C O A S T A L E N G I N E E R I N G
Volume I
I N T R O D U C T I O N
C o a s t a l E n g i n e e r i n g Group
D e p a r t m e n t of C i v i l E n g i n e e r i n g
D e l f t U n i v e r s i t y of T e c h n o l o g y
D e l f t , The N e t h e r l a n d s
Volume I - I n t r o d u c t i o n e d i t e d by W.W. M a s s i e , P.E. Coastal E n g i n e e r i n g Group Department o f C i v i l E n g i n e e r i n g D e l f t U n i v e r s i t y o f Technology DELFT The N e t h e r l a n d s 1976
" I f you s t a y w i t h a problem l o n g enough you w i l l get t h e answer. I t may not be t h e one you e x p e c t e d , b u t t h e chances are i t w i l l be t h e t r u t h . "
TABLE OF CONTENTS - VOLUHE I
INTRODUCTION TO COASTAL ENGINEERING
1 . I n t r o d u c t i o n 1 1.1 Purpose 1 1.2 S u b d i v i s i o n s 1 1.3 P e r i o d i c a l L i t e r a t u r e 2 1.4 Reference Books 3 1.5 C o n t r i b u t o r s 4 1.5 M i s c e l l a n e o u s Remarks 5 2 . Overview o f Coastal E n g i n e e r i n g 6 2 . 1 D e f i n i t i o n 6 2.2 Background S t u d i e s 6 2.3 S u b d i v i s i o n s 6 2.4 Harbors 6 2.5 Coastal Morphology 7 2.6 O f f s h o r e E n g i n e e r i n g 8 3. Oceanography 9 3 . 1 I n t r o d u c t i o n 9 3.2 D e s c r i p t i o n o f The Oceans 10 3.3 Wind D r i v e n Ocean C u r r e n t s 11 3.4 Dynamics of Ocean C u r r e n t s 11 3.5 Eckman Wind D r i f t 13 3.6 P h y s i c a l P r o p e r t i e s o f Sea water 16 3.7 D e n s i t y C u r r e n t s 21 4 . B e a u f o r t Wind Scale 22
5. Short Wave Theory 24 5 . 1 I n t r o d u c t i o n 24 5.2 General R e l a t i o n s h i p s 24 5.3 S i m p l i f i c a t i o n s 27 5.4 A p p r o x i m a t i o n s f o r Deep Water 27 5.5 A p p r o x i m a t i o n s f o r Shallow Water 29 5.6 I n t e r m e d i a t e Water Depths 30 5.7 A C r i t i c a l Reexamination 30 5.8 Examples 32
6. Wave Speed and Length Computations 33
6 . 1 I n t r o d u c t i o n 33 6.2 I t e r a t i o n Method 33 6.3 Use of Tables 35 7. E f f e c t s o f Shoal i n g Water 37 7 . 1 I n t r o d u c t i o n 37 7.2 Wave H e i g h t Changes 37 7.3 Example 39 7.4 Review o f Example 41 7.5 Breaking C r i t e r i a 41
i i 8. Types o f Breakers 43 8 . 1 I n t r o d u c t i o n 43 8.2 Breaker Types 43 8.3 Q u a n t i t a t i v e C l a s s i f i c a t i o n s 44 8 . 4 Reexamination o f Breaking C r i t e r i a 46 9. Wave R e f r a c t i o n and D i f f r a c t i o n 47 9 . 1 I n t r o d u c t i o n 47 9.2 Wave R e f r a c t i o n 47 9.3 Wave D i f f r a c t i o n 50 10. Wave S t a t i s t i c s R e l a t i o n s h i p s 51 10.1 I n t r o d u c t i o n 51 10.2 The Phenomona and I t s C h a r a c t e r i z a t i o n s 51
10.3 D e t e r m i n a t i o n o f Frequency o f Occurrence 55
10.4 Wave Periods 55
1 1 . A p p l i c a t i o n o f Wave S t a t i s t i c s 57
11.1 I n t r o d u c t i o n 57 11.2 Problem Statement and Assumptions 57
11.3 The Numerical Treatment 53
11.4 Example Problem 60 11.5 A Second Type o f Problem 62
11.6 Example 62 1 1 . 7 Ttie, inver3e pi-oUem ^<(^
12. Wave Data 63 1 2 . 1 I n t r o d u c t i o n 63 12.2 E x i s t i n g Data 63 12.3 Measurement Program 63 12.4 Use o f S u b s t i t u t e Data 64 12.5 SMB P r e d i c t i o n Method 64 13. Optimum Design 67 1 3 . 1 I n t r o d u c t i o n 67 13.2 P r o j e c t C r i t e r i a 67 13.3 O p t i m a l i z a t i o n Procedure 67 13.4 I m p l i c i t Assumptions 67 14. H i s t o r y o f Harbor Developments 69 1 4 . 1 I n t r o d u c t i o n 69 14.2 E a r l y H i s t o r y 69 14.3 The I n f l u e n c e o f Dredging 69 14.4 Modern Developments 70 15. Approach Channels 7^ 1 5 . 1 I n t r o d u c t i o n 71 15.2 Problems Encountered 71 15.3 The O p t i m a l i z a t i o n Problem 72
73 16. Dredging Equipment 1 6 . 1 I n t r o d u c t i o n 16.2 General P r i n c i p l e s 73 16.3 P l a i n S u c t i o n Dredge 73 16.4 C u t t e r S u c t i o n Dredge 78 16.5 T r a i l i n g S u c t i o n Hopper Dredge 16.6 Bucket Dredge 16.7 F u r t h e r Developments 17. Dredging S p o i l Disposal 1 7 . 1 I n t r o d u c t i o n 17.2 Marine Disposal 17.3 Land Disposal 18. Breakwaters 18.1 I n t r o d u c t i o n 18.2 M o r p h o l o g i c a l F u n c t i o n of Breakwaters 18.3 Other C o n s i d e r a t i o n s 19. Seiches 1 9 . 1 D e f i n i t i o n 19.2 Simple Cases 19.3 E f f e c t s of Seiches 19.4 Seiche P r e v e n t i o n 20. T i d a l R i v e r s 2 0 . 1 I n t r o d u c t i o n 20.2 R i v e r Mouths 2 1 . 80 80 83 84 84 84 85 86 86 86 87 89 89 90 90 90 2 0 . 3 R i v e r Channels 91 2 0 . 4 T i d a l C u r r e n t s 92 20.5 R i v e r N a v i g a t i o n 20.6 Example 20.7 Other T i d a l E f f e c t s 98 98 103 104 104 R i v e r T i d e Measurements 2 1 . 1 I n t r o d u c t i o n ^^'^ 21.2 P r e c i s e Problem Statement 21.3 A Simple Method o f S o l u t i o n 21.4 A B e t t e r S o l u t i o n 107 21.5 Example 108 21.6 A Reexamination H I 22. D e n s i t y C u r r e n t s i n R i v e r s 112 2 2 . 1 I n t r o d u c t i o n 22.2 S a l i n i t y V a r i a t i o n s w i t h T i d e 112 22.3 D e n s i t y - S a l i n i t y R e l a t i o n s h i p 116 2 2 . 4 S t a t i c s of S t r a t i f i e d Water Masses 116 22.5 I n t e r n a l Waves 117 22.6 The " S t a t i c " S a l t Wedge 119 22.7 S i l t a t i o n Problems 121 22.8 P o l l u t i o n Problems 124 22.9 Methods t o Combat D e n s i t y C u r r e n t I n f l u e n c e s 124 i n R i v e r s
i v 2 3 . D e n s i t y C u r r e n t s i n Harbors 2 3 . 1 T i d e Flow i n Harbor i 2 6 2 3 . 2 D e n s i t y C u r r e n t i n Harbor 127 2 3 . 3 S u p e r p o s i t i o n o f C u r r e n t Components 130 2 3 . 4 C u r r e n t s i n F i n i t e Harbors 131 2 3 . 5 The P r a c t i c a l Problem 134 2 3 . 6 Other C u r r e n t I n f l u e n c e s 135 2 3 . 7 Harbor S i l t a t i o n 2 3 7 2 3 . 8 Methods t o Combat D e n s i t y C u r r e n t s i n Harbors 1 4 3
2 3 . 9 Review ^45 2 4 . P o l l u t i o n 2 4 . 1 D e f i n i t i o n ^ 4 7 2 4 . 2 P o l l u t i n g M a t e r i a l s 147 24..,S C o n t r o l Measures 253 2 4 . 4 Proposed D i s p o s a l Systems 150 2 5 . Beach P r o f i l e 2 5 2 2 5 . 1 I n t r o d u c t i o n 2 5 2 2 5 . 2 Beach Dynamic E q u i l i b r i u m 2 5 2 2 5 . 3 Dunes 254 2 5 . 4 I n f l u e n c e o f Storms 2 5 5
2 6 . Sediment T r a n s p o r t Along Coasts 2 5 7
2 6 . 1 D e f i n i t i o n s 257 2 6 . 2 The C.E.R.C. Formula 2 5 7
2 6 . 3 The B i j k e r Formula 2 5 9 2 6 . 4 Sediment T r a n s p o r t Along t h e P r o f i l e 159
2 6 . 5 Computation o f Coastal Changes 2 6 0
2 7 . Mud Coasts i c o Loc 97 1 D h w c - i ^ - , ! . . . • i i j ' o i ^ . u i u c s o i i p i . i u r i 2 6 2 2 7 . 2 P r o p e r t i e s and T r a n s p o r t Process 2 6 2 2 7 . 3 I n f l u e n c e o f R i v e r s 2 6 3 2 7 . 4 Examples 2 6 5 2 7 . 5 The Coast o f Suriname 2 6 5
2 8 . Coastal Formations 2 8 . 1 I n t r o d u c t i o n 2 6 7 2 8 . 2 S p i t 2 8 . 3 B a r r i e r 259 2 8 . 4 Tombolo 2 9 . D e l t a s 2 9 . 1 I n t r o d u c t i o n 273 2 9 . 2 D e l t a s on Q u i e t Coasts 2 7 3 2 9 . 3 D e l t a s w i t h Moderate D i s t r i b u t i n g I n f l u e n c e s 1 7 6 2 9 . 4 D e l t a s w i t h S t r o n d D i s t r i b u t i n g I n f l u e n c e s 2 7 8 2 9 . 5 I n f l u e c e o f Longshore T r a n s p o r t 2 8 0
3 0 . Shore P r o t e c t i o n
3 0 . 1 I n t r o d u c t i o n 182 30.2 Eroding and A c c r e t i n g Shores 182
3 0 . 3 J e t t i e s 183 30.4 G r o i n s 183 30.5 Detached Breakwaters 185 30.6 Seawalls 186 30.7 A Remaining Problem 186 3 0 . 8 Sand By-Passing 186
3 1 . Coastal M o r p h o l o g i s t s ' Ten Commandments 187
3 2 . O f f s h o r e E n g i n e e r i n g 188 3 2 . 1 D i s c i p l i n e s I n v o l v e d 188 32.2 Types of O f f s h o r e S t r u c t u r e s 188 3 2 . 3 Uses of O f f s h o r e S t r u c t u r e s 193 32.4 C i v i l E n g i n e e r i n g Aspects 196 32.5 Other Problems 199 Symbols and N o t a t i o n 200 References 208
v i LIST OF TABLES Table T i t l e Page number 1.1 C o n t r i b u t i n g S t a f f 4 3 . 1 Polynomial C o e f f i c i e n t s f o r c o e f f i c i e n t s 18 3.2 C o e f f i c i e n t s f o r c o m p u t a t i o n 18 3.3 °t f u n c t i o n o f t e m p e r a t u r e and s a l i n i t y 20 4 . 1 B e a u f o r t v/ind f o r c e s c a l e 23
5.1 Deep and s h a l l o w water d e f i n i t i o n s 31
.6.1 Wave l e n g t h i t e r a t i o n 34 6.2 F u n c t i o n s o f h/X^ 36 7 . 1 Wave s h o a l i n g c o m p u t a t i o n 40 8 . 1 Breaker c l a s s i f i c a t i o n s 46 9 . 1 Wave r e f r a c t i o n c o m p u t a t i o n 49 1 0 . 1 R a y l e i g h d i s t r i b u t i o n data 53 1 1 . 1 P r o b a b i l i t y of exceedance c o m p u t a t i o n 61 1 6 . 1 C u t t e r s u c t i o n dredge p r o d u c t i o n 78 16.2 Bucket dredge p r o d u c t i o n 83 2 0 . 1 T i d e and c u r r e n t a t Rotterdam 93 20.2 T i d e and c u r r e n t f o r Western Schelde 96
2 0 . 3 I n t e g r a t i o n c o m p u t a t i o n 101
2 1 . 1 Example t i d e data 105 21.2 Example t i d e data 108
2 2 . 1 C u r r e n t and s a l i n i t y a t Rotterdam 112
22.2 R i v e r m i x i n g c r i t e r i a 114 2 2 . 3 Suspended load a t Rotterdam 123
T a b l e number 2 3 . 1 23.2 2 3 . 3 2 3 . 4 23.5 2 4 . 1 2 7 . 1 3 1 . 1 Symbols T i t l e Page Harbor l e v e l and f i l l i n g c u r r e n t 126 D e n s i t y c u r r e n t a t Pvotterdam 129 S e d i m e n t a t i o n summary 140 S e d i m e n t a t i o n summary 143 T i d e data f o r Hook of H o l l a n d 145 C o n c e n t r a t i o n s of heavy metals 149 P r o p e r t i e s o f s l i n g mud 163 Ten commandments 187 Roman l e t t e r s 200 Greek l e t t e r s 203 S p e c i a l symbols 204 S u b s c r i p t s 205 F u n c t i o n s 205 Dimensions and u n i t s 207
LIST OF FIGURES
F i g u r e T i t l e Page number
3-1 Depth d i s t r i b u t i o n o f Oceans 1 0
5 . 1 H y p e r b o l i c f u n c t i o n s 27 5.2 O r b i t a l motion i n deep water 28
5.3 O r b i t a l motion i n s h a l l o w water 30 8 - 1 S p i l l i n g breaker 4 3 8.2 P l u n g i n g breaker 4 4 8 . 3 Surging breaker 4 4 9- 1 Wave r e f r a c t i o n p a t t e r n 48 9.2 Wave d i f f r a c t i o n p a t t e r n 5 0 1 0 . 1 I r r e g u l a r wave p r o f i l e 51 10.2 R a y l e i g h d i s t r i b u t i o n graph 5 4
1 0 - 3 Long term wave h e i g h t d i s t r i b u t i o n 56
1 2 . 1 Fetch - d u r a t i o n r e l a t i o n s h i p 65
14.1 Ship camel 7 0
1 6 . 1 S u c t i o n dredge 7 4 16.2 Barge l o a d i n g s u c t i o n dredge 7 5
1 6 . 3 Dredge pump parameters 7 5 16.4 Barge u n l o a d i n g dredge 7 7 16.5 C u t t e r s u c t i o n dredge 7 9 16.6 T r a i l i n g s u c t i o n hopper dredge 81 16.7 Bucket dredge 82 1 8 . 1 Columbia R i v e r e n t r a n c e 87 1 9 . 1 Standing v/ave i n c l o s e d b a s i n 88 19.2 Seiche i n harbor b a s i n 88 1 9 . 3 F i f t h harmonic s e i c h e 89 2 0 . 1 Schelde R i v e r a t Antwerp 9 1 2 0 . 2 Schelde R i v e r near Hansweert 9 2
2 0 . 3 C u r r e n t a t Rotterdam 9 3 2 0 . 4 I d e a l i z e d t i d e l e v e l and c u r r e n t curves 9 4 2 0 . 5 T i d e data a t Rotterdam 9 5 2 0 . 6 T i d e l e v e l s i n Western Schelde 9 7 2 0 . 7 Example r i v e r p r o f i l e and t i d e 9 9 2 0 . 8 Ship p o s i t i o n - t i m e c u r v e s 1 0 2
F i g u r e number T i t l e Page 2 1 . 1 R i v e r pTan 1'04 21.2 Uinoorrected t i d e curves 105 21.3 'Dornected t i d e curves 106 2 1 . 4 Example t i d e data 109 21.5 V - t curves H O 21.6 G r a p h i c a l s o l u t i o n 110 2 2 . 1 C u r r e n t and s a l i n i t y a t Rotterdam 113 22.2 Pressure on v e r t i c a l i n t e r f a c e 117 22.3 I n t e r n a l wave 119 22.4 " S t a t i c " s a l t wedge 120 22.5 Suspended load a t Rotterdam 123
2 3 . 1 Harbor l e v e l and f i l l i n g c u r r e n t 127 2 3 . 2 Dry bed c u r v e 128 23.3 Harbor s a l i n i t y and d e n s i t y c u r r e n t 129 23.4 Harbor e n t r a n c e v e l o c i t y p r o f i l e s 130 23.5 D e n s i t y c u r r e n t progress 131 23.6 D e n s i t y c u r r e n t i n harbor 133 23.7 Harbor example sketch 138 2 3 . 8 Summary of a l l t i d a l data f o r Rotterdam 146
2 4 . 1 Lead c o n c e n t r a t i o n s 149
2 5 . 1 Beach p r o f i l e 153 25.2 Flow i n t h e breaker zone 154
25.3 Plan of Scheveningen 154 2 5 . 4 Dunes a l o n g Oregon c o a s t 155 25.5 Beach changes i n a storm 156
2 6 . 1 S i n g l e l i n e s c h e m a t i z a t i o n 150 26.2 Two l i n e schematimation 161
2 7 . 1 P r o p e r t i e s o f s l i n g mud 164 27.2 Features o f mud shoals 166
2 8 . 1 Beach near Budva, Y u g o s l a v i a 168 28.2 Block I s l a n d s p i t , U.S.A. 168 28.3 Wadden I s l a n d s , N e t h e r l a n d s 169 28.4 B a r r i e r c o a s t , U.S.A. 170 28.5 B a r r i e r e n c l o s i n g l a k e , U.S.A. 171 28.5 N a t u r a l t o m b o l o , U.S.A. 171 28.7 A r t i f i c i a l t o m b o l o , U.S.A. 172
X F i g u r e T i t l e pgge number 29-1 D e l t a development w i t h o u t waves 1 7 4 2 9 ' 2 Lyéna d e l t a , U.S.S.R. 1 7 5 29-3 M i s s i s s i p p i d e l t a d e t a i l U.S.A. 1 7 5 29-4 M i s s i s s i p p l i d e l t a U.S.A. 1 7 5 29-5 D e l t a w i t h moderate v;ave a t t a c k 1 7 5 29.6 N i l e d e l t a d e t a i l , Egypt 1 7 7 29-7 Niger d e l t a , N i g e r i a 1 7 3 2 9 . 8 Amazon d e l t a , B r a z i l 1 7 9 29.9 Coos Bay, U.S.A. IQQ 29- 10 N e t h a r t s Bay, U.S.A. i g ^
30- 1 Outer Cape Cod, U.S.A. 1 3 2 •^0-2 A c c r e t i o n by Brouwersdam, N e t h e r l a n d s 183
30.3 G r o i n s along coast IQ^^ 30.4 G r o i n s a l o n g c o a s t 3 0 . 5 G r o i n s t r u c t u r e examples 1 3 5 3 2 . 1 Sketch of ANDOC g r a v i t y s t r u c t u r e 189 -^2.2 Models o f j a c k e t c o n s t r u c t i o n s 1 9 0 32.3 F l o a t i n g j a c k - u p p l a t f o r m igi 32.4 Crane s h i p a t work 1 9 2 32.5 Model o f s e m i - s u b m e r s i b l e p l a t f o r m 192 32.6 F l o a t i n g o i l s t o r a g e buoy 1 9 3 32.7 L i g h t tower Goeree 1 9 4 32.8 E k o f i s k o i l s t o r a g e tank 1 9 5 32.9 P r o d u c t i o n p l a t f o r m i n storm 1 9 7
1 . INTRODUCTION W.W. Massie
1 . 1 . Purpose
T h i s s e t o f l e c t u r e notes i s w r i t t e n p r i m a r i l y t o s u p p l e -ment the c l a s s e s conducted by P r o f . E.W. B i j k e r which a r e held
i n D e l f t , both a t the U n i v e r s i t y o f Technology and a t the I n t e r -n a t i o -n a l Course i -n H y d r a u l i c E -n g i -n e e r i -n g . The l e c t u r e t i m e w i l l be used p r i m a r i l y t o d i s c u s s and a m p l i f y these notes and answer q u e s t i o n s .
Some can p r o b a b l y l e a r n much from these books w i t h o u t having a t t e n d e d the c l a s s e s a t a l l . Questions are o f t e n posed w i t h i n the t e x t ; a l l are intended t o s t i m u l a t e t h o u g h t and v e r i f y u n -d e r s t a n -d i n g . 1 . 2 . S u b d i v i s i o n s The e n t i r e m a t e r i a l o f c o a s t a l e n g i n e e r i n g presented by P r o f . B i j k e r a t t h e D e l f t U n i v e r s i t y of Technology i s c u r r e n t l y d i v i d e d i n t o t h r e e c o u r s e s : a . I n t r o d u c t i o n t o Coastal E n g i n e e r i n g - r e q u i r e d f o r a l l h y d r a u l i c e n g i n e e r i n g s t u d e n t s .
b. T o p i c s i n Coastal E n g i n e e r i n g a more advanced t r e a t ment o f c e r t a i n s p e c i f i c more s p e c i a l i z e d t o p i c s , r e -q u i r e d f o r a l l c o a s t a l e n g i n e e r i n g s t u d e n t s .
c. Breakwater Design - t r e a t s t h a t p a r t i c u l a r ^ s p e c i a l i z e d t o p i c .
This s u b d i v i s i o n has been r e t a i n e d i n the p r e p a r a t i o n o f t h e s e books; the m a t e r i a l i s d i v i d e d i n t o t h r e e s e p a r a t e v o l -umes, w i t h each volume prepared f o r one o f t h e t h r e e courses 1 i s t e d above.*
Another s u b d i v i s i o n i s a l s o p o s s i b l e ; i t i s o f t e n handy t o s u b d i v i d e the m a t e r i a l o f c o a s t a l e n g i n e e r i n g i n t o t h r e e broad areas a c c o r d i n g t o t h e types o f problems whi:ch a r e t r e a t e d . These t h r e e broad c a t e g o r i e s a r e H a r b o r s , M o r p h o l o g y , and O f f s h o r e and a r e d i s c u s s e d f u r t h e r i n chapter 2 . T h i s d i v i s i o n has been r e t a i n e d i n t h e f i r s t two volumes of t h i s book. W i t h i n each of t h e s e volumes m a t e r i a l has been grouped i n each of t h e s e c a t e -g o r i e s . T h i s s u b d i v i s i o n i s not a p p a r e n t i n volume I I I s i n c e breakwaters f a l l a l m o s t e x c l u s i v e l y i n t o t h e harbor c a t e g o r y .
A f o u r t h c a t e g o r y o f i n f o r m a t i o n has been added i n these notes t o r e v i e w necessary background t h e o r y n o r m a l l y p r e s e n t e d i n o t h e r c o u r s e s ; t h i s i s done f o r c o m p l e t e n e s s . Many can s k i p over t h i s c a t e g o r y c o m p l e t e l y , o t h e r s w i l l f i n d i t u s e f u l . The u n d e r s t a n d i n g o f t h i s background i s , however, o f v i t a l i m -p o r t a n c e f o r t h e t r u e c o a s t a l e n g i n e e r i n g t o -p i c s which are
X I t has l a t e r been decided t o s e p a r a t e the o f f s h o r e e n g i -n e e r i -n g i -n a s e p a r a t e volume. Thus, t h i s appears as volume I V .
2 b u i l t upon t h i s f o u n d a t i o n .
1 . 3 . P e r i o d i c a l l i t e r a t u r e .
S p e c i f i c l i t e r a t u r e r e f e r e n c e s have been i n c l u d e d a t the end o f each o f the f o u r volumes. These a r e indeed r e f e r e n c e s ; they p r o v i d e background i n s t e a d o f h i g h l i g h t i n g the most r e c e n t developments. P e r i o d i c a l l i t e r a t u r e p r o v i d e s the best means o f keeping up t o d a t e . Such l i t e r a t u r e can be grouped i n t o f i v e s o r t s , each i s d e s c r i b e d a b i t below.
General
E n g i n e e r i n g p e r i o d i c a l l i t e r a t u r e o f t h i s s o r t covers a broad spectrum o f t o p i c s w i t h i n e n g i n e e r i n g and, as s u c h , o c c a s i o n a l l y c o n t a i n s something o f d i r e c t i n t e r e s t t o c o a s t a l e n g i -n e e r s , eve-n though such a r t i c l e s o f t e -n l a c k s p e c i f i c t e c h -n i c a l d e t a i l . Examples o f such p e r i o d i c a l s a r e :
a . E n g i n e e r i n g New Record, p u b l i s h e d v/eekly by McGraw H i l l P u b l i c a t i o n s , New York, U.S.A.
b. De I n g e n i e u r , p u b l i s h e d weekly by t h e Royal S o c i e t y of Engineers ( K o n i n k l i j k I n s t i t u u t van I n g e n i e u r s ) , The Hague, The N e t h e r l a n d s
c . C i v i l E n g i n e e r i n g , p u b l i s h e d m o n t h l y by t h e American So-c i e t y o f C i v i l E n g i n e e r s , New York, U.S.A.
General S p e c i f i c
This group o f j o u r n a l s p r o v i d e general i n f o r m a t i o n about a s p e c i f i c t o p i c a r e a . These u s u a l l y c o n t a i n i n f o r m a t i o n o f d i r e c t i n t e r e s t but s p e c i f i c t e c h n i c a l d e t a i l s are u s u a l l y s t i l l l a c k i n g . Examples o f t h i s s o r t o f l i t e r a t u r e a r e :
a . Ocean I n d u s t r y , p u b l i s h e d m o n t h l y by the G u l f P u b l i s h i n g C o . , Houston, Texas, U.S.A.
b. The Dock and Harbor A u t h o r i t y , p u b l i s h e d m o n t h l y by Foxlow P u b l i c a t i o n s , L t d . , London.
T e c h n i c a l S p e c i f i c
This group o f p u b l i c a t i o n s p r o v i d e , i n g e n e r a l , most o f t h e s p e c i f i c t e c h n i c a l d e t a i l s o f a problem and i t s s o l u t i o n , and a r e o f t e n found i n t h e r e f e r e n c e s l i s t e d i n a r t i c l e s found i n the above s o r t s o f p e r i o d i c a l s . Examples o f t e c h n i c a l s p e c i f i c l i t e r a t u r e a r e :
a . J o u r n a l o f t h e Waterways, H a r b o r s , and Coastal E n g i n e e r i n g D i v i s i o n , p u b l i s h e d q u a r t e r l y by t h e American S o c i e t y o f C i v i l E n g i n e e r s , New York, U.S.A.
b. Shore and Beach, p u b l i s h e d s e m i a n n u a l l y by American Shore and Beach P r e s e r v a t i o n A s s o c i a t i o n , M i a m i , F l o r i d a , U.S.A. c . Coastal E n g i n e e r i n g i n J a p a n , p u b l i s h e d a n n u a l l y by Japan
Strange Technical
These j o u r n a l s p r o v i d e t h e same t y p e o f i n f o r m a t i o n as t h e p r e -v i o u s s o r t of j o u r n a l s , but are i n t e n d e d f o r an e n t i r e l y d i f f e r e n t s p e c i a l t y g r o u p . I t t a k e s a b i t o f i n g e n u i t y on t h e p a r t of t h e
i n v e s t i g a t o r t o d i s c o v e r r e l a t e d t o p i c areas and p a t i e n c e t o seek through i t s l i t e r a t u r e on the small chance t h a t i t c o n t a i n s somet h i n g u s e f u l . O f somet e n somet h i s s e a r c h i n g can be avoided by u s i n g an a b -s t r a c t index - -see below. The example-s l i -s t e d below -serve o n l y t o i l l u s t r a t e t h a t u s e f u l i n f o r m a t i o n can be f o u n d i n t h i s s o r t o f j o u r n a l .
a . An a r t i c l e on wave f o r c e s : Journal o f t h e E n g i n e e r i n g Mecha-n i c s D i v i s i o Mecha-n , p u b l i s h e d by t h e AmericaMecha-n S o c i e t y o f C i v i l E n g i n e e r s , New York, U.S.A.
b. An a r t i c l e on wave a c t i o n i n h a r b o r s : J o u r n a l o f the Acous-t i c a l S o c i e Acous-t y o f A m e r i c a , New York, U.S.A.
A b s t r a c t s
A b s t r a c t s , indexed i n some way, serve t o p r o v i d e easy access and q u i c k r e f e r e n c e t o the v a s t domain o f l i t e r a t u r e . A b s t r a c t s , o f t h e m s e l v e s , do not p r o v i d e any new i n f o r m a t i o n ; the s i m p l y c o n -dense and index e x i s t i n g a r t i c l e s . Among the e x c e l l e n t a b s t r a c t and i n d e x i n g s e r v i c e s a r e :
a. Documentation D a t a , p u b l i s h e d by the D e l f t H y d r a u l i c s Labo-r a t o Labo-r y , D e l f t , The N e t h e Labo-r l a n d s
b. E n g i n e e r i n g I n d e x , p u b l i s h e d by the E n g i n e e r i n g S o c i e t i e s L i b r a r y , New York, U.S.A.
Both o f t h e s e s e r v i c e s are a v a i l a b l e i n the Main L i b r a r y o f t h e D e l f t U n i v e r s i t y o f Technology. The E n g i n e e r i n g Index a b s t r a c t s can be examined v i a a d i s p l a y t e r m i n a l t h e r e , even though t h i s t y p e o f work i s e x p e n s i v e . I n a d d i t i o n a f i l e o f t h e Documentation Data
i s m a i n t a i n e d i n t h e L a b o r a t o r y o f F l u i d Mechanics o f t h e C i v i l E n g i n e e r i n g Department.
1 . 4 . Reference Books.
A few general r e f e r e n c e books o f s p e c i f i c i n t e r e s t t o c o a s t a l engineers a r e l i s t e d h e r e . Each o f these w i l l t e l l something but u s u a l l y n o t e v e r y t h i n g about a wide spectrum o f c o a s t a l e n g i n e e r i n g t o p i c s .
a . Per Bruun ( 1 9 7 3 ) : P o r t E n g i n e e r i n g : G u l f P u b l i s h i n g Company, Houston, Texas, U.S.A.
b. A r t h u r T. Ippen ( 1 9 6 6 ) : Estuary and C o a s t l i n e Hydrodyna-m i c s : M c G r a w - H i l l , New York.
c. H. Lamb ( 1 9 6 3 ) : Hydrodynamics ( 6 t h e d i t i o n ) : Cambridge U n i v . P r e s s ,
d . Muir Wood, A.M. (1963) Coastal H y d r a u l i c s : M a c m i l l a n and Co. L t d . , London, England.
e. Robert L. Wiegel ( 1 9 6 4 ) : Oceanographioal E n g i n e e r i n g : Pren-t i c e - H a l l , I n c . , Englewood C l i f f s N . J . , U.S.A.
4 1.5. C o n t r i b u t o r s
These books a r e prepared by the e n t i r e s t a f f o f the Coastal E n g i n e e r i n g Group o f the D e l f t U n i v e r s i t y o f Technology. The p r i -mary a u t h o r s o f each s e c t i o n are l i s t e d a t the b e g i n n i n g . Many o t h e r s o f t h e s t a f f reviewed each s e c t i o n ; f i n a l e d i t i n g and a s s a n b l y was t h e r e s p o n s i b i l i t y of W.W. M a s s i e . Table 1 . 1 . l i s t s t h e e n t i r e c o n t r i b u t i n g s t a f f f o r t h i s volume i n a l p h a b e t i c a l o r d e r .
Table 1 . 1 . C o n t r i b u t o r s t o t h i s volume
I r . E. A l l e r s m a , C h i e f E n g i n e e r , Hydrodynamics and Morphology B r a n c h , D e l f t H y d r a u l i c s L a b o r a t o r y , D e l f t .
P r o f . Or. I r . E.W. B i j k e r , P r o f e s s o r o f Coastal E n g i n e e r i n g , D e l f t U n i v e r s i t y o f Technology, D e l f t .
I r . C . J . P . van Boven, D i r e c t o r Harcon I n c . , The Hague.
I r . J . B r a k e l , Research E n g i n e e r , A d r i a a n V o l k e r , I n c . , Rotterdam. I r . J . J . van D i j k , Senior S c i e n t i f i c O f f i c e r , D e l f t
U n i v e r s i t y o f T e c h n o l o g y , D e l f t .
I r . L. E. van Loo, Senior S c i e n t i f i c O f f i c e r , D e l f t U n i v e r s i t y o f T e c h n o l o g y , D e l f t
W.W. M a s s i e , M.Sc, P . E . , Senior S c i e n t i f i c O f f i c e r , D e l f t U n i v e r s i t y o f Technology, D e l f t .
I r . J . de Nekker, C h i e f Engineer f o r H a r b o r s , Department o f P u b l i c Works, Rotterdam.
I r . A. Paape, D i r e c t o r o f D e l f t Branch, D e l f t H y d r a u l i c s L a b o r a t o r y , D e l f t .
1 . 6 . M i s c e l l a n e o u s Remarks
The s p e l l i n g used i n t h i s s e t o f books i s American r a t h e r than E n g l i s h .
A s i n c e r e a t t e m p t has been made t o use c o n s i s t e n t , unambiguous n o t a t i o n . Symbols are d e f i n e d when f i r s t i n t r o d u c e d i n each c h a p t e r and a comprehensive l i s t o f symbols i s p r o v i d e d a t the end o f each volume.
L i t e r a t u r e i s c i t e d i n t h e t e x t by a u t h o r and y e a r d a t e . A com-p l e t e l i s t o f r e f e r e n c e s used i s i n c l u d e d a t t h e end o f each book.
F i g u r e s shown are drawn t o s c a l e whenever p o s s i b l e . D i s t o r t e d f i g u r e s w i l l be s p e c i f i c a l l y p o i n t e d o u t . Many f i g u r e s i n these books are reproduced a t 80°^ o f t h e i r o r i g i n a l s i z e . T h e i r o r i g i n a l dimensions can thus be r e c o n s t i t u t e d by measuring w i t h a 1 : 1250 s c a l e .
Many t e c h n i c a l terms used i n these notes a r e l i s t e d i n a sepa-r a t e g l o s s a sepa-r y g i v i n g d e f i n i t i o n s and Dutch t sepa-r a n s l a t i o n s .
Since the E n g l i s h system o f u n i t s i s s t i l l i n common use i n the marine i n d u s t r y several t a b l e s o f u n i t s c o n v e r s i o n f a c t o r s are
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2. OVERVIEW OF COASTAL ENGINEERING E.WV Bi.jker
2 . 1 . D e f i n i t i o n
Coastal e n g i n e e r i n g i s the c o l l e c t i v e term encompassing most o f the e n g i n e e r i n g a c t i v i t i e s r e l a t e d t o works along t h e c o a s t s . In r e c e n t y e a r s , c o a s t a l engineers have o f t e n been i n v o l v e d i n e n g i n e e r i n g o f s t r u c t u r e s t o be placed o f f s h o r e as w e l l . I t i s t h e i r p r i m a r y t a s k t o a p p l y t e c h n i c a l knowledge t o t h e c o n s t r u c -t i o n o f v a r i o u s works a l o n g coas-ts and o f f s h o r e . U s u a l l y , designs are needed f o r works f o r which o n l y i n c o m p l e t e t h e o r e t i c a l models a r e a v a i l a b l e , thus a fundamental knowledge o f t h e phenomona i n -v o l -v e d i s r e q u i r e d as w e l l . O f t e n , c o a s t a l e n g i n e e r s must extend the f i e l d o f t e c h n i c a l knowledg.e.
An a d d i t i o n a l c o m p l i c a t i m g f e a t u r e o f coastaT e n g i n e e r i n g i s t h a t many o f the independent v a r i a b l e s i n v o l v e d a r e o f a s t o c h a s t i c n a t u r e . S t a t i s t i c a l computations form the basis f o r t h e o p timum design t e c h n i q u e s a p p l i e d t o many c o a s t a l e n g i n e e r i n g p r o -blems,
2 . 2 . Background s t u d i e s .
Among t h e fundamental problems f a c i n g t h e c o a s t a l e n g i n e e r a r e the water movements along a c o a s t , the i n t e r a c t i o n s between moving water and l o o s e beach and sea bed m a t e r i a l s , and t h e hydrodynamic f o r c e s e x e r t e d by waves and c u r r e n t s on v a r i o u s c o n s t r u c t i o n s . These a r e s i m p l y examples f o r t h e fundamental phenomona; o t h e r s w i l l become a p p a r e n t l a t e r . The i n v e s t i g a t i o n o f these phenomona forms the b a s i s f o r c o a s t a l e n g i n e e r i n g r e s e a r c h .
2 . 3 . S u b d i v i s i o n s
Coastal e n g i n e e r i n g has a l r e a d y been s u b d i v i d e d i n t o main d i -v i s i o n s i n t h e general i n t r o d u c t i o n . Here we s h a l l summarize t h e t e c h n i c a l c o n t e n t of each o f these d i v i s i o n s .
2 . 4 . Harbors
Harbors have developed a l o n g w i t h man's d e s i r e t o move goods by s h i p . I t i s i m p o r t a n t t o d e v e l o p harbors i n such a way t h a t t h e y a r e both c o n v e n i e n t and economical f r o m a l l p o i n t s o f v i e w . T h i s must o b v i o u s l y r e s u l t i n a compromise. These a s p e c t s a r e t r e a t e d p r i -m a r i l y i n volu-me I I . The c o o p e r a t i o n o f naval a r c h i t e c t s and -m a r i n e r s i s o f t e n v e r y h e l p f u l when c o n s i d e r i n g t h i s o p t i m i z a t i o n p r o b l e m .
Many harbor e n t r a n c e s a r e p r o t e c t e d by some form o f b r e a k w a t e r ; t h e d e s i g n o f these s t r u c t u r e s i s t h e main t o p i c o f volume I I I o f t h e s e n o t e s .
Since many harbors a r e s i t u a t e d i n r i v e r mouths or n a t u r a l e s t u a r i e s , t h e f o r m a t i o n of shoals and channels i n t i d a l r i v e r s i s o f -t e n imcluded i&l-t;n o o a s -t a l e n g i n e e r i n g . O b v i o u s l y , -t h i s a s p e c -t i s a l s o c l o s e l y r e l a t e d t o r i v e r e n g i i n e e r i n g . S p e c i a l a t t e n t i o n i s paid t o t h e i n f l i u e n c e o f ' d e n s i t y c u r r e n t s and t i m e dependent s a l i n i t y v a r i a t i o n s on t h e behavior o f s i l t i n h a r b o r s . ' D e n s i t y c u r r e n t s a r e a p
-proached f r o m a v e r y p r a c t i c a l v i e w p o i n t i n these n o t e s ; fundamental t h e o r y i s handled \n o t h e r books and c o u r s e s . The behavior o f s i l t i n harbors and r i v e r mouths can be o f extreme importance s i n c e t h i s mud can o f t e n dominate t h e d r e d g i n g problems of the harbor and can o c c a s i o n a l l y even dominate t h e c o a s t a l morphology over a c o n s i d e r a b l e d i s t a n c e as w e l l . Harbor d e s i g n problems a r e o f t e n c l o s e l y l i n k e d t o c o a s t a l m o r p h o l o g i c a l problems. I n d e e d , i t i s o f t e n i m p o s s i b l e t o separate these problems. Among t h e more s i g n i f i c a n t m o r p h o l o g i c a l problems d i r e c t l y r e l a t e d t o harbors are t h e s i l t a t i o n o f approach channels and t h e i n f l u e n c e of breakwaters on the c o a s t a l p r o c e s s e s . 2 . 5 . Coastal Morphology
Coastal morphology i s t h e s t u d y of the i n t e r a c t i o n o f waves and c u r r e n t s w i t h the c o a s t . Most o f t e n t h i s c o a s t w i l l be formed f r o m sandy m a t e r i a l ; t h e s e o f t e n respond t h e most r a p i d l y t o the
i n f l u e n c e o f the waves and c u r r e n t . Rocky c o a s t s u s u a l l y respond v e r y s l o w l y t o these i n f l u e n c e s and as such a r e more o f concern t o the g e o l o g i s t than t o the c o a s t a l e n g i n e e r . Why do c o a s t s c o n -s i -s t i n g o f mud a l -s o re-spond r e l a t i v e l y -s l o w l y t o the a c t i o n o f waves and c u r r e n t s ? T h i s i s answered i n c h a p t e r 27 on Mud C o a s t s .
L u c k i l y , t h e most common c o a s t a l m a t e r i a l i s sand. We a r e l u c k y because i t can be moved r a t h e r e a s i l y by d r e d g i n g and the changes which occur on sand c o a s t s can be r e a s o n a b l y a c c u r a t e l y p r e d i c t e d u s i n g mathematical m o d e l s . These models are b r i e f l y d e s c r i b e d i n t h i s v o l u m e ; more complete i n f o r m a t i o n i s g i v e n i n volume I I .
I t should be c l e a r t h a t one must f i r s t u n d e r s t a n d the m o t i o n o f water (wave a c t i o n and o t h e r c u r r e n t s ) a l o n g a coast b e f o r e he can p r e d i c t m o r p h o l o g i c a l changes. I n d e e d , many concepts from hyd r a u l i c s are neehydehyd; some o f t h e more s p e c i a l i z e hyd t o p i c s a r e r e -viewed i n t h e i m m e d i a t e l y f o i l o w i n g , c h a p t e r s .
The e f f e c t o f waves and c u r r e n t s on beaches i s s t i l l n o t com-p l e t e l y u n d e r s t o o d . Longshore and on and o f f s h o r e t r a n s com-p o r t o f sand i s an i m p o r t a n t t o p i c o f c o a s t a l e n g i n e e r i n g r e s e a r c h . Re-s u l t Re-s of t h i Re-s r e Re-s e a r c h are c o n t i n u a l l y being uRe-sed t o improve t h e mathematical models used t o p r e d i c t c o a s t l i n e changes.
Since not a l l n a t u r a l c o a s t a l changes are d e s i r a b l e , c o a s t a l defense works can a l s o be needed. Defense works are used t o r e t a r d t h e n a t u r a l c o a s t a l processes o r , sometimes, s i m p l y t o n e u t r a l i z e
8
t h e i r e f f e c t s . For example, g r o i n s can be c o n s t r u c t e d p e r p e n d i c u -l a r or p a r a -l -l e -l t o a c o a s t t o r e t a r d e r o s i o n . Another a -l t e r n a t i v e i s t o a r t i f i c i a l l y move sand from areas o f a c c r e t i o n t o areas o f e r o s i o n . Coastal defense works w i l l be c o n s i d e r e d l a t e r i n t h i s volume.
Not o n l y harbor breakwaters and approach channels d i s t u r b t h e c o a s t a l m o r p h o l o g y ; n a t u r a l r i v e r s and e s t u a r i e s do t h i s as w e l l . T h i s i s a l s o discussed i n d e t a i l l a t e r i n t h i s volume.
2 . 6 . O f f s h o r e E n g i n e e r i n g
U n t i l r e c e n t l y , h a r b o r s and c o a s t a l morphology formed t h e main t o p i c s a s s o c i a t e d w i t h " c o n v e n t i o n a l " c o a s t a l e n g i n e e r i n g . I n r e -c e n t t i m e s man's i n t e r e s t i n w o r k i n g a t sea has i n -c r e a s e d r a p i d l y . The o f f s h o r e branch i s d e v e l o p i n g r a p i d l y as c o a s t a l e n g i n e e r s who have worked a l o n g r e l a t i v e l y s h a l l o w c o a s t l i n e s have been asked t o s o l v e c o m p l e t e l y new problems i n t h e deep sea. I n d e e d , t h e f o l l o -wing c h a p t e r on oceanography i s i n c l u d e d because o f an i n c r e a s i n g need t o understand t h e processes which take p l a c e i n t h e deeper ocean w a t e r s . The p r i m a r y s t i m u l u s f o r o f f s h o r e e n g i n e e r i n g has come from the p e t r o l e u m companies.
The term " o f f s h o r e e n g i n e e r i n g " i s u s e d , h e r e , t o r e f e r t o e n g i n e e r i n g f o r works which have no d i r e c t c o n n e c t i o n t o t h e m a i n -l a n d . Some peop-le a -l s o r e f e r t o t h i s t o p i c as "ocean e n g i n e e r i n g " b u t t h e whole s t u d y area i s t o o young t o have developed a u n i f o r m t e r m i n o l o g y . Confusion o f t e r m i n o l o g y i s bound t o r e s u l t ; f o r example, some marine e n g i n e e r s d e s i g n o f f s h o r e works w h i l e o t h e r s d e s i g n power p l a n t s f o r s h i p s !
Ships underway do not have a c o n n e c t i o n t o the m a i n l a n d , but a r e s t i l l excluded f r o m o f f s h o r e e n g i n e e r i n g ; these a r e l e f t f o r the naval a r c h i t e c t s . On t h e o t h e r hand, p o s s i b l e impact l o a d s upon o f f s h o r e s t r u c t u r e s caused by s h i p s can be v e r y i m p o r t a n t t o u s .
The o f f s h o r e engineer draws on the s p e c i a l i z e d knowledge o f o t h e r f i e l d s . M i n i n g e n g i n e e r i n g . Mechanical e n g i n e e r i n g , and Naval a r c h i t e c t u r e can a l l c o n t r i b u t e t o o f f s h o r e e n g i n e e r i n g a l o n g w i t h C i v i l e n g i n e e r i n g . Here i n D e l f t , these departments a r e now cooper a t i n g c l o s e l y on an i n t e cooper d i s c i p l i n a cooper y pcooperogcooperam o f o f f s h o cooper e e n g i -n e e r i -n g .
3 . OCEANOGRAPHY W.W. Massie
3 . 1 . I n t r o d u c t i o n
Oceanography i s s t u d y of t h e oceans. Man has s t u d i e d t h e oceans f o r c e n t u r i e s . Count L.F. M a r s i g l i w r o t e one o f t h e f i r s t books on t h e s u b j e c t , p u b l i s h e d i n 1725. A Dutch t r a n s l a t i o n o f t h i s book was prepared i n 1786 by Boerhaave; a copy e x i s t s i n the L i b r a r y o f Leiden U n i v e r s i t y .
M.F. Maury, a U n i t e d S t a t e s Naval O f f i c e r , w r o t e t h e f i r s t "mo-d e r n " oceanography book i n 1855 w h i l e he was S u p e r i n t e n "mo-d e n t o f the Naval Hydrographic O f f i c e . Many of h i s o b s e r v a t i o n s - compiled f r o m s h i p s l o g s - a r e e x c e l l e n t ; a l l are i n t e r e s t i n g l y e x p l a i n e d , even though he had no knowledge o f g e o p h y s i c s .
The f i r s t s y s t e m a t i c , s p e c i f i c s t u d y o f the oceans was c a r r i e d o u t by t h e H.M.S. C h a l l e n g e r . The s h i p s a i l e d from P o r t s m o u t h , England on 21 December 1872 and i n 3 | y e a r s s a i l e d more than 100,000 km p r o -d u c i n g a 50 volume r e p o r t . This was a l s o the f i r s t r e p o r t t o s u b -d i v i -d e oceanography i n t o i t s f o u r modern major f i e l d s : b i o l o g i c a l , c h e m i c a l , g e o l o g i c a l , and p h y s i c a l .
What i s t h e importance o f oceanography t o t h e c o a s t a l engineer? T h i s w i l l be h i g h l i g h t e d i n the f o l l o w i n g more d e t a i l e d d e s c r i p t i o n s o f each f i e l d .
B i o l o g i c a l Oceanography
B i o l o g i c a l Oceanography concerns i t s e l f w i t h l i v i n g m a t t e r i n the seas. Coastal e n g i n e e r s a r e seldom d i r e c t l y i n v o l v e d w i t h b i o l o g i -c a l p r o b l e m s , but b i o l o g i -c a l f a -c t o r s -can p l a y i m p o r t a n t i n d i r e -c t r o l e s . Marine f o u l i n g o f s t r u c t u r e s and e n v i r o n m e n t a l impact s t u d i e s can be i m p o r t a n t , f o r example.
Chemical Oceanography
The c h e m i s t r y o f sea water i s o b v i o u s l y of g r e a t importance t o t h e marine b i o l o g i s t s but i t i s becoming more i m p o r t a n t t o e n g i n e e r s c o n c e r n i n g w i t h s t r u c t u r e s i n t h e sea as w e l l . M a t e r i a l s used i n c o n s t r u c t i o n i n the oceans can behave i n what seem l i k e s t r a n g e ways when exposed to sea w a t e r under a c o n s i d e r a b l e p r e s s u r e ( d e p t h ) ; Concrete t e c h n o l o g i s t s w o r r y about c o n c r e t e i n water depths o f a few hundred m e t e r s . S p e c i a l c o r r o s i o n and f r a c t u r e problems develop w i t h s t e e l a t somewhat g r e a t e r d e p t h s .
10 G e o l o g i c a l Oceanography
The g e o l o g i s t s who f i n d c o m m e r c i a l l y v a l u a b l e m i n e r a l s on the bottom o f and lundar t h e sea a r e i n d i r e c t l y r e s p o n s i b l e f o r p r o v i d i n g j o b s f o r mainy'Coastal e n g i n e e r s . While c o a s t a l e n g i n e e r s a r e not 'expected t o be g e o l o g i s t s , t h e m s e l v e s , t h e y can c e r t a i n l y g e t p r e l i m i -inary i n f o r m a t i o n about p o s s i b l e f o u n d a t i o n problems f o r a proposed
o f f s h o r e s t r u c t u r e from marine g e o l o g i s t s .
Physical Oceanography
Physical oceanographers a r e most l i k e t h e c o a s t a l e n g i n e e r s . Both w o r r y about waves, t i d e s and hydrodynamic problems i n g e n e r a l . The concern w i t h waves i s i n t e r e s t i n g , i f n o t s e r i o u s . The oceanogra-phers u s u a l l y c o n s i d e r waves t o be a necessary n u s i a n c e ; c o a s t a l e n g i n e e r s , on t h e o t h e r hand, d e r i v e t h e i r most c h a l l e n g i n g problems from them. As o f f s h o r e work progresses i n t o s t i l l deeper w a t e r , c o a -s t a l e n g i n e e r -s mu-st a l -s o begin t o t h i n k about a t o p i c which h a -s , i n t h e p a s t , been r e s t r i c t e d t o p h y s i c a l oceanography: t h e l o c a t i o n and s t r e n g t h o f major ocean c u r r e n t s .
3 . 2 . D e s c r i p t i o n o f the Oceans
A b r i e f r e v i e w o f t h e p h y s i c a l f e a t u r e s of t h e oceans w i l l be h e l p f u l f o r our u n d e r s t a n d i n g o f t h e dynamic processes which occur i n the ocean.
F i g u r e 3 . 1 . shows t h e d e p t h d i s t r i b u t i o n o f t h e oceans. The mean d e p t h i s about 3800 m. and the volume o f t h e oceans i s about 1370 X 10 m . By c o n t r a s t , the N o r t h Sea has a mean d e p t h o f 94 m and a w a t e r volume of 0.054 x 10^^ m'^ - p r e t t y i n s i g n i f i c a n t !
The s h a l l o w e s t 200 m o f t h e ocean (7.6% o f t h e t o t a l a r e a ) i s c a l l e d t h e c o n t i n e n t a l s h e l f . Only r e c e n t l y have c o a s t a l e n g i n e e r s been asked t o v e n t u r e beyond t h e s h e l f t o the c o n t i n e n t a l s l o p e s ; hence, t h e need t o know a b i t more about oceanography, now. Shelves border most o f the c o n t i n e n t a l c o a s t s and range i n w i d t h up t o about 1200
km.
cunnuLative percent of ocean area 0 20 40 60 80 100 F i g u r e 3.1 DEPTH DISTRIBUTION OF THE OCEANS data f r o m : Sverdrup etal 1942
The w i d e s t c o n t i n e n t a l s h e l f i s i n t h e A r c t i c Ocean, n o r t h of S i b e r i a ; h a r d l y any s h e l f i s p r e s e n t a l o n g the west coast o f t h e Americas ( e a s t c o a s t o f the P a c i f i c Ocean).
The oceans a r e f u r t h e r d i v i d e d i n t o a s e r i e s of i n t e r c o n n e c t e d basins i n which most o f the i n t e r e s t i n g p h y s i c a l oceanographic a c -t i v i -t y -takes p l a c e . These basins are 3 -t o 5 km deep w i -t h o c c a s i o n a l deeper or s h a l l o w e r s p o t s .
Most of t h e i n t e r e s t i n g : a c t i v i t y i n t h e oceans takes: place i n t h e u p p e r 1 t o 2 km.. Deeper than t h i s , the. oceans, a r e ' o f r a t h e r u n i -f o r m s a l i n i t y ( 3 5 t o - see s e c t i o n : 3 . 6 ) and t e m p e r a t u r e -f s " - 4 ° C ) . A l s o , c u r r e n t s i n t h i s deep zone a r e v e r y weak - o f t e n assumed t o be z e r o . C u r r e n t s i n t h e upper l a y e r s are discussed i n t h e n e x t s e c t i o n s , w h i l e the p h y s i c a l p r o p e r t i e s o f sea water a r e t r e a t e d s e -p a r a t e l y i n s e c t i o n 3 . 6 .
3 . 3 . Wind-Driven Ocean C u r r e n t s
The major d r i v i n g f o r c e f o r ocean c u r r e n t s r e s u l t s from t h e wind f o r c e s on t h e ocean s u r f a c e . The t r a d e winds and the p r e v a i l i n g wes-t e r l i e s r e s u l wes-t i n a g e n e r a l l y weswes-tward ocean c u r r e n wes-t a wes-t low l a wes-t i wes-t u d e s and an eastward c u r r e n t a t h i g h l a t i t u d e s . T h i s m a n i f e s t s i t s e l f i n t h e N o r t h A t l a n t i c i n t h e f o l l o w i n g c u r r e n t p a t t e r n :
The N o r t h E q u a t o r i a l C u r r e n t f l o w s westward from the Cape Verde I s l a n d s t o t h e Caribbean Sea. A p o r t i o n e n t e r s t h i s sea and a p o r -t i o n -t u r n s n o r -t h w e s -t eas-t o f -t h e Caribbean I s l a n d s ( A n -t i l 1 e s C u r r e n -t ) and j o i n s the F l o r i d a C u r r e n t . Water f l o w s o u t o f t h e Caribbean be-tween F l o r i d a and Cuba i n t h e F l o r i d a C u r r e n t . The F l o r i d a C u r r e n t
( o f t e n c a l l e d the G u l f Stream) c o n t i n u e s n o r t h along N o r t h America
. rt r O M n _ j . j j . . . j _ .A .14 4 . , . v . « . o V.H a n H c n v ^ o a r l c n i i t f n r
-ZO aOOUt t o n. I d t i u u u t ; w j i c i c i i- u u i l u . . . • - •
ming the N o r t h A t l a n t i c C u r r e n t . A branch o f t h i s t u r n s s o u t h , a l o n g Portugal t o f o r m t h e Canary C u r r e n t and c l o s e the c i r c u i t .
S i m i l a r c u r r e n t p a t t e r n s can be f o u n d i n the South A t l a n t i c and t h e o t h e r oceans. These major e a s t w e s t c u r r e n t s correspond i n l a t i -tude t o the p r e v a i l i n g w i n d s . The n o r t h - s o u t h c u r r e n t s g u a r a n t e e c o n t i n u i t y and c o n s e r v a t i o n of mass.
How do the winds generate these major e a s t - w e s t c u r r e n t s ? T h i s i s answered l a t e r i n t h i s c h a p t e r b u t f i r s t , the dynamic e q u i l i b r i u m o f a f l o w i n g ocean c u r r e n t w i l l be examined.
3 . 4 . Dynamics o f Ocean C u r r e n t s
The f a m i l i a r balance o f g r a v i t y and f r i c t i o n f o r c e s which leads t o the w e l l - k n o w n Chézy Equation which i s used t o d e s c r i b e r i v e r f l o w s does n o t work i n de deep oceans. Since t h e oceans are so deep and t h e v e l o c i t i e s a r e n o r m a l l y small ( l e s s t h a n 1 m / s ) , f r i c t i o n f o r c e s become r e l a t i v e l y u n i m p o r t a n t . On t h e o t h e r hand, s i n c e the
12
ocean c u r r e n t s extend over g r e a t d i s t a n c e s on the s u r f a c e o f a r o -t a -t i n g e a r -t h , a n o -t h e r i n f l u e n c e , -t h e C o r i o l i s F o r c e ^ , does become i m p o r t a n t .
Consider a c u r r e n t moving w i t h c o n s t a n t speed a l o n g a " s t r a i g h t " p a t h . ( " S t r a i g h t " means t h a t i t f o l l o w s a g r e a t c i r c l e p a t h . )
The C o r i o l i s a c c e l e r a t i o n a c t i n g on a u n i t mass o f t h i s water i s :
a^ = 2 s i n (f. V where: a^ = t h e C o r i o l i s a c c e l e r a t i o n il = t h e a n g u l a r v e l o c i t y o f the e a r t h = 0.729 x lO'^/s . V = t h e c u r r e n t v e l o c i t y , and iji = the l a t i t u d e
F u r t h e r , t h i s a c c e l e r a t i o n ( o r f o r c e per u n i t mass) a c t s toward the r i g h t f a c i n g i n t h e f l o w d i r e c t i o n i n the n o r t h e r n hemisphere. (The d i r e c t i o n i s o p p o s i t e south o f t h e e q u a t o r ) . I f t h i s c u r r e n t i s moving i n a " s t r a i g h t " l i n e , then t h e r e s u l -t a n -t a c c e l e r a -t i o n p e r p e n d i c u l a r -t o -t h e c u r r e n -t d i r e c -t i o n mus-t be z e r o . The C o r i o l i s a c c e l e r a t i o n i s balanced by a p r e s s u r e g r a d i e n t . T h i s i s a h o r i z o n t a l g r a d i e n t a l s o p e r p e n d i c u l a r t o the c u r r e n t d i -r e c t i o n and c o u n t e -r a c t i n g the C o -r i o l i s a c c e l e -r a t i o n . E q u i l i b -r i u m o f these two components y i e l d s :
i U = 2 n s i n ,^ V ( 3 . 0 2 ) where: P i s t h e water d e n s i t y , and 8 £ i s the p r e s s u r e g r a d i e n t normal t o t h e c u r r e n t . 3 n D e n s i t y d i f f e r e n c e s a r e n o t s u f f i c i e n t t o cause t h i s p r e s s u r e g r a d i e n t , b u t a water s u r f a c e s l o p e c a n , and does p r o v i d e t h e e q u i l i b -r i u m . Thus, t h e -r e a -r e d i f f e -r e n c e s i n mean sea l e v e l between p o i n t s on the ocean s u r f a c e .
T h i s i s demonstrated by computing t h e mean sea l e v e l d i f f e r e n c e a c r o s s t h e S t r a i t o f F l o r i d a ( a c r o s s the F l o r i d a C u r r e n t ) . This i s l o c a t e d a t l a t i t u d e 26° N . , the c u r r e n t i s about 1.0 m / s . , and t h e s t r a i t i s about 80 km w i d e .
A good r e v i e w o f C o r i o l i s a c c e l e r a t i o n s can be found i n c h a p t e r 2 o f Housner and Hudson ( 1 9 5 9 ) .
T h i s a n g u l a r v e l o c i t y i s t h e a b s o l u t e a n g u l a r v e l o c i t y based upon the s i d e r i a l day.
( 2 ) ( 0 . 7 2 9 X 1 0 " ^ ) ( s i n 2 6 ° ) ( 1 . 0 ) 6 . 4 X 10 p sec In 80 km t h e r e i s an e l e v a t i o n d i f f e r e n c e o f : . A Z = ^ - ^ ^ ^ ° ^ X 80 X 10^ = 52. X 1 0 ' ^ m. 9 . 8 1
This agrees r e a s o n a b l y w e l l w i t h an observed 45 cm v a l u e .
The c u r r e n t s j u s t d e s c r i b e d are conmonly c a l l e d g e o s t r o p h i c c u r r e n t s .
Another i n t e r e s t i n g , ( b u t l e s s i m p o r t a n t from an oceanographic v i e w p o i n t ) r e s u l t can be o b t a i n e d i f we do a l l o w our c u r r e n t t o t u r n and l e t the h o r i z o n t a l p r e s s u r e g r a d i e n t be z e r o . In t h i s c a s e , t h e C o r i o l i s a c c e l e r a t i o n i s balanced by the c e n t r i p e t a l a c c e l e r a t i o n . 2 p s i n .j. V ( 3 . 0 3 ) 2 n s i n •!> ( 3 . 0 4 ) where r i s t h e r a d i u s o f c u r v a t u r e .
C u r r e n t s o f t h i s s o r t cause l i t t l e more than minor d i s t u r b a n c e s i n oceanographic measurements; however, t h e y can become a nusiance e l s e w h e r e . Such c u r r e n t s caused c o n s i d e r a b l e problems i n a s e n s i t i v e h y d r a u l i c model a t a l a b i n the U.S. some y e a r s ago. P e r f e c t l y q u i e t water w i t h o u t t u r b u l e n c e was r e q u i r e d i n a c i r c u l a r tank about 4 m
i n d i a m e t e r . A f t e r f i l l i n g t h e t a n k and l e t t i n g i t stand o v e r n i g h t , the i n v e s t i g a t o r found a slow c i r c u l a t i o n c u r r e n t i n the tank t h e next m o r n i n g . Since the l a b was l o c a t e d a t l a t i t u d e 45° N, t h i s c u r -r e n t was 0.2 mm/s ,
These c u r r e n t s j u s t d e s c r i b e d a r e independent o f d e p t h ; they a r e c o n s t a n t over t h e e n t i r e d e p t h , s i n c e f r i c t i o n has been i g n o r e d . This c o n t r a d i c t s t h e e a r l i e r o b s e r v a t i o n t h a t t h e r e i s l i t t l e a c t i -v i t y i n the ocean deeper than 1 t o 2 km. A c t u a l l y , t h e r e i s no r e a l con
t r a d i c t i o n h e r e , s i n c e we have n o t y e t d i s c u s s e d the cause o f t h e g e o s t r o p h i c c u r r e n t s , t h e w i n d , w h i c h , o f c o u r s e , a c t s over t h e s u r -f a c e o -f t h e oceans.
3 . 5 . Eckman Mind D r i f t
Hansen (1902) r e p o r t e d o b s e r v a t i o n s o f t h e d r i f t o f sea i c e i n t h e N o r t h P o l a r Sea. He found t h a t the i c e d r i f t e d not i n t h e wind d i r e c t i o n , b u t a t an a n g l e o f 20° t o 40° f r o m the w i n d . He e x p l a i n e d t h i s as r e s u l t i n g from the C o r i o l i s e f f e c t and f u r t h e r s p e c u l a t e d t h a t the c u r r e n t i n s u c c e s s i v e l y deeper ocean l a y e r s , d r i v e n by shear s t r e s s e s f r o m l a y e r s above, must d e v i a t e even more t o the r i g h t .
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Eckman i n v e s t i g a t e d t h i s m a t h e m a t i c a l l y on t h e s u g g e s t i o n o f Nansen. His r e s u l t s , p u b l i s h e d a l s o i n 1902, w i l l n o t be d e r i v e d h e r e . We s h a l l concern o u r s e l v e s o n l y w i t h t h e basic s t a r t i n g p o i n t and the r e s u l t . His work was done f o r an i n f i n i t e ocean ( a l s o i n f i n i t e l y deep) w i t h a wind o f c o n s t a n t speed and d i r e c t i o n over the e n t i r e s u r f a c e . The ocean s u r f a c e remains h o r i i z o n t a i l i t h e oniliy d r i v i n g f o r c e comes f r o m the wind shear s t r e s s . . Tn; t h e steady s t a t e , , (no a c c e l e r a t i o n ) t h i s r e s u l t s i n : ; — — 2 " = + 2 f! s i n ,j) V ( 3 . 0 5 ) ^7 - J - = - 2 Sl s i n <(i u ( 3 . 0 6 ) J 3 Z where:
u i s the v e l o c i t y component along a h o r i z o n t a l x a x i s V i s t h e v e l o c i t y component along a h o r i z o n t a l y a x i s
z i s the v e r t i c a l c o o r d i n a t e measured f r o m the ocean s u r f a c e (+ u p ) , and
i s t h e v e r t i c a l eddy v i s c o s i t y c o e f f i c i e n t .
The f u r t h e r mathematics i s g i v e n by Neumann and Pierson ( 1 9 6 6 ) . When t h e y assume t h a t t h e wind blows o n l y i n t h e y d i r e c t i o n , the shear s t r e s s a t t h e water s u r f a c e i s : dv Z u Z ^ J . u / ; and a c t s a l o n g t h e y a x i s . This a l l r e s u l t s i n t h e f o l l o w i n g : u = V^e ^ cos ( 4 5 ° + z ) ( 3 . 0 8 ) TJ.; •' z V = V^e " s i n ( 4 5 " + ^ z ) ( 3 . 0 9 )
which g i v e t h e v e l o c i t y components a t any d e p t h , once V ^ , t h e v e l o -c i t y a t the s u r f a -c e , and D are known.
( 3 . 1 0 )
IT T V 2Dp n s i n (j)
Eckman c a l l s D t h e " d e p t h of f r i c t i o n a l i n f l u e n c e " ; t h e d e p t h o v e r which t h e t u r b u l e n t eddy v i s c o s i t y i s i m p o r t a n t . A t t h i s d e p t h t h e v e l o c i t y i s about 1/23 o f i t s v a l u e a t t h e s u r f a c e , and i s d i -r e c t e d im t h e 'Oipposite . d i -r e c t i o n , . TMs i s i n keeping w i t h t h e hypo-t h e s i s o f Nansen imenhypo-t*o.ned e a r l i e r . D i s .normally abouhypo-t 50 m e hypo-t e r s , b u t i n c r e a s e s v e r y r a p i d l y t o » a t the e q u a t o r .
S u b s t i t u t i o n o f z = 0 i n t o 3.08 and 3.09 y i e l d s a t o t a l v e l o c i t y o f magnitude V d i r e c t e d 45° t o t h e r i g h t ( i n t h e n o r t h e r n hemisphere) o f the wind d i r e c t i o n .
The d e t a i l s o f the c u r r e n t p r o f i l e i n t h r e e dimensions can be examined more c o n v e n i e n t l y by i n t r o d u c i n g p o l a r c o o r d i n a t e s .
V = e ^ ' ( 3 - 1 2 )
e = 4 5 ° + 'Jz ( 3 . 1 3 )
I n d e e d , the v e l o c i t y , V , decreases e x p o n e n t i a l l y w i t h d e p t h and the a n g l e between t h e wind and c u r r e n t d i r e c t i o n i n c r e a s e s l i n e a r l y w i t h d e p t h i n a c l o c k w i s e d i r e c t i o n . The magnitude and d i r e c t i o n o f the r e s u l t a n t t r a n s p o r t o f ocean water i s found by i n t e g r a t i n g 3.08 and 3.09 from z = -<» t o z = 0.
^x = ^ V 3 D ( 3 . 1 4 )
0 ( 3 . 1 5 )
where q^ and q^ are volume f l o w r a t e s per u n i t o f ocean w i d t h . The r e s u l t a n t t r a n s p o r t i s p e r p e n d i c u l a r i n the wind d i r e c t i o n !
This i n f o r m a t i o n does n o t seem t o o u s e f u l t o us as c o a s t a l e n g i -n e e r s . However, by a l l o w i -n g t h e ocea-n t o have a c o a s t , a s u r f a c e s l o p e , and a f i n i t e d e p t h i t i s p o s s i b l e t o begin t o a t t a c k t h e problem o f p r e d i c t i n g storm surges near c o a s t s . Such p r e d i c t i o n can be v e r y i m p o r t a n t e s p e c i a l l y i n l i g h t o f t h e d e v a s t a t i o n t h a t such surges can cause.
Eckman (1905) c o n s i d e r e d the problem o f an enclosed sea o f f i n i t e , c o n s t a n t d e p t h . An i m p o r t a n t r e s u l t i s :
^ This i s indeed s t i l l o n l y a b e g i n n i n g . I n f l u e n c e s of t h e b a r o m e t r i c p r e s s u r e changes and o f complex bottom bathymetry a r e s t i l l b e i n g n e g l e c t e d .
16
V/her e:
e = t h e water s u r f a c e s l o p e h = the d e p t h , and
A = a c o e f f i c i e n t
Values o f A v a r y between 1.0 f o r v e r y deep water (h » TT J l ^2
jp n s i n (J)-"
and 1.5 f o r s h a l l o w water or where C o r i o l i s i n f l u e n c e s a r e n e g l e c t e d . A c c o r d i n g t o Neumann and Pierson (1966) C o r i o l i s f o r c e s can be n e g l e c -t e d i n wind s e -t - u p problems and -the d i r e c -t i o n of -t h e maximum s u r f a c e g r a d i e n t does not d e v i a t e more than 10° f r o m the wind d i r e c t i o n .
I f , however, the depth o f the body o f water v a r i e s (as i t g e n e r a l l y does) and the i n f l u e n c e o f the storm surge i t s e l f on t h e d e p t h i s i n -c l u d e d then we a r e f o r -c e d t o -carry o u t a b r u t e f o r -c e i n t e g r a t i o n o f :
d z ' ET
where z ' i s now the d e p t h measured f r o m the a c t u a l water s u r f a c e .
Han
The s o l u t i o n t o t h i s i s beyond the scope o f t h e s e l e c t u r e n o t e s , sen (1956) and H a r r i s (1963) o u t l i n e an approach t o the problem.
3 . 6 . P r o p e r t i e s o f Sea Mater
The most i m p o r t a n t p r o p e r t y o f sea water f r o m a c o a s t a l e n g i n e e r i n g p o i n t o f v i e w i s i t s d e n s i t y . I t s d e n s i t y i s a f u n c t i o n o f t h r e e
v a r i a b l e s : s a l i n i t y , t e m p e r a t u r e , and p r e s s u r e . Of t h e s e , t h e p r e s s u r e i n f l u e n c e i s l e a s t i m p o r t a n t and we can n e g l e c t i t u n l e s s we a r e wor-k i n g a t depths more t h a n , s a y , 500 m.
In c o n t r a s t t o pure w a t e r , most sea water w i l l c o n t i n u o u s l y i n -crease i n d e n s i t y as i t c o o l s u n t i l i t reaches i t s f r e e z i n g tempera-t u r e . Mostempera-t sea watempera-ter has a s a l i n i tempera-t y v a r y i n g betempera-tween 34 and 36%o ( p a r t s per thousand by w e i g h t ) . Some s m a l l e r i s o l a t e d seas can have s i g n i f i c a n t v a r i a t i o n s , however. The B a l t i c Sea, f o r example, sometimes has a s a l i n i t y as low as 7%o. The Red Sea, on t h e o t h e r h a n d , has as much as 4 1 % s a l i n i t y .
U n f o r t u n a t e l y , the dependence o f d e n s i t y , p , on s a l i n i t y ^ S , and t e m p e r a t u r e , T , i s n o t s i m p l e . F i s h e r , W i l l i a m s , and D i a l (1970) pu-b l i s h e d an e m p e r i c a l l y d e r i v e d e q u a t i o n f o r the s p e c i f i c v o l u m e , v , o f water as a f u n c t i o n o f s a l i n i t y , t e m p e r a t u r e , and p r e s s u r e . T h e i r e q u a t i o n i s : K^S \ + KgS + p ( 3 . 1 8 )
i n w h i c h : Kj^ i s a t e m p e r a t u r e dependent c o e f f i c i e n t having u n i t s o f 3 cm , K., i s a t e m p e r a t u r e dependent c o e f f i c i e n t w i t h u n i t s — ^ ^ fo i s a t e m p e r a t u r e dependent c o e f f i c i e n t w i t h u n i t s o f 3 bars cm > g i s a t e m p e r a t u r e dependent c o e f f i c i e n t w i t h u n i t s o f b a r s , p i s t h e a b s o l u t e p r e s s u r e i n b a r s , S i s t h e s a l i n i t y i n to 3 V i s t h e s p e c i f i c volume i n ^ ü l - , and 9 3 v ^ i s a t e m p e r a t u r e dependent c o e f f i c i e n t having u n i t s o f g
The f i v e c o e f f i c i e n t s , K3>' K4 and v ^ a r e r e l a t e d t o t h e tem-p e r a t u r e , T i n degrees C e l c i u s , by tem-polynomial e q u a t i o n s o f f o r m :
E a . T^ C ï . 1 9 )
i = 0
The c o e f f i c i e n t s , a,., f o r these p o l y n o m i a l s a r e g i v e n i n t a b l e 3 . 1 , Equation 3.18 i s v a l i d f o r t h e f o l l o w i n g r a n g e s : - 2 ° < T < 100° C; 0 < p' < 1000 b a r s ; 0 < S < 50to A l l o f t h i s makes e q u a t i o n 3.18 a c t u a l l y r a t h e r cumbersome i n use. T h e r e f o r e , Table 3.2 l i s t s v a l u e s o f c o e f f i c i e n t s f o r e q u a t i o n 3.18 e v a l u a t e d f o r v a r i o u s temperatures u s i n g t a b l e 3 . 1 and e q u a t i o n 3 . 1 9 .
The water d e n s i t y i n ^ can be determined from the s p e c i f i c m volume o f e q u a t i o n 3.18 as f o l l o w s : P = 7 X 10^ ( 3 . 2 0 ) i n which p i s t h e d e n s i t y i n kg/m^. ^ 1 bar i s 10 dynes/cm or a p r e s s u r e o f 10 N/m ; a b o u t 0.987 atmosphere.
18
TABLE 3 . 1 Polynomial C o e f f i c i e n t s a . , f o r K p Kg, K^, and V
COEFFICIENT AW lUiNITS h h h s 3 3 cm /bars> /bars cm \ 0 2..'679xT{!)"'* 10.874 1788.316 5918.499 0.6980547 1 2 . 0 2 x 1 0 ' ^ - 4 . 1 3 8 4 x 1 0 " ^ 21.55053 58.05267 - 7 . 4 3 5 6 2 6 x 1 0 " ^ 2 - 6 . 0 x 1 0 " ^ -0.4695911 -1.1253317 3.704258x10"^ 3 3 . 0 9 6 3 6 3 x l 0 " 3 6.6123869xl0"3 6.315724x10"^ 4 - 7 . 3 4 1 1 8 2 x 1 0 " ^ -1.4661625x10"^ 9.829576x10"^ 5 -1.197269x10"-^' 6 1.005461x10"-^' 7 5.437898x10"^' 8 1.69946x10"^'' 9 - 2 . 2 9 5 0 6 3 x 1 0 " ^ ' TABLE 3.2 C o e f f i c i e n t s f o r Eqn. 3.18 f o r v a r i o u s t e m p e r a t u r e s
COEFFICIENT AND UNITS
T ^1 Kg ^4 v 00 :'^c) 3 /cm ' W o o ) ^barsx •o/oo^ / b a r s cm^, ^ g ' ( b a r s ) ( — ) ^ g ' 0 2.6790x10' -4 10.87400 1788.315 5918.499 0.6980547 2 2.7192x10' -4 10.79123 1829.563 6030.155 0.6967108 4 2.7588x10' -4 10.70846 1867.201 6133,124 0.6956351 6 2.7930x10' -4 10.62570 1901.373 6227,712 0.6948023 8 2.3368x10' -4 10,54293 1932.222 6314.225 0.6941902 10 2.8750x10' -4 10.46016 1959.885 6392.958 0.5937790 12 2.9128x10' -4 10,37739 1984.500 6454.205 0.6935516 14 2.9500x10' -4 10.29462 2006.198 5528.253 0.6934924 16 2.9868x10' -4 10.21186 2025.111 6585.380 0.6935878 18 3.0232x10' -4 10.12909 2041.355 6635,864 0.6938257 20 3.0590x10' -4 - 10.04632 2055.085 6679,793 0.6941953 22 3.0944x10' -4 9.96355 2066,395 5717.971 0.6946869 24 3.1292x10' -4 9.88078 2075.413 5750.117 0.6952918 26 3.1636x10' -4 9.79802 2082.253 5775.553 0.6960021 28 3.1976x10' -4 9.71525 2087.030 5797.857 0.6968106 30 3.2310x10' -4 9.53248 2089.855 6813.939 0.5977110 32 3.2640x10' -4 9.54971 2090.836 5825.146 0.6986973 34 3.2964x10' -4 9.46694 2090.075 5831.707 0.6997638 36 3.3284x10' -4 9.38418 2087.679 6833.847 0.7009055 38 3.3600x10" -4 9.30141 2083.743 6831.785 0.7021179 40 3.3910x10" -4 9.21864 2078.365 6825.734 0.7033962
Since t i i e d e n s i t y o f s a l t water i s u s u a l l y a b i t more than 1 0 0 0 k g / m ^ , Oceanographers o f t e n s u b t r a c t 1 0 0 0 f r o m the d e n s i t y v a l u e s and denote the v a l u e by sigma. I f t h i s i s done f o r a t m o s p h e r i c p r e s -s u r e , then a -s u b -s c r i p t t i -s u -s u a l l y added. Thu-s:
a = p - 1000 ('3.21);
i n whiiichi p. iis evalluated! a t atmospheric pres^suire.
Values o f as a. f u n c t i o n o f s a l i k i i t y and t e m p e r a t u r e a r e l i s -ted! im t a W e 3 v 3 - . , These tateTes were; computed usfngi e q u a t i o n 3 . 1 8
w i t h : p" = l i . 0 1 3 ! 3 ' b a r s = 1 atmosphere-..
Since t h e e q u a t i o n s (.and t h e , i r r e s u l t i n g t a b l e s ) a r e a b i t cumbersome i n u s e , t h e D e l f t " Hydrauiüües L a b o r a t o r y uses a s i m p l e r r e l a t i o n s h i p . In- t h e notatiiani a l r e a d y u s e d ,
a:^ = 0.75 S ( 3 . 2 2 )
Equation 3 . 2 2 n e g l e c t s i n f l u e n c e s of t e m p e r a t u r e and p r e s s u r e and i s t h e r e f o r e more l i m i t e d i n use than e q u a t i o n 3 . 1 8 . I n p r a c t i c e , c i v i l engineers w i l l sometimes f i n d e q u a t i o n 3 . 2 2 t o be s u f -f i c i e n t -f o r problems i n which d e n s i t y d i -f -f e r e n c e s r e s u l t e x c l u s i v e l y f r o m s a l i n i t y d i f f e r e n c e s and t h e water t e m p e r a t u r e i s n o t extreme.
With t h i s i n f o r m a t i o n on d e n s i t y we can r e t u r n b r i e f l y t o t h e d e s c r i p t i o n o f t h e oceans, t h e m s e l v e s . U s u a l l y , both s a l i n i t y and t e m p e r a t u r e decrease w i t h i n c r e a s i n g depth i n the ocean. E v a p o r a t i o n i s r e s p o n s i b l e f o r the h i g h e r s a l i n i t y o f t h e s u r f a c e l a y e r ; how can t h i s f l o a t on l e s s s a l i n e deeper water? The t e m p e r a t u r e d i f f e -rences a r e s u f f i c i e n t t o m a i n t a i n a d e n s i t y p r o f i l e which i n c r e a s e s w i t h d e p t h .
D e n s i t y v a r i a t i o n s caused by d i f f e r e n c e s i n s a l i n i t y and temp e r a t u r e can be used i n i n g e n i o u s ways such as to d r i v e a s a l t f o u n -t a i n , made i n -the f o l l o w i n g way:
We t a k e a l o n g ( 1 km) p i p e and extend i t v e r t i c a l l y down f r o m t h e ocean s u r f a c e . N e x t , we a t t a c h a pump and s l o w l y draw up t h e deep w a t e r . We do t h i s s l o w l y so t h a t t h e water r i s i n g i n t h e pipe can be warmed by t h e s u r r o u n d i n g ocean. A f t e r deep water reaches t h e s u r f a c e we remove the pump and f i n d t h a t the water c o n t i n u e s t o f l o w . Why does i t f l o w ? No, i t i s not p e r p e t u a l m o t i o n ; t h e process stops as soon as t h e upper 1 km l a y e r o f the ocean has become m i x e d .
C u r r e n t s caused by d e n s i t y d i f f e r e n c e s are d i s c u s s e d i n the n e x t s e c t i o n and a g a i n , i n d e t a i l , i n c h a p t e r 2 2 .
