H^^dro - morphological study

(1)

A l M I N I S T R A Q t o » Q E R A L D O ^X)flTO D E L I S B O N

H^^dro - morphological study

Tagus Estuary

Additional worl(

Wave penetration model

^ t e e s / M 7 3

PORT AND "^ï^miM ENGINEERS

hyöRonó.miG

(2)

ADMINISTRAQAO ~ G E R A L DO PORTO DE LISBOA

H y d r o - m o r p h o l o g i c a l s t u d y

T a g y s E s t u a r y

Additional work

Wave penetration model

_ April 1982 / P473

PORT AND W A T E R W A Y E N G I N E E R S

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1. INTRODUCTION

T h i s a d d i t i o n a l study is made on request o f AGPL in o r d e r t o answer

some q u e s t i o n s i n r e l a t i o n t o the f e a s i b i l i t y o f a coal t e r m i n a l a t

B u g i o . The q u e s t i o n s w i t h r e l a t i o n t o t h e wave c l i m a t e were d i s c u s s e d

s h o r t l y in our proposal o f March l 8 t h , 1982. During a meeting w i t h

AGPL on March 1 9 t h , 1982, Hydronamic was g i v e n consent t o proceed

w i t h t h i s a d d i t i o n a l w o r k .

In t h i s r e p o r t t h e wave data measured by i n s t i t u t e H i d r o g r a f i c o in

1979/1981 are compared w i t h t h e data from F i g u e i r o da Foz ( 1 9 5 ^ / 1 9 6 0 ) .

The F i g u e i r a da Foz data are used t o d e t e r m i n e a new i n s h o r e wave

c l i m a t e at L i s b o n . For t h i s purpose a l s o 7 e x t r a wave p e n e t r a t i o n

-c a l -c u l a t i o n s were made.

A seasonal breakdown o f t h e wave data is a l s o d e t e r m i n e d , t o a l l o w

downtime c a l c u l a t i o n s o f t h e new b e r t h s at t h e coal t e r m i n a l .

F i n a l l y some aspects r e g a r d i n g the wave i n p a c t on t h e coast between

S. J u l i a and Padrou^os a r e made.

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2. COMPARISON OF AVAILABLE WAVE DATA

The wave data o r i g i n a l l y used in the V/ave P e n e t r a t i o n Model were based

upon measurements by I n s t i t u t e H i d r o g r a f i c o at Lagoa d ' A l b u f e i r a , from

August 1979 t i l l A p r i l I98O. The wave h e i g h t s and wave p e r i o d s were

measured w i t h a wave r i d e r buoy. The d i r e c t i o n was observed v i s u a l l y

from the beach.

In s h a l l o w w a t e r t h e wave d i r e c t i o n s are i n f l u e n c e d too much by

r e f r a c t i o n . T h e r e f o r e the d i r e c t i o n a l d i s t r i b u t i o n as presented by

the Ocean V/aves S t a t i s t i c s were used f o r t h a t purpose in the V/ave

P e n e t r a t ion Model.

On request o f AGPL the wave p e n e t r a t i o n a n a l y s i s is r e c a l c u l a t e d ,

u s i n g the data a v a i l a b J e from F i g u e i r a da Foz. T h i s was requested

because the o b s e r v a t i o n s a t Lagoa d ' A l b u f e i r a c o v e r o n l y 9 months.

The F i g u e i r a da Foz data cover a p e r i o d o f s i x y e a r s . The data used

are from LNEC-pub1icat ion 290, A g i t a c a o M a r f t i m a na c o s t a o e s t e de

P o r t u g a l M e t r o p o l i t a n o , by Reis de Carvalho and B a r c e l o , 1966.

The waves were observed u s i n g a t h e o d o l i t e and buoy. V/ith t h e t h e o d o l i t e

the v e r t i c a l movement o f t h e buoy was o b s e r v e d ; The.buoy was placed

approx. IAOO m from t h e t h e o d o l i t e , in a w a t e r d e p t h o f approx. 12 m.

The p e r i o d s observed a t F i g u e i r a da Foz are much h i g h e r than observed

near L i s b o n . For comparison see f i g . 1 and 2. In f i g . 2 are presented

a l s o the data from o b s e r v a t i o n s a t Lagoa d ' A l b u f e i r a in 1969, from t h e

Ocean Wave S t a t i s t i c s and from a h i n d c a s t c a l c u l a t i o n u s i n g wind data

from the Portuguese c o a s t .

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In f i g . 3 ttie same type o f diagram withi regard t o the wave h e i g h t s

is p r e s e n t e d .

One can observe t h a t the data from F i g u e i r a da Foz are t h e h i g h e s t

values in most cases. The recent wave h e i g h t o b s e r v a t i o n s a t Lagoa

d ' A l b u f e i r a g i v e very low v a l u e s .

I t is not p o s s i b l e t o draw a c o n c l u s i o n on t h e e f f e c t s o f these

d i f f e r e n c e s w i t h o u t talcing i n t o account the nearshore e f f e c t s .

An complete r e - e v a l u a t i o n o f the wave h e i g h t s a p p l y i n g t h e data f r o m

F i g u e i r a da Foz is presented in c h a p t e r 3- In general one can say

t h a t p r o b a b l y t h e wave p e r i o d s at F i g u e i r a da Foz are somewhat

o v e r e s t i m a t e d .

Although i t is a long term measurement, t h e r e l i a b i 1 i t y , is r a t h e r low

due t o the o b s e r v a t i o n method. The measurements, which are made

nowadays w i t h wave r i d e r buoys, should be c o n t i n u e d in o r d e r t o get

a long term wave c l i m a t e o f f the Portuguese c o a s t .

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3. RECALCULATION QF WAVE CLIMATE USING FIGUEIRA DA FOZ DATA

The data from F i g u e i r a da Foz were regrouped in the c l i m a t e elements

f o r which the o r i g i n a l wave p e n e t r a t i o n c a l c u l a t i o n s were c a r r i e d

o u t . Waves f r o m 3 0 0 ° - 3 6 0 ° and from 1 8 0 ° were o m i t t e d , because

waves from these d i r e c t i o n s do not e f f e c t t h e Bugio area (see our

r e p o r t o f Nov. 1 9 8 1 ) .

Because very long waves were o r i g i n a l l y not c a l c u l a t e d , seven

a d d i t i o n a l wave p e n e t r a t i o n c a l c u l a t i o n s have been made:

run

H

T

di r

TG 81

6

15

210

TG

82 1.2

15

210

TG

83 1.2

15

270

TG 84

3 . 5

15

210

TG

85 3 . 5

15

240 TG

86 6

15

240 TG

87 8

15

270

The usual diagrams are reproduced a t t h e end o f t h i s r e p o r t .

To get a l s o an impression o f t h e wave impact on t h e coast between

S. J u l a o and Pedrougos, these c a l c u l a t i o n s were c a r r i e d out f o r h i g h

w a t e r .

From the diagrams one can see t h a t v e r y long waves h a r d l y e n t e r t h e

Barra S u i . Waves are always r e f r a c t e d t o the A l p e i d a o area or the

Cachopo del N o r t e .

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v/aves which cross the Bugio banks from a s o u t h e r l y d i r e c t i o n a r e

mostly trapped by the n o r t h e r n s i o p e o f t h e bank and are curved

back.

But a l s o a c o n s i d e r a b l e p a r t o f t h e waves may pass t h e banks and w i l l

a t t a c k the coast between S. J u l a o and Pedrou?:os.

in t h e runs TG 83 and TG 8? the wave rays c o n t i n u e on t h e shore near

Caparica. This is due t o t h e f a c t t h a t we r a i s e d the w a t e r l e v e l w i t h

h m e t e r s . The o r i g i n a l land was e n t e r e d in t h e computer w i t l i a l e v e l

o f o n i y 1 m p l u s z e r o .

Due t o t h i s f a c t a small wave (a few c e n t i m e t e r s ) occurs on t h e l a n d .

This wave can be o m i t t e d and has no i n f l u e n c e on t h e o t h e r p a r t o f t h e

c a l c u l a t i o n .

For the F i g u e i r a da Foz data we have determined t h e f o l l o w i n g wave

cl i mate.

H

T

d i r

%

1.2

15.0

210

0.14

1.2

15.0

270

4.52

3.5

15.0

210

0.12

3.5

15.0

240

5.85

6

15.0

240

0.12

8

15.0

270

1.47

1.72

5.6

210

0 . 1 2 0 . 7 2

3.8

270 0.09

1.71

5.6

270

18.24

1.15

7.8

270

6.08

2.80

7.7

270

5.50

3.50

10.2

270 1.24

0.8

5.0

245

0 , 0 3

0.8

6.0

250 0 . 0 3

1.7

6.0

235

0.03

1.7

6.0

240

0.03

1.6

5.0

245

0.09

1.7

6.0

250

0.55

2.8

7.7

235

0.17

2.8

7.7

240

0.03

2.8

7.7

245

0.06

2.8

7.7

250

0.37

3.5

10.2

250

0 . 2 3

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Because these c l i m a t e elements cause n e a r l y no wave a c t i o n in the

t e r m i n a l a r e a , the r e s u l t i n g wave h e i g h t is l e s s than the o r i g i n a l l y

used wave c l i m a t e . For the l o c a t i o n s 4 and 8 new exceedance diagrams

are made. See f i g 4 and

5-The wave d i r e c t i o n s near the new t e r m i n a l s i t e are a l l determined by

r e f r a c t i o n . A l l waves w i l l come from a d i r e c t i o n 260-270 degrees.

Very c l o s e t o t h e b e r t h s they w i l l r e f r a c t somewhat more on the south

slope o f t h e f l o w c h a n n e l , so t h a t the waves w i l l reach t h e s h i p from

d i r e c t i o n s o f 2 7 0 - 2 7 5 degrees.

R e f l e c t i o n o f waves from the o t h e r s i d e o f t h e channel is not e x p e c t e d ,

because

* t h e waves which reach t h e shore between S. J u l i a and Pago d ' A r c o s

are v e r y smal 1.

* t h e c o a s t l i n e is not v e r t i c a l in t h i s s t r e t c h .

Besides t h a t , most o f t h e waves which reach t h a t s t r e c h have passed

the Bugio banl<. I f a t e r m i n a l , is c o n s t r u c t e d t h a t is no longer p o s s i b l

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k. SEASONAL BREAKDOWN

For the d e t e r m i n a t i o n o f t h e down-time o f a b e r t h , the seasonal

breal<dov,/n o f t h e wave c l i m a t e is i m p o r t a n t . U n f o r t u n a t e l y n e i t h e r

t h e data from A l b u f e i r a nor F i g u e i r a da Foz are g i v e n per season.

In o r d e r t o have an impression o f d i s t r i b u t i o n o f t h e waves over t h e

y e a r , we have used the data from t h e Ocean Wave S t a t i s t i c s . In f i g . 6

and f i g . 7 t h e exceedance f o r t h e wave p e r i o d s is g i v e n . In f i g . 8

and f i g . 9 t h e exceedance o f t h e wave h e i g h t s f o r p o i n t k and 8 is

g i ven.

For r e f e r e n c e the same p o i n t s are a l s o g i v e n w i t h the data from t h e

I n s t i t u t e H i d r o g r a f i c o ( f i g . 10 and f i g . 1 1 ) .

These f i g u r e s were a l r e a d y g i v e n in our r e p o r t * o f November 1981.

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breakdown o f expected p e r i o d s ( i n percent o f t i m e )

per i od

dec- feb

0-5

10. 4

6-7

11. 6

8-9

9 . 4

10-11

5. , 1

12-13

2, .5

14-15

1 .1

16-17

0 .3

18-19

0 . 1

>20

0 .3

mar- may

j u n - aug

12. 4

12. 1

11 .

6 6. 1

n

O c '

O . U

•

' 4. 4

0. 8

1, .9

0. 3

0, .8 .

0. , 1

0 .3

0, .0

0 .0

0 .2

0 .3

sep- nov

yea r

10. 6

11.4 7. 0

8.6 4. 5

6.2 2. 0

3-1

0, ,8

1.4 0, .2

0.6 0 . 1

0.2 0 .0

0.0 0 .2

0.2

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exceedance frequency o f wave p e r i o d s ,

seasonal breakdown

( a c c o r d i n g t o Ocean Wave S t a t i s t i c s )

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WAVE-HEIGHT

A. G. P. L.

MATHEMATIGAL MODEL TAGUS ESTUARY

h y ö R o n d m i c

-ol iodr'ooht. h-olland

CALCULATED WAVE HEIGHTS

POINT

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CALCULATED WAVE HEIGHTS

POINT

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WAVE HEIGHTS

s c a l e 1: iOOOOO

I w a v e h e i g h t o f

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4.50 m o r l e s s

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WAVE HEIGHTS

s c a l e 1: 100000

i w a v e h e i g h t o f 6.00 m on more

. w a v e h e i g h t o f 3.00 m o r l e s s

TC3

83

(25)

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H y d r o - h i o r p h o l o g i c j a i s t u d y Tagus e s t u a r y 7 / 5 / 1 9 8 ^ "'^"'•'CTION T h i s r e p o r t d e a l s w i t i i t i i e h y d r o m o r p h o l o g i a l i m p a c t o f

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n^.v^- t e . ' -m i n a l a t B u g i o f o r t h e t r a n s s h i p . n e . i t o f c o a l . T h e s t u d y p r e s e n t e d i n t h i s r e p o r t i s a p a r t o f t h e a d d i t i o n a l woric as p r o p o s e d b y H y d r o n a n i c b . v . , i n a p r o p o s a l d a t e d M a r c h l 8 t h , 1 9 3 2 . D u r i n g s m e e t -i n g ' . v -i t h AGPL on March 1 9 t h , 1 9 8 2 t h e c o m p u t e r r u n s t o ba p a r f o r m ^ -i d ' . a r e f i n a l l y d e f i n e d and H y d r o n a n i c was g i v e n c o n s é n t t o p r o c e e d w i t h t h i s a d d i t i o n a l w o r k « The a d d i t i o n a l w o r k c o n s i s t o f t w o p a r t s s -» R a a n a l y s i s o f t h e w a v e - c l i m a t e a t t h e B u g i o b a n k s - H y d r c m o r p h o l o g i c a l c a l c u l a t i o n s f o r t h e f o l l o w i n g c a s e s s 1 . P r e s e n t s i t u a t i o n , b u t w i t h a d r e d g e d a c c e s s c h a n n e l t h r o u g h t h e B a r r a S u l . 2 . As c a s e 1 , b u t a l s o '. , J u d i n g a l i n s l o f 1 5 0 0 x 6 0 0 m w i t h a w e s t e r n l o c a t i o n and a c o n n e c t i o n t o t h e Bug i o 1 i g h t h o u s e . 3 . As c a s o 1 , b u t a l s o i . i c l u d i n g a t > , . . . i i n a l o p 1 5 0 0 x 6 0 0 m w i t h an e a s t e r n 1 - ^ . t i o n and v / i t h o u t a c o n n e c t i o n t o t h e B u g i o l i g h t h o u s e . The r e s u l t s o f t h e r e a n a l y s i s o f t h e wave c l i m a t e w e r e a l r e a d y p r e s e n t e d i n o u r r e p o r t o f A p r i l 1 9 8 2 , t i t l e d " H y d r o - m o r p h o l o g i c a l s t u d y Tagur, e s t u a r y ; A d d i t i o n a l w o r k ; Wave p e n e n t r a t i o n m o d e l " . The r e s u l t s o f t h e a d d i t i o n a l h y d r o - m o r p h o l o g i c a l r u n s a r e p r e s e n t e d i n t h i s r e p o r t , t o g e t h e r w i t h a s h o r t d i s c u s s i o n o f t h e r e s u l t s .

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2 H y d r o - m o r p h o l o g i c a l s t u d y Tagus e s t u a r y 7 / 5 / 1 9 8 2 The c a l c u l a t i o n s w e r e e x e c u t e d w i t h t h e m a t h e m a t i c a l m o d e l s o f t h e o u t e r Tagus e s t u a r y , as d e v e l o p e d b y H y d r o n a m i c b . v , f o r AGPL. A d e t a i l e d d e s c r i p t i o n o f t h e m o d e l s i s n o t g i v e n i n t h i s r e p o r t . Such a d e s c r i p t i o n w i l l be p r e s e n t e d i n t h e f i n a l r e p o r t o n t h e d e v e l o p -ment o f t h e m a t h e m a t i c a l m o d e l s . The f i n a l r e p o r t on t h e d e v e l o p m e n t o f t h e m a t h e m a t i c a l m o d e l s i s n e a r l y c o m p l e t e d a t t h i s m o m e n t . B e c a u s e o f t h e h i g h u r g e n c y o f t h i s a d d i t i o n a l w o r k we h a v e p o s t p o n e d r e p o r t i n g o f t h e model t i l l May 1 9 8 2 .

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3

H y d r o - m o r p h o l o g i c a l s t u d y Tagus e s t u a r y 7 / 5 / 1 9 8 2

2 . DESCRIPTION OF THE GENERAL MORPHOLOGY

In t h i s c h a p t e r t h e g e n e r a l m o r p h o l o g y i s o n l y d i s c u s s e d i n r e l a t i o n t o t h e c o n s t r u c t i o n s s t u d i e d i n t h i s a d d i t i o n a l w o r k . F o r a m o r e o v e r a l l d e s c r i p t i o n o f t h e m o r p h o l o g y o f t h e B u g i o a r e a c a n be r e f e r r e d t o t h e f i n a l r e p o r t o n t h e d e v e l o p m e n t o f t h e m a t h e m a t i c a l m o d e l s . The model c a l c u l a t e s f o r t h e p r e s e n t s i t u a t i o n a r a t h e r h i g h v a l u e o f e r o s i o n a t t h e f o l l o w i n g l o c a t i o n s : - a t t h e n o r t h e r n s l o p e o f t h e B u g i o b a n k , e s p e c i a l l y c l o s e t o Cova da Vapor - a t t h e w e s t e r n s i d e o f t h e Cachopo do Sul ( w e s t o f B u g i o ) - i n t h e e n t r a n c e c h a n n e l s o u t h o f Paco d ' A r c o s S e d i m e n t a t i o n c a n be f o u n d a t : - an a r e a s o u t h o f t h e B u g i o b a n k - an a r e a s o u t h o f t h e B a r r a Sul T h e B a r r a Sul i t s e l f i s r e l a t i v e l y s t a b l e . T h e a b o v e m e n t i o n e d l o c a t i o n s o f e r o s i o n and s e d i m e n t a t i o n h a v e b e e n c a l c u l a t e d w i t h an a v e r a g e wave c l i m a t e . D u r i n g s t o r m s t h e s i t u a t i o n w i l l b e c o n -s i d e r a b l y d i f f e r e n t . D u r i n g a h e a v y -s t o r m -s i t u a t i o n m o r e -s t i r r i n g w i l l o c c u r a t t h e o u t s i d e a r e a s . The s e d i m e n t s w h i c h h a v e s e t t l e d d u r i n g c a l m s e a s o n s s o u t h o f t h e B a r r a Sul and B u g i o b a n k a r e t r a n s p o r t e d t o t h e c o a s t b e t w e e n C o s t a de C a p a r i c a and Cova da V a p o r . H o w e v e r , b e c a u s e t h i s c o a s t I s n o t a s t a b l e c o a s t , t h e

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h H y d r c j - m o r p h o l o g i c a l s t u d y Tagus e s t u a r y 7 / 5 / 1 9 8 2 s e d i m e n t w i l l be t r a n s p o r t e d t o t h e n o r t h w i t h a l i t t o r a l , wave i n d u c e d c u r r e n t . The wave i n d u c e d l i t t o r a l c u r r e n t i s n o t s i m u l a t e d i n t h e m a t h e m a t i -c a l -c u r r e n t model ( t h e s -c a l e o f t h e -c u r r e n t model i s n o t f i t t e d f o r m o d e l l i n g l i t t o r a l c u r r e n t s ; a l i t t o r a l c u r r e n t o c c u r s o n l y i n t h e z o n e w h e r e t h e waves b r e a k , t h i s z o n e i s r e l a t i v e l y n a r r o w i n r e l a -t i o n -t o -t h e m e s h - s i z e o f -t h e m o d e l ( 2 0 0 m ) ) F o r d e -t e r m i n a -t i o n o f -t h e v e l o c i t i e s and s e d i m e n t t r a n s p o r t c a p a c i t i e s o f t h i s l i t t o r a l c u r -r e n t , a s e p e -r a t e c o m p u t e -r p -r o g -r a m s h o u l d be -r u n n e d ( p -r o g -r a m BYKBAT). T h i s w a v e - i n d u c e d l i t t o r a l c u r r e n t t r a n s p o r t s t h e sand o f t h e b e a c h i n a n o r t h w a r d d i r e c t i o n t o Cova da V a p o r . Near t h e Cova da V a p o r g r o i n t h e r e i s a r a t h e r c o m p l i c a t e d c u r r e n t s y s t e m , w h i c h t r a n p o r t s t h e s e d i m e n t o v e r t h e B u g i o - b a n k t o w a r d s t h e m a i n c h a n n e l o f t h e T a g u s e s t u a r y . B e s i d e s t h e t i d a l c o m p o n e n t o f t h e c u r r e n t , t h e r e i s a l s o a s o c a l l e d s e t u p c u r r e n t . T h i s s e t u p c u r r e n t g i v e s an a d d i -t i o n a l -t r a n s p o r -t -t o w a r d s -t h e n o r -t h . C o n s e q u e n -t l y -t h e r e w i l l be an i n c r e a s e d t r a n s p o r t t o t h e n o r t h . T h i s means t h a t t h e e r o s i o n n e a r Cova da Vapor ( a s c a l c u l a t e d b y t h e m o r p h o l o g i c a l m o d e l ) Is p a r t l y n u l l i f i e d b y t h e a b o v e d e s c r i b e d t r a n s p o r t . T h i s c l e a r l y I n d i c a t e s t h a t t h e r e I s a k i n d o f c o u n t e r c l o c k w i s e c i r -c u l a t i o n o f s e d i m e n t a r o u n d t h e B u g i o - b a n k . The b o t t o m o f t h e Tagus c h a n n e l s u f f e r s , a c c o r d i n g t o t h e m o d e l , t o e r o s i o n , e s p e c i a l l y i n t h e d e e p e r s e c t i o n s . In r e a l i t y t h e r e w i l l be n o t s u c h an e r o s i o n . T h i s i s due t o t h e f a c t t h a t t h e m o r p h o l o g i c a l model n o t r e a l l y c a l -c u l a t e s t h e s e d i m e n t t r a n s p o r t b u t t h e s e d i m e n t t r a n s p o r t -c a p a -c i t y . T h i s means t h a t t h e v a l u e s p r e s e n t e d a r e t h e q u a n t i t i e s o f s e d i m e n t

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5 H y d r o - m o r p h o l o g i c a l s t u d y Tagus e s t u a r y 7 / 5 / 1 9 8 2 t r a n s p o r t e d , i f s u c h q u a n t i t i e s o f s e d i m e n t a r e a v a i l a b l e f o r t r a n s p o r t ( a s s u m p t i o n o f a l l u v i a l b e d ) . On r o c k y b o t t o m s , b u t a l s o on b o t t o m s w i t h r e l a t i v e l y c o a r s e m a t e r i a l , t h e r e i s no s e d i m e n t a v a i l a b l e f o r t r a n s p o r t , and t h u s , t h e r e w i l l be no t r a n s p o r t . The d e e p e r s e c t i o n s o f t h e Tagus c h a n n e l c o n s i s t o f c o a r s e m a t e r i a l . T h i s means t h a t t h i s m a t e r i a l i s n o t t r a n s p o r t e d . T h i s means a l s o t h a t t h e r e w i l l be no e r o s i o n i n t h e s e d e e p e r s e c t i o n s . I f t h e s u p p l y o f s e d i m e n t f r o m t h e b e a c h n e a r C o s t a de C a p a r i c a i s s t o p p e d b e c a u s e o f c o n s t r u c t i o n w o r k s , i t i s n o t e x p e c t e d t h a t t h e c h a n n e l w i l l become d e e p e r . H o v e v e r , we may e x p e c t t h a t t h e e r o s i o n o f t h e n o r t h e r n s l o p e o f t h e B u g i o - b a n k w i l l be no l o n g e r n u l l i f i e d b y t h e s u p p l y o f b e a c h - s a n d . T h i s w i l l c a u s e s o u t h w a r d movement o f t h e s l o p v . , i f no p r o t e c t i o n i s a v a i l a b l e . B e c a u s e q u a y - w a l l s and j e t t i e s a r e d e s i g n e d a t t h i s s l o p e , i t i s t h e s l o p e c a n n o t move t o t h e s o u t h . T h u s t h e r e w i l l be a b o t t o m e r o s i o n n e a r t h e s e c o n s t r u c t i o n s . The b o t t o m w i l l go down u n t i l a p o i n t w e r e a n o t h e r e q u i l i b r i u m w i l l o c c u r . One may e x p e c t t h a t t h i s i s a t a p -p r o x . 2 0 - 3 0 m b e l o w l e v e l , b e c a u s e t h i s i s a l s o t h e e q u i l i b r i u n d e p t h o f t h e m a i n c h a n n e l . T h e c o n s e q u e n c e o f t h i s f a c t i s t h a t o n e has t o t a k e c a r e o f t h e s t a b i l i t y o f t h e f o u n d a t i o n s o f t h o s e c o n -s t r u c t i o n -s . On t h e o t h e r h a n d , n e a r l y no m a i n t a n a n c e d r e d g i n g w i l l b e n e c e s s a r y . The r e s u l t s o f t h e s e d i m e n t a t i o n c a l c u l a t i o n f o r t h e nowadays s i t u a -t i o n a r e p r e s e n -t e d i n f i g u r e 1 . In -t h i s f i g u r e a r e d c r o s s i n d i c a -t e s s i l t a t i o n and a b l u e c r o s s i n d i c a t e s e r o s i o n . The s i z e o f t h e c r o s s -e s i s a m -e a s u r -e o f t h -e q u a n t i t y o f s i l t a t i o n , r -e s p . -e r o s i o n .

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6

3 . SITUATION WITH A TERMINAL (WESTERN LOCATION)

Two f i g u r e s a r e p r e s e n t e d w h i c h g i v e t h e b o t t o m c h a n g e s due t o t h e c o n s t r u c t i o n o f a w e s t e r n t e r m i n a l . In f i g . 2 t h e a b s o l u t e v a l u e o f t h e e r o s i o n i s g i v e n . I n f i g u r e 3 t h e d i f f e r e n c e b e t w e e n f i g u r e 1 and f i g u r e 2 i s p l o t t e d . T h i s f i g u r e r e a l l y i n d i c a t e s w h a t i s t h e e f f e c t o f t h e c o n s t r u c t i o n o f a t e r m i n a l n e a r B u g i o . On c a n see t h a t s o u t h o f t h e B u g i o b a n k s , t h e r e w i l l o c c u r e r o s i o n . One c a n s e e t h a t o n f i g u r e 3 a l s o v a l u e s a r e i n d i c a t e d on t h e l o c a t i o n s o f t h e t e r m i n a l . T h i s i s due t o t h e f a c t t h a t t h e r e i s e r o s i o n o r s e d i m e n t a -t i o n g i v e n on f i g u r e 1 a -t -t h a -t l o c a -t i o n . On f i g u r e 2 -t h e r e i s o f c o u r s e no e r o s i o n o r s e d i m e n t a t i o n . C o n s e q u e n t l y t h e d i f f e r e n c e b e -t w e e n f i g u r e 1 and f i g u r e 2 g i v e s a l s o f o r -t h e -t e r m i n a l l o c a -t i o n a c e r t a i n v a l u e .

Near t h e Cova da Vapor f l o w c h a n n e l t h e r e i s no more c u r r e n t , and c o n s e q u e n t l y no m o r e s e d i m e n t t r a n s p o r t . The e r o s i o n o f t h a t c h a n n e l

i s s t o p p e d . T h i s i s i n d i c a t e d by r e d c r o s s e s on f i g u r e 3 f o r t h a t l o c a t i o n .

A v e r y i m p o r t a n t o b s e r v a t i o n i s t h a t t h e r e w i l l be some more e r o s i o n o f t h e B u g i o bank s o u t h - w e s t o f t h e new t e r m i n a l . T h i s means t h a t i t

i s v e r y i m p o r t a n t t o make a good p r o t e c t i o n o v e r t h e r e t o p r e v e n t a t -t a c k on -t h e -t e r m i n a l b o -t h by waves and c u r r e n -t .

A l s o an i n c r e a s e d e r o s i o n o f t h e Cachopo d e l N o r t e c a n be o b s e r v e d . T h i s e r o s i o n can be e x p l a i n e d q u i t e e a s i l y . B e c a u s e o f c l o s i n g t h e G o l a d a s and t h e f l o w c h a n n e l n e a r Cova da V a p o r , much m o r e w a t e r has t o f l o w t h r o u g h t h e B a r r a Sul d u r i n g e a c h t i d e . T h i s means t h a t t h e

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7 H y d r o - m o r p h o l o g i c a l s t u d y Tagus e s t u a r y 7 / 5 / 1 9 8 2 c u r r e n t v e l o c i t i e s w i l l i n c r e a s e , and e s p e c i a l l y o v e r s h a l l o w a r e a s t h i s c a u s e s i n i n c r e a s e o f s e d i m e n t t r a n s p o r t . An i n c r e a s e d s e d i m e n t t r a n s p o r t f r o m t h e b a n k s t o w a r d s d e e p e r w a t e r c a u s e s an e r o s i o n o f t h o s e b a n k s . I n t h e m a i n c h a n n e l i t s e l f , n o r t h o f t h e new t e r m i n a l , a l s o some i n -f l u e n c e o -f t h e t e r m i n a l has been o b s e r v e d i n t h e c a l c u l a t i o n s . I n r e a l i t y t h i s i n f l u e n c e w i l l be l i m i t e d . As a 1 r e a d y m e n t i o n e d b e f o r e , t h e model i n d i c a t e s s e d i m e n t t r a n s p o r t c a p a c i t i e s . A c h a n g e i n t r a n s p o r t c a p a c i t y w i l l o n l y be e f f e c t u a t e d i f t h e r e i s e n o u g h m a t e r i a l a v a i l a b l e t o be t r a n s p o r t e d . I t i s q u i t e c l e a r t h a t t h i s i s n o t t h e c a s e i n t h e c e n t e r o f t h e m a i n c h a n n e l . So t h e v a l u e s p r e s e n t e d i n f i g u r e 3 f o r t h e c e n t e r o f t h e m a i n c h a n n e l n o r t h o f t h e new t e r m i n a l a r e n o t r e a l c h a n g e s , i n b o t t o m t o p o g r a p h y . In o t h e r w o r d s : t h e b o t t o m o f t h e m a i n c h a n n e l s h o u l d c h a n g e u n d e r i n f l u e n c e o f t h e c o n t r u c t i o n o f a t e r m i n a l , i f t h i s b o t t o m had t h e p h y s i c a l a b i l i t y t o c h a n g e . H o w e v e r , b e c a u s e t h e b o t t o m has n o t t h e a b i l i t y t o c h a n g e t h e r e w i l l be no c h a n g e s . A m o r e s e r i o u s p r o b l e m may a r i s e f o r t h e s e d i m e n t b u d g e t o f t h e s o u t h e r n s i d e o f t h e b a n k . As a l r e a d y i n d i c a t e d a b o v e , t h e r e w i l l be l e s s s e d i m e n t a t i o n on t h a t s i d e . T h i s i s due t o t h e f a c t t h a t b o t h t h e c u r r e n t t r o u g h t h e G o l a d a s , as w e l l as t h e c u r r e n t t r o u g h t h e f l o w c h a n n e l n e a r Cova da Vapor i s s t o p p e d . D u r i n g e b b - t i d e t h e s e c u r r e n t s t r a n s p o r t e d s e d i m e n t f r o m t h e b a n k s i n a s o u t h w a r d d i r e c t i o n . As d i s c u s s e d i n t h e c h a p t e r o f t h e g e n e r a l m o r p h o l o g y , t h e B u g i o b a n k i s e r o d e d d u r i n g days o f c a l m w e a t h e r by t h e t i d a l c u r r e n t s .

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8 H y d r o - m o r p h o l o g i c a l s t u d y Tagus e s t u a r y 7 / 5 / 1 9 8 2 w h i l e d u r i n g days w i t h m o r e h e a v y w a v e s , s e d i m e n t i s t r a n s p o r t e d f r o m t h e d e e p e r a r e a s s o u t h o f B u g i o t o w a r d s t h e c o a s t , and f r o m t h e r e t o w a r d s t h e b a n k . T h i s " s t o r m t r a n s p o r t " w i l l o c c u r a l s o a f -t e r c l o s i n g -t h e G o l a d a s and -t h e Cova da V a p o r c h a n n e l . C o n s e q u e n -t l y t h e r e w i l l be no r e a l e r o s i o n o f t h e s o u t h e r n s i d e o f t h e b a n k , b u t t h e r e w i l l be an i n c r e a s e d t e n d e n c y o f t h e s e d i m e n t t o move t o w a r d s t h e c o a s t . T h i s means t h a t t h e b e a c h s l o p e s o f t h e s o u t h e r n s i d e o f t h e bank w i l l become s t e e p e r t h a n t h e y a r e n o w a d a y s .

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9 H y d r o - m o r p h o l o g i c a l s t u d y Tagus e s t u a r y ll^h^^l

SITUATION WITH A TERMINAL (EASTERN LOCATION)

In f i g u r e s h and 5 t h e e f f e c t i s p r e s e n t e d o f a t e r m i n a l i n an e a s t -e r n p o s i t i o n . Th-e g -e n -e r a l p i c t u r -e i s i d -e n t i c a l t o a t -e r m i n a l i n a m o r e w e s t e r n l o c a t i o n . The d i f f e r e n c e s b e t w e e n t h e t w o l o c a t i o n s a r e ( c o m p a r e f i g . 3 and f i g . 5 ) l e s s e r o s i o n on t h e Cachopo d e l N o r t e , on t h e Cahopo d e l Sul and l e s s " s e d i m e n t a t i o n " i n t h e m a i n c h a n n e l n o r t h w e s t o f B u g i o . The d i f f e r e n c e i n " s e d i m e n t a t i o n " o f t h e m a i n c h a n n e l i s n o t i m p o r t a n t , b e c a u s e t h i s c a l c u l a t e d s e d i m e n t a t i o n w i l l n o t be e f f e c t u a t e d , as a l r e a d y d i s c u s s e d a b o v e . The d e c r e a s e d e r o s i o n on b o t h t h e Cachopo b a n k s i s c a u s e d b y t h e f a c t t h a t t h e t i d e i s s t i l l a b l e t o f l o w t h r o u g h t h e G o l a d a s . So f r o m t h a t p o i n t o f v i e w , an e a s t e r n l o c a t i o n s h o u l d be p r e f e r r e d t o a w e s t e r n l o c a t i o n . H o w e v e r , a c u r r e n t t h r o u g h t h e G o l a d a s w i l l h a v e e f f e c t s on t h e w e s t e r n p r o t e c t i o n o f t h e t e r m i n a l . B e c a u s e i t i s r e q u i r e d t h a t t h e amount o f s p r a y b y waves on t h e s t o c k p i l e s i s s m a l l , a r e l a t i v e l y w i d e , s h a l l o w b u f f e r z o n e i s n e c e s s a r y . I t w i l l b e v e r y d i f f i c u l t t o m a i n t a i n s u c h a b u f f e r z o n e i f t h e r e i s a c u r -r e n t t h -r o u g h t h e G o l a d a s , T h i s c u -r -r e n t w i l l deepen t h e b u f f e -r z o n e ; c o n s e q u e n t l y h i g h e r waves may r e a c h t h e w e s t e r n s h o r e o f t h e t e i — m i n a l and m o r e s p r a y w i l l o c c u r . The e r o s i o n o f t h e s o u t h s l o p e o f t h e B u g i o bank ( s o u t h o f t h e t e i — m i n a l ) w i l l be somewhat l e s s w i t h an e a s t e r n l o c a t i o n o f t h e t e i — m i n a l t h a n w i t h a w e s t e r n l o c a t i o n o f t h e t e r m i n a l . H o w e v e r , as o n e c a n s e e , c o m p a r i n g f i g . 3 and f i g . 5 t h i s d i f f e r e n c e i s v e r y s m a l l .

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H y d r o - m o r p h o l o g i c a l s t u d y Tagus e s t u a r y

5 . THE EFFECT OF DREDGING THE BARRA SUL

In f i g u r e 6 and 7 t h e r e s u l t s o f a s e d i m e n t a t i o n c a l c u l a t i o n w i t h o n l y a d r e d g e d c h a n n e l a r e p r e s e n t e d . F i g u r e 6 l o o k s q u i t e i d e n t i c a l t o f i g u r e 1 , so o n e may e x p e c t t h a t t h e i n f l u e n c e o f d r e d g i n g a c h a n n e l t h r o u g h t h e B a r r a Sul i s s m a l l . S t u d y i n g f i g u r e 7 shows t h i s i n m o r e d e t a i l . F i g u r e 7 i s t h e d i f f e r e n c e b e t w e e n f i g u r e 1 and f i g u r e 6 . One c a n see t h a t t h e r e i s some s i l t a t i o n i n t h e n e w l y d r e d g e d c h a n n e l , and t h a t a l s o some m i n o r c h a n g e s may be e x p e c t e d i n t h e m a i n c h a n n e l . H o w e v e r , t h i s a r e a l s o c h a n g e s i n t r a n s p o r t c a p a c i t y , and no c h a n g e s i n t r a n s p o r t , as a l r e a d y d i s c u s s e d i n t h e f o r m e r c h a p t e r . So we d o n ' t e x p e c t b o t t o m c h a n g e s i n t h e e x i s t i n g m a i n c h a n n e l . T h e r e a r e a l s o no c h a n g e s t o be e x p e c t e d o n t h e Cachopo d e l N o r t e o r on t h e B u g i o b a n k . .

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11 H y d r o - m o r p h o l o g i c a l s t u d y Tagus e s t u a r y 7 / 5 / 1 9 8 2

6 . CIRCULATION PATTERN NEAR THE TERMINAL AND THE BERTHS

As an a p p e n d i x t o t h i s p r e l i m i n a r y r e p o r t we p r e s e n t f l o w c h a r t s o f t h e c i r c u l a t i o n c a l c u l a t i o n s f o r h i g h w a t e r , l o w w a t e r , m a x . f l o o d c u r r e n t and m a x . ebb c u r r e n t . T h e s e c h a r t s a r e d r a w n f o r t h e e x i s t

-i n g s -i t u a t -i o n , f o r t h e s -i t u a t -i o n w -i t h a c h a n n e l o n l y , f o r a c h a n n e l and a w e s t - t e r m i n a l and f i n a l l y f o r a c h a n n e l and an e a s t - ^ t e r m i n a l . T h e s e d i a g r a m s a r e n o t d i s c u s s e d i n d e t a i l h e r e . I t t a k e s . a l o t o f pages t o d e s c r i b e t h e s e p a t t e r n s , w h i l e a s i m p l e l o o k t o t h e s e d i a g r a m s w i l l t e l l m o r e t h a n a l l t h e s e pages o f t e x t . N e x t woek we w i l l make m o r e d e t a i l e d d r a w i n g s o f t h e c u r r e n t p a t t e r n c l o s e t o t h e b e r t h s . T h e s e d r a w i n g s w i l l be made f o r e v e r y h o u r , t h u s 1 2 d r a w i n g s w i l l be made f o r e a c h s i t u a t i o n .

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7 o CURRENTS AT THE BARRA SUL

As an a p p e n d i x t o t h i s r e p o r t a s e t o f d i a g r a m s w i t h t h e c a l c u l a t e d c u r r e n t s and w a t e r l e v e l s f o r s e v e r a l s t a t i o n s i n t h e a r e a i s p r e s e n t e d . T h e s e s t a t i o n s a r e i d e n t i c a l t o t h e s t a t i o n s w h e r e a n u m -b e r o f c u r r e n t m e a s u r e m e n t s w e r e made -by AGPL i n 1 9 7 3 / 1 9 7 ' ' * I t i s p o s s i b l e t o c o m p a r e t h e m e a s u r e d v e l o c i t i e s w i t h t h e c a l c u l a t e d d a t a f o r t h e p r e s e n t s i t u a t i o n , i f o n e t a k e s i n t o a c c o u n t t h e r e l a t i o n b e t w e e n t h e t i d a l s i t u a t i o n o f t h e moment o f m e a s u r e m e n t and t h e m o -ment o f c a l c u l a t i o n (we h a v e c a l c u a l t e d t h e f i r s t s p r i n g t i d e o f 1 9 8 2 ) , I n t h e t a b l e b e l o w t h e v e l o c i t i e s f o r 7 p o i n t s o f t h e e s t u a r y a r e g i v e n f o r t h e a l t e r n a t i v e s 0 ( p r e s e n t s i t u a t i o n ) , 1 ( o n l y d r e d g e d c h a n n e l ) and 2 ( t e r m i n a l i n a w e s t e r l y l o c a t i o n ) . L o c a t i o n 5 0 * Near c o n t a i n e r t e r m i n a l 5 4 * N e a r c o a l t e r m i n a l 1 0 0 * I n B a r r a N o r t e 1 0 3 * Cova da Vapor c h a n n e l 1 0 8 * E a s t o f B a r r a Sul 1 1 0 * S o u t h o f G o l a d a s 1 1 9 " West o f B a r r a Sul A l t . 0 A l t . 1 A l t . 2 6 8 / 1 2 0 6 8 / 1 2 0 ' 4 2 / 7 8 1 3 0 / 1 7 5 1 3 0 / 1 7 5 1 2 7 / 1 0 0 1 1 0 / 6 2 1 1 0 / 6 2 1 1 0 / 5 0 8 8 / 1 1 2 8 8 / 1 1 2 0 / 0 5 2 / 1 1 8 5 2 / 1 1 8 5 0 / 9 5 2 8 / 3 5 2 8 / 3 5 2 0 / 3 0 4 8 / 3 8 3 5 V e l o c i t i e s a r e g i v e n i n c m / s e c ; f i r s t v e l o c i t y i s f l o o d c u r r e n t .

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From t h e above f i g u r e s f o l l o w s t h a t d r e d g i n g t h e B a r r a Sul has o n l y a m a r g i n a l e f f e c t on t h e v e l o c i t i e s i n t h e c h a n n e l . T h e e f f e c t o f c o n s t r u c t i n g a t e r m i n a l i s much m o r e i m p o r t a n t . T h e f l o o d c u r r e n t i s n o t c h a n g e d v e r y m u c h , b u t t h e e b b c u r r e n t w i l l d e c r e a s e w i t h a s u b -s t a n t i a l v a l u e , e -s p e c i a l l y e a -s t o f B u g i o . I n t h e B a r r a t h e c h a n g e -s a r e n o t so c o n s i d e r a b l e . T h i s can b e e x p l a i n e d b y t h e f a c t t h a t , b e -c a u s e o f -c l o s i n g t h e f l o w -c h a n n e l s o v e r t h e B u g i o b a n k , t h e r e w i l l b e no a d d i t i o n a l w a t e r p r e s s e d i n t o t h e e s t u a r y f r o m o v e r t h e b a n k s . S o , t h e q u a n t i t y o f w a t e r e n t e r i n g t h e " C o r r e d o r " w i l l be somewhat l e s s , w h i c h r e s u l t s i n a d e c r e a s e o f t h e v e l o c i t y . F o r t h e maximum f l o o d s i t u a t i o n t h e r e i s n o t so much i n f l u e n c e , b e c a u s e t h e f l o o d f l o w o v e r t h e B u g i o b a n k s i s n o t as s t r o n g as t h e e b b - f l o w ( s e e a l s o v a l u e s o f s t a t i o n 1 0 3 and 1 1 0 , a l t e r n a t i v e 0 ) . From t h e a b o v e o n e may c o n c l u d e t h a t c o n s t r u c t i n g a t e n n i n a l o n t h e B u g i o b a n k w i l l c h a n g e t h e v e l o c i t i e s i n t h e t n t r a n c e o v e r t h e B a r r a i n a p o s i t i v e w a y . T h e a d d i t i o n a l c u r r e n t w i l l n o t c a u s e p r o b l e m s f o r n a v i g a t i o n ( t h e a b s o l u t e v a l u e r e m a i n s q u i t e l o w ) b u t f r o m a m o r p h o l o g i c a l p o i n t o f v i e w t h e s i t u a t i o n a t t h e B a r r a w i l l become b e t t e r . See a l s o c h a p t e r 3 and k o f t h i s r e p o r t .

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8 . REQUIREMENTS FOR THE SOUTHERN PROTECTION

The d i r e c t wave a t t a c k on t h e s o u t h e r n s h o r e o f t h e t e r m i n a l i s v e r y l i m i t e d , as f o l l o w s f r o m t h e wave p e n e t r a t i o n c a l c u l a t i o n s . From t h e above m o r p h o l o g i c a l d i s c u s s i o n s f o l l o w s t h a t t h e s l o p e o f t h e s o u t h e r n s i d e o f t h e B u g i o bank w i l l become somewhat s t e e p e r . T h i s means t h a t t h e waves w i l l b r e a k n o t as s p i l l i n g b r e a k e r s b u t p r o b a b

-l y as p -l u n g i n g b r e a k e r s . The s e d i m e n t t r a n s p o r t c a u s e d b y p -l u n g i n g b r e a k e r s i s m o r e c o n c e n t r a t e d i n a s m a l l z o n e t h a n i t i s by s p i l l i n g b r e a k e r s . I n g e n e r a l t h i s a l s o means t h a t t h e t o t a l amount o f s e d i -ment t r a n s p o r t e d a l o n g s u c h a s l o p e i s somewhat l e s s . I f one i s a b l e t o c o n s t r u c t a b e a c h w i t h a c o r r e c t shape ( t h u s t h e b e a c h a l -ways p e r p e n d i c u l a r t o t h e i n c o m i n g wave r a y s ) , s u c h a b e a c h w i l l b e v e r y s t a b l e . In g e n e r a l t h i s i s t h e c h e a p e s t way o f c o a s t a l p r o t e c -t i o n . One has -t o -t a k e c a r e -t h a -t a s -t a b l e b e a c h i s a l w a y s i n a d y n a m i c e q u i l i b r i u m , and t h u s t h a t a b u f f e r z o n e i s a l w a y s r e q u i r e d . The a d v a n t a g e o f s u c h a b e a c h s o l u t i o n i s t h a t t h e i n i t i a l c o s t s c a n b e k e p t r e l a t i v e l y l o w . M a i n t e n a n c e may be somewhat h.igher t h a n u s i n g a " h a r d " c o a s t a l p r o t e c t i o n , b u t i n g e n e r a l t h e t o t a l e x p e n d i -t u r e s ( i n i -t i a l c o s -t s + c a p i -t a l i z e d m a i n -t e n a c e ) a r e l e s s f o r b e a c h so 1 u t i o n s .

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9 . REQUIREMENTS FOR THE WESTERN PROTECTION

The w e s t e r n p r o t e c t i o n w i l l be a t t a c k e d by waves and by c u r r e n t s . E s p e c i a l l y i n c a s e o f t h e e a s t e r n s o l u t i o n t h e c u r r e n t s a r e impoi— t a n t . I n c a s e o f a w e s t e r n s o l u t i o n t h e waves w i l l be more i m p o r -t a n -t . The wave h e i g h -t w i l l i n g e n e r a l be q u i -t e m o d e r a -t e . I -t i s n o -t n e c e s s a r y t o b u i l d h e a v y c o n s t r c t i o n s f o r p r o t e c t i o n a g a i n s t w a v e s . T h e s e m o d e r a t e waves w i l l , h o w e v e r , c a u s e a s e d i m e n t t r a n s p o r t a l o n g t h e t e r m i n a l ( p r o b a b l y f r o m n o r t h t o s o u t h ) and t h i s t r a n s p o r t w i l l b e a d a n g e r f o r t h e w e s t e r n s l o p e . The b e s t s o l u t i o n f o r t h e w e s t e r n s i d e o f t h e t e r m i n a l i s a l s o a b e a c h , b u t i n c l u d i T i g some s t r u c -t u r e s -t o p r e v e n -t s e d i m e n -t m o v e m e n -t s . T h e s e c o n s -t r u c -t i o n s may be s t o n e g r o i n s , p e r m e a b l e t i m b e r o r s t e e l g r o i n s o r an o f f s h o r e b r e a k -w a t e r . I t i s e x p e c t e d t h a t an o f f s h o r e b r e a k -w a t e r -w i l l be e x p e n s i v e , b e c a u s e t h i s b r e a k w a t e r has t o be c o n s t r u c t e d i n r e l a t i v e l y d e e p w a t e r . The d i s t a n c e b e t w e e n t h e g r o i n s and ( i f a p e r m e a b l e g r o i n s y s t e m I s c h o o s e n ) t h e d i s t a n c e b e t w e e n t h e p i l e s o f t h e g r o i n h a v e t o be c a l c u l a t e d I n d e t a i l . I t m i g h t be n e c e s s a r y o n c e i n s e v e r a l y e a r s t o s u p p l y sand t o t h i s b e a c h . Such a s u p p l y c a n be made q u i t e e a s i l y f r o m t h e s h o r e . R e g u l a r m a i n t e n a n c e o f b e a c h e s , as a l r e a d y m e n t i o n e d a b o v e , i s i n g e n e r a l c h e a p e r t h a n t h e c o n s t r u c t i o n o f " h a r d " p r o t e c t i o n s . The b e a c h w i l l a l s o p r e v e n t h i g h s p o u t i n g w a v e s , and p r e v e n t i n t h i s way a l s o a c o n t i n u o u s s p r a y o v e r t h e s t o c k - p i l e s .

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1 0 . A CLOSED HARBOUR BASIN

The a d v a n t a g e o f a c l o s e d h a r b o u r b a s i n i s t h a t t h e s h i p s m o o r e d a t t h e quay a r e n o t i n f l u e n c e d by c u r r e n t - c o m p o n e n t s p e r p e n d i c u l a r t o t h e s h i p ' s a x i s . T h e s e c u r r e n t s a r e r e l a t i v e l y s m a l l . The d i s a d v a n t -a g e s o f s u c h -a c l o s e d h -a r b o u r b -a s i n -a r e h i g h c o n s t r u c t i o n c o s t s , -and a l s o r e l a t i v e l y h i g h m a i n t e n a n c e c o s t s . In an o p e n b a s i n h a r d l y any s i l t a t i o n has t o be e x p e c t e d , b u t i n a c l o s e d b a s i n , s u c h a s i l t a t i o n may be c o n s i d e r a b l e . The v e l o c i t i e s a r e l o w , t h u s f i n e p a r -t i c l e s may s e -t -t l e e a s y . Each -t i d e -t h e w a -t e r i s r e f r e s h e d w i -t h new p a r t i c l e s , and i n t h i s way s u c h a b a s i n w i l l s i l t u p .

From o u r m e a s u r e m e n t s i n t h e B u g i o a r e a f o l l o w s t h a t t h e w a t e r i s v e r y c l e a r . T h e r e f o r e we e x p e c t t h a t t h e e f f e c t o f t h i s s i l t a t i o n i s smal 1 .

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TABLE OF CONTENTS

1 . INTRODUCTION • 2

2 . DESCRIPTION OF THE GENERAL MORPHOLOGY h 3 . S ITUATION WITH A TERMINAL (WESTERN LOCATION) 7

h. S ITUATION WITH A TERMINAL (EASTERN LOCATION) 10

5 . THE EFFECT OF DREDGING THE BARRA SUL 11 6 . CIRCULATION PATTERN NEAR THE TERMINAL AND THE BERTHS 12

7 . CURRENTS AT THE BARRA SUL 1 3 8 . REQUIREMENTS FOR THE SOUTHERN PROTECTION 1 5

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