w hich c h a r a c te r is tic a lly
d is c h a rg e fo r only a few days o r w eeks d u rin g the w in te r. D uring i n
te r v a ls of d is c h a rg e , m a jo r s tr e a m s b uild v isib le acc u m u la tio n s of
sed im en t te m p o r a r ily se a w a rd into w a te r as deep as 30 fe e t and d i s
c o lo r w a te r m o re th a n 2 m ile s fro m s h o re . T hroughout the y e a r, h ow
e v e r, se d im e n t is s o rte d and tr a n s p o r te d by w aves and litto r a l c u r
re n ts at the sh o re and by w a v e -in d u c e d su rg e and o th e r c u r r e n ts s e a
w a rd of the su rf. The r e s u lt is e ro s io n of the a cc u m u la te d se d im e n t at
8
c o a s ta l p o in ts of s tr e a m d is c h a rg e and e sta b lis h m e n t of a m o re o r le s s
s y s te m a tic d is trib u tio n of it on the b e ac h and o ffsh o re. L ag d e p o sits of
c o a r s e m a te r ia l co m m o n ly r e m a in at th e point w h e re s tr e a m s debouch,
fo rm in g a "b o u ld er d e lta ," as at the m o u th s of V en tu ra and T iju an a
r i v e r s and a t C apitan, R incdn and o th er c re e k s in Santa B a r b a r a and
V en tu ra C ounties.
It is ax io m a tic that se d im e n t m o v e m e n t on g e n tly -slo p in g s e a
b ed s is a function of th re e v a ria b le s : w a te r m o v em en t, b o ttom slope
and se d im e n t p a r a m e te r s , m a in ly g ra in size. In asm u ch a s w a te r
m o v e m e n ts a t sea cannot be c o n tro lle d , but the g ra in size of t r a c e r
sa n d can, it w as d e s ir a b le to u s e s c r e e n e d sand of known b u t lim ite d
g r a in - s iz e ra n g e .
B a se d on the o b se rv e d m ode of e n try of sed im en t into the litto
r a l zone it w as concluded th a t t r a c e r san d s of known s o rtin g and of
c o m p o sitio n s im ila r to indigenous sand could be re le a s e d at m an y d if
f e r e n t s ite s and s till, to a re a so n a b le d e g re e , sim u la te the n a tu ra l c o n
d itio n of s o rtin g and tr a n s p o r t.
T r a c e r te s ts of both long and s h o r t te r m w e re m a d e . R esu lts
show that san d su sc e p tib le to even m o d e ra te ly ra p id t r a n s p o r t s p re a d s
in an in te rp re ta b le p a tte r n f o r only a few h o u rs befo re b eing " s m e a r e d "
by the effe cts of dilution, b u r ia l of the so u rc e , v a ria b le w ave d ire c tio n
an d c h a r a c te r , and shifting c u r r e n ts induced by tid a l flu ctu atio n s and
w ind. Sand m oved only by p e a k w a te r v e lo c itie s tended to re m a in in
the re le a s e a r e a fo r ex tended p e rio d s and y ie ld e d u n ifo rm p a tte rn s
a f te r w eeks and ev en m onths. They a r e e s s e n tia lly lag d e p o sits, the
g e n e ra l f o r m s of w h ich are a re c o r d of th e ir re a c tio n to m an y sh ifts of
9
w a te r f o r c e s .
A m a jo r o b stac le in th is study to re la tin g w a te r m o v e m e n ts to
sed im en t m o v e m e n ts w as the la c k of in s tru m e n ts and m a n p o w er to r e
c o rd data co n tinuously o v er a long p e rio d of tim e . H ow ever, r e a s o n
ably a c c u ra te m e a s u r e m e n ts of w av es and c u r r e n ts w e re m ad e fo r a
p e rio d of up to 24 h o u rs using sim p le in s tru m e n ts and v is u a l e s tim a te s .
A cco rd in g ly , s h o r t- te r m te s ts can be re la te d to h y d ro g ra p h y w ith som e
c e rta in ty but lo n g -te rm te s ts only in a g e n e ra l way.
A cknow ledgm ents
The w r ite r g ra te fu lly acknow ledges the v a rio u s s o u rc e s of a c a
dem ic, fin a n c ial and field a s s is ta n c e n e c e s s a r y to a cc o m p lish th is
study. The a c a d e m ic b a se fo r the stu d y w as the D e p a rtm e n t of G eology,
U n iv e rsity of S o u th ern C alifo rn ia. D r. Donn S. G o rslin e w as i n s t r u
m e n ta l in obtaining the n e ed e d fin a n c ial su p p o rt, p ro v id e d stim u la tin g
e n c o u ra g e m e n t th ro u g h o u t the c o u rse of the w o rk and c r itic a lly r e a d
the manusv.. nt. S pecial thanks a re due J a m e s C. Ingle, J r . of the D e
p a rtm e n t w hose w o rk in the use of flu o r e s c e n t sand t r a c e r s on b e ac h e s
d e m o n s tra te d the e ffe c tiv e n e ss of th e se in m e a s u rin g san d m o v em en t.
He a lso gave g e n e ro u sly of h is tim e in the fie ld to a s s i s t in the d e v e l
opm ent of te ch n iq u es applicable in th e w a te r beyond the su rf.
The chief so u rc e of fin an cial a id w as the C o asta l E n g in e e rin g
R e s e a r c h C en ter, U. S. A rm y , C o rp s of E n g in e e rs (C o n tra c t D A -49"
0 5 5 -C iv -E n g -6 3 -l 3). The U n iv e rsity of S o u th ern C a lifo rn ia p ro v id e d
boat and la b o ra to ry fa c ilitie s . A dditional s o u rc e s in clu d ed a G ra n t-in -
Aid fro m the A m e ric a n A sso c ia tio n of P e tro le u m G eo lo g ists, and
10
G e n era l O c ea n o g ra p h ies, Inc. who p ro v id e d boat u se in the San Diego
a re a .
A s s is ta n c e on and u n d e r the s e a w as re c e iv e d fro m a la rg e
n u m b e r of the g ra d u a te stu d en ts e n ro lle d in the G eology D e p artm en t.
All have the w r i t e r 's g ra titu d e . S pecial thanks a re given to H. J. S um
m e r s , U nited S tates N aval O rdnance T e s t Station; J. A. F o rm a n , M obil
Oil Com pany; F . S eg esm an , S anta P a u la , C alifornia; and P. J. C ra m p -
ton, S c rip p s In stitu tio n of O ceanography.
D r s. R ic h a rd O. Stone, John W. R eith, and H a ro ld H. Sullw old
re a d the m a n u s c rip t and su g g este d ch an g es of in te rp re ta tio n and org an i
zation.
M ETHODS
T r a c e r Sand and Dyeing
Sand for u s e as t r a c e r w as o b tain ed fro m the C alifo rn ia Sand
C om pany, E l Segundo, C alifo rn ia . This com pany ex ca v a tes san d fro m
c o a sta l dunes le s s th a n 1 m ile fro m the b each . It is c o m m e rc ia lly
s c r e e n e d by the co m p an y fo r s e v e r a l building and in d u s tria l a p p lic a
tions. G ra in size d is trib u tio n s of the t r a c e r san d s a r e shown in F ig u re
1. The san d s w e re q u a r tz - f e ld s p a r sa n d s containing only a s m a ll f r a c
tio n of h eav y m in e r a ls . A eo lian tr a n s p o r t fro m the beach to th e point
of e x cav atio n is not b e liev ed to have h ad any sig n ifican t e ffe ct upon the
hy d ro d y n am ic p r o p e r tie s of th e g ra in s. Any m in o r s u rfic ia l fe a tu re s
d ev eloped by a eo lian t r a n s p o r t a re su b d u ed by dyeing.
The two fra c tio n s w e re dyed in c o n tra stin g flu o re s c e n t c o lo rs
by the G re a t A m e ric a n C olor C om pany of Los A n g eles, C alifo rn ia . The
c o lo rs u s e d w ere g re e n and r e d w hich w e re in c o rp o ra te d in an a i r -
cu rin g p la s tic b a s e . Ingle (in p r e s s ) r e p o r te d th a t dyeing d o es not a f
fe c t the h y d ro d y n a m ic p r o p e r tie s of the san d sig n ifican tly .
Sand fro m S c rip p s B each w as u s e d in s e v e r a l te s ts m a d e in the
San Diego a re a .
W ords u s e d h e re in d e s c rip tiv e of sed im en t g ra in s iz e s conform
to the sta n d a rd W entw orth g ra d e scale.
11
F ig u re 1 ,— G ra in siz e d is trib u tio n c u rv e s of
t r a c e r sands u sed . N u m b e rs on c u rv e s a re m e d ia n
g ra in siz e . The 0.42 m m and 0.25 m m sands a r e
s c r e e n e d fra c tio n s; the 0.10 m m sa n d is fro m
S c rip p s B each, L a Jo lla , C alifo rn ia.
DIAMETER IN mm.
N
CUMULATED FREQUENCY
_ ro o i o > - « j a > < o o
o o o o o o o o o o
0.10
u >
14
Diving O p eratio n s
E x ecu tio n of the field w o rk of th is p ro je c t w as m ad e p o ssib le by
the d ev elo p m en t of fr e e -d iv in g eq u ip m en t known a s SCUBA (Self C o n
tain ed U n d e rw a te r B re ath in g A p p a ra tu s). F ie ld w o rk fo r th is p r o je c t
re q u ire d about 400 dives to depths a s g re a t as 100 feet.
A lthough a few te s ts w e re m ad e using te ch n iq u es not involving
diving, it w as soon e s ta b lis h e d th at diving p ro v id e d s e v e ra l ad v an tag es
which m a d e its u se highly ad v an tag eo u s. A m ong the m o re im p o rta n t of
th ese a r e n e a tn e s s of t r a c e r san d r e le a s e , p r e c is io n of sam p le lo c a
tions r e la tiv e to th e r e le a s e point, ra p id ity of sam p lin g , u se of u n d e r
w a te r p h o to g rap h y , o b s e rv a tio n s of m ic ro -to p o g ra p h y and w a te r m o v e
m en ts.
T r a c e r Sand R e le a se and Sam ple P o sitio n in g
M o st of the te s ts c o n sis te d of r e le a s in g a few pounds to s e v e ra l
h u n d red pounds of flu o r e s c e n t dyed sa n d at a p o in t on the o cean bottom .
At tim e d in te rv a ls ran g in g fro m a few m in u te s to s e v e r a l m o n th s s a m
p les of s a n d w e re ta k en in the v icin ity of the p o in t of r e le a s e . T h ese
alw ays in clu d ed the su rfa c e but s o m e tim e s ad d itio n al sa m p le s w e re r e
c o v e re d a s deep a s s e v e ra l in ch es below the se d im e n t su rfa c e .
S m a ll a m o u n ts of sand, up to 15 pounds, w e re c a r r i e d to the
bottom in p la stic b a g s or in a h a rd p la s tic c o n ta in e r having a tig h tly -
fitting top (Fig. 2). To in s u re w etting of the g ra in s and to p re v e n t them
fro m flo atin g , the sand w as m ix e d w ith s e a w a te r containing hou seh o ld
d e terg en t. H ow ever, w hen la r g e am ounts of san d w e re r e le a s e d it w as
not p r e - w e tte d but w as d ro p p e d to the bottom in s tu rd y p a p e r b ag s.
F ig u re 2 . — M ethod u se d fo r e m p la c e m e n t of
dyed sand on bottom fo r sm all, s h o r t- te r m t r a c e r
te s t.

17
W hen r e le a s e d , som e g ra in s flo a te d b e c a u se of a tta ch e d a ir bubbles,
and th e s e m a y have in tro d u c e d m in o r e r r o r s in the e a r ly sam p lin g , but
p ro b a b ly did not have an im p o rta n t effect on r e s u lts of sa m p le s tak en
s e v e r a l h o u rs, days o r w eek s a f te r re le a s e .
T e s ts w e re m ad e w ith the g re e n and r e d sand m ix e d or s e p a
ra te . W hen r e le a s e d s e p a ra te ly th ey w e re p la c e d in p ile s the ed g es of
w hich w e re touching (F ig . 3). U su ally the to p s of the p ile s w e re f l a t
te n ed to co n fo rm so m ew h at w ith the se d im e n t s u rfa c e . The bags of
sand w e re p la c e d on the s e a flo o r and opened by cutting the bottom s u r
face, allow ing the san d to flow out sm oothly. When the h a r d p la stic
c o n ta in e r w as u s e d the cap w as co m m o n ly re m o v e d and the c o n tain er
in v e rte d and h e ld a fr a c tio n of an inch above the s e a flo o r. As the san d
flow ed fro m b e n ea th the lip the c o n ta in e r w as r a is e d slow ly until all the
sand w as re m o v e d . T h is technique m in im iz e d the a r e a c o v e re d by the
sand.
A buoy o r stake w as u tiliz e d to m a r k the r e le a s e p o sitio n . A
stake w as u sed only w h e re n e a rb y r e fe re n c e points in s u re d th a t it
could be re lo c a te d . A sta k e o r the a n ch o r of the buoy a lso s e r v e d a s a
m a r k e r fo r p o sitio n in g the sa m p le s .
Buoys a lre a d y in p lace fo r o th er p u rp o s e s w e re u s e d to m a r k
the r e le a s e p oint when p o s sib le . W h ere none w as av ailab le , buoys w e re
c o n stru c te d of 1 -g allo n p a in t c an s and p o le s w ith fla g s. The top of the
pole w as p la ce d at a known d ista n c e above th e top of the su p p o rtin g
can s, u su ally b etw een 5 and 10 fe e t. D uring the in itia l p h a se of s a m
pling fro m b o a ts the p o sitio n of the boat re la tiv e to the buoy (the r e
le a s e point) w as d e te r m in e d by m e a s u rin g th e d ista n ce w ith a s ta d i-
F ig u re 3 .— T r a c e r san d on bottom at s t a r t of
lo n g -te rm te s t. T e st Z, P a r s o n s Landing, Santa
C atalin a Island. W ater Depth 35 feet. B ottom is
g ra v e lly w ith inactiv e rip p le s of w ave length of
about 1.5 feet.

20
m e t e r and the b e a r in g w ith a c o m p a s s . The known h eig h t of the pole on
the buoy p ro v id e d the n e c e s s a r y r e f e r e n c e . W here ob jects of known
h e ig h t w e re n e a r the r e le a s e point th e se w e re u se d in a s i m i l a r m a n n e r
to d e te r m in e the b o a t’s p o sitio n . S am pling fro m the bo at p ro v e d to be
difficult, tim e -c o n s u m in g and p o sitio n s w e re not su fficien tly a c c u ra te
fo r sam p lin g c lo se to the r e le a s e point. T his m eth o d w as th e n a b a n
doned in fa v o r of sam p lin g by d iv e rs .
S am ple lo c a tio n s w e re m a d e u n d e rw a te r by d iv e rs u sin g a line
m a r k e d at a p p ro p ria te d is ta n c e s . The line w as a tta c h e d to the stake or
buoy and the d iv e rs m a in ta in e d a m e a s u r e d d ista n ce fro m the r e le a s e
p o in t as th ey sw am in c o n c e n tric c ir c le s . P o s itio n s along the c i r c u m
fe re n c e of the c ir c le s w e re u su a lly d e te rm in e d by c o m p a ss b e a rin g s
ta k e n along the line (F ig. 4). W h ere w a te r v is ib ility w as good, p o s i
tio n s on the c ir c le s w e re m ad e by using the san d rip p le p a tte r n fo r
r e fe re n c e . On som e te s t s the sam p le lo c atio n technique w as m o d ified
fo r a se le c tiv e c lo s e - in sam p lin g p a tte rn . W ire m a r k e r s ta k e s w e re
in s e r te d along the c r e s t s of the rip p le s at m e a s u r e d d is ta n c e s fro m the
r e le a s e p oint (Fig. 5). The rip p le p a tte r n w as th en m e a s u r e d and p lo t
ted. S am p les w e re r e c o v e r e d along lin e s p e rp e n d ic u la r to the rip p le
tr e n d and th e ir p o sitio n s on the c r e s ts ,tr o u g h s and flanks w e re r e
c o rd e d on a s la te . C o n c u rre n tly , p h o to g ra p h s w e re ta k en to show the
d is trib u tio n of the c o lo re d g ra in s .
Sam pling
S am p les to d e te rm in e flu o r e s c e n t sand g ra in c o n c e n tra tio n s
w e re ta k en by p r e s s in g c a r d s c o ated w ith p e tro le u m je lly (c ry s ta l w hite
F ig u re 4 . — M ethod of m e a s u rin g b e a rin g and
d is ta n c e to r e le a s e p oint d u rin g sam p lin g .
22
« '- V
F ig u re 5 .— M a r k e r stak e s u s e d to c o n tro l
lo c atio n of s a m p le s .

25
USP) a g ain st the sed im en t s u rfa c e (Fig. 6). To obtain sa m p le s below
the su rfa ce a tro w e l (Fig. 7) w as u s e d to re m o v e the s u rfa c e sand.
S am p les fo r g ra in size a n a ly se s w e re tak en in g la ss v ia ls (Fig. 8). The
m o s t s a tis fa c to ry c a r d s w e re of b la ck vinyl p la s tic 0.015 inch thick,
w hich w e re m a c h in e -c u t to 2 x 2 in ch es. C om m only 25 to 30 s a m p le s
w e re tak en on one dive. The sa m p lin g c a r d s w e re n u m b e re d s e q u e n tia l
ly and c o v e re d w ith su fficien t p e tro le u m je lly to in su re co m p lete c o v
e ra g e of the c a r d even a fte r the c o v e r c a r d w as rem o v ed . On each w as
p la c e d an id e n tic a l c o v e r c a rd w hich s e rv e d the dual p u rp o s e of p r e
venting c o n tam in atio n a fte r sam p lin g and allow ed the s a m p le r to c a r r y
th e m stack ed . One c o r n e r of e ac h co v er c a r d w as clipped to aid in
se p a ra tin g the two c a r d s u n d e rw a te r. D uring a sam p lin g ru n one d iv e r
su rv e y e d and pointed to the lo c atio n s fo r sa m p lin g w hile the o th er d iv e r
sam p led . The s a m p le r s e p a ra te d the sam p lin g c a rd at the top of the
p a ck fro m its c o v er c a rd , took the sam p le at the in d icated p o sitio n by
p r e s s in g the c a r d gently a g a in st the se d im e n t su rfa c e , re p la c e d the
c o v e r c a r d and m oved both c a r d s to the b o ttom of the pack . When s a m
pling n e a r the r e le a s e p o sitio n it w as p o ssib le to re c o v e r 25 sa m p le s
in 10 m in u te s.
S en sitiv ity of the g re a s e d c a r d m eth o d is a function of the c a r d
siz e . Using c a r d s 2 x 2 inches it is p o ssib le to c o lle ct about 40,000
g ra in s w ith a m e d ia n d ia m e te r of 0.25 m m o r about 14,000 g ra in s w ith a
m e d ia n d ia m e te r of 0.42 m m . A cco rd in g ly , the se n s itiv ity is about
1/40,000 and 1/14,000 re s p e c tiv e ly .
U n d e rw a te r P h o to g rap h y
U n d e rw a te r s till p h o to g rap h s in c o lo r and b lack and w hite w e re
i O
F ig u re 6 . — S am ple re c o v e ry of the su rfa c e
la y e r of san d using a g re a s e d c a rd .
27
C
J
F ig u re 7 . — M ethod of opening sand rip p le s
to obtain s a m p le s fro m the in te r io r .
K
29
•'i¥\
F ig u re 8 . — Sam ple c o lle c tio n at c r e s t of
rip p le fo r g ra in size a n a ly sis.
31
32
u s e d to r e c o r d the p a tte r n of flu o r e s c e n t san d s p re a d n e a r the re le a s e
p o in t (Fig. 9). P h o to g rap h s w e re ta k en on e ac h sam p lin g day w hen p o s
sib le . To so m e extent tim e - la p s e and m o tio n p ic tu re c a m e r a s w e re
u s e d to study m ic ro -to p o g ra p h y and sand m ig ra tio n . T im e - la p s e p h o
to g ra p h s of san d rip p le s w e re obtained o v e r p e rio d s of s e v e r a l h o u rs
u sin g in te rv a ls b etw een p h o to g rap h s of 2.5 to 45 seco n d s (Fig. 10).
T h e se tech n iq u es a s s is te d in re c o rd in g the m o v e m e n t of san d on the
rip p le c r e s t s d e s c rib e d in the s e c tio n on w ave su rg e .
Sand rip p le d im e n sio n s w e re r e c o r d e d at e a c h te s t site (Fig. 11),
and th e ir tr e n d was m e a s u r e d w ith an u n d e rw a te r c o m p a ss. W here
b o tto m slope w as g r e a te r th an 2 to 3° and the w a te r v is ib ility w as good
it w as p o ssib le to d e te rm in e w ith a c o m p a ss the d ire c tio n of slope.
W ave and C u rre n t M e a s u re m e n ts
W aves and c u r r e n ts w e re m e a s u r e d w hen p o ssib le . W ave p e r i
od w as tim e d w ith a sto p -w a tc h and w ave h eig h ts e s tim a te d or m e a s
u r e d w ith a s m a ll float sliding on an a n c h o re d nylon fishing lin e. Wave
d ire c tio n w a s e s tim a te d w ith a c o m p a ss. W here m u ch sand w as in m o
tio n the san d rip p le tr e n d w as a re lia b le in d ic a to r of the o rie n ta tio n of
the su rfa ce w aves and could be m e a s u r e d u n d e rw a te r. R ep eated c o m
p a r is o n s of the s u rfa c e w ave tre n d s w ith th o se of san d rip p le s e s ta b
lis h e d that th e y are e s s e n tia lly p a ra lle l. C u rre n ts w e re m e a s u r e d
fr o m the b o at with f r e e or captive d ro g u e s, or u n d e rw a te r w ith fre e
n e u tra lly -b u o y a n t d ro g u e s (Fig. 12). U se of d ro g u e s by d iv e rs is m o s t
co n v en ien t a t tim e s of good w a te r v isib ility . The d ro g u es w e re c o n
s tr u c te d of p la s tic b ag s containing a p iece of w hite p a p e r or o th e rw ise
F ig u re 9 . — T r a c e r sand s c a tte r e d on the s e a
bed by w a te r m o v e m e n ts. T r a c e r sand w a s p la ce d
at in d ic a te d r e le a s e p o in ts. C o m p are w ith F ig u re
3 (T e st Z).
3 4
F ig u re 10. — T im e - la p s e c a m e r a u s e d to
p h o to g rap h san d rip p le s .

F ig u re 1 1 .— M ethod u sed to d e te rm in e sand
rip p le d im e n sio n s.

F ig u re 1 2 .— M ethod by w hich c u r r e n t v elo city
along b o ttom w as m e a s u r e d w ith n e u tra lly -b u o y a n t
d ro g u e. D rogue h as m o v ed aw ay fro m the t r a c e r
r e le a s e p o sitio n .
7 *
.
f *
f
41
m a r k e d to im p ro v e th e ir v isib ility . T hey w e re re le a s e d at a kno\yn
point, u su a lly the point of t r a c e r sa n d re le a s e , and o b s e rv e d to the lim it
of w a te r v isib ility . T r a v e l tim e , d ista n c e and d ire c tio n of tr a v e l w e re
m e a s u r e d and re c o rd e d . O c ca sio n ally a p iece of kelp (tied in a knot to
d istin g u ish it fro m o th e rs n e arb y ) w a s su b stitu te d fo r the p la s tic
drogue. W hen w a te r v is ib ility w as le s s than 5 to 10 feet the d iv e rs
h e ld a line of know n len g th a tta ch e d to the r e l e a s e point and follow ed
the drogue the length of the line. The e la p s e d tim e w as th e n noted and
the b e a rin g and d ista n ce to the r e le a s e point m e a s u re d .
L a b o ra to ry
P r o c e s s in g the sa m p le c a r d s in the la b o r a to r y in clu d ed a count
of the n u m b e rs of re d and g re e n flu o r e s c e n t san d g ra in s on the sam p le
and c o v e r c a r d s and co m p u tatio n of the n u m b e r of g rain s p e r sq u are
inch. S h o rt-w a v e u ltr a - v io le t light w as used. The sam p le c a r d s w e re
p la c e d on a tab le and view ed th ro u g h a 2 .5 -p o w e r read in g g la ss . A
cu m u lativ e to ta l of g ra in s counted w a s m ade on a h a n d -h e ld m e c h a n ic a l
co u n ter. A ll flu o r e s c e n t g ra in s on th e c a rd w e r e counted, ex cep t on
c a r d s containing s e v e r a l h u n d red g ra in s p e r s q u a r e inch. On th e se a
m in im u m of one sq u a re inch u su a lly w as counted. The a r e a to be
counted w as e ith e r m a r k e d by s c rib in g lin es in the p e tro le u m je lly o r
by p lacin g a te m p la te of b la ck p la s tic containing a 1-in c h - s q u a r e o p e n
ing o v e r the a r e a to be counted. T he la tte r m e th o d is the m o s t s a t i s
fa c to ry b e c a u se it e lim in a te s d is tra c tin g effe cts of flu o re s c e n c e fro m
the a r e a not u n d e r c o n sid e ra tio n .
S am ple lo c atio n s w e re p lo tte d on tr a c in g p a p er la id ov er an
42
a p p ro p ria te g rid . C o n cen tratio n s of f lu o r e s c e n t g ra in s p e r sq u a re inch
w e re re c o r d e d a t the p r o p e r p o sitio n s and iso p le th s draw n.
A ll g ra in siz e a n a ly se s w e re m a d e using a settlin g tube (E m e ry ,
1938).
C H ARA CTERISTICS OF T E S T AREAS
T r a c e r te s t s w ere m ad e at 1 5 s ite s along the m a in la n d c o a s t
and at Santa C atalin a Islan d (Fig. 13). S u c c essfu l te s ts w e re m ad e in
w a te r depths ra n g in g fro m 8 to 60 fe e t. One te s t w as a tte m p te d a t a
depth of 100 fe e t off P oint L o m a but the r e le a s e point could not be l o
cated a fte r the day of r e le a s e . T e s t site s w e r e s e le c te d on the b a s is of
a v a ila b ility of b o a ts, sea and sw ell co n d itio n s, and m a r k e r buoys a v a il
able. At all te s t s ite s the s e a bed w as sandy and rip p led .
San Diego
M uch of the p r e lim in a r y te s tin g of eq u ip m en t and tech n iq u es
w as a c c o m p lish e d during th e c o u rs e of te s ts at San D iego. C o n se q u e n t
ly, r e s u lts w e re le s s co m p lete than la te r t e s t s . S e v e ra l in -p la c e buoys
and the U nited S ta te s Navy E le c tro n ic s L a b o ra to ry o c ea n o g ra p h ic to w er
w e re u s e d as r e le a s e s ite s w h ere as m u ch as 400 pounds of flu o r e s c e n t
t r a c e r san d w as re le a s e d f o r a sin g le te s t. W a te r v is ib ility w as p o o r
m o s t of the tim e , e sp e c ia lly on Z uniga shoal, d e c r e a s in g the e ffe c tiv e
n e ss of the u n d e rw a te r w o rk . B ottom slope w a s le s s th a n 2° at a ll te s t
s ite s.
S anta C atalin a Island
T e s ts at C atalin a Isla n d (F ig. 13) w e re confined to coves along
the n o rth co ast, w hich a re ex p o sed only to w a v es g e n e ra te d in the
43
F ig u re 13. — L o catio n of sa n d t r a c e r te s ts ,
so u th e rn C alifo rn ia c o ast.
45
LONG
BEACH
PORTUGESE C BEND
HUNTINGTON BEACH
NEWPORT
tfBAY
LAGUNA
BEACH
SANTA
CATALINA
ISLAND
STATUTE MILES
LA JOLLA
N.E.L.
TOWER
SAND TRACER
TEST SITES
SOUTHERN
CALIFORNIA
COAST
SAN
DIEGO
ZUNIGA
SHOAL
C O R O N A D g J J ^
"MEXICO
STATUTE MILES
46
C ata lin a Channel and sw ell fro m the open P a c ific r e f r a c te d aro u n d the
ends of the isla n d . They a r e not ex p o se d to the fully dev elo p ed ocean ic
sw ell. Wave h e ig h ts in sh allo w w a te r in the a r e a a v e ra g e le s s th an 1
foot, fo rm in g s m a ll b r e a k e r s 1.5 to 2.0 feet high. A v erag e wave p e rio d
is about 6 sec o n d s. W ater v is ib ility is u su ally good and at tim e s e x
ceed s 60 feet.
S edim ent in the c o v e s ra n g e s fro m fine san d to g ra v e l and,
w h e re re a c h e d by wave s u rg e , is rip p le d e x cep t in the s u r f zone. T h ese
rip p le s m ove v e r y slowly o r not a t all. The co v es contain pocket
b e a c h e s behind w hich the la n d r is e s a b ru p tly . S easo n al s tr e a m s w ith
w a te r sheds of a few s q u a re m ile s d is c h a rg e into the co v es. B ottom
slo p es in the te s t a re a s ra n g e d fro m 2 ° to 6°.
Bottom conditions at P a r s o n s Landing n e a r the w e st end of
C atalin a Island a r e unusual and re q u ire ad d itio n al d e sc rip tio n . The
bottom is g ra v e lly (Fig. 3), ex cep t f o r s c a tte r e d p a tch e s of sand w hich,
w ith changing w av e conditions and se d im e n t d is c h a rg e s fro m the
s tr e a m th at d r a in s to the b e ac h , te m p o r a r ily a cc u m u la te on the g ra v e l
b o ttom . T est U w as p e r f o r m e d on one of th e se p atch es about 100 fe e t
in d ia m e te r , w h ich re s e m b le d a fla t-to p p ed , rip p led , snow d rift o r sand
dune. When the t r a c e r w a s r e le a s e d th e p a tch w as about o n e-h alf foot
thick co m p o sed of sand w ith a m e d ia n d ia m e te r of 0.17 m m . A pipe to
m a r k the r e le a s e point w as d riv e n into the b o tto m until it p ro je c te d
about o n e -h a lf foot. It w a s e a s ily found on su b seq u en t d iv es until, a fte r
a h e av y ra in s to r m a cc o m p a n ied by la r g e w av es, the stak e w as b u rie d
by san d c a r r ie d se a w a rd f r o m the b each . At th is tim e the sand p a tc h
w as ab o u t 2 fe e t thick, the in sh o re edge of the p a tc h standing at the
angle of re p o se of the sand. To s e a w a rd th e sand th in n ed g ra d u a lly w ith
no a b ru p t slope to the g ra v e l b o tto m . The b o ttom slope is 5° to 6°.
San P e d ro Bay
T e s ts w e re m ad e along fo u r c o a s ta l re a c h e s , P o rtu g u e s e B end
Cove, H untington B each, C o ro n a del M a r and Laguna B each. E x p o su re
to s e a and sw ell w as about the sa m e at all th e se p la c e s . Sw ells d u rin g
te s ts w e re 1 to 5 fe e t high w ith p e rio d s of 8 to 14 seco n d s. T h ese cam e
fro m the open P a c ific th ro u g h the San P e d r o C hannel.
P o rtu g u e s e Bend is an a rc u a te r e c e s s io n of the cliffs, c o n ta in
ing a sandy b each and bottom flan k ed by ro c k y h e ad la n d s. B ottom slope
a v e ra g e s 3°. T e s ts in th is cove w e re h a m p e r e d by p o o r w a te r v is ib ili
ty.
H untington B each is long and s tra ig h t w ith an offshore g ra d ie n t
of 2°. M uch fine se d im e n t is o ffsh o re w hich, u n d er a v e ra g e sw ell c o n
ditions, is s tir r e d , re s u ltin g in low w a te r v isib ility . M edian d ia m e te r
of the bottom sed im en t w as 0.11 m m at the te s t point in w a te r 23 fe e t
deep.
M o st of the te s ts w e re m ad e b etw een C o rona del M a r and L a g u
na B each w h ere w a te r v is ib ility w as g e n e ra lly good, a re fle c tio n of the
so m ew h at c o a r s e r se d im e n t and a b se n c e of a s ilt fra c tio n . M edian d i
a m e te r s ran g ed fro m 0.14 m m n e a r the s u rf to 0.09 m m in w a te r 20 to
35 fe e t deep. B ottom slo p es n e a r the s u rf a v e ra g e d 4°, in deep w a te r
HYDRODYNAMIC SETT IN G
W a v e -in d u c e d Surge
B ecau se w a v e -in d u c e d su rg e is the p rin c ip a l w a te r m o tio n
a v ailab le to m ove sed im en t on m o s t of the shelf, its c h a r a c te r and e f
fects upon sea flo o r s e d im e n ts a re d e s c r ib e d as a b ack g ro u n d fo r the
follow ing section.
T h e o re tic a l and o b s e rv a tio n a l d a ta on the n a tu re of w a te r m o v e
m en ts acco m p an y in g p r o g r e s s iv e s u rfa c e w aves a r e in g e n e r a l a g r e e
m ent. M ovem ent of w a te r p a r tic le s u n d e r a w ave is e s s e n tia lly o rb ita l.
M ovem ent p e r s i s t s w ith d e c r e a s in g o rb ita l d ia m e te r and v e lo city to a
depth of about o n e -h a lf the len g th of the w ave. As w aves e n te r shoaling
w a ter, the affected w a te r at the bottom is fo rc e d into o s c illa to r y s u rg e s
p a r a lle l to the b o tto m . The su rg e m o v e s in the d ire c tio n of w ave a d
vance u n d e r the w ave c r e s t and c o n tra ry to w ave advance u n d e r the
trough. T h ere is a sm a ll net tr a n s p o r t of w a te r in the d ire c tio n of w ave
p ro p ag atio n .
S urge v e lo c itie s ra n g e fro m th o se in cap ab le of m oving any b o t
tom se d im e n t w h e re w aves f i r s t "feel b o tto m " to s t r e s s e s n e a r the s u rf
capable of m oving sand, p e b b le s and b o u ld e rs. D etailed m e a s u r e m e n ts
of the d ista n ce w a te r is d is p la c e d and th e v e lo city atta in ed by su rg e a r e
not a v ailab le . H ow ever, the w r i t e r h as e s tim a te d an a v e ra g e v elo city
of 2 fe e t p e r sec o n d a t the bottom n e a r the s u rf f o r a n e u tra lly -b u o y a n t
object. This w as in w a te r 10 fe e t deep w ith s u rfa c e w aves 2.5 feet high
48
49
of 10 second p e rio d . The p e ak v e lo city of th a t su rg e w as p e rh a p s 2 o r 3
tim e s the a v e ra g e , but m u ch le s s th a n the su rg e acco m p an y in g la r g e r
w av es.
B etw een in te rv a ls of su rg e , w a te r and se d im e n t on the bottom
a re at r e s t until, as the w ave c r e s t a p p ro a c h e s, w a te r b egins to flow
sh o re w a rd . W ate r v e lo c ity in c r e a s e s ra p id ly until the th re s h o ld v e lo c
ity of se d im e n t p a r tic le s at the rip p le c r e s t s is e x ce e d ed and th ey b e
gin to m ove w ith the w a te r, som e in s a lta tio n and so m e tu m bling and
ro llin g c h a o tic a lly o v er rip p le c r e s t s and tro u g h s alik e. N e ar the s u rf
the in c re a s e in su rg e v e lo city is so ra p id u n d e r so m e w aves th a t sand
lite r a lly ex p lo d es fro m the rip p le c r e s t s w hen its th re s h o ld velo city is
ex ceed ed . At su ch tim e s the rip p le c r e s t s a r e te m p o r a r ily tru n c a te d
or the rip p le s a r e o b lite ra te d , but a re re f o r m e d by su b se q u e n t low er
v elo city s u rg e s . In a tr a in of w av es of v a ria b le len g th and am plitude
the bottom n e a r the s u rf is a lte rn a te ly rip p le d and sm o o th in re sp o n se
to the v a ria b le su rg e acco m p an y in g individual w av es. At p e ak surge
v e lo c itie s the se d im e n t is p a r t of a ch ao tic s e d im e n t- w a te r la y e r s e v
e r a l in ch es th ic k in w hich p a r tic le s m ove ra n d o m ly by ro llin g , sliding
and saltatio n .
N e ar the lo w e r lim it of w ave su rg e capable of m oving sed im en t
the bottom is rip p le d in a s e m i- p e r m a n e n t p a tte rn . M o st of the s e d i
m e n t p a r tic le s w hich a r e s t i r r e d by su rg e m ove in tr a c tio n only. C o m
m only only g ra in s at the rip p le c r e s t s a re m oved, u s u a lly le s s than 1
inch. U nder th e se conditions the rip p le c r e s t s o s c illa te th ro u g h about
the sam e d ista n c e . S ed im en t on the u p - c u r r e n t side of the rip p le c r e s t
is e ro d e d and d e p o site d on the d o w n -c u rre n t side, re s u ltin g in d is-
50
p la c e m e n t of the rip p le c r e s t. The bulk of the rip p le re m a in s u n d is
tu rb e d . The sa m e g ra in s continue to o s c illa te in this m a n n e r u n til a
l a r g e r - th a n - a v e r a g e w ave p a s s e s w hose su rg e m a y c a r r y c r e s t s e d i
m e n t a c r o s s s e v e r a l rip p le s and d ro p it at ra n d o m .
P r o g r e s s iv e s u rfa c e w aves c a u se a n e t tr a n s p o r t of w a te r in the
d ire c tio n of w ave advance. This w as deduced th e o re tic a lly and c o n
firm e d e m p ir ic a lly by o b se rv in g flo atin g o b je cts at the su rfa c e . T h eo ry
a lso in d ic a te s th a t a net tr a n s p o r t of w a te r sh ould o ccu r along the b o t
tom (Bagnold, 1963). T his is m o re difficult to o b se rv e but t r a c e r te s ts
in co n n ectio n w ith th is study, and w ave tank t e s t s by o th e rs (Ippen and
E a g le so n , 1955), show th a t such m o v e m e n t d o es take p la c e . W ater,
ho w ev er, cannot be p iled a g a in st the sh o re in d efin itely w ithout a r e tu r n
flow. The m a n n e r and p la c e s w h e re th is flow o c c u rs is only p a r tia lly
known (S hepard, 1951). F u r th e r study of such c irc u la tio n is needed.
T r a n s p o r t of w a te r and s e d im e n t along the bottom r e s u lts b e
cau se of the n et m o v e m e n t of the w a te r in the d ire c tio n of w ave p r o p a
gation. This n et d is p la c e m e n t m a y only be a few in ch es as fo r ex am p le
fo r a w ave in w hich the d ista n c e m o v e d by the w a te r m a s s fo rw a rd and
b ack co m m o n ly e x ceed s 10 fe e t the net d is p la c e m e n t fo r w a rd m a y be
only a few in c h es.
B ottom Slope
B ottom slope is an im p o rta n t fa c to r affectin g the ra te and d i r e c
tion of se d im e n t m ig r a tio n in th a t it c o n tro ls the d e g re e to w hich the
fo rce of g ra v ity is involved. G ra v ita tio n a l fo rc e acting on a sloping
su rfa c e can be re s o lv e d into co m p o n en ts actin g p e rp e n d ic u la r and
51
p a r a lle l to the slope. The fo rc e p e rp e n d ic u la r to the slope of a s e a
floor in h ib its the m o v e m e n t of se d im e n t by in ten sify in g fric tio n a l fo rc e s
am ong the g ra in s. But, fo rc e s th at act p a r a lle l to the slope a s s i s t s e d i
m en t to m ove dow nslope. As bottom slope in c r e a s e s the com ponent of
fo rce a ctin g dow nslope in c r e a s e s . W hen slope angle ex ceed s the s e d i
m e n t's angle of re p o s e the se d im e n t m o v e s dow nslope in re s p o n s e to
the g ra v ity co m ponent alone.
W hen c o n sid e rin g su rg e in re la tio n s h ip to g ra v ita tio n a l fo r c e s
acting on sloping s u rfa c e s it should be r e m e m b e r e d th at g ra v ity fo rc e s
act dow nslope in c o n c e rt w ith su rg e flow ing c o n tra ry to the d ire c tio n of
wave ad v an ce. M o re o v e r, fo r a given slope the g ra v ity co m p o n en t a c t
ing down the slope is the sam e at all w a te r depths. On the c o n tra ry ,
the n et advance of w a te r in su rg e d e c r e a s e s w ith depth ex p onentially.
It follow s th at fo r a given slope at som e depth the c o n tra ry su rg e plus
the g ra v ity com ponent dow nslope eq u als the fo rw a rd su rg e m in u s the
g rav ity com ponent. Below th is depth, if the w a te r v e lo c itie s a re su ffi
cient to m ove se d im e n t, dow nslope m ig r a tio n of se d im e n t r e s u lts .
O b se rv a tio n s by d iv e rs of ste e p ly -slo p in g b o tto m s su p p o rt this
line of re a so n in g . Off ro ck y h e ad la n d s, fo r ex am p le, steep bottom
slopes a r e ty p ic a lly co m p o sed of g ra v e l o r c o a r s e r m a te r ia l re s tin g on
b are " b e d ro c k ." The steep slope p e r s i s t s down to a r o c k -s e d im e n t
contact w h e re the bottom fla tte n s ab ru p tly . It is in f e r r e d fro m th e se
re la tio n s h ip s that se d im e n t not only is unable to m ig r a te up the steep
slope b u t th at s e d im e n t p a r tic le s su sc e p tib le to m o v e m e n t by su rg e
cannot r e m a in on the steep slope but m u s t m ig r a te dow nslope to the
ro c k -s e d im e n t c o n tac t o r beyond. If th is w e re not tru e , the ste e p slope
52
w ould be c o v e re d w ith sed im en t. E m an a tin g fro m th e se id e as is the
concept of p r o c e s s e s a c tin g in the d ire c tio n of a state of e q u ilib riu m in
w hich u n ifo rm w a te r m o v e m e n ts, long continued, p ro d u ce a sed im en t
d is trib u tio n and slope p ro file no lo n g e r su b je c t to change.
The Null P o in t C oncept
M ille r and Z e ig le r (1958) re v ie w the "n u ll point o r lin e" c o n cep t
p r e lim in a r y to th e o r e tic a l and fie ld stu d ies of the b each and n e a r s h o r e .
T his concept, b rie fly sta te d , is: fo r given s lo p e s and w ave c h a r a c t e r
is tic s e ac h p a rtic le h a s a "null p o in t" w h ere n et m o v em en t is z ero ;
p a r tic le s s h o re w a rd of the null p o in t m ove o n sh o re and th o se s e a w a rd
m ove offshore.
M u n c h - P e te r s o n (1950) h e ld th a t the n u ll point th e o r y is not v a l
id in th at the influence of g ra v ity re la tiv e to w ave p r e s s u r e is too s m a ll
to be c o n sid e re d im p o rta n t, no m a t t e r what the bottom slope is. H o w
e v e r, e x p e rim e n ta l w o rk in wave ta n k s (Ippen and E ag leso n , 1955) and
on n a tu ra l b e a c h e s and n e a r s h o r e (M ille r and Z e ig le r, 1958) p a rtly
c o n firm e d the v alid ity of the null p o in t concept. The M ille r and Z e ig le r
ap p ro a ch w as to c o n s tru c t th e o re tic a l m o d els b a se d on the null point
concept and c o m p a re th e m w ith the d is trib u tio n of se d im e n t p a r a m e te r s
at s e v e ra l c o a s ta l p o in ts. As w ill be seen, r e s u lts of th e p r e s e n t study,
em ploying s till an o th er technique (flu o re sc e n t t r a c e r s ) , a ls o su p p o rt
the null point concept.
P A T T E R N S OF T R A C E R SAND DISPERSION
T r a c e r sand d is p e r s e s fro m the point of re le a s e h o riz o n ta lly
and v e r tic a lly in d is tin c t p a tte rn s w hich a re tra n s itio n a l one to the
o th e r. H o rizo n tal d is p e r s io n can be co n v en ien tly c la s s ifie d as o n sh o re,
n e u tra l, o ffsh o re, and lo n g sh o re . V e rtic a l m ix in g p a tte rn s a re in c o m
p le te ly known and difficult to in te r p r e t. All te s t s w e re m a d e u n d er the
influence of o s c illa to r y su rg e induced by w aves a p p ro a ch in g sh o re.
Sand g ra in s m o v ed a lte r n a te ly s h o re w a rd and se a w a rd in th is su rg e
tra c in g a z ig za g p ath w hich could have a n et m o v e m e n t in any d ire c tio n .
The m o v e m e n t of se d im e n t u n d er the influence of o s c illa to r y su rg e w as
d e s c rib e d e a r lie r .
H o riz o n ta l
O nsh o re
The m o s t com m on, b e s t defined, and m o s t ra p id ly developed
d is p e r s io n p a tte rn s show o n sh o re tr a n s p o r t of t r a c e r san d s of all g ra in
siz e s te ste d . O nshore m o v e m e n t w as o b s e rv e d v isu a lly and r e s u lts of
sam p lin g c o n firm the o b s e rv a tio n s . E x a m p le s a r e te s ts D (Fig. 14), G
and H (Fig. 15), M and N (F ig. 16), and S ilv er S tran d (F ig. 17). W hen
te s ts w e re p e r f o r m e d in good w a te r v is ib ility and high w ave en erg y , as
at L aguna B each, the s p re a d of the t r a c e r sand w as c le a r ly o b serv ed .
The pile of m ix e d re d and g re e n t r a c e r sand w a s p la ce d in a low m ound
about 1 foot in d ia m e te r. S h o rew a rd s u rg e fro m each w ave p la ce d
53
F ig u re 14. — T e st D. Iso p leth s showing t r a c e r
san d m ig r a tio n to be p rin c ip a lly in the d ire c tio n of
w ave advance. (T est site sand 0.22 m m m e d ia n d i
a m e te r.)
o
o
o
RELEASE +33m in.
TRA CER SA N D — M E D IA N
DIAMETER-0.25 M M .
T E S T “D"
W A TER DEPTH 8 FT .
LAGUNA BEACH, EMERALD BAY
4-16-69
CONTOURS'- GRAINS/INCH SO.
3 POUNDS TRACER SAND
O
O
O
R E L E A S E + 3 3 m in .
TR A C ER SA N D -M ED IA N
DIAM ETER- 0.42 M M .
co l —
III! •
> * -'
0
F T .
5
T E S T "D"
W A T E R DEPTH 8 FT.
LAGUNA BEACH, EMERALD BAY
4-16-69
CONTOURS—GRAINS/INCH SO.
3 POUNDS TRACER SAND
U i
U l
F ig u re 1 5 .— T e s ts G and H p e rfo rm e d c o n
c u r r e n tly depicting san d m ig r a tio n in d ire c tio n of
w ave advance at w a te r depths of 23 and 35 feet.
(T est site san d m e d ia n d ia m e te r at G, 0.14 m m ;
at H, 0.10 m m .)
WAVES
A VE R A G E 2.5 FT.
RELEASE-*-20mln. RELEASE+220n*i
WATER
DEPTH
2 3 FT.
» O O ||| ® 0 O
T E ST "G1
l - M - U
9 R O M M T * « C t* IN I
RELEASE-*- 20mln. RELEASE-*-220min.
RELEASE-*- I03mln. RELEASE* 243mln.
35 FT.
e o o
RELEASE-*- I03mln. RELEASE+243mln.
< L
10
FEET
TEST "H
i M I M A N K a , IM Itit ) A T
2 - M -tt
c m to u r i M A n i/m c a M
I W A M tU H IlM t
0.25m m .
TRACER SAND MEDIAN DIAMETER 0.42m m .
F ig u r e 16. — T e sts M and N w hich show d if f e r
en tial r a te s of t r a c e r san d tr a n s p o r t of d iffe re n t
g ra in s iz e s at w a te r depths of 12 and 35 fe e t. S a m
ple lo c a tio n fo r e ac h sam p le tim e w a s 45° a p a r t on
c o n c e n tric c ir c le s 3, 6 and 9 feet fro m the r e le a s e
point. (T e st site san d m e d ia n d ia m e te r, T e s t M,
0.14 m m ; T e s t N, 0.09 m m .)
59
0
k.
10
— I
FEET
PERIOD
10 M C .
HEIGHT
2 -4 ft.
WATER
DEPTH
12 FT.
TEST "M"
LU
>
<
c r
o
6 5 MIN. 150 MIN.
FINE SAND
65 MIN. 150 MIN.
COARSE SAND
0 . 4 2 MM.
3 5 FT. Hfc TEST
120 MIN. 2 2 5 MIN. 120 MIN. 225MIN.
"N"
EFFECTS OF WATER DEPTH ON
SAND MOVEMENT
CORONA DEL MAR, CALIF 2-11-65 3 lbs tin*. 31b* coorw TRACER SAND
CONTOURS, ORAINS OF TRACER/SO.INCH
VEANOM 1 9 6 5
sh ee ts of t r a c e r in m o tio n , som e in sa lta tio n a s high as o n e-h alf foot
above the bottom and ro lle d a d en se la y e r up the sea bed, m ix in g it w ith
indigenous sand. W hen the su rg e r e v e r s e d d ire c tio n m u c h of the t r a c e r
san d w as c a r r i e d to w a rd the r e le a s e point and m o re t r a c e r sand w as
s trip p e d fro m the pile and c a r r i e d s e v e ra l fe e t se a w a rd . In su ch a te s t
it w as e v id en t th at the t r a c e r s o u rc e w ould be sig n ifican tly d ep leted
w ithin a few m in u te s. T h e re fo re , sa m p le s w e re tak en a s soon as 20
m in u tes a f te r r e le a s e . E v en in th is s h o rt in te rv a l v is ib le c o n c e n tr a
tio n s of t r a c e r had s p re a d in a 1 to 2 feet w ide s trip m o r e than 10 feet
s h o re w a rd of the r e le a s e point. To sea w ard , s c a tte r e d g ra in s w e re
noted as f a r as 3 fe e t fro m the r e le a s e . S u rface la y e r s of the t r a c e r
san d pile w e re v isib ly d ilu te d w ith indigenous sand m ig ra tin g o v e r it.
H ow ever, u n d ilu ted and u n d istu rb e d t r a c e r san d w as ex p o se d by digging
below the m ix e d la y e r s .
Iso p leth s of te s t s p e r f o r m e d u n d er th e s e conditions and p r e
sen ted h e r e in a re d e p en d en t fo r th e ir fo rm to a c o n sid e ra b le d e g re e on
p a tte rn s of d is p e r s io n o b s e rv e d u n d e rw a te r.
A p p ro x im a te ly the sam e p a tte r n of t r a c e r d is p e r s io n w as o b
s e rv e d w hen rip p le s w e re p r e s e n t o r ab sen t, as they w e re in te r m itte n t
ly in te s ts m ad e c lo se to the s u rf. The o v e ra ll im p r e s s io n re c e iv e d
fro m te s ts p e r f o r m e d w h e re su rg e is s tro n g is th at w a te r fo r c e s w hich
im p el the se d im e n t c o m p le tely o b sc u re or o v e rrid e the effects of subtle
sed im en t p a r a m e te r s a s shape and s u rfa c e te x tu re s of the individual
g ra in s, and the so rtin g and sk e w n e ss of the t r a c e r san d c o n s id e re d as
a w hole. In o th er w o rd s , in the zone of v io len t, w a v e -in d u c e d s u rg e ,
m in o r se d im e n to lo g ic a l fe a tu re s do not have sig n ifican t effects on the
ra te o r d ire c tio n of m ig r a tio n of sand g r a in s . This co n clu sio n is c o n
t r a r y to the concept th a t fo r v a lid t r a c e r te s t s indigenous sand m u s t be
u sed a s t r a c e r .
In the S ilv er S tra n d te s t (Fig. 17) v e r y fine san d (0.10 m m ) w as
r e le a s e d th a t r e s u lte d in a b ro a d ly d is p e r s e d p a tte r n b eliev ed to have
b een c a u s e d by a p re p o n d e ra n c e of the t r a c e r sand tr a n s p o r te d in s u s
p en sio n . D uring th is and o th e r te s ts in w hich v e ry fine sand w a s e m
ployed, d iv e rs noted th a t each su rg e p la c e d la rg e am o u n ts of the sand
in s u sp e n sio n a foot o r m o re above the b o tto m . But, during te s t s e m
ploying c o a r s e r sand the sand m o v e d p rin c ip a lly by tra c tio n and s a l t a
tion, re s u ltin g in the w ell defin ed p a tte rn s shown in F ig u r e s 14, 15 and
16. The S ilv er S tra n d t e s t is, h o w ev er, an a cc e p tab le exam ple of the
p re d o m in a te ly o n sh o re m ig r a tio n of fine san d u n d er m o d e ra te w ave
conditions in shallow w a te r . The e r r a t i c p a tte rn and the w idely sp ac e d
s a m p le s p re c lu d e a s o p h istic a te d in te rp re ta tio n .
An anom alous a sp e c t of the d is p e r s io n p a tte rn s of T e sts G and
M is an a r e a of high t r a c e r g ra in c o n c e n tra tio n w hich developed 5 to 8
feet s h o re w a rd of the re le a s e point. T h is p henom enon w as a lso m a n i
fe s t u n d e rw a te r on so m e te s ts a s a low m o u n d of t r a c e r sand. The
re a s o n fo r th is a n o m aly in the p a tte r n is not defin itely known but is b e
liev ed to be re la te d to the sp ee d and d u ra tio n of the su rg e , the p ile a c
cu m u latin g at the a v e ra g e s a lta tio n d ista n c e of the g ra in s in one su rg e .
O b se rv a tio n s m ad e d u rin g the study r e v e a l th at u n d e r conditions of the
te s ts a n e u tra lly -b u o y a n t ob ject n e a r the bottom m o v es s h o re w a rd
about 10 fe e t in a sin g le s u rg e . F o r so m e d ista n ce le s s than 10 fe e t the
su rg e fr o m the sa m e w ave w ould be flow ing above the th re s h o ld
F ig u re 17. — V ery fine san d t r a c e r te s t at S ilv e r
S tran d B each. Sand w as su sc e p tib le to in te rm itte n t
tr a n s p o r t in su sp e n sio n .
! < 4 j
MiN
359
MIN
SILVER STRAND
BEACH
O '*
00
64
velo city of the t r a c e r sand and w ould c a r r y it in saltatio n , a cco rd in g ly ,
a so m ew h at l e s s e r d ista n ce .
W ith the ex cep tio n of the S ilv er S tran d T e s t two s iz e s of g ra d e d
sand w e re re le a s e d and the fine san d alw ays m o v ed m o re ra p id ly th an
the c o a r s a sand. Som e sand m ig r a te d s e a w a rd of the r e le a s e point in
re sp o n se to the s e a w a rd su rg e and the a s s is tin g g ra v ita tio n a l pull down
the in c lin e d sea bed. H ow ever, the dom in an t on sh o re m ig r a tio n te n d e n
cy p re v e n te d sig n ifican t n u m b e rs of t r a c e r g ra in s fro m m oving m o re
than a few feet sea w ard .
It is evident in te s ts p e r f o r m e d sim u lta n e o u sly in d ifferen t
w a te r d ep th s that the t r a c e r d is p e r s e d m o s t ra p id ly at the sh allo w est
depth. T h is re la tio n sh ip a g re e s w ith th e o ry (Bagnold, 1963) and d iv e r
o b se rv a tio n s w hich c le a rly ind icate a d e c r e a s e in su rg e v e lo city w ith
in c re a s in g depth. The ra p id in c re a s e in the r a te of sed im en t m o v e m e n t
n e a r the s u rf m ay be the r e s u lt of a tr a n s itio n of tr a n s p o r t m ode fro m
tra c tio n to saltatio n .
N e u tra l
T r a c e r d is p e r s io n p a tte r n s in w hich n e ith e r an o n sh o re no r an
offshore m ig ra tio n p re d o m in a te s a re c la s s ifie d as n e u tra l. M ost a re
stro n g ly elongate p a r a lle l to the a v e ra g e w ave o rthogonal (F ig s. 18, 19,
and 20). The p a tte rn s in F ig u re 20 a re fro m se d im e n t s u rfa c e sa m p le s
only. T h o se in F ig u r e s 18 and 19 w e re obtained by sam p lin g at the s u r
face, w ith in and at the base of the rip p le d la y e r . In T e st Y only the
t r a c e r d is trib u tio n at the rip p le c r e s t s w as n e u tra l, a t m id d le and b a se
the d is trib u tio n w as d isp la ce d to w a rd sh o re .
F ig u re 1 8 .— T e st Y, t r a c e r sand at s u rfa c e
h as a n e u tra l d is trib u tio n . T r a c e r sand below the
s u rfa c e shows o n sh o re tr a n s p o r t. (T est site sand
m e d ia n d ia m e te r 0.19 m m .)
W A V ES
(EST. AVERAGE)
RELEASE-*-96 D A Y S
TRACER MEDIAN DIAMETER
0.42 M M
/ / / WATER DEPTH - 12 FT.
/ / / SANTA CATALINA ISLAND
/ / T O YO N BAY
/ / I 0 - I S - S 4
/ C O N T O U R S - M A I N S / I N C H SB.
1 0 0 POUNDS TRACER 8A N 0
RIPPLE CREST
8 FEET
s a n o n i p p l e s
o
RIPPLE M ID D LE
5 FEET
RIPPLE BASE
o
O'
F ig u re 1 9 .— T e st W, show ing e s s e n tia lly
n e u tra l tr a n s p o r t p a tte rn a t and below the s u rfa c e .
{Test site sand m e d ia n d ia m e te r 0.17 m m .)
TEST "W "
WATER DEPTH- 12 FT
SANTA CATALINA ISLAND
RIPPER'S COVE
1 0 - 1 5 - 6 4
CONTOURS " 6 N A I N S / INCH SO.
100 POUNDS T R A C E R SAND
o
SANO N IP P L E S
5 FEET
o
RIPPLE CREST
RELEASE+ 41 DAYS
TRACER MEDIAN DIAMETER
0.42 M M .
CREST
MIDDLE
BASE
SAND R I P P L E S SANO R IP P L E S
5 FEET
S FEET
.4 0
30"
RIPPLE MIDDLE
RIPPLE BASE
O'
00
F ig u re 2 0 .— T e st T, a fte r th r e e sam pling
ounds. A n e u tr a l p a tte rn developed. (T est site
and m e d ia n d ia m e te r 0.20 m m .)
TRACER M EDIAN DIAM ETER
70
0.42m m 0.25m m
RELEASE* 240min.
RELEASE+24hr. 30min.
T E S T "T
WATER D C R T M - l i F T , -
•ANTA CATALINA ItL A N O O 4
P M I O M LANDWA J
i*i4-m FEET
COMTOUNA- M A IM /IN C M 90.
• M U N O t T N A C tN SANO
I
71
C om m on to a ll the n e u tra l te s ts is the condition th at the t r a c e r
w as p la c e d on la rg e , slo w ly -m o v in g or s ta tio n a ry san d rip p le s . All
w e re su b je c t to low (le s s than 1 foot) u su a lly s h o rt p e rio d w av es on the
n o rth c o a st of S anta C atalin a Island. O th e r e x am p les of n e a r ly n e u tra l
d is p e r s io n w e re o b tain ed in w a te r 30 fe e t o r d e e p e r along the m a in la n d
c o ast, as in T e s t N (F ig . 16).
The fine san d in th e se te s t s a lso d is p e r s e d m o re ra p id ly than
the c o a r s e , shown e sp e c ia lly w e ll in T e s t T (F ig. 20).
T e s ts Y and W (F ig s. 18, 19) show the d is trib u tio n of c o a r s e
t r a c e r san d 1 to 3 m o n th s a fte r r e le a s e . T h ese a re "la g " d e p o sits of
g ra in s w hich m u s t be in d e lic ate b alan ce w ith the p re v a ilin g h y d ro d y
n a m ic and bottom co n d itio n s and can be m o v ed only s h o rt d is ta n c e s.
S im ila r p a tte r n s w e re obtained by sam p lin g th e se te s t s ite s as m u ch as
185 days a fte r r e le a s e . In te s t s Y and W fine sand, r e le a s e d s im u lta
neously, w as tr a n s p o r te d s h o re w a rd w h e re it w as d e te c te d m ix e d w ith
the b each sand. A g ra d u a l d ep letio n of t r a c e r g ra in s at the re le a s e
point w as d is c e rn ib le v isu a lly and is show n by plotting t r a c e r g ra in
c o n c e n tra tio n s a g a in s t tim e (F ig s. 30, 31).
T e s ts Y and W w e re o b s e rv e d and sa m p le d m a n y tim e s and
u su ally the su rg e w as gentle and sand w as o scillatin g only on the rip p le
c r e s ts . O c ca sio n al l a r g e r w av es p ro d u c e d su rg e cap ab le of m oving the
s m a lle r g ra in s a foot o r m o re in sa ltatio n w h e re a s the c o a r s e t r a c e r
g ra in s at the su rfa c e m o v ed only a few in ch es in tra c tio n . T his d e g re e
of m otion, p re v a ilin g o v e r w eek s and m o n th s, re s u lte d in co m p lete r e
m o v al of the fine t r a c e r sand, h o m o g en eo u s m ixing of th e c o a r s e t r a c e r
w ith the indigenous sand to d ep th s g r e a te r th an the rip p le am plitude,
72
and g ra d u a l d e p letio n of the c o a r s e sand.
O ffshore
Only a few te s t s c le a rly show p re d o m in a n tly o ffsh o re m ig ra tio n
of t r a c e r san d u n d er the influence of o s c illa to ry , w a v e-in d u ce d su rg e .
The b e s t e x am p le is t e s t U m ad e in 30 fe e t of w a te r a t P a r s o n s L a n d
ing, Santa C atalin a Island. T h e re , a fte r 7 days, offshore m ig r a tio n of
both the c o a r s e and the fine t r a c e r sand w a s in d icated (Fig. 21). The
o ffshore t r a c e r m ig r a tio n tre n d s shown fo r T e st U a r e in g e n e ra l
a g re e m e n t a t the c r e s t, m id d le and base of the rip p le s . T r a c e r sand
d is trib u tio n a t the s u rfa c e is a d eq u a te ly c o n tro lle d by 25 sa m p le s .
F e w e r s a m p le s w e re ta k e n below the s e d im e n t s u rfa c e , thus re s u ltin g
in som e u n c e rta in ty in d raw in g the iso p le th s. The p a tte rn s show n a re
m o s t lik ely b e c a u se th ey exhibit the sam e tre n d as the s u rfa c e p a tte rn .
In o th er t e s t s , w hich w e re sa m p le d m o re c o m p letely below the s e d i
m e n t s u rfa c e (F ig s. 18, 19), the p a tte r n s at all th re e le v els p o s s e s s e d
the sam e tre n d . D espite the u n c e rta in ty of p a tte rn tre n d , o ffsh o re m i
g ra tio n of the t r a c e r san d is c le a r ly e sta b lish e d .
A ll the p a tte rn s in T e st U a re elo n g ate at a su b sta n tia l angle to
the a v e ra g e w ave orth o g o n al in f e r r e d fro m the tre n d of the san d r i p
p le s at the tim e of sam p lin g . It is p o ssib le th at d u rin g the e la p s e d 7
days b etw een r e le a s e and sam p lin g , w aves that p a r a lle le d the e lo n g a
tio n of the t r a c e r p a tte r n w e re dom inant, re su ltin g in the o b s e rv e d p a t
te rn .
T e s t Q (F ig. 22) shows a co m p lex p a tte r n c a u s e d by s ta tic sand
rip p le s in w h ich the c o a r s e t r a c e r g ra in s have a n e t o ffsh o re com po-
F ig u r e 21. — T e s t U, an ex am p le of offshore
m ig r a tio n of t r a c e r sand. (T e s t site san d m e d ia n
d ia m e te r 0.17 m m .)
WAVES
TEST "U "
RELEASE+ 7 DAYS
TRACER MEDIAN DIAMETER
0.42 M M .
WATER D E P T H -3 0 F T .
S A N T A C A T A L IN A IS L A N D
P A R S O N S L A N D IN G
lf-4 -6 4
C O N T O U R S G R A I N S /I N C H SO.
0 S 3 P O U N D S T R A C E R SAND
5 FEET
RIPPLE CREST
cs
5 FEET
CO
RIPPLE M IDDLE
SAND N IP P L E S
5 FEET
RIPPLE BASE
F ig u re 2 2 .— T e st Q, w hich show s the e ffe c ts of
sand rip p le s on t r a c e r san d tr a n s p o r t and o ffsh o re
m o v e m e n t of t r a c e r sand. Sam ple p o ints (not shown)
a re on c r e s t s , tro u g h s, and flanks in lin es 1 foot
a p a rt and n o rm a l to the san d rip p le s . Shape of the
c o n to u rs w as, in p a rt, c o n tro lle d by o b se rv e d and
p h o to g rap h ed t r a c e r san d d is trib u tio n . (T est site
sand m e d ia n d ia m e te r 0.24 m m .)
SHOREWARD
7 0 m in . I40m in. 2 3 0 min. 2 2 h r 20m in.
FINE
SAND
COARSE __
SAND
BOTTOM
LOP
DOWN
PERIOD 6 SEC., HEIGHT 1 -3 FT.
HOGONAL
CREST
- m w
TROUGH
WATER DEPTH 2 5 FEE T
TEST "Q"
EFFEC TS OF SAND RIPPLES ON TRACER SAND MOVEMENT
PARSONS LANDING, SANTA CATALINA ISLAND, CALIFO RNIA JANUARY 2 8 -2 9 ,1 9 6 5
0
U
F E E T
TRACER SAND, 3LBS. F IN E , 3 LBS. COARSE
MEDIAN DIAMETER 0.25mm. 0.42mm.
77
nent of m o v e m e n t as w ell as along the rip p le s .
On s e v e ra l te s ts along the m a in la n d in w a te r s m o re th an 30 fe e t
deep o ffsh o re m o v e m e n t w as r e c o r d e d on one sam p lin g but a s u b s e
quent sam p lin g show ed o n sh o re m o v e m e n t. A lthough they m a y a c c u
ra te ly r e c o r d w hat happened, the s m a ll n u m b e r of g ra in s r e c o v e re d by
the f i r s t sam p lin g in tro d u ce d a s u b sta n tia l e le m e n t of u n c e rta in ty as to
w h eth er o r not o ffsh o re m o v e m e n t o c c u r re d . W here p o sitiv e o ffsh o re
t r a c e r m ig ra tio n w as d etected , the bottom slope w as s u b sta n tia lly
g r e a te r th a n at o th e r te s t s ite s , pointing to slope as an im p o rta n t fa c to r
in c o n tro llin g d ire c tio n of se d im e n t m ig ra tio n . F o r e x am p le, at T e s ts
U (Fig. 21) and Z (F ig. 9) at P a r s o n s Landing, and T e st Q (F ig. 22) in a
sm all cove n earb y , the bottom slope w as a p p ro x im a te ly 5° to 6° c o m
p a re d w ith a m a x im u m of 4° at the o th e r te s t s ite s .
L o n g sh o re
" L o n g sh o re " is defined as a t r a c e r d is p e r s io n d ire c tio n at so m e
su b sta n tia l angle to the w a v e-in d u ce d s u rg e . Such sp re a d in g m a n i
fe ste d its e lf e ith e r in d is p e r s io n p a tte rn s as equal bulges on both sid e s
of the r e le a s e point o r as a p ro m in e n t bulge on one side a cc o m p a n ied
by flatten in g on the opposite sid e. The p rin c ip a l c a u se s fo r u n b alan ced
p a tte rn s a r e v a ria b le c u r r e n ts , b o ttom slope and san d rip p le e ffe cts.
E qual bulging of the d is p e r s io n p a tte rn s p ro b a b ly r e s u lts fro m d if f e r
en ces in d ire c tio n of w a v e-in d u ce d s u rg e w hich in tu r n a re c au se d by
v a ria tio n s in the d ire c tio n of w ave a p p ro a ch o r the in te rfe re n c e of tw o
wave tr a in s fro m d iffe re n t d ire c tio n s .
An ex am p le of the e ffe ct of a lo n g sh o re c u r r e n t on a d is p e r s io n
78
p a tte r n is T e s t O (Fig. 23) in w hich a c u r r e n t w hich a c te d fro m rig h t to
left r e s u lte d in t r a c e r san d tr a n s p o r te d to the left as w ell as o n sh o re.
S im ila rly in T e s t S (Fig. 24) a c u r r e n t th a t m o v ed to the rig h t is a co n
trib u tin g fa c to r, along w ith bottom slope and wave d ire c tio n , to s p re a d
the san d to the rig h t and dow nslope.
In T e s t Z a t P a r s o n s Landing, S anta C atalin a Island, th e o b
s e r v e d slope w as to the le ft of the w ave o rth o g o n al (F ig. 9), c o n trib u t
ing to the v isib le s p re a d of san d to the left. T e st Z is on a g ra v e l b o t
to m w hich m a k e s it p o ssib le to d istin g u ish the t r a c e r sand fro m the
n a tu ra l m a te r ia ls w ith b la ck and w hite pho to g rap h y . T e st Z w a s ob
s e r v e d re p e a te d ly fo r m o re th a n 7 m o n th s until m o s t of the t r a c e r sand
d is a p p e a re d . A g ra d u a l sh iftin g dow nslope and lo n g sh o re of the m a jo r
c o n c e n tra tio n s of c o a r s e t r a c e r sand w as noted.
T e s t Q w as p e r f o r m e d to d e te rm in e the effects of la rg e , static
sand rip p le s on san d t r a n s p o r t (Fig. 22). Both the fine and c o a r s e sand
w e re "ch an n eled " along the s e a w a rd flan k s of the rip p le s and w e re also
s p re a d p a r a lle l to the wave o rthogonal. Both the w ave d ire c tio n and
bottom slope d ire c tio n co n tain a com ponent to the le ft w hich a ls o
c a u se d t r a c e r to s p re a d m o s t ra p id ly in th a t d ire c tio n . The p a tte r n in
T e s t Q is m u c h le s s elongate p a r a lle l to the wave o rth o g o n al th an o r
d in a rily ex p ected . T his is p ro b a b ly a lso a r e s u lt of the sand rip p les
w hose ste e p flanks inhibit m o v e m e n t of the t r a c e r g ra in s n o rm a l to the
rip p le s .
O b stru c tio n s
O b stru c tio n s to the m ig ra tio n of t r a c e r sand r e s u lts in d i s t o r
tion of the u su a l d is p e r s io n p a tte rn s . A ro c k y h ead lan d is a co m m o n
F ig u re 2 3 .— T e st O, w av e and c u r r e n t effects
of t r a c e r sand m ig ra tio n . (T e s t site sa n d m ed ian
d ia m e te r 0.11 m m .)
8 0
SHOREWARD
WATER DEPTH
2 3 FEET
•C ' f e r
'«»S> 5 FEET
RELEASE+I20min
r
r 5T
T E S T "0 "
WAVE AND CURRENT
EFFECTS
HUNTINGTON BEACH, CALIF. 2-5-65
TRACER SAND 3lbs. 0.25 m m
F ig u re 2 4 .— T e st S. E ffe cts of c u rre n t, w av es,
and b o ttom slope on t r a c e r san d m ig ra tio n . (T est
site san d m e d ia n d ia m e te r, rip p le c r e s t, 0.65 m m ;
rip p le tro u g h , 0.57 m m .)
82
RELEASED 143 MIN.
TRACER M ED IA N D IA M ETER
0.25 MM.
o O
RIPPLE CREST
I FO O T
CREST
CREST
l " ® TE S T “S"
\ W A TER DEPTH -20FT.
SANTA CATALINA ISLAND
EMERALD BAY
1 — 21 — 6 8
CONTOURS- 6R A IN S /IN C H SQ.
3 POUNOS TRACER SAND
o b stru c tio n e n c o u n te re d by sand m ig ra tin g lo n g sh o re and on the shelf.
F ig u re 25 show s a ty p ical h eadland, the site of T e s t A. T e s ts E and A
(F ig s. 26, 27) w e re along the r o c k -s a n d contact on the se a w a rd sid es of
ro c k y h e ad la n d s. The c o n ta c t is c h a r a c te r iz e d by a sc o u r tro u g h 1 foot
to s e v e r a l feet w ide. E x p o se d ro c k r i s e s sh a rp ly on one sid e and a
rid g e of san d 1/2 to 1 1/2 fe e t in height r i s e s on the o th e r. It h a s b een
o b s e rv e d on m a n y dives in s im ila r situ a tio n s th at th e w idth and depth of
the tro u g h a re a function of su rg e v e lo city . L a rg e w aves and stro n g
su rg e p ro d u ce la rg e sc o u r tro u g h s. D uring T e s t A the sand fo r a d i s
tan ce of 20 to 30 fe e t fro m the ro c k w as shaped in to sand w av es p a r a l
le l to the r o c k - s a n d c o n tact. The w av es had a le n g th of 1 to 4 feet and
fo rm e d the s u rfa c e of a san d y slope su b sta n tia lly s te e p e r th a n the m o re
d is ta n t sea bed. On the m o r e gently sloping sand bottom w e re rip p le s
of about the s a m e a v erag e d im e n sio n s as those on the su rro u n d in g sea
flo o r.
L a rg e san d w aves w ith lengths in e x c e ss of 5 feet w e re noted
also n e a r a r o c k se d im e n t co n tact at P a r s o n s L anding. T h e se w e re
co m p o sed of c o a r s e san d and g ra v e l. Sand w aves of th is size a re u n
co m m o n on the s e a floor. The lim ite d n u m b er of o b s e rv a tio n s a v a il
able in dicate th a t they a r e r e la te d to s h a r p in c r e a s e s in slope fro m
w hich w a te r m o tio n s in w av es a re re fle c te d . It h a s been n o ted w hen
diving in th e se a r e a s th at u n u su al, tu rb u le n t w a te r m o tio n s a r e e x p e r i
en ced but th e se have b een n e ith e r m e a s u r e d nor d e sc rib e d .
The t r a c e r sand fo r T e s t E w as re le a s e d a t the top of the f i r s t
sand w ave 10 fe e t fro m the ro ck . C are fu l study of the t r a c e r sand d i s
trib u tio n during the te s t did not re v e a l any p r e f e r r e d d ire c tio n of
F ig u re 2 5 .— A e ria l view of A balone P oint,
site of T e s t A, a ty p ic a l ro ck y p ro m o n to ry th at
in te r r u p ts the m o v e m e n t of sand on the shelf
and along the beach .

F ig u re 2 6 .— T e st E. E ffect of ro c k o b stac le
on sand m ig ra tio n .
5 FEET
\
RE LE A SE+ I64min
TRACER MEOIAN DIAMETER
0.2S MM.
CO
liI
>
<
£
o
£
o
TEST "E"
WATER DEPTH -ISFT.
LAGUNA BEACH, EMERALD BAY
4 - 1 6 - 6 8
CONTOURS— GRAINS/INCH SO.
3 POUNDS TRACER SAND
R E LEA SE* j64min. o
TRACER MEDIAN DIAMETER
0.42 MM.
C O
id
>
<
TEST
ll^ll
WATER DEPTH-I5FT.
LAGUNA BEACH, EMERALD BAY
4 -IG -G S
C O N T O U R S- GRAINS/INCH SO.
S POUNDS TRACER SAND
F ig u re 2 7 .— T e s t A, san d tr a c e r m ig ra tio n
n e a r a ro c k y h eadland. (T est site sand m ed ian
d ia m e te r 0.19 m m .)
TRACER
RELEAS
PO INT
LAGUNA
BEACH
TRACER“ ’0.25 m m ?
RELE ASE+ 63min.°
SAND
/
/
A
• o
o
o
/
o
2,0 ”
.\ 0'
5 F E E T
E FF E C T S OF ROCKY HEADLAND
ON SAND T R A N S P O R T
L /
TRACER 0.42 m m .
RELEASE+ 63min:
SAND
5 F E E T
TEST "A1 1
WATER D EPTH 2 6 F T .
LAGUNA BEACH, ABALONE POINT.
4 - 23-65
CONTOURS- GRAIN S/1 NCH SQ.
3 POUNDS TRAC ER SAND
90
m ovem ent. S and s p re a d slow ly in all d ire c tio n s fo rm e d a ro u g h ly c i r
c u la r p a tte rn . T his o b se rv a tio n w as su b sta n tia te d by the d is trib u tio n as
d e te rm in e d by sam p lin g .
A su b se q u e n t te s t in w hich the t r a c e r sand w as r e le a s e d in the
sc o u r trough ( T e s t A, F ig . 27) r e s u lte d in ra p id m o v em en t of the t r a c e r
sand out of the tro u g h and in a g e n e ra l s e a w a rd d ire c tio n . T e s t A w as
m ad e under c o n s id e ra b ly m o re v ig o ro u s su rg e th an T e s t E. A c c o m p a
nying the w av es w as an o ffsh o re -tre n d in g c u r r e n t of 3 feet p e r m in u te
a p p ro x im a te ly p a r a lle l to the ro c k - s a n d co n tact. Both c o a r s e and fine
san d re sp o n d ed in a s im ila r m a n n e r and, as in o th e r te s ts , the fine san d
m o v ed m o re r a p id ly th a n the c o a r s e .
As w ill be seen, the sea flo o r m o rp h o lo g y and the m o v e m e n t of
t r a c e r sands n e a r the r o c k - s a n d co n tact a r e im p o rta n t p a r ts of the
sh elf sed im en t c irc u la tio n sch e m e .
V e rtic a l
Studies in wave ta n k s and d ir e c t o b se rv a tio n s on the s e a flo o r
d e m o n stra te th a t o s c illa to r y rip p le s m ove. F ro m th is it is re a so n a b le
to conclude th a t the sand la y e r involved in the rip p le m o v e m e n t w ould
be at le a s t as th ic k as th e ripple am p litu d e and th at sed im en t is m ix ed
to th a t depth. A s a r e s u lt of one san d t r a c e r te s t Inm an (1963) c o n
cluded that the th ic k n e ss of sed im en t, w hich is su b je c t to m o v e m e n t in
the n e a rs h o re a r e a , is eq u al to the height of the sand rip p le s . The b a
sis fo r this co n clu sio n w a s the d e te c tio n of the r e le a s e d t r a c e r sand at
a lim ite d d ista n c e below the s u rfa c e , w hich w as about equal to the sand
rip p le am p litu d e. F u r th e r c o n firm a tio n of th is concept fro m field
91
o b s e rv a tio n s is d e s ir a b le and data o b tain ed fro m th is study a r e a p p li
cab le.
A fte r t r a c e r r e l e a s e s at Toyon Bay and R ip p e rs Cove w e re su b
je c te d to o s c illa to r y wave su rg e fo r s e v e r a l w eek s it was e v id en t that
la rg e am ounts of c o a rse t r a c e r sand re m a in e d in the vicinity of the r e
le a s e point, and w as m ix ed w ith the indigenous, rip p le d sand. It w as
hoped th at v e r tic a l d is trib u tio n of the c o a r s e san d would be a good in d i
c a to r of the th ic k n e ss of th e sed im en t la y e r s u b je c t to m o v em en t.
S am p les c o lle c te d using g r e a s e d c a r d s w ere obtain ed at the rip p le
c r e s t s and v a rio u s le v els in the in te r io r s by cu ttin g the rip p le s w ith a
tro w e l. W hen g ra in c o n c e n tra tio n s w e r e plotted in c r o s s - s e c tio n , v e r
tic a l d is trib u tio n p a tte rn s w e re ob tain ed (F igs. 28, 29). D e tailed in te r
p re ta tio n of th e se p a tte rn s is difficult b e ca u se c r itic a l data on changes
in sed im en t le v el a re lack in g .
H ow ever, v e r tic a l d is trib u tio n p a tte rn s, to g e th e r w ith c u rv e s
th at show d e p letio n of the t r a c e r san d so u rc e (F ig s. 30, 31), c a r r y i m
p lic a tio n s of a .g e n e ra l n a tu r e to the p ro b le m . T h is is tru e w ith re s p e c t
to the depth of in v o lv em en t of bottom sed im en ts in tra n s p o rt, t r a c e r
depletion r a te s , and a r e a s w ithin w hich sam pling y ie ld s sig n ific a n t
n u m b e rs of t r a c e r g ra in s f o r in te rp re ta tio n . D epletion of the t r a c e r
sand a t the r e le a s e points w a s continuous at all le v e ls from rip p le
c r e s t to below the base and w as s lo w e s t at and below the rip p le b ase.
T his su g g ests a lte rn a te e r o s io n and d ep o sitio n of the sea bed, w hich
fro m tim e to tim e b rin g s ev en the m o s t deeply b u r ie d t r a c e r g ra in s
into the la y e r of se d im e n t m o v em en t.
As the t r a c e r san d w as d is p e rs e d , the c o n to u r of a g iv en tr a c e r
F ig u re 28. — T est Y, v e r tic a l d is p e r s io n
t r a c e r sand w ithin and below the s a n d rip p les
(T e st site san d m e d ia n d ia m e te r 0.19 m m .)
WAVES
93
RELEASE+68 D A Y S
RIPPLE
RIPPLE
MIDDLE
R 1PSLE
BASE
RELEASE* 96 D A Y S
RIPPLE
CREST
RIPPLE
MIODLE
TEST V
WATER DEPTH-12 FT.
IA N T A CATALINA ISLANO
TOT OH SAY
1 0 - 1 8 -A 4
CO N T O U R S--' •R A IN S /IN C H 1 0 .
1 0 0 PO O N O t T R A C E R OANO
RELEASES-132 D A Y S RIPPLE
CREST
MIODLE
RIPPLE
BASE
BELOW RIPPLE
BASE
5 FEET
RELEASE* 185 D A Y S RIPPLE
CREST
RIPPLE
MIDDLE
RIPPLE
BASE
BELOW RIPPLE
BASE
RELEASE A REA
TRACER MEDIAN DIAMETER
0.42 mm.
F ig u re 2 9 .— T e s t W. V e rtic a l d is p e r s io n of
t r a c e r san d in and below the rip p led la y e r of sand.
(T est site san d m e d ia n d ia m e te r 0.17 m m .)
T E S T " W M
WATER DEPTH 12 FT.
SANTA CATALINA ISLAND
m m W covi
CONTOURS"* OR ANN/INCH 1 0 .
IOO PO U N D S TSACCA SAND
V E R N O N (1**5)
O
5 FEET
WAVES
RELEASE* 13 DAYS
RIPPLE
CREST
BASE
RELEASE* 3 2 DAYS
CREST
2 0 1
Ml DOLE
BASE
BELOW BASE
RELEASE+39 DAYS
RIPPLE
CREST
MIODLE
BASE
\ S
RELEASE* 130 DAYS
CREST
MIDDLE
BA3E
BELOW
AREA RELEASE
TRACER MEDIAN DIAMETER
0.4 2 mm.
F ig u re 3 0 .— T e st Y. C u rv e s w hich show d e
p le tio n of t r a c e r sand at th e re le a s e point durin g
a p e rio d of 6 m o n th s. (T e st site sand m e d ia n d i
a m e te r 0.19 m m .)
GRAINS TRACER / IN C H SQUARE
229 r
200 -
179 -
190 -
129 “
100 -
79 -
90 -
2 9 -
97
t e s t"y "
WATER DEPTH —12 FT.
SANTA CATALINA IS L A N D
T 0 Y 0 N BAY
DEPLETION OF TRACER
SAND AT RELEASE POINT
M ED IA N D IAM ETER
0.42 mm
JULY AUO. SEPT. OCT. NOV.
DATE 1 9 6 4 -6 5
DEC. JAN.
F ig u re 3 1 .— T e st W. C u rv e s th at d e p ict d e
p le tio n of t r a c e r sand at the r e le a s e point d u rin g
a 4 -m o n th p e rio d . (T e s t site san d m ed ian d ia m e
t e r 0.17 m m .)
GRAINS TRACER / INCH SQ UARE
99
8 0 0
TEST "W”
W A TER DEPTH -1 2 FT.
SANTA CATALINA ISLA N D
RIPPER’S COVE
7 0 0
6 0 0
D EPLETIO N OF TR A C ER
SAND AT R E LE A S E P O IN T
MEDIAN DIAMETER
0.42 mm.
5 0 0
4 0 0
3 0 0
200
100
gELO W B A SE
SEPT. OCT. N O V . D EC . JAN.
DATE 1 9 6 4 - 6 5
100
g ra in c o n c e n tra tio n m oved o u tw a rd fro m the r e le a s e point to a m a x i
m u m d ista n ce w h e re they re m a in e d u ntil the so u rc e w as sig n ifican tly
d epleted. T h e re a fte r, they m o v e d in w a rd and dow nw ard to w ard th e
o rig in a l b a se of the sand pile r e le a s e d (note iso p le th 20, F ig u re 28, and
iso p le th 10, F ig u r e 29).
The s tro n g tendency f o r the iso p le th s to be n e a r ly v e r tic a l in
m o s t of the d ia g ra m s is a m a n ife s ta tio n of the high d e g re e of m ix in g of
the c o a rs e t r a c e r sand w ith indigenous san d . Such m ix in g o c c u rs only
w ith in the s e d im e n t la y e r su b je c t to m o v em en t. Im p licit in m ix in g is
the m ig ra tio n of the rip p le s b e c a u se , lo g ic a lly , t r a c e r sand can b eco m e
m ix e d at the in te r io r of the rip p le only a f te r the rip p le has m o v ed about
o n e -h a lf w ave length.
ANALYSIS OF DISPERSION P A T T E R N S
D ata thus f a r p re s e n te d show th at t r a c e r sand g e n e ra lly s p re a d s
in an elongate p a tte r n a p p ro x im a te ly p a r a lle l to the w ave orthogonal.
M o re o v er, the p a tte r n can be b a la n c e d or im b a la n c e d e ith e r to w a rd or
aw ay fro m the sh o re o r lo n g sh o re b ecau se of o th er c u r r e n ts . The
b ro a d sp e c tru m of w ave conditions u n d er w hich te s ts w e re m ade in th is
study m a k e s u n ificatio n of the d a ta difficult. The device s e le c te d w as
to group te s ts m ad e u n d e r s im ila r w ave co n d itio n s. B ecau se w ave
h eig h ts and p e rio d s v a rie d th ro u g h a c o n sid e ra b le ran g e during in d iv id
ual te s ts , a v e ra g in g f o r a given te s t w as n e c e s s a r y . T e s ts using g ra d e d
sand a re grouped fo r a n aly tica l p u rp o s e s on the b a s is of th re e a v e ra g e
wave conditions: 0.7 5 feet, 1.5 fe e t and 2.5 feet.
O n sh o re/O ffsh o re and O ffsh o re/O n sh o re R atio s
As a m e a s u r e of the te n d en c y of t r a c e r sand to m ove o n sh o re or
o ffsh o re, the ra tio s o ffsh o re /o n sh o re and o n sh o re /o ffsh o re w e re c o m
puted fro m m e a s u r e m e n ts of th e te s t p a tte r n s . T hese m e a s u re m e n ts
w e re m ad e fro m the re le a s e p o in t to the e x tre m e p o sitio n s o n sh o re and
offshore of w e ll-c o n tro lle d c o n to u rs of the p a tte r n s . The la r g e r d i s
tance w as p la ce d in th e n u m e ra to r of the r a tio . Thus, a n u m b e r g r e a te r
th an unity w as alw ays obtained. Unity in d ic a te s a p e rfe c tly b a la n c e d
p a tte rn , th a t is, o n sh o re and o ffsh o re s p re a d of the t r a c e r w e re id e n ti
cal. The v a lu es thus obtained fr o m te s ts along the m a in la n d p ro d u c e a
101
102
c u rv e in d icatin g high o n sh o re /o ffsh o re ra tio s in shallow w a te r d e c r e a s
ing to w a rd u n ity in deep w a te r (F ig. 32). T his cu rv e, a c o m p a ris o n of
all te s ts m ad e during a p p ro x im a te ly the sa m e w ave conditions (2.5 feet
w ave height and 10 seco n d s p e rio d ), c le a rly show s th at u n d er th e se c o n
ditions no o n sh o re m ig r a tio n of sand of m e d ia n d ia m e te r 0.25 m m
should o c cu r below about 40 fe e t w a te r depth. U nfortunately, no c o m
p a ra b le te s t d a ta a re a v ailab le w hich m e a s u r e t r a c e r sand re s p o n se
below 35 feet.
A s im ila r plot of te s t d a ta fro m the n o rth sh o re of S anta C a ta
lin a Islan d w h e re w aves a v e ra g e about 0.75 fe e t p ro d u c e d the p a tte r n
shown in F ig u re 33. H e re , the ra tio s fo r both 0.42 m m and 0.25 m m
m e d ia n d ia m e te r san d a r e plotted. D espite the c o n sid e ra b le s p re a d of
p o in ts, a definite tre n d e m e r g e s to show an o n sh o re m ig ra tio n ten d en cy
in shallow w a te r and an o ffsh o re ten d en cy in deep w a te r. A lthough th is
ap p lies to both g ra in s iz e s , the change of m ig r a tio n d ire c tio n o c c u rs at
the g re a te s t depth fo r the fin e r sand. The w a te r depth at w hich the
c u rv e s c r o s s the "1" line is the null point fo r th a t san d size u n d e r a v
e ra g e wave conditions and bottom slope in the coves.
The null point co n cep t p ro v id e s a m e c h a n is m fo r o ffsh o re m i
g ra tio n of san d to w a rd the lim it of w a v e-in d u ce d su rg e . The n et r e s u lt
of p ro lo n g ed o p e ra tio n of th is m e c h a n is m is p ro g ra d in g of the sh elf by
a w e d g e -sh a p e d se d im e n t body w hich u ltim a te ly lead s to o v e r - s te e p e n
ing of the s e a w a rd face of the se d im e n t w edge. In c re a s e d im p o rta n c e
of g ra v ita tio n a l effects is p ro d u c e d by o v e r-s te e p e n in g , a condition
w hich w ould ten d to m ove sed im en t, g ra in by g ra in , down the w edge
face in the a r e a below su rg e b ase and also to induce slum ping down the
*VJ
F ig u re 3 2 .— O n sh o re/o ffsh o re ra tio s of t r a c e r
san d m ig ra tio n re la te d to w a te r d epths at t e s t site s.
WATER DEPTH (feet)
0
i---------------------1 -------------------- 1 -------------------- r
1 0 -
2 0 -
30 -
40
I
WAVE
HEIGHT
2.5 FEET
TRACER SAND MEDIAN DIAMETER
0.28 MM.
VERNON
J___________ I___________ L. 19 65-
10 1 5 20
ONSHORE
OFFSHORE
25
F ig u re 3 3 .— R a tio s of o n sh o re and offshore
m ig r a tio n d ista n ce s r e la te d to w a te r depth at site s
of te s t.
WATER DEPTH-FEET
106
oo
20
WAVE
HEIGHT
2 5 -
0.75 FEET
3 0
SAND M EDIAN DIAMETER
• 0.25 M M .
o 0.42 M M .
TRACER
3 5
VERNON
1965
4 0
6 5 4 3 2 2 3 4 5 6
OFFSHORE/ONSHORE ONSHORE/OFFSHORE
107
w edge face into d e e p e r w a te r.
F o r a given w ave c h a r a c te r and s e d im e n t size the p o sitio n of the
null point is m a in ly a function of b o ttom slo p e. On g en tly sloping b o t
to m s it is n e a r the lim it of se d im e n t m o v e m e n t. As slo p e in c r e a s e s
the null point m o v es to w a rd sh o re as fa r a s th e s u rf a t steep ro c k y
p ro m o n to rie s .
R ates of T r a c e r Sand M ig ra tio n
M ig ra tio n r a te s of t r a c e r san d w e re e s tim a te d by m e a s u rin g the
o u te r lim it of t r a c e r g r a in d is p e r s io n and dividing by the tim e fo r m i
g ra tio n . T his is the m eth o d u sed by Inm an (1963) and y ield s an a v e ra g e
g ra in m ig ra tio n speed. F o r p u rp o s e s of a n a ly s is the f a r th e s t p o in t of
m ig ra tio n w as a ss u m e d to be the 0.5 g ra in p e r sq u are inch iso p leth ,
w hich in m o s t te s ts w as the lo w e st g ra in c o n c e n tra tio n re lia b ly d e
p ic te d on the d ia g ra m s . As a r e s u lt, the v a lu e s o b tained a re lo w er th an
tru e a v e ra g e g ra in m ig r a tio n r a te s . C om putations of a v e ra g e t r a c e r
m ig ra tio n r a te s w e re p e rfo rm e d f o r a ll te s t s in w hich the d a ta w e re
am en ab le to th is a n a ly s is . Only s h o r t- te r m te s ts y ie ld re lia b le r e s u lts
b e ca u se d ilu tio n of the t r a c e r san d below d e tec ta b le lim its w ith in
c re a s in g tim e p re c lu d e s e s tim a tio n of the m a x im u m d is ta n c e of m i g r a
tion.
R ate of m ig ra tio n w as p lo tte d a g a in st depth of w a te r fo r two d if
fe r e n t w ave h e ig h ts (F ig s. 34, 35). S e p a ra te plots w e re m ad e f o r t r a c e r
san d of m e d ia n d ia m e te r 0.42 and 0.25 m m . A lthough the p o in ts a re
c o n sid e ra b ly s c a tte re d , it is p o s sib le to d ra w b e s t- fit c u rv e s.
C u rv e s b a se d on the eq u atio n of B agnold (1963) fo r w a te r d rift
F ig u re 3 4 .— T r a c e r sand m ig ra tio n r a te s
r e la te d to w a te r depth. W ave h eig h ts a v e ra g e d
1.5 feet.
WATER DEPTH™FEET
2 0
WAVE H E IG H T -1 .5 FEET
3 0
4 0
TRACER SAND MEDIAN DIAMETER
• 0.25 MM.
o 0.42 MM.
5 0
VERNON
1965
6 0
•5 1.0 1.5 2 .0 2.5
SAND M IG R AT I O N -FT./M IN .
3.0
3 5
F ig u re 3 5 .— T r a c e r sand m ig r a tio n ra te s
re la te d to w a t e r depths. W ave heights a v e ra g e d
2.5 feet.
WATER D E PT H -FE E T
20
3 0
WAVE H E IG H T -2 .5 FEET
4 0
5 0
TRACER SAND MEDIAN DIAMETER
• 0.25 MM.
o 0 .4 2 MM.
VERNON
1965
6 0
0.5 I 1.5 2 2 5
SAND MIGRATION* -FT./MIN.
3.0 3.5
112
u n d er the influence of p ro g r e s s iv e w av es a re shown fo r c o m p a riso n .
T h ese c u rv e s w e re co m p u ted fro m the equation:
u = I" (^ -) c when h L
in which:
u = p re d ic te d w a te r d rift v e lo c ity along the sea bed
H = w ave height
h = w a te r depth
C = w ave velo city
L = w ave length
S ed im en t m ig r a tio n ra te is e s tim a te d by Bagnold (1947) to be
about o n e -th ird the w a te r d rift and th is fa c to r w as applied to the e q u a
tion.
B ag n o ld 1 s eq u atio n does n ot take into acco u n t bottom slope o r
sed im en t g ra in size, but its p o sitio n and shape, w hen p lo tted on the d i
a g ra m s , p ro v id e s an in s tru c tiv e c o m p a riso n . C o n sid erin g the m any
v a ria b le s w hich in flu en ced the p lo ts of t r a c e r m ig ra tio n r a te and the
p ro b le m s of m o d el sc a le in h e re n t in B ag n o ld 's study, the s im ila r itie s
a re m a rk e d .
The d e m o n s tra te d a p p ro x im a te a g re e m e n t b etw een the th e o r e t i
cal and the e x p e rim e n ta l data re m o v e s som e of the u n c e rta in ty in m a k
ing co m p u tatio n s of am o u n ts of s e d im e n t m o v ed in the n e a r s h o r e a r e a .
V o lu m etric co m p u tatio n s a re p r e s e n te d la te r.
S e v e ra l te s ts w e re m ade in th e San D iego a r e a using v e ry fine
sand (0.10 m m m e d ia n d ia m e te r). The m o st re lia b le a v e ra g e g ra in
speeds o btainable fro m th e se te s ts w e re p lo tte d and c o m p a re d w ith san d
m ig ra tio n p lo ts fro m B ag n o ld 's eq u atio n s fo r w ave h e ig h ts of 1.5 and
113
2.5 fe e t (Fig. 36). A v erag e w ave h e ig h t du rin g the te s t s w as e s tim a te d
to be 2.0 feet. M o st of the t r a c e r t e s t points p lo t b etw een the tw o th e o
r e tic a l c u rv e s. P lo tte d a lso on the fig u re is the r e s u lt of one t e s t by
Inm an (1963) w hich su g g e sts a slo w er ra te at the sam e w a te r d epth fo r
a s im ila r sand. In m a n 's e s tim a te of g ra in m ig r a tio n r a te w as b a s e d on
the d is p e r s io n p a tte r n of about 2 pounds of ra d io a c tiv e t r a c e r sand, d e
te rm in e d 7.5 h o u rs a fte r r e le a s e at a d ista n ce of about 30 m e te r s . The
w r i t e r 's e x p e rie n c e in d ic a te s th at In m a n 's te s t p ro b a b ly had b e en in
p r o g r e s s so long th a t the t r a c e r w as dilu ted below the lim its of re lia b le
d e tec tio n at the o u te r lim its of d is p e rs io n . T his c a u se d h is m ig ra tio n
ra te to be too slow .
V o lu m e tric C alcu latio n s
O nshore m ig r a tio n of sand along the s e a bed at m e a s u ra b le
r a te s shown by t r a c e r te s ts m a k e s p o s sib le c o m p u tatio n s of the am ount
of san d tr a n s p o r te d . Such co m p u tatio n s re q u ire an a ssu m p tio n of bed
lo ad th ic k n e ss. O b se rv a tio n s of the m oving sa n d la y e r show th a t at
le a s t one la y e r of sand g ra in s m o v es and p ro b a b ly at le a s t two la y e r s .
In v io len t su rg e m u c h of the f i r s t la y e r is saltatin g , th u s exposing the
u n d erly in g g ra in s to the m o v in g w a te r. A lthough the bed load th ic k n e ss
is not known, a th ic k n e ss of tw o g ra in s is c o n sid e re d r e a lis tic and c o n
se rv a tiv e (Inm an, 1963).
F o r an ex am p le of v o lu m e tric calcu latio n , the follow ing c o n d i
tio n s a re ch o se n fro m v a lu e s p r e s e n te d on F ig u re 34: w ave h eig h t, 1.5
feet; san d m e d ia n d ia m e te r, 0.25 m m ; and w a te r depth, 10 feet. The
in d icated m ig r a tio n ra te fro m the g ra p h is about 1.0 foot p e r m in u te.
F ig u re 3 6 .— M ig ra tio n r ite s of v e r y fine
(0.10 m m ) t r a c e r sand r e la te d to w a te r depth
and p re d ic tio n s b a se d on B ag n o ld 's equation.
A v erag e w ave h eig h t 2.0 feet.
WATER DEPTH-FEET
Oh
io -
20 -
30 -
4 0 -
50 -
60 L
• (IN M A N , 1963)
BAgNOkH---— rT r
TRACER TESTS
AVERAGE WAVE HT. 2.0 FT.
SAND-MEDIAN DIAMETER
0.10 MM. •
V E R N O N
19 6 5
1 .6 2 2.5
SPEED FT/MIN.
SAND MIGRATION
3.0 3.5
U i
116
Using an a ss u m e d b ed lo ad th ic k n e ss of two g ra in s , 2.4 cubic fe e t of
sand m o v es d aily into the s u rf zone along e ac h foot of s u rf. T his is ap
p ro x im a te ly 0.1 cubic y a rd p e r day. U nder the sam e conditions e ac h
1000 fe e t of s u rf w ould re c e iv e 100 cubic y a rd s p e r day and 36,500
cubic y a rd s p e r y e a r . A v e rag e litto r a l d rift r a te s e s tim a te d fro m
t r a c e r san d stu d ie s on b e a c h e s and a c c re tio n at je ttie s along the C a li
fo rn ia c o a s t in d icate th at about 1000 cubic y a rd s of sand m ove along the
b each if the w av es in the ex am p le w e re ap p ro ach in g the sh o re at an
angle of 45° b efo re re fra c tin g . On a b e ac h m o r e than 10,000 fe e t in
length, the volum e of sand m oving into the s u rf ex ceed s the ra te of l i t
to r a l d rift, th at is, the p o w er to m ove it. The r e s u lt is a c c re tio n of the
beach.
Sand m o v e s s h o re w a rd m o re ra p id ly in shallow w a te r th a n in
deep w a te r . U n less sand is supplied by som e o th e r m e a n s , fo r e x a m
ple, rip c u r r e n ts , e r o s io n of the bottom r e s u lts . E r o s io n o ffshore and
sim u ltan eo u s a c c re tio n of the beach ten d to ste e p e n the slo p es up which
the sand m u s t m ig r a te , th u s slow ing the ra te of m ig ra tio n . A cco m p an y
ing the d im in u tio n of m ig r a tio n ra te due to slope in c re a s e is a d e c r e a s e
in the g ra in size s u sc e p tib le to s h o re w a rd m o v em en t. T hus, it follow s
th at w hen a b each is a c c re tin g the la s t d e p o sited sand should be the
fin est. T his ded u ctio n is in a c c o rd w ith m e a s u r e d g ra in size d is tr ib u
tions in b e ac h e s (E m e ry , I960; V ernon, 1962).
The p rin c ip a l n et san d co n trib u tio n s to b e ac h e s fro m o ffsh o re
p ro b a b ly a re s e a s o n a l and in te rm itte n t follow ing la rg e ad d itio n s of
fr e s h m a te r ia l by s tr e a m s o r a fte r s to rm w av es have e ro d e d san d from
b each es. D uring p r o tr a c te d p e rio d s d u rin g w hich wave conditions
117
re m a in unchanging an e q u ilib riu m condition is a p p ro a ch e d in w hich o n
sh o re sand tr a n s p o r t by w aves is about equal to the o ffsh o re tr a n s p o r t
by rip c u r r e n ts .
SAND TR A N SPO R T SYSTEM
S y n th esized data o b tain ed from sa n d t r a c e r te s ts b ro a d ly o u t
line the re g im e n of n e a r s h o re sand c irc u la tio n . In p ro file (F ig. 37), it
can be s e e n that s a n d m ig r a te s s h o re w a rd fro m the null point w ith e v e r
in c re a s in g speed w ith d e c r e a s in g w a te r depth. S eaw ard fro m the null
point sa n d m ig r a te s slow ly to the point of no m o v em en t, the lo w er lim it
of w a v e-in d u ce d s u rg e . Sand m o v es s e a w a r d fro m the su rf in rip c u r
re n ts w hich, at le a s t in p a rt, re p la c e th e sand m o v ed s h o re w a rd by the
wave s .
The plan view of sand c irc u la tio n along a c o a s t is d ia g ra m m a ti-
cally d e p icted in F ig u r e 38. W aves a re shown th at a p p ro ach the co ast
o
at an angle of a p p ro x im a te ly 45 . As th e w aves e n te r shallow w a te r
they c a u s e o s c illa to r y c u r r e n ts on the b o tto m at a d epth equal to about
on e-h alf th e ir w ave length. T he sand, ten d in g to m o v e in the d ire c tio n
of wave advance in s h o re fro m the null lin e , m ig r a te s s h o re w a rd and
down c o a s t and, u ltim a te ly , in to the s u rf zone. T h e re it m o v es down
co ast at an a c c e le r a te d ra te u n til in te rru p te d by a rip c u rre n t, rocky
headland o r s u b m a rin e canyon.
R ip c u r r e n ts funnel la r g e am ounts of sand th ro u g h the s u rf zone.
C o a r s e r sand is d e p o sited n e a r the s e a w a r d edge of the s u rf and the
finer se d im e n t is c a r r i e d f a r t h e r sea w ard , s o m e tim e s a d ista n c e of
s e v e ra l h u n d red fe e t. U ltim a te ly all b u t the silt and fin e r fr a c tio n s s e t
tle to the sea flo o r and a re a g a in caught up in the d om inant s h o re w a rd
118
F ig u re 3 7 .— D ia g ra m m a tic p ro file show ing
c o a s ta l san d c irc u la tio n fo r a sin g le g rain s iz e .
T he length of the a rro w s su g g est re la tiv e sp e e d s
of m ig ra tio n .
I
BEACH
RIP CUR
' r r .
NULL POINT
LOWER LIMIT OF
W AVE SURGE
VERNON (1955)
120
F ig u re 3 8 .— D ia g ra m m a tic p la n view of
c o a sta l san d c irc u la tio n . L engths of a rro w s
su g g est r a te s of sand m ig ra tio n .
R O C K Y
HEADLAN1 BEACH BEACH
SURF
SEAWARD L IM IT OF WAVE^ SURGE ON BOTTOM
SUBMERSED
ROCK 4
SUBM ARINE
/C A N Y O N N
S U B M E R G E D
R O C K
VERNON ( 1 9 6 5 )
122
sand m o v em en t.
A t ro ck y p ro m o n to rie s sand m o v e s s e a w a rd along the ro c k -s a n d
in te rfa c e . If the null line is se a w a rd of the headland, as show n in F ig
u re 38, the sand co n tinues to the point and again is m oved to w a rd sh o re
by the p a ss in g w av es. On the o th er hand, if the null line is s h o re w a rd
of the tip of the headland, san d m ig ra tin g se a w a rd is d ep o sited . The
sand a c c u m u la te s along the point in a w edge, the u p p e r s u rfa c e of w hich
m a y a p p ro a ch the angle of re p o s e of the sand. A s the w a te r shoals it
fo rc e s the null line sea w ard , u ltim a te ly to and beyond the tip of the
headland, and san d m a y ag ain m ig ra te aro u n d the point.
S eaw ard of the null line sand m ig r a te s slow ly s e a w a rd to a point
w h ere the su rg e v e lo city is too sm a ll to m ove it f a r th e r . It is d e p o s
ited th e re until w aves of g r e a te r size ag ain p lace it in m otion.
W here s u b m a rin e canyons h ead s h o re w a rd of the null line they
in te rc e p t sand m oving on the sh elf and, once below the canyon rim , it is
p e rm a n e n tly lo st fro m the s y ste m . It u ltim a te ly m o v e s s e a w a r d down
the canyon into deep w a te r (Dill, 1964).
SILT AND C L A Y -S IZ E P A R T IC L E
TRA N SPORT SYSTEM
F lu o r e s c e n t d y es w e re u se d in the study only on g rain s of sand
s iz e . A cco rd in g ly d a ta app licab le only to th o se s iz e s w e re obtained.
M uch se d im e n t o c c u rs in the C alifo rn ia n e a r s h o r e w a te r s in the silt
and c la y - s iz e ra n g e s . The m ode of m o v e m e n t of th e s e p a rtic le s tends
to be d o m in an tly in su sp e n sio n w hen su b je c te d to high speed c u r r e n ts ,
w h a te v e r th e ir o rig in . It is re a so n a b le to in fe r th at p a rtic le s in the
s ilt size ran g e behave m u ch as sand w hen su b jec te d to gentle o r slow ly
m oving c u r r e n ts . M any o b serv atio n s by th e w r ite r of the re s p o n s e of
s ilty sand u n d e r gentle w ave s u rg e c o n firm th is in fe re n c e . H ow ever,
at th e se tim e s w a te r c la r ity w a s u su ally c o n sid e ra b ly red u ced by s u s
p en d ed se d im e n t n e a r the bottom .
W here w ave su rg e is s tro n g silt and c la y - r ic h bottom se d im e n t
b eco m e ro iled , red u cin g v is ib ility to n e a r z e r o and d isco lo rin g the
w a te r fro m s u rfa c e to bottom . C om m only w a te r to a depth of 50 to 60
fe e t is s e d im e n t-c h a rg e d . The co n tact of th is tu rb id w a te r w ith c le a r
w a te r offshore is co m m o n ly s h a r p (Fig. 39). U nder unu su ally high
w ave conditions w hich o c cu r p e rh a p s once o r tw ice a y e a r c o a s ta l
w a te r is c h a rg e d w ith se d im e n t as m uch as 2 m ile s fro m shore w h ere
d epth is 100 fe e t or m o r e .
A p henom enon a lm o st alw ays noted w hen diving in tu rb id co astal
w a te r is an a b ru p t re d u c tio n of v isib ility w ith in 1 to 5 fe e t of the b o t-
124
F ig u r e 3 9 .— Clouds of tu rb id w a te r g e n e ra te d
by hig h e n erg y w av es shown w ith c le a r w a te r o ff
sh o re. At S c rip p s su b m a rin e canyon. S u m n er
b ra n c h of the can y o n lie s below the fin g e r of c le a r
w a te r extending s h o re w a rd .

127
tom , indicating the p re s e n c e of a c o n sid e ra b ly m o r e dense, tu rb id
la y e r. M o re o v er, it is a c o m m o n c irc u m s ta n c e to dive th ro u g h the
c le a r w a te r s e a w a rd of the s e d im e n t- d is c o lo re d n e a r s h o re w a te r and
find a lso a tu rb id la y e r s e v e r a l feet th ic k on the bottom . W ate r v i s i b i l
ity at the bottom m a y not e x c e e d a few inches but a few fe e t above in
" the o v erly in g c le a r w a te r h o riz o n ta l w a te r v is ib ility m ay ex ceed 10
feet. It h a s been o b se rv e d a ls o that the tu rb id bottom la y e r offshore
co m m o n ly is p r e s e n t a fter th e n e a r s h o r e w a te r h a s to a la r g e extent
c le a re d .
Suspended sed im en t m o v e s in a d ire c tio n w hich is the s u m m a
tion of the c u rre n t v e c to rs of the suspending w a te r m a s s . But if only
the e ffe c ts of c u r r e n ts acco m panying p r o g r e s s iv e su rface w aves a r e
c o n sid e re d the n e t m o v e m e n t of the w a te r and susp en d ed sed im en t in
shallow w a te r is o n sh o re. T u rb id w a te r thus p ile d a g ain st the sh o re
m u st e sc a p e s e a w a rd again by a c u r r e n t sy ste m w hich is only p a r tia lly
u n d ersto o d . O n sh o re m a s s m o v e m e n t of su rfa c e w a ter te n d s to p r e
vent d is p e rs io n of su sp en d ed se d im e n t offshore and, on the c o n tra ry ,
tends to confine it n e a r the s h o re . T h is is in a c c o rd with stu d ies of
su sp en d ed se d im e n t in s o u th e rn C alifo rn ia w a te r s (Rodolfo, 1964).
The su g g este d in te rre la tio n s am ong th e se p h en o m en a are show n
d ia g ra m m a tic a lly in F ig u re 40. W ithin the tu rb id c o asta l w a te r se ttlin g
of silt and c la y - s iz e p a rtic le s c re a te s a dense la y e r at the bottom b u t
they a r e p re v e n te d by wave s u rg e fro m being d e p o sited p e rm a n e n tly .
This la y e r m o v es d o w n -slo p e as a d e n sity c u r r e n t flow b e n ea th the
c le a r o ffshore w a te r . As w ave su rg e d e c r e a s e s w ith depth sed im en t
p a rtic le s a re d e p o site d fro m the tu rb id la y e r in co n fo rm ity w ith th e ir
F ig u re 4 0 .— T u rb id shallow w a te r and its
re la tio n s h ip to tu rb id bottom w a te r o ffshore.
Silt and c la y - s iz e p a r tic le s only.
BEACH
IPxCURRENT_^ ^
CLEAR
WATER
\T U R B IQ
WATE
\
LOWER LIM IT OF
WAVE SURGE
VERNON (1965)
130
settlin g v e lo c itie s . At p r e s e n t no d a ta a re av ailab le to indicate the d i s
tan ce the tu rb id la y e r m a y m ove b e fo re a ll p a r tic le s a re deposited. If
the d e s c rib e d m e c h a n ism functions as outlined, it p ro v id e s a m e an s fo r
the tr a n s p o rta tio n of la rg e v o lu m es of fine sed im en t to d eep w ater.
This is, of c o u rs e , a v a ria tio n of the tu rb id ity c u rre n t concept. It i s a
w o rk in g h y p o th esis w hich r e q u ir e s ad d itio n al s y s te m a tic o b s e rv a tio n to
ev alu ate. The c r itic a l o b s e rv a tio n a b se n t is th a t the la y e r does m o v e
dow n-slope as a d e n sity c u rre n t. O b se rv a tio n s by the w r i t e r in d icate
th at the m o v em en t, if any, is le s s th an 1 foot p e r m inute down a g e n tly
sloping bottom . S eaw ard r e tu r n flow of w a v e - tr a n s p o r te d w ater m a y
a s s i s t tu rb id flow in o v erco m in g the o n sh o re m o v em en t induced by
w av es. As w ave e n e rg y d e c r e a s e s , re s is ta n c e to tu rb id flow d o w n -slo p e
along the bottom n e c e s s a r ily d e c r e a s e s also .
CONCLUSIONS
1. W av e-in d u ced s u rg e m o v es sand on the open sh elf in s y s
te m a tic p a tte rn s w hich a re m o d ified by g ra in s iz e , bottom slo p e and
c u r r e n ts of o th e r o rig in s. The d o m in an t d ire c tio n of sand m o v e m e n t is
in the d ire c tio n of w ave ad v an ce. D ire c tio n and r a te of m o v e m e n t can
be d e te rm in e d by the use of t r a c e r sand.
2. W av e-in d u ced s u rg e on the s e a bed fo r a given w ave is
s tro n g e r in shoal th a n in d eep w a te r, th e re fo re :
a. Sand of a given g ra in s iz e on a g iv en slope m o v e s m o re
rap id ly in shoal th a n in deep w a te r.
b. W ave su rg e m o v e s fine sand m o re ra p id ly th a n c o a rs e
sand.
3. A null p o in t is p r e s e n t fo r a given g ra in size, bottom slope
and w ave c h a r a c te r , fro m w hich sand m o v e s s h o re w a rd and sea w ard .
To s e a w a rd it c a n m ove only to the lim it of w a v e-in d u ce d s u rg e . Tixe
null p o int fo r c o a r s e sand is in s h o a le r w a te r th a n fo r fine sand.
4. The n u ll point f o r a given g ra in size u n d e r the influence of
w aves of a given c h a r a c te r is n e a r e r sh o re on a stee p ly slo p in g bottom
than on a gently sloping bottom .
5. M o re o r le s s s ta tio n a ry sa n d rip p le s te n d to c h an n el m oving
sed im en t along th e ir tre n d .
6. The th e o re tic a l m o d e l by B agnold of se d im e n t m ig ra tio n r a te
on the s e a bed is e s s e n tia lly c o r r e c t fo r fine san d on gently sloping s e a
131
beds.
7. The la y e r of se d im e n t involved in m o v e m e n t on the s e a bed
is at le a s t equal to the sand rip p le am p litu d e.
8. L itto ra l san d m o v es a ro u n d p ro m o n to rie s w hen the o rth o g
onal of ap p ro ach in g w av es is le s s th a n 90° to the sh o re .
9. Sand m oving on the sh elf is tra p p e d by su b m arin e canyons
heading n e a r s h o r e and re m o v e d fro m the sy ste m .
10. Silt and c la y - s iz e se d im e n t fo rm a tu rb id la y e r on the b o t
to m w hich m a y m ove slow ly d o w n -slo p e to deep w a te r.
11. The v olum e of sand m o v ed s h o re w a rd into the su rf zone
u n d er som e w ave conditions is su fficien t to cau se a c c re tio n of the
beach.
R E F E R E N C E S
R E F E R E N C E S
A jbulatov, N., V. B oldyrev and H. G r ie s s e ie r , 1961, Das Stadium d e r
S ed im en t Bewegung in F liiss e n und M e e re n m it H ilfe von lu m in e s -
z ie re n d e n F a rb s to ffe n und ra d io a k tiv e n Isotopen: P e te m a n n s G eo-
g ra p h isc h e M itteilu n g en , p. 177-263.
Bagnold, R. A., 1946, M otion of w aves in shallow w a te r. In te ra c tio n b e
tw e en w aves and sand b o tto m s: P r o c . Roy. Soc., London, A 187,
p. 1-18.
________________, 1947, Sand m o v e m e n t by w av es: Some s m a ll- s c a le e x
p e rim e n ts w ith sand of v e r y low den sity : J. Inst. Civ. E ng., P a p e r
5554, p. 447-469.
________________ , 1963, M ech an ics of m a r in e sed im en ta tio n : The Sea, In
te r s c ie n c e P r e s s , New Y ork, v. 3, p. 507-528.
C aldw ell, J. M ., 1956, W ave a c tio n and san d m o v e m e n t n e a r A naheim
Bay, C alifo rn ia: U. S. A rm y , C o rp s of E n g in e e rs , B each E r o s io n
B o ard , Tech. M em . 68, 21 p.
C ric k m o re , M. J., and G. H. Lean, 1962, The m e a s u r e m e n t of san d
tr a n s p o r t by m e a n s of ra d io a c tiv e t r a c e r s : P r o c . Roy. Soc., L o n
don, A, v. 266, p. 402-421.
Dill, R. F ., 1964, C o n te m p o ra ry su b m a rin e e ro s io n in S c rip p s s u b m a
rin e canyon: U npublished d is s e rta tio n , S c rip p s In stitu tio n of
O ceanography, L a Jo lla , C alif., 267 p.
E m e ry , K. O., 1938, R apid m e th o d of siz e a n a ly sis: J o u r. Sed. P e tr o l -
ogy, v. 8, n. 3, p. 105-111.
_____________, I960, The s e a off s o u th e rn C alifo rn ia: Jo h n W iley and
Sons, Inc., New York, 366 p.
G alvin, C. J., 1964, A s e le c te d b ib lio g rap h y and b rie f rev iew of the th e
o ry and use of t r a c e r s in se d im e n t tr a n s p o r t stu d ies: U. S. A rm y ,
C o rp s of E n g in e e rs , C o a s ta l E n g in e e rin g R e s e a r c h C en ter, v. 1,
p. 5-12.
Ingle, J. C., J r ., In p r e s s , The m o v e m e n t of b e ac h sand: E ls e v ie r
P r e s s , A m s te rd a m .
Inm an, D. L., 1957, Wave g e n e r a te d rip p le s in the n e a r s h o r e san d s: U.
S. A rm y , C o rp s of E n g in e e rs , B each E r o s io n B oard, T ech. M em .
134
135
100, 42 p.
Inm an, D. L ., and T. K. C h a m b e rla in , 1959, T ra c in g b e ac h sand m o v e
m e n t w ith ir r a d ia te d qu artz: J. Geophys. R es., v. 64, n. 1, p. 41-47.
______________, and R. A. Bagnold, 1963, L itto ra l p r o c e s s e s : The Sea,
In te rs c ie n c e P r e s s , New York, v. 3, p. 529-553.
Ippen, A. T., and P . E a g le so n , 1955, A study of sed im en t so rtin g by
w aves sh o alin g on a plane beach: M. I. T. H y d ro d y n am ics Lab.
Technol. R ept. n. 18.
Joliffe, I. P ., 1963, A stu d y of san d m o v em en ts on the L ow estoft s a n d
bank u sin g f .u o r e s c e n t t r a c e r s : G eo g rap h ical J o u r., v. 129, p. 480-
493.
L o n q u et-H ig g in s, M. S., 1953, M ass tr a n s p o r t in w a te r w av es: P h il.
T ra n s. R oy. Soc., London, A 245, p. 535-581.
M ille r, R. L ., and J. M. Z e ig le r, 1958, A m o d el re la tin g d y n am ics and
sed im en t p a tte rn in e q u ilib riu m in the re g io n of sh o alin g w av es,
b r e a k e r zone, and fo r e s h o re : Jo u r, of G eol., v. 66, n. 4, p. 417-
441.
M u n c h -P e te rs o n , 1950, M u n c h - P e te r s o n 's litto r a l d rift fo rm u la: Bull.
Beach E r o s io n B o ard , v. 4, n. 4, 31 p.
R an ee, R. J., 1963, The d e te rm in a tio n of q u a n titie s of se d im e n t t r a n s
p o rt in o s c illa to r y m o tio n by c o n sid e ra tio n of d is p e r s io n of t r a c e r
sed im en t: Int. A sso c , fo r H y d rau lic R es., 10th C o n g re ss, London,
P a p e r n. 1.25, p. 181-188.
Rodolfo, K. S., 1964, S uspended se d im e n t in so u th e rn C a lifo rn ia w a te rs:
Univ. S o u th ern C alifo rn ia, U npublished m a s t e r 1 s th e s is in Geology,
90 p.
S h ep ard , F. P ., and D. L. Inm an, 1951, N e a rs h o re c irc u latio n : P r o c .
F i r s t Conf. C o astal E ng., C ouncil on W ave R e s e a rc h , Univ. C alif.,
p. 50-59.
T r a s k , P . D., 1955, M o v em en t of san d aro u n d so u th e rn C alifo rn ia
p ro m o n to rie s: U. S. A rm y, C o rp s of E n g in e e rs, B each E ro s io n
Board, T ech . M em . 76, 6 p.
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Creator Vernon, James Wesley (author)

Core Title Shelf Sediment Transport System

Degree Doctor of Philosophy

Degree Program Geology

Publisher University of Southern California (original), University of Southern California. Libraries (digital)

Tag Geology,OAI-PMH Harvest

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Advisor Gorsline, Donn S. (committee chair), Reith, John W. (committee member), Stone, Richard O. (committee member)

Permanent Link (DOI) https://doi.org/10.25549/usctheses-c18-190310

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