Doyro Hydro-morphoiogica!

ADMINISTRACAO DOS PORTOS DO DOURO E LEIXÖES

Hydro-morphoiogica! study

Doyro Estuary

Part 8

Analysis of old charts

TABLE OF CONTENTS

1. INTRODUCTION • 1

2. DATA GATHERING f 3. DATA PROCESSING ^ U. ANALYSIS AND INTERPRETATION 5

U.1. CONDESCRIPTIVE 5 U.2. PEARSON CORRELATION ° I4.3, ANALYSIS OF VARIANCE OF CABEDELO SHAPE 7

k.k. SCATTERGRAMS 9

U.5. THE EFFECT OF SEASONS 12 U.6. THE RELATION WITH DISCHARGE 13

5. VISUAL ANALYSIS 15 5.1. SOURCES USED , 15 5.2. SITUATION BEFORE I 8 5 O 15 5.3. SITUATION IN 1861/1862 16 3.k. SITUATION IN 1872 16 5.5. CHRISTMAS 1909 1"^ 5.6. THE PERIOD FROM 1920-1960 19

5.7. JANUARY 1962 19 5.8. THE PERIOD AFTER I962 20

1, INTRODUCTION

As a c o n t i n u a t i o n o f the i n i t i a l study on the morphology o f the Douro mouth, p e r f o m e d by Hydronamic i n I 9 8 2 , the Adm i n i s t r a ? ao dos Portos de Douro e Leixoes eommisioned Hydronsmiic bv t o c o n s t r u c t a mathematical hydro-morphological model of the Douro mouth.

W i t h i n the framework of the study an a n a l y s i s o f o l d c h a r t s , a v a i l -able i n the archives of A.P.D.L. has been made. The charts cover the p e r i o d between i 8 6 0 and I 9 8 3 . Both a s t a t i s t i c a l as a v i s u a l analysis of the charts has been made.

The ptirpose of th© v i s u a l a n a l y s i s i d t o get a b e t t e r i n s i g h t o f the morphological processes as they appeared i n the past.

Studying these charts gives a very good f e e l i n g on the r e a l be-haviour of the r i v e r . With such a more profound i n s i g h t a more r e a l i s t i c mathematical model can be developed. I n chapter 5 the v i s u a l a n a l y s i s i s discussed.

The purpose o f the s t a t i s t i c a l a n a l y s i s i s t o provide data f o r the c a l i b r a t i o n of the mathematical model. The data obtained from the charts are put i n t o th© computer and analysed. See chapter 2 and 3 . The r e s u l t s o f the mathematical operations are discussed i n depth i n chapter k.

2. DATA GATHERING

I n J u l y 1983 the 100 o l d charts o f the Douro bar, were reviewed and s i g n i f i c a n t i n f o r m a t i o n was d i g i t i s e d . The c h a r t s , covering a p e r i o d between I 8 6 I and I962 were a v a i l a b l e i n the o f f i c e o f A.P.D.L. The charts were a l l on a scale 1:2500. Most o f t h e c h a r t s , n r . 1-68 were from the p e r i o d before I9OO. From t h e charts the f o l l o w i n g i n f o r m a t i o n was gathered:

- surface area o f the Cabedelo, i n m2

- average angle o f the beach o f the Cabedelo; when t h e nor-mal o f the beach i s d i r e c t e d between west and south, then the sign o f the angle i s negative, when th© normal o f t h e beach i s d i r e c t e d between n o r t h and west; then the sign o f the angle i s p o s i t i v e .

- the coordinates (U.T.M.) o f the most n o r t h e r l y p o i n t o f the Cabedelo (east and n o r t h coord.).

- the coordinates (U.T.M.) o f the most w e s t e r l y p o i n t o f t h e Cabedelo (east and n o r t h coord.).

- maximum depth o f the r i v e r , south o f Felgueiras ( i n m). - maximvun depth o f the r i v e r , n o r t h o f p o i n t nx, ny ( i n m). - maximiun depth o f the r i v e r , south o f Cantareira ( i n m). - w i d t h o f the r i v e r , n o r t h of p o i n t nx, ny ( i n m).

- w i d t h o f the r i v e r , south o f Cantareira ( i n m).

- maximum width ( i n east-west d i r e c t i o n ) o f t h e head o f t h e Cabedelo.

- most w e s t e r l y l o c a t i o n o f the - 3 bottom contour l i n e . - most w e s t e r l y l o c a t i o n o f the -5 bottom contour l i n e . - most w e s t e r l y l o c a t i o n of the -7 bottom contour l i n e . - c l a s s i f i c a t i o n o f shapes o f the Cabedelo; see f i g . 1 f o r

d e f i n i t i o n .

The data were measured from the chart by Eng. H.J. Verhagen o f Hydronamic and Mr. J. Abrantes o f Hidrotop. The surfaces were measured w i t h a p l a n i g r a p h .

Besides t h e data mentioned above, also some copies o f i n t e r e s t i n g charts were made, as w e l l as g a t h e r i n g other i n f o r m a t i o n , mentioned on the chax'ts. These a d d i t i o n a l data w i l l be discussed i n d e t a i l i n chapter

5-A few o l d e r charts were also a v a i l a b l e , and probably more o l d e r charts can be found i n l i b r a r i e s and archives. No i n v e s t i g a t i o n on these types o f charts t<ras made, because g e n e r a l l y the q u a l i t y o f o l d e r charts i s q u i t e d o u b t f u l . They can be used only f o r q u a l i t a -t i v e morphological i n -t e r p r e -t a -t i o n o f -the rivermou-th. I n a f u r -t h e r stage o f the a n a l y s i s o f the Douro mouth t h i s w i l l be a u s e f u l study, b u t a t t h i s moment such a study i s not recommended.

For such a study one may go very f a r i n t o h i s t o r y , because the Douro was even long ago of worldwide importance. On one o f the f i r s t Portuguese maps o f the w o r l d , drawn by Diego Homem i n the 15th century, the Cabedelo i s c l e a r l y i n d i c a t e d .

surface angle nx, ny wx, wy depl dep2 dep3 w i d i wid2 head west3 west5 west7 type

Also the c o r r e l a t i o n has beeen determined between the topography and the r i v e r discharge. River discharge data were obtained from E.D.P.

3. DATA PROCESSING

The data gathered i n P o r t u g a l were processed w i t h a s t a t i s t i c a l com-p u t e r com-program SPSS, o r i g i n a l l y develocom-ped by the S t a n f o r d U n i v e r s i t y

i n 1965 and commercially a v a i l a b l e since I9TO. The program has been improved and extended by many i n s t i t u t e s a l l over the world and i t

i s nowadays the most used s t a t i s t i c a l program a l l over the w o r l d . The data from the Douro were processed w i t h the SPSS v e r s i o n , which

i s running on a C o n t r o l Data Cyber machine. For more backgrounds on the mathematical methods a p p l i e d by t h e program can be r e f e r r e d t o : Nie, H u l l , Jenkins, Steinbrenner and Bent, SPSS, 2nd e d i t i o n 1975, McGraw-Hill Inc.

The computer output i s presented i n an annex t o t h i s r e p o r t . Only those pages which give u s e f u l i n f o r m a t i o n were copied. Pages w i t h only i n f o r m a t i o n on computer performance and w i t h i n t e r m e d i a t e r e s u l t s were not copied, but are a v a i l a b l e on request.

I n the output s e v e r a l sections can be d i s t i n g u i s h e d :

page 8 -Pearson Corr page 2 - Condescriptive

page 22 -Breakdown

page 51 - Scattergrams

- gives general s t a t i s t i c a l parameters o f the data from the charts

- gives t h e c o r r e l a t i o n between t h e various data

- gives t h e data s p e c i f i e d per tjrpe o f Cabedelo and gives an a n a l y s i s o f variance

- gives p l o t s o f two v a r i a b l e s :

p 51 and 52 - charts o f N and W t i p o f the Cabedelo p 53 t o 80 - v a r i a b l e s p l o t t e d vs. year p 83 t o 128 - r e l a t i o n between v a r i a b l e s w i t h a h i g h c o r r e l a t i o n

p 201 t o 238 - gives the e f f e c t o f the year and an a n a l y s i s o f variauice

p 301 t o 32k The e f f e c t o f discharges

k. ANALYSIS AND INTERPRETATION

k.1. CONDESCRIPTIVE

The general s t a t i s t i c a l parameters, as presented by the output o f the condescriptive subprogram (page 25) do not r e q u i r e much i n t e r -normal d i s t r i b u t i o n both the values f o r k u r t o s i s and skewness have to be zero.

I n t e r e s t i n g i s t o compare the values f o r the water depth ( i n m); Felgueiras Cabedelo Cantareira

mean 6.7 7.0 k.6

standard d e v i a t i o n 1.3 1.5 0.7

minimum observed 3.6 2.6 2.9

maximtun observed 10.2 11.0 7.0

95% i n t e r n a l 6.5 - 7.0 6.8 - 7.k H.k - k.7

The value "93% i n t e r v a l " means t h a t 95?^» o f the observation l i e s be-tween 6.5 and 7 m ( f o r exajnple a t F e l g u e i r a s ) . One may conclude from t h e above t h a t the depth a t Cantareira i s r a t h e r constauit, and thus n o t a very good d e s c r i p t i v e parameter f o r the changes i n t h e morphology. There i s not much d i f f e r e n c e between the standard d e v i a t i o n o f the depth a t Felgueiras and a t Cabedelo. However, t h e absolute value o f k u r t o s i s and skewness i s lower f o r F e l g u e i r a s . So one may conclude t h a t t h e depth a t Felgueiras i s (from the t h r e e given depths) the best d e s c r i p t o r f o r changes.

The v a r i a b l e s W e s t 3 , West5 and West? are s t a t i s t i c a l l y q u i t e i d e n t i -c a l ; the only p o i n t i s t h a t the k u r t o s i s o f West? i s r a t h e r h i g h , which makes W e s t 3 and West5 more a t t r a c t i v e f o r s t a t i s t i c a l msmipulation.

The surface o f the Cabedelo i s not a very good d e s c r i p t o r , i t has a h i g h value f o r k u r t o s i s and skewness. This means n o t only t h a t t h e process i s badly described by the value o f the surface, but a l s o t h a t i t w i l l be q u i t e d i f f i c u l t t o compute the surface-area o f t h e Cabedelo w i t h s t a t i s t i c a l methods, e s p e c i a l l y because o f the b i g s t a n d a r d - d e v i a t i o n .

The two observed values o f the channel-width are s t a t i s t i c a l l y com-p l e t e l y d i f f e r e n t . The v a r i a b l e wid2 has an extremely h i g h value f o r k u r t o s i s aind skewness. This i s caused by the f a c t t h a t wid2 ( = width a t Cantareira) has a maximum of 370 m, which maximum occurs very o f t e n . The distance between Cantareira and t h s Pedras do Lima

(Molhe Luis de Carvalho) i s 370 m and the channel cannot be wider. Therefore wid2 proves t o be a v a r i a b l e which cannot be used f o r s t a t i s t i c a l a n a l y s i s .

F i n a l l y the w i d t h o f the head o f the Cabedelo has also a r e l a t i v e l y high value f o r k u r t o s i s and skewness, but having also a high value f o r the standard d e v i a t i o n the. v a r i a b l e can p o s s i b l y be used.

U.2. PEARSON CORRELATION

On page 8-11 the pearson c o r r e l a t i o n c o e f f i c i e n t s o f a l l v a r i a b l e s are presented. The c o r r e l a t i o n c o e f f i c i e n t s higher than kO% are un-d e r l i n e un-d . I f a c o r r e l a t i o n i s less than U0%, there i s probably no p h y s i c a l r e l a t i o n . The value p gives the s i g n i f i c a n c e o f the r e l a -t i o n , f o r example a p-value o f .06? says -t h a -t w i -t h a c e r -t a i n -t y o f 93.3% there i s some l i n e a r r e l a t i o n between t h e v a r i a b l e s , however w i t h o u t i n d i c a t i n g the r e l a t i o n i t s e l f .

I n the t a b l e below the more important c o e f f i c i e n t s are summarized: wx wy depl west3 west5 west 7 w i d i head

angle ny wx wy depl west3 west5 w i d i i+0 k2 5U Uo 62 5U U2 56 59 72 U6 U2 U2 55 U3 Uo 56 77 U9 59 U2 77 U5 U3 61 79 77 72 55 U9 U5 73 U2 Values i n %

I n t e r p r e t i n g the above t a b l e , one has t o r e a l i s e t h a t the high cor-r e l a t i o n between west3, west5 and west? only i n d i c a t e s t h a t t h e slope o f the foreshore i s q u i t e constant. With other words, when tho -3 l i n e i s moved 100 m towards the west, also the -7 m l i n e w i l l be moved 100 m towards the west.

I f one omits the r e l a t i o n between west3, west5 and west?, one may conclude t h a t :

7 v a r i a b l e s have a s i g n i f i c a n t c o r r e l a t i o n w i t h wy 6 v a r i a b l e s have a s i g n i f i c a n t c o r r e l a t i o n w i t h w i d i 5 v a r i a b l e s have a s i g n i f i c a n t c o r r e l a t i o n w i t h wx, ny U v a r i a b l e s have a s i g n i f i c a n t c o r r e l a t i o n w i t h d e p l , west3

R e a l i s i n g t h a t ny and w i d i are b a s i c a l l y d e s c r i b i n g t h e same v a l u e , one can choose one o f these f o r f u r t h e r a n a l y s i s . Because t h e cor-r e l a t i o n c o e f f i c i e n t s o f w i d i acor-re s l i g h t l y highecor-r than those o f ny,

i t i s b e t t e r t o use w i d i .

This can also p h y s i c a l l y be explained; i t i s clear t h a t there i s a f i x e d r e l a t i o n between the whole morphology and t h e channel w i d t h .

The northern t i p o f t h e Cabedelo (ny) l i e s a t the distance w i d i south o f the quay w a l l o f the Avenida dom Carlos I , which i s an east-west l i n e . However, i f the head o f the Cabedelo l i e s south o f Cantareira or south o f F e l g u e i r a s , the p o s i t i o n o f ny i s more south, even w i t h the same value o f w i d i .

From the c o r r e l a t i o n a n a l y s i s one may conclude t h a t t h e best d e s c r i p t o r s are: wy, w i d i , wx, depl and west3.

ReiTiark; xhe v a r i a b l e t y ^ e has uéén iiicluued i i i cOiTipUtér a n a l y s i s , although i t i s n o t completely c o r r e c t , because the value o f type has no p h y s i c a l meaning, i t i s only a code f o r t h e type. The c o r r e l a t i o n values f o r type are t h e r e f o r e n o t i n -cluded i n t h e t a b l e i n t h i s chapter. The v a r i a b l e type w i l l be analysed i n d e t a i l i n the next chapter.

U.3. ANALYSIS OF VARIANCE OF CABEDELO SHAPE

Seven types o f Cabedelo shapes can be d i s t i n g u i s h e d . For t h e d e f i n i t i o n o f the v a r i o u s types i s r e f e r r e d t o f i g u r e 1. The occur-rance o f the various tjrpes i s p r i n t e d i n the computer output o f f i g u r e 2. I t i s q u i t e c l e a r t h a t types 1 and type 5 are t h e most common types. Type k i s n o t present i n the set o f data, type k oc-curs only s h o r t l y d u r i n g h i g h discharges; no complete chart o f such a s i t u a t i o n was found.

On pages 22-50 o f t h e annex a l l v a r i a b l e s are p r i n t e d as a f u n c t i o n of the type o f Cabedelo.

For example (see page 22) the average angle o f t h e beach i s f o r Cabedelo type 1 -5 degrees ( w i t h a stand, dev. o f 6.8 degrees), and f o r a Cabedelo type n r . 3 +5 degrees ( w i t h a stand, dev. o f U.5 degrees).

I n t h e t a b l e on page 22 (ANOVA means ANalysis Of VAriance) the values r e q u i r e d f o r such an a n a l y s i s are p r i n t e d . As can be seen, the degrees o f freedom between the groups are always 5 and w i t h i n the groups i n the order o f 90.

These degrees o f freedom give the f o l l o w i n g F-test values: 0.5^0 u n c e r t a i n t y F = 3. 66

1.0% u n c e r t a i n t y F = 3. 26

2.5% u n c e r t a i n t y F = 2. 73 5.0% u n c e r t a i n t y F = 2. 33 10.0% u n c e r t a i n t y F = 1. 93

One may s t a t e t h a t , i f t h e F-value o f the sajnple, as p r i n t e d i n the computer o u t p u t , i s higher than the F-value given above, than there i s a s i g n i f i c a n c e d i f f e r e n c e f o r the various tjrpes o f shapes f o r the c r i t e r i o n v a r i a b l e .

Thus, (see page 22) because the F-value of the sample i s 7.31, one may s t a t e w i t h q u i t e a high c e r t a i n t y t h a t the angle i s d i f f e r e n t f o r each type of Cabedelo (because 7-31 > 3.66).

I n the t a b l e below a l i s t of a l l v a r i a b l e s i s given w i t h the F-values from the output:

v a r i a b l e F-value angle 7.31 nx 5.93 ny 8.62 wx 27.76 wy 17.25 depl

k.ok

From the t a b l e one may conclude t h a t the values f o r dep2, dep3, west7, surface and wid2 do not have any r e l a t i o n w i t h the type o f Cabedelo shape. The l o c a t i o n of westem t i p , however, i s s t r o n g l y r e l a t e d t o the shape. The channel w i d t h n o r t h o f the Cabedelo i s also s t r o n g l y r e l a t e d t o the t y p e , as w e l l as the w i d t h of the head. I n the t a b l e below the average values of the most important v a r i -ables are given f o r each type:

t y p e l type 2 type3 type5 type6 type7

-5.3 792 238 555 i+oi+o 161 366 -i+.i 8U1 212 713 U122 156 258 +5.0 978 207 790 3797 162 221 -2.5 832 22I+ 7U5 3997 162 191 +7.2 809 181 571 3636 209 281 -17.7 803 107 302 3603 29k 512

One can say t h a t the various types are determined by the 7 v a r i a b l e s i n t h i s t a b l e . This i s q u i t e an important conclusion f o r automatic i n t e r p r e t a t i o n of data. Coding the type of Cabedelo from the o l d charts was done manually. However, i n the s i m u l a t i o n program t o be developed, the computer has t o determine the type, and a computer cainnot compare some r e s u l t s w i t h f i g . 1.

Another important conclusion i s t h a t type 6 and 7 are t y p i c a l l y r e -l a t e d t o a -l a r g e channe-l w i d t h (high va-lue of w i d i and -low va-lue o f n y ) . P h y s i c a l l y a l a r g e channel w i d t h i s r e l a t e d t o a high r i v e r

discharge. This means t h a t type 6 and 7 w i l l occur a f t e r a year w i t h a h i g h r i v e r discharge.

A remarkable p o i n t i s t h a t the channel depth i s o f minor importance. The Fvalue o f k.Ok f o r depl i n d i c a t e s t h a t there i s a s l i g h t d i f

-ference i n depth f o r each type, but t h a t the d i f f e r e n c e s are n o t very convincing.

U.U. SCATTERGRAMS

A scattergram i s a computer-made p l o t o f two v a r i a b l e s . These p l o t s van be used f o r various purposes.

On page 51 sind 52 the coordinates nx, ny and wx, wy are p l o t t e d . I n f a c t page 51 and 52 are charts o f the mouth o f the r i v e r i n d i c a t i n g a l l p o s i t i o n s o f the northern and western t i p o f the Cabedelo. For reference t h e topography o f the n o r t h bank, the Pedras do Lima (Molhe Luis de Carvalho) and the p o s i t i o n s o f the Cabedelo i n I 9 I O

and 1982 are i n d i c a t e d .

On page 5 I one can see the area where the n o r t h t i p o f the Cabedelo was located between 1873 and I960. I t i s c l e a r t h a t mostly the t i p was somewhere south o f Meia Laranja (+ sjmibol i n d i c a t e s the average l o c a t i o n ) . I n recent year ( a f t e r I96O) the Cabedelo was c l e a r l y east o f i t s average p o s i t i o n . On page 5I the l o c a t i o n o f the most w e s t e r l y p o i n t o f the Cabedelo i s p l o t t e d . From t h i s diagram i t i s very c l e a r t h a t the present s i t u a t i o n i s h i g h l y uncommon. For d e c i -sions t h i s aspect i s very importaint, regarding the o v e r a l l s t a b i l i t y of the Cabedelo. The p a t t e m o f west p o i n t s i s not a cloud, l i k e the n o r t h p o i n t s , i t i s a t r i a n g u l a r zone. The explanation f o r t h i s

i s q u i t e simple. When a f l o o d occures the sand o f the Cabedelo i s moved towards the sea and the Cabedelo w i l l grow i n west d i r e c t i o n

(type 1 ) . However, i f the west p o i n t has reached open water (ap-prox. a t I5U5OO) the wave forces are pressing the sandbank towards the south, so t h a t the Cabedelo can grow only i n a SW d i r e c t i o n . A f t e r the t r a n s p o r t o f sand has stopped (decrease o f the h i g h r i v e r run- o f f ) the waves w i l l t r a n s p o r t the sand back towards the coast. The Cabedelo has had the f o l l o w i n g sequence o f shapes:

tjrpe 1 - type 7 - type 6.

Because the charts were from various months, the p a t t e m o f west p o i n t s becomes a t r i a n g l e , as i n d i c a t e d on page 52 o f the computer output.

On page 53-8O a l l the v a r i a b l e s are p l o t t e d as a f u n c t i o n o f t h e year. I n t e r p r e t i n g these scattergrams, one should r e a l i s e t h a t before I9OO more charts were made than a f t e r I9OO, and t h a t con-sequently the p o i n t s before I 9 O O are more dense.

Tlie angle (p. 53) shows t h a t a f t e r I9OO the v a r i a t i o n i n angle i s less than before. This might be caused by the f a c t t h a t the r i v e r

discharge i s now more r e g u l a t e d , but t h i s explanation i s more or less s p e c u l a t i v e .

The p o s t i o n o f the n o r t h p o i n t o f the Cabedelo (p 5U-56) shows t h a t t h e r e i s a s l i g h t tendency t o move towards the n o r t h - e a s t , but u n t i l i960 t h i s tendency i s not very c l e a r .

As w i l l be explained, l a t e r , a f t e r I96O the n o r t h p o i n t i s moved q u i t e f a s t towards the east.

The p o s i i i i on o f t h e w e s t p o i n t \p pS-oO) shows no c l e a i " c o r r e l a t i o n

w i t h the year.

The water depth i n the access channel (p 62-66) also does not show some tendency t o change. Tlie average maximum water depth i s r a t h e r constaint over the years.

I n the l o c a t i o n s of the -3, -5 and -J bottom contour l i n e s (p 68-72) also no changing tendency can be d i s t i n g u i s h e d ; the same can be con-cluded f o r the surface area (p 7^) and the channel w i d t h a t the n o r t h p o i n t of the Cabedelo (p 76). The channel w i d t h a t Cantareira

(p 78) i s not very i n t e r e s t i n g . The d i s t r i b u t i o n o f the w i d t h o f the Cabedelo head (p 80) shows t h a t very wide Cabedelos d i d only oc-cur u n t i l 1916 and t h a t a f t e r t h a t year the w i d t h was l i m i t e d t o ap-prox. 50 m. On the other hand also very narrow Cabedelos ( w i d t h less than I50 m) are also more seldom than i n recent years. I t can-not be determined on beforehand i f t h i s i s also caused by r e g u l a t i o n o f the r i v e r discharge. This has t o be explained by the t e s t s i n the mathematical model.

On page 83-128 p l o t s are presented of v a r i a b l e s w i t h a s i g n i f i c a n t c o r r e l a t i o n . For reference see the t a b l e below.

page nr. w i d i wx wy west3 west5

depl 83 101 97 dep2 85 99 ny 125 119 95 wy 87 93 121 head 89 127 west3 91 93

On the page f o l l o w i n g the scattergram some s t a t i s t i c a l i n f o r m a t i o n i s given, l i k e c o r r e l a t i o n , slope and i n t e r c e p t . With the l a s t two values the regression l i n e i s determined. For example (see p, 83-8U) the r e l a t i o n between channel width and channel depth i s :

w i d i = -22.5 + 30.U X depl

However, because the c o r r e l a t i o n i s not very high ( o n l y 55%) the p r e d i c t i v e s i g n i f i c s u i c e of the formula i s not very h i g h . For example, f o r a waterdepth o f 7.8 m the channel w i d t h acc, t o the f o r -mula i s 215 m, w h i l e i n r e a l i t y the channel w i d t h v a r i e s between 100 and 350 m. From these diagrams i t i s not possible t o p r e d i c t f u t u r e

s i t u a t i o n s w i t h simple formulae, but one can f i n d p h y s i c a l r e l a t i o n s to be b u i l t i n i n t o a mathematical model.

Between the channel w i d t h and the n o r t h coordinate o f the west p o i n t of the Cabedelo (p 87-88) the c o r r e l a t i o n i s much higher (72%) Also i n t h i s case one should not use the r e g r e s s i o n l i n e f o r p r e d i c t i o n , but f o r e x p l a i n i n g the p h y s i c a l process. For wide channels the west t i p i s more t o the south than f o r narrow channels. This i s caused by the f a c t t h a t wide channels tend t o a type 6 or type 7 shape, which have south l o c a t i o n s o f the west p o i n t .

The r e l a t i o n between the w i d t h of the channel and the w i d t h o f the head i s not very strong (p 89-9O), the c o r r e l a t i o n i s only H2%, but from the diagram one may conclude t h a t the combination l a r g e w i d t h of the head w i t h a narrow channel does not occur, w h i l e on the o t h e r hand a wide channel i n combination w i t h a narrow head does occur. Also the r e l a t i o n between the channel w i d t h and the -3 bottom con-t o u r i s nocon-t a very impressive one. This r e l a con-t i o n cannocon-t be used very w e l l i n f u r t h e r a n a l y s i s .

The r e l a t i o n between the east-coordinate of the w e s t - t i p and the -3 contour l i n e should have, from a p h y s i c a l p o i n t o f view q u i t e a good r e l a t i o n ( i f the Cabedelo moves west one should expect t h a t also the -3 l i n e moves west). I t proves however, t h a t t h i s r e l a t i o n (see p 93-9U) i s less c l e a r than expected, w i t h a c o r r e l a t i o n of 56%. I t i s t h e r e f o r e very strange t o see t h a t a c o r r e l a t i o n between the w e s t - t i p and the -5 l i n e (see p. 121-122) has a c o r r e l a t i o n of 59%-Also v i s u a l l y observed the r e l a t i o n w i t h the -5 l i n e i s s t r o n g e r than w i t h the -3 l i n e (compare p.93 w i t h p. 121).

The r e l a t i o n s on p. 95-102 w i l l not be discussed here, because they are not very i l l u s t r a t i v e , and cannot be used i n f u t u r e a n a l y s i s . However, between wy and ny a r a t h e r c l e a r r e l a t i o n e x i s t s (see p. 119-120) w i t h a c o r r e l a t i o n of 62%. The mathematical l i n e a r regres-sion l i n e (p. 119) i s v i s u a l l y not f i t t i n g very w e l l through a l l p o i n t s ; the r e l a t i o n i s probably not l i n e a r , but more ore less quadratic.

Page 125 shows the best r e l a t i o n fovmd i n the complete a n a l y s i s . The r e l a t i o n i s , however q u i t e obvious. When the Cabedelo reaches more t o the n o r t h , the channel i s narrower. I t i s t h e r e f o r e even d i f f i c u l t t o e x p l a i n why the value of the slope i s -0.79 i n s t e a d o f

-1.0 and why the i n t e r c e p t i s U6I435I instead o f U6U375 ( c o o r d i n a t e of Meia L a r a n j a ) . These d i f f e r e n c e s are caused by the f a c t t h a t i f the channel i s near C a n t a r e i r a or near F e l g u e i r a s , the same channel w i d t h causes a more south l o c a t i o n of the n o r t h t i p .

The c o r r e l a t i o n between the w i d t h of the Cabedelo and the west coor-d i n a t e of the west p o i n t i s also q u i t e high ( 7 6 % ) . This means t h a t the east side o f the Cabedelo i s on a r e l a t i v e l y s t a b l e p o s i t i o n , t h e o r e t i c a l l y a t coordinate 15^835. Also f o r t h i s conclusion i t has to be stressed t h a t i t i s mainly based upon data before 1920,

considering also the data u n t i l I960. Data a f t e r i960 were not taken i n t o c o n s i d e r a t i o n .

From page 12? f o l l o w s t h a t the east side of the Cabedelo was q u i t e stable a t I5U835, but since I96O the whole Cabedelo i s a t a p o s i t i o n much more t o the east. The east side i s now approx. a t I5525O, which i s a d i f f e r e n c e o f more than kOO m.

H.3. THE EFFECT OF SEASONS

On page 201-202 the d i s t r i b u t i o n of charts a l l over the year are given. Most charts were made i n May ( 1 5 - 5 % ) , while A p r i l i s the month w i t h the lowest number of charts (only 3.1%). But g e n e r a l l y one may draw some conclusions on the i n f l u e n c e of the season on the v a r i a b l e s s t u d i e d .

On page 205-206 the r e l a t i o n between the month and the type o f Cabedelo i s given. The values are also p l o t t e d i n f i g . 3. From these data one may conclude t h a t type 5 t y p i c a l l y occurs i n autumn, and somewhat less i n w i n t e r . Type 1 i s a spring-type shape. Tjrpes 6 and 7 occur i n summer and s p r i n g , but not i n autumn. The types 2 and 3 are not c l e a r l y r e l a t e d t o a season.

The a n a l y s i s of variance (p. 208-238) i s siommarized i n the t a b l e below. v a r i a b l e F-value aingle 0.71 nx 0.69 ny 1.37 wx I. 6 I 4 wy 1.08 depl 0.59 dep2 1.18 dep3 0.79 west3

l.kS

i.kg

For 11 and 90 degrees of freedom the F-value has t o be higher than 1.66, i n order t o s t a t e w i t h 10% u n c e r t a i n t y t h a t there i s any d i f -ference f o r the month. As can be seen i n the t a b l e above, only the F-value f o r wx reaches a value i n the same order. Consequently one may conclude t h a t , besides wx (east coordinate of west p o i n t ) no d i r e c t r e l a t i o n between the season and the c r i t e r i o n v a r i a b l e s caji be ascertained. The reason of t h i s i s t h a t the standard d e v i a t i o n has a higher value thaji the d i f f e r e n c e i n mean value f o r each month.

k. 6 . THE RELATION WITH DISCHARGE

For the years between 1932 and I96O also discharge data were a v a i l -able. The a n a l y s i s o f the e f f e c t o f the discharge i s presented on page 3OI-33U. Four new v a r i a b l e s have been introduced:

cyear - discharge i n the 12 months before chart survey c l 2 - discharge i n 2 months before chart survey c l - discharge i n the iiiöiiuh bêfórê chart survey . c2 - discharge one month e a r l i e r .

On page 301 the s t a t i s t i c a l parameters o f these v a r i a b l e s are presented.

On page 302 the c o r r e l a t i o n c o e f f i c i e n t i s p r i n t e d . The u n d e r l i n e d values are more than kO%. The c o r r e l a t i o n between cyear, c l 2 , c l and c2 themselves are not discussed; they are o f course very h i g h . There i s a c l e a r d i f f e r e n c e i n the e f f e c t o f the discharge o f the f u l l year and o f the l a s t one or two months.

Related t o the discharge i n a f u l l year are: ny - n o r t h coordinate n o r t h t i p

depl - depth a t Felgueiras west5 - l o c a t i o n o f -5 l i n e west7 - l o c a t i o n o f -7 l i n e

w i d i - chemnel w i d t h n o r t h o f Cabedelo

Related t o the discharge short before the chart was surveyed are: wy - n o r t h coordinate o f west t i p

head - w i d t h o f t h e Cabedelo head

On page 303 t o 323 scattergrams are presented, p l o t t i n g the r e l a -t i o n s be-tween -the v a r i a b l e s . Because -the numer o f observa-tions i s not so high (only 12 or l e s s ) the r e l i a b i l i t y o f the found r e l a t i o n s

i s not very h i g h .

A high y e a r l y discharge moves the -5 and -7 l i n e f a r i n t o the sea, which can be explained e a s i l y on a p h y s i c a l b a i s . I t i s t h e r e f o r e r a t h e r strange t h a t such a r e l a t i o n does n o t e x i s t between the year-l y discharge and the -3 year-l i n e . The r e year-l a t i o n s between the discharge and the values o f ny and w i d i and also w i t h depl are q u i t e obvious. More discharge makes a wider opening.

The r e l a t i o n s between s h o r t term discharge and wy and head i s d i f -f i c u l t t o e x p l a i n . At t h i s moment i t i s n o t p o s s i b l e t o give a proper p h y s i c a l e x p l a n a t i o n . . But e s p e c i a l l y the very high c o r r e l a t i o n {Jk%) between c2 and i n d i c a t e s t h a t t h e r e has t o be some p h y s i -c a l r e l a t i o n .

A s p e c u l a t i v e e x p l a n a t i o n i s t h a t the western e x t e n t i o n o f the Cabedelo (which i s i n f a c t wy) i s governed by the discharge o f t h a t moment and t h a t consequently the e x t e n t i o n i s continuously adapted t o t h a t discharge.

Because we have only 9 cases i n which we have data o f both wy and c2, i t i s d i f f i c u l t t o prove the above explanation.

5. VISUAL ANALYSIS

3.1. SOURCES USED

Because o f the vast number o f a v a i l a b l e c h a r t s , and also because t h e number o f charts g i v i n g r e l e v a n t i n f o r m a t i o n i s l i m i t e d , not a l l t h e

c h a r t s w i l l be d i s c u s s e d i n defcetil. O n l y p e r i o d s i n which d s t a i l s d

i n f o r m a t i o n i s a v a i l a b l e , or periods w i t h important events w i l l be discussed.

On some charts ( e s p e c i a l l y between I893 and I 9 I O ) also i n f o r m a t i o n i s a v a i l a b l e on the weather, s t a t e o f the sea, e t c . Unfortvmately t h i s i n f o r m a t i o n i s too fragmentary f o r c o r r e l a t i o n w i t h topographi-c a l topographi-changes i n the morphology.- For f u r t h e r studies i t i s advisable to search f o r more complete weather i n f o r m a t i o n . This i n f o r m a t i o n can probably be found i n the o l d archives o f APDL. I t can be a very good basis f o r r e f i n i n g the model i n f u t u r e . Some o f the charts are reproduced i n t h i s r e p o r t , i n order t o ease the discussions, because the o r i g i n a l charts are not very accessible (they e x i s t only as o r i g i n a l s ) .

3.2. SITUATION BEFORE I83O

The o l d e s t , accurate chart being present i n the set o f o l d charts i s a r e p r o d u c t i o n o f a chart made by Luiz Gomez de Carvalho, g i v i n g t h e s i t u a t i o n i n the p e r i o d between 17^2 and I817. This c h a r t i s reproduced and can be foxmd i n the p l a s t i c p o r t f o l i o a t t h e end o f t h i s r e p o r t . The scale o f t h i s chart i s approx. 1:7500.

One o f the most i n t e r e s t i n g aspects o f t h i s chart i s t h a t also a s i t u a t i o n i s presented before the c o n s t r u c t i o n o f the seawall o f t h e Passeio Alegre. Although not c l e a r l y i n d i c a t e d t h i s seawall i s probably b u i l t a f t e r I789. Before 1789 the n o r t h t i p o f t h e Cabedelo was much more towards the n o r t h than a f t e r I789. I t i s also very c l e a r t h a t t h e entrance o f t h e r i v e r was extremely dan-gerous because o f the rocks Joao boy, Cruz de Ferro and Arribadouro. The general morphology, however, was the same as i t i s today. Sometimes the Cabedelo reached f a r towards the west ( l i k e 17^2), sometimes there was only a type 5 Cabedelo ( I 7 8 9 ) .

An important p o i n t t o n o t i c e i s t h a t t h e "Cabedelo quaze i n v a r i a v e l " i s e x a c t l y south o f Meia Laranja.

The p l a n o f Luiz Gomez de Carvalho o f c o n s t r u c t i n g a south mole from Afurada u n t i l the Fogamanadas was a r e l a t i v e l y good idea. I n t h i s way the maximum r u n - o f f could be used t o clean up the entrance and to make i t a l i t t l e b i t deeper. The w i d t h o f the rivermouth i s probably choosen a l i t t l e b i t too wide, which would cause the forma-t i o n o f a shoal along forma-the souforma-th breakwaforma-ter.

I t i s also very d o u b t f u l i f c o n s t r u c t i o n of the seaward end of t h i s breakwater (near F) could be r e a l i s e d w i t h the t e c h n i c a l means of those days.

5.3. SITUATION IN I 8 6 I / I 8 6 2

The p o s i t i o n of the Cabedelo on a chart of 1862 i s reproduced i n f i g u r e U. According t o i n f o r m a t i o n from the archive of the P i l o t O f f i c e a t Foz do Douro, i n the w i n t e r of I 8 6 I / I 8 6 2 there was no b i g r i v e r r u n - o f f (the Cais da R i b e i r a was not f l o o d e d ) .

I n f i g u r e U the seasonal cycle of the Cabedelo shape can be f o l l o w e d q u i t e c l e a r . I n August a type 5 Cabedelo e x i s t e d . I n the p e r i o d between August and October nothing s p e c i a l happened and due t o the set-up c u r r e n t sand was t r a n s p o r t e d towards the n o r t h . One can ob-serve an erosion of the western c o a s t l i n e and an a c c r e t i o n i n the n o r t h . Because the r i v e r discharge u n t i l October i s s m a l l , the r i v e r d i d not t r a n s p o r t the sand away. I n October a channel of only 100 m w i d t h remained. I n the w i n t e r (probably i n February) there was r e l a t i v e l y high r i v e r r u n - o f f not causing an extreme high water l e v e l , but p e r s i s t i n g s e v e r a l weeks. This r u n - o f f eroded the head of the Cabedelo, the w i d t h of the access-channel became n e a r l y 300 Much sand was deposited sout-west of F e l g u e i r a s , c r e a t i n g a wide, shallow area. A small e x t e n t i o n of the Cabedelo was fonned. I n March the floods came t o an end and wave a c t i o n t r a n s p o r t e d sand from the shallow area somewhat t o the south, c r e a t i n g a west exten-t i o n o f exten-the Cabedelo of n e a r l y 60O m (exten-type 7 ) . During exten-the f o l l o w i n g month wave a c t i o n eroded the westem e x t e n t i o n by t r a n s p o r t i n g sand both i n south-east as i n north-east d i r c t i o n , c r e a t i n g a type 6 Cabedelo.

Between J u l y 1862 and October 1862 the erosion continued and the " f i n a l " s i t u a t i o n of 1862 r e l a t i v e l y i d e n t i c a l t o the s i t u a t i o n of

1861.

The cycle as described above can be found on many c h a r t s , however mostly not documented i n such d e t a i l . There are not very much "nor-mal" years w i t h observations every 2-3 months.

5.H. SITUATION IN 1872

Although from a morphological p o i n t of view not so i n t e r e s t i n g , the chart of 1872 w i l l be discussed because of i t s h i s t o r i c a l value. A copy of the chart i s included i n the p o r t f o l i o at the end of t h i s r e p o r t . The copy i s of q u i t e a poor q u a l i t y , due t o the f a c t t h a t the o r i g i n a l i s i n a bad s t a t e . The I872 chart i s no. 1 of the s e r i e of 100, which continued u n t i l I962. On t h i s charts the f i r s t r i v e r improvement works are i n d i c a t e d . The works on the n o r t h side of the r i v e r were almost completed i n t h a t year, the r a i l w a y f o r the e a r t h f i l l a t the Passeio Alegre i s s t i l l working. On the south side

the Molhe Luiz Gomez de Carvalho (on map 1 c a l l e d Molhe do Sol) was constructed u n t i l the Cabedelo. I t was, (and s t i l l i s ) a r e l a t i v e l y low rubble mound f l o w g u i d i n g s t r u c t u r e . The r a i l w a y f o r the con-s t r u c t i o n o f t h e wet p a r t o f t h a t breakwater i con-s i n d i c a t e d . The l o c a t i o n a t the Cabedelo i n May, Jvine, August and October i s given. Between May and June the north-west beach has been a c c r e t i n g some-what w i t h sand eroding from the south-west beach. A f t e r June th© south-west beach was r a t h e r s t a b l e , but the north-west beach s t a r t e d to erode, t r a n s f o r m i n g the Cabedelo from a type 5 t o a type 3.

I t i s also remarkable, t h a t the navigable entrance t o the r i v e r was north-west o f Felgueras. The longshore t r a n s p o r t from the n o r t h

(which e x i s t e d i n those years, but was q u i t e l i m i t e d , see volume 5 of t h i s study) was i n 1872 r e c e n t l y stopped because o f the construc-t i o n o f construc-the Molhe do Norconstruc-te from construc-the C a s construc-t e l l o da Foz construc-t o Felgueiras. So, sand coming from the n o r t h , and t r a n s p o r t e d near the coast was a l l trapped behind t h e new mole. On a greater depth, t r a n s p o r t towards the south continued and the o f f s h o r e bars moved towards t h e south. I n t h i s way t h e northern ebb channel could become t h e deepest access t o the r i v e r . I n 1872 t h i s process was a f i n a l stage a number of years a f t e r a high discharge ( i n I869 the l a s t high run-o f f run-occurred, l e v e l 6.k8 above Z.H.).

Consequently i n I872 a r e l a t i v e l y s t a b l e s i t u a t i o n occurred, mainly governed by the sea, w i t h only minor i n f l u e n c e o f the r i v e r .

5.5- CHRISTMAS 1909

The o l d e r people i n Porto s t i l l remember Christmas I909, which was one o f the h i g h e s t f l o o d s ever known. Only t h e f l o o d o f 1739 i s said t o be higher (SU cm near the Ponte L u i z ) , b u t o f course t h e r e l i a b i l i t y o f the 1739 value i s q u i t e low. The water l e v e l near the bridge was 11.I6 m above Z.H., the l e v e l at the Maregrafo of Foz was 5-30 m. Very f o r t v u i a t e l y t h e e f f e c t s o f t h i s f l o o d are very w e l l documented. Copies o f two important charts are included i n the p o r t f o l i o a t the end o f t h i s r e p o r t . The f i r s t one shows the p o s i -t i o n o f -the Cabedelo be-tween March aind Augus-t I9IO (scale 1:10,000), the other gives a complete bathymetric survey and the p o s i t i o n o f the Cabedelo i n January, August and October. The inner area was surveyed between January and March, the outer area between March and August, because o f bad weather i n s p r i n g I 9 I O .

The water l e v e l i n s i d e t h e estuary became very high i n December 1909, w h i l e the sea was s t i l l a t sea l e v e l . I t i s not known i f the Cabedelo was moved away by water f l o w i n g over i t . Real overflow i s q u i t e u n l i k e l y . The c r e s t o f the Cabedelo i s nowadays 7-8 m above Z.H. The maximum l e v e l a t C a n t a r r e i r a was 5.3 m. The l e v e l a t the other s i d e , near the Pedras do Maroi^o was higher, but probably not more than 1-1.15 m.

But d u r i n g low sea water t h e r e was an extremely high d i f f e r e n c e be-tween the water l e v e l i n s i d e and outside the Cabedelo causing a b i g gradient i n ground-water slope, causing an extreme groundwater f l o w

through the very porous sand o f the Cahedelo, Such a h i g h ground-water v e l o c i t y induces s o i l s t a b i l i t y f a i l u r e a t the side where the water flows i n t o the sea. One can image t h a t due t o t h i s b u i l d - u p of pressure i n t o the sand, at a c e r t a i n moment the whole Cabedelo consisted o f quicksand and s t a r t e d t o move suddenly. A f t e r t h i s breakthrough the vast amount o f water i n the estuary could f l o w

i n t o the sea, moving the sand f a r i n t o the sea. A f t e r the d i s a s t e r , wave a c t i o n s t a r t e d t o r e b u i l d the coast. Because of setup d i f

-. p o r ' o i - -. o iha main f l n w channel immediately went t o the n o r t h , a l l o w

-ing s i l t a t i o n i n the south. I n January some kind of an i n i t i a l Cabedelo s t a r t e d t o grow from the Pedras do marai?o. Also s a l t a t i o n occurred around the Molhe Luiz de Carvalho and around ( e s p e c i a l l y at the south side o f ) the Fogamanadas. The o f f s h o r e area could not be surveyed i n s p r i n g , but i t i s expected, t h a t i t was a wide, shallow area of loose packed sands. The heavy wave a c t i o n , which prevented the survey campaigns t r a n s p o r t e d the sand over the shallow area towards the coast, c r e a t i n g a south-west d i r e c t e d sandbank (perpen-d i c u l a r t o the (perpen-d i r e c t i o n of the incoming waves). This process con-t i n u e d and i n March a very long s p i con-t i n soucon-th-wescon-t d i r e c con-t i o n can be observed.

Behind t h a t s p i t a r e l a t i v e l y calm area i s created where sand can s e t t l e . The whole area behind the s p i t i s r e l a t i v e l y shallow and no b i g t i d a l c u r r e n t s w i l l occur. I n A p r i l and May the west and n o r t h -west waves move the c o a s t l i n e o f the s p i t towards the east, espe-c i a l l y beespe-cause the b i g supply o f sand from the r i v e r deespe-creases. I n June the Cabedelo i s closed again and also a northward e x t e n t i o n towards Passeio Alegre has been formed. Between August and October the set-up current causes a t r a n s p o r t towards the n o r t h , eroding the beach o f the Cabedelo ( t r a n s p o r t from deeper water towards the coast does not occur i n summer, because the waves are not b i g enough). On the chart on scale 1:5,000 the d i f f e r e n c e i n l o c a t i o n between August and October can be seen c l e a r l y .

On t h i s c h a r t one can also observe t h a t the h i g h f l o o d o f December p r i n c i p a l l y made two f l o w channels, separated by the Molhe Luiz de Carvalho. The k m contour l i n e reaches very near t o the coast of the south end of the Cabedelo.

The next a v a i l a b l e c h a r t i s the survey o f 1913 (see f i g . 5 ) - Tiie c o a s t l i n e has been moved f a r t o the west. During the storm seasons between 1910 and 1913 sand from the shallow o f f s h o r e zone has been moved towards the coast, moving the c o a s t l i n e westward and s t a b i l i z

-ing the Cabedelo. Because o f the abundance of sand the r i v e r entrance tends t o c l o s e , the t i p o f the Cabedelo reaches f a r t o the n o r t h . The i n t e r a c t i o n between ebb t i d e and f l o o d t i d e makes t h a t the head of the Cabedelo v a r i e s c o n s t a n t l y between type 1, type 2 and type 3.

5-6. THE PERIOD FROM I92O-I96O

I n f i g u r e 6 the shape of the Cabedelo i n 1921, 1930, I9U6, 1950 and 1951 i s given. On the chart of 1921 a very s t r a i g h t Cabedelo ap-pears, w i t h shallow o f f s h o r e banks. Also the Enseiada de S. Paio has completely s i l t e d up. Although the chart (August I 9 2 I ) shows a type 5 Cabedelo, i n s p e c t i o n of the bottom contours reveals t h a t i n f a c t type 1 i s present. Ten years l a t e r (August 1930) a type 2 l y washed away by t i d a l creeks. The main channel i s deep and wide, although no extreme high water l e v e l occurred i n the previous w i n t -er. I n I 9 U I (summer?) a t3^e 1 Cabedelo appears. The head o f the Cabedelo i s q u i t e b i g , the erosion of the Enseiada de S. Paio has continued. According t o the discharge data a v a i l a b l e from I9UO-I9UI the average discharge i n t h a t year was q u i t e h i g h (1219 m 3/ h r ) , which i s the second highest i n the p e r i o d I 9 3 2 - I 9 6 3 ( t h e p e r i o d from which we have d e t a i l e d i n f o r m a t i o n ) . The maximum discharge was on January 2!4th, I 9 U I w i t h an average o f 6k29 m3/s. This value i s not very extreme, i t was exceeded i n k3 days i n the p e r i o d I 9 3 2 - I 9 6 3 . This observation shows t h a t a wide entrance and b i g e r o s i o n o f the Cabedelo head i s not caused by a long p e r i o d of h i g h discharge, but s p e c i a l l y on those few days w i t h a discharge of more than 7500

m3/sec.

I n the p e r i o d from I 9 U O - I 9 6 O there were only minor f l o o d s . The charts of 1950 and 1959 show s t a b l e and wide type 1 Cabedelos.

5.7- JANUARY 1962

I n January I962 again a very extreme discharge occurs. The f o l l o w -ing discharges were measured:

dec 31 9271 m3/s jan 1 8775 m3/s jan 2 I U 2 3 I m3/s jan 3 15909 m3/s jan U 11510 m3/s jan 5 7275 m3/s jan 6 5551 in3/s

The w a t e r l e v e l on January 3rd was I.60 m under the ponte Dom L u i z . Acording t o v e r b a l i n f o r m a t i o n there was also a breakthrough through the Cabedelo.

Because i n I962 the economical importance of the Douro was of less importance than i n I 9 I O (because of the development i n Leixoes) the s i t u a t i o n i s not so w e l l documentated as i t was i n I910. F i g . 7 gives the most important f e a t u r e s o f the survey made i n June I 9 6 2 . Between January zmd June the Cabedelo was closed again and b u i l d up u n t i l a considerable h e i g h t (8-9 m) . Analysing the topography o f June 1962 probably two f l o w channels have been formed south o f the Pedras do Maroi<;o. The southern channel was closed f i r s t .

A remarkable d i f f e r e n c e between I962 and I 9 I O i s also t h a t the s h a l -low o f f s h o r e area created by the f l o o d i s somewhat smaller. Also c o n t r a r y t o 19IO q u i t e deep f l o w channels were eroded i n the main channel, w i t h depth o f 9-IO m.

One may s t a t e t h a t i n I962 the t o t a l q u a n t i t y o f sand was less than i t was i n I 9 I O . This may be caused by the f a c t t h a t due to the con-s t r u c t i o n of damcon-s i n the lower con-s e c t i o n of the Douro, the t o t a l amount o f sand a v a i l a b l e f o r t r a n s p o r t by r i v e r f l o o d s had become less ( i t was trapped behind the dams).

5.8. THE PERIOD AFTER I962

The a v a i l a b l e charts (see f i g . 8) from t h i s p e r i o d are not very d e t a i l e d , because of the decreasing economical importance of the harbour f a c i l i t i e s i n the Douro r i v e r . The p a t t e r n s o f s i l t a t i o n are approx. the same as they were i n the past, although the t r e n d i s t h a t the Cabedelo moves towards the east l a c k i n g a vast supply o f sand from the r i v e r , and the continuous t r a n s p o r t of sand from o f f -shore bsinks towards the south, the Cabedelo has withdrawn u n t i l a p o s i t i o n were not any more sand i s l o s t towards the south.

I n years w i t h a h i g h discharge ( l i k e 1979) s t i l l a type 7, f o l l o w e d by a type 6 i s formed but the westem extent ions are lass t o west than they were before I96O.

The l o c a t i o n s of type 2, 3 and U i s considerably much more t o the east than they were before I 9 6 2 .

6. CONCLUSIONS

The f i r s t conclusion a f t e r analysing a l l the i n f o r m a t i o n i s t h a t a l -ready during a long time the p o r t a u t h o r i t i e s have done very good, accurate work by r e g i s t r a t i n g every change i n the morphology o f the r i v e r . There are not many p o r t s i n the world where d e t a i l e d surveys are a v a i l a b l e , covering a p e r i o d of more than 120 years.

The mathematical operations d i d provide a number o f v a r i a b l e s d e s c r i b i n g the status o f the r i v e r mouth, and gave the s t a t i s t i c a l parameters o f these v a r i a b l e s , so t h a t they can be used f o r c a l i b r a t i n g the model.

The general r e s u l t o f the analysis i s a strong c o n f i r m a t i o n o f t h e d e s c r i p t i o n o f t h e morphology, as presented i n p a r t 5 of these r e p o r t s . One may conclude t h a t the morphology o f the r i v e r mouth i s h i g h l y v a r i a b l e , and mainly governed by r i v e r discharge and wave ac-t i o n . Consequenac-tly a s ac-t o c h a s ac-t i c approach, as w i l l be used i n ac-the model t o be developed, i s a b s o l u t e l y required.

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