Studies and reports in hydrology

Studies and reports i n hydrology 45

Recent titles in this series:

5. Discharge of selected rivers of the world (English/French/Spanish/Russian). Volume 111 (Part IV): Mean monthly and extreme discharges (1976-1979). 1985.

30. Aquqer contamination andprotection. 1980. (Also published in French and Arabic.)

31. Methods of computation of the water balance of large lakes and reservoirs. Volume I : Methodology. 1981.

Volume II: Case studies. 1984.

32. Application of results from representative and experimental basins. 1982.

33. Ground water in hard rocks. 1984.

34. Ground-water models. Volume I : Concepts, problems and methods of analysis with examples of their application. 1982.

35. Sedimentation problems in river basins. 1982. (Also published in French.) 36. Methods of computation of low stream flow. 1982.

31. Proceedings of the Leningrad Symposium on specific aspects of hydrological computations for water projects. 1981. (Russian only.)

38. Methods of hydrological computations for water projects. 1982. (Also published in French.) 39. Hydrological aspects of drought. 1985.

40. Guidebook to studies of land subsidence due to ground-water withdrawal. 1984.

41. Guide to the hydrology of carbonate rocks. 1984.

42. Water and energy: demand and effects. 1985.

43. Planning and design of drainage systems in 'urban areas. (2 volumes.) (To be published.) 44. Systems analysis in hydrology. (To be published.)

45. Ground waterproblems in coastal areas. (To be published.)

46. The role of water in socio-economic development. (To be published.) 41. Communication strategies for heightening awareness of water. 1981.

48. Casebook of methods for computing hydrological parameters for water projects. 1981.

Groundwater problems in coastal areas

A contribution to the International Hydrological Programme

Publication o f the I H P Working Group on Changes in the salt-fresh water balance in deltas, estuaries and coastal zones due to structural works and groundwater exploitation

Prepared by E. Custodio, Chairman, with the collaboration o f

G. A. Bruggeman

and the contribution o f case histories by other experts

In this work, countries or parts o f countries are referred to as geographical areas and not as political entities. The designations employed and the presentation o f the material herein do not imply the expression of any opinion whatsoever on the part of Unesco concerning the legal status o f any country or territory, or i t s authorities, or concerning the frontiers o f any country or territory.

Published in 1987 by the United Nations

Educational, Scientific and Cultural Organization, 7, place de Fontenoy, 75700 Paris

Printed by

Imprimerie Bietlot Frères, Fleurus, Belgique ISBN 92-3-10241 5-9

Preface

Although t h e t o t a l amount o f water on earth i s generally assumed t o have remained v i r t u a l l y constant, the rapid gr& of population, together w i t h the extension of i r r i g a t e d agriculture and i n d u s t r i a l developnent, are stressing the quantity and q u a l i t y aspects o f t h e natural system. Because of the increasing problems, man has begun t o r e a l i z e t h a t he can no longer follow a 'use and discard' milosophy

-

e i t h e r w i t h water resources or any other natural resources. Aç a result, t h e need f o r a consistent p l i c y o f r a t i o n a l nianagement o f water resources has become evi&nt.

Rational water manaçement, hwever, should be founded upon a thorough understanding of water a v a i l a b i l i t y and m o v m t . %us, as a contribution t o t h e solution of the world's water problms, Unesoo, i n 1 9 6 5 , began the first worldwide p r o g r m of studies of the hydrological cycle

-

the International Hydrological k c a & (IHD). The research programme was complemented by a major e f f o r t i n the f i e l d of hydroloqicai education and t r a i n i n g . The a c t i v i t i e s undertaken w i n g the Decade proved t o be o f great i n t e r e s t and value t o Member Stated. By the end of t h a t period, a majority o f Unesco's Member States had formed IHü National Committees t o carry out relevant national a c t i v i t i e s and t o p a r t i c i p t e i n regional and international c o - o p r a t i o n w i t h i n the IHD progarme. The knowledge of the world's water resources had substantially improved. Hydrology became widely recognized as an independent professional option and f a c i l i t i e s f o r the t r a i n i n g of hydrologists had been developed.

Qnscious of the need t o e x m d upon the e f f o r t i n i t i a t e d during the International Hydrological Decade and f o l l w i n g t h e r e c m n d a t i o r s o f Memt=er States, Unesco, i n 1 9 7 5 , launched a new long-term i n t e r g o v e r m n t a l programme, t h e International Hydrological Programme (IHP) , t o follow t h e Cecade.

Although the M P i s basically a s c i e n t i f i c and educational p r o g r m e , Unesco has been aware from t h e beginning of a need t o d i r e c t i t s a c t i v i t i e s toward the p r a c t i c a l solutions of the world's very r e a l water resources prob- lems. Acmrdingly, and i n l i n e w i t h the r e c m n d a t i o n s o f the 1977 U n i t e d Nations Water anference, the objectives of the International y ï d r o l o i c a l Pro- gramme have been gradually expanckd i n order t o Cover not only hydroloical processes considered i n i n t e r r e l a t i o n s h i p w i t h the environment and ^hlanan a c t i v i t i e s , but also t h e s c i e n t i f i c a s p c t s of multipurpose u t i l i z a t i o n and conservation o f water resources t o meet the needs of economic and s o c i a l àevelopnent. Thus, w h i l e maintaining IHP's s c i e n t i f i c concept, the objectives have s h i f t e d I p r c e p t i b l y tawards m u l t i d i s c i p l i n a r y aFproach t o t h e assessrent, planning, and r a t i o n a l rrianagenient of water resources.

As p r t o f Unesco's contribution t o the objectives of the IHP, two publi- cation series are issued: 'Studies and R e p r t s i n Hydrology' and 'Technical Papers i n Hydrology'. in addition t o these publications, and in order t o expedite exchange of information i n t h e areas i n which i t i s m s t needed, works of a preliminary nature are issued in the form of Technical Documents.

The p u p s cf t h e contimifig series ‘Studies ârLd R e p r t s i n Eydrclcgy’

t o w h i c h t h i s voltme belongs, i s t o preseKt &ta ccllected and the min r e s u l t s of hydrological studies, as w e l l as t o provice i n f o m i t i o n on hydro- l o g i c a l research teclmicpes. 3 e proceedings of sympsia are also scrretims

included. prac-

t i c a l and theoretical i n t e r e s t t o wzter resources s c i e n t i s t s and also t o those involved i n water resources assessment and the p l a r i n g f o r r a t i o n a l water resources mnaqement

.

I t i s h o p d t \ a t these volmes w i l l furnish m a t e r i d G f both

Contents

Chapter 1

.

General consicerations (E

.

^Custcdio)

...

¹

Chapter 2

.

^{Coastal aquifers (E}

.

^Custodio)

...

⁶

2 . 1 Gerieral

...

⁶

2 . 2 TyFes o f coast

...

⁷

2.3 Sources o f s a l t

...

^{1 0} Chapter 3

.

Salt-fresh a t e r interrelationships under natural conditions

..

^{1 4} (E

.

^Custcdio) 3 . 1 Basic concepts

...

^{1 5} 3 . 4 Mixed ground-surface water conditions

...

⁸⁸

3 . 2 Coastal conditions

...

⁴⁰

3.3 Application t o several t y p s o f coastal areas

...

^{5 8} Chapter 4

.

^{Effects o f} human a c t i v i t i e s on salt-fresh water relationships i n coastal aquifers (E

.

W t o d i o )

...

⁹⁷

4 . 1 Direct e f f e c t s

...

⁹⁸

4 . 2 I n d i r e c t effects

...

^{1 0 8} 4.3 Other effects related t o groundwater exploitation

...

¹¹⁰

4 . 4 Mixed surface-ground water situations

...

¹¹²

Chapter 5

.

^Methods o f calculation

...

^{1 1 8} 5 . 1 Parameters and variables (G.A. Bruggeman)

...

^{1 1 9} 5 . 2 Analytical methods o f calculation (G.A. Bruggeman)

...

¹²⁷

5.3 Wdels (E

.

^Custodio)

...

¹⁷⁸

Chapter 6

.

Hydrogeochemistry and tracers (E

.

^Custcdio)

...

²¹³

6.1 S a l i n i t y and water q u a l i t y

...

²¹³

6.2 Fresh water. sea water and mixtures

...

²¹⁷

6.3 Ion exchange @enornena and alkaline i o d c h l o r i d e r a t i o

..

²¹⁹

6.4 Other chemical modifications

...

²²⁸

6.5 Other saiine groundwaters i n coastal aquifers

...

^{2 3 1} 6 . 6 Minor and trace constituents

...

²³⁶

6.7 a-iemical mapping and geochm.iczl reFresentations

...

^{23 7}

6.8 Interpretation o f r e s u l t s

...

^{2 5 1}

6.9 Sampling problems

...

²⁵²

6.10 Use o f stable isotopos i n the study o f salt-fresh

...

^{2 5 5} water relationships 6 . 1 1 Enviromental r a d i o i s o t o p s i n the stuc!y o f salt-fresh

..

²⁵⁷

groundwater relationships 6.12 Groun&ater temperature

...

²⁶⁰

Chapter 7

.

^{Ekthods of study} and survey (V

.

Cotecchia. w i t h additions

....

²⁷⁰

o f E

.

^Custodia) 7.1 7.2 7.3 7.4 7.5 7.6 7.7 7.8 7.9 7

.

^{1 0} 7.11 7.12 General hydrogeological studies

...

^{2 7 1} Inventories

...

²⁷³

Observation wells

...

²⁷³

S a l i n i t y logging

...

²⁷⁸

Temperature logging

...

²⁸²

Representativity o f bre-hole r r e a s u r a n t s

...

²⁸²

Groundwater sampling

...

²⁸⁴

Borehole geo&ysicai logging

...

²⁸⁴

L i m i t s and u t i l i t y o f qeoghysical investigtiorxà

...

²⁸⁹

Use o f a r t i f i c i a l tracers

...

²⁹⁵

I d e n t i f i c a t i o n and monitoring o f zone of d i s p r s i o n

....

³⁰⁵

Remote sensing

...

^{3 0 8} Chapter 8

.

Prediction methods (E

.

^Custcdio)

...

³¹⁷

8 . 1 Forecasting based on case studies

...

^{3 1 8} 8.2 Prediction based on calculation methods

...

^{3 3 1} 8.3 Prediction methods by mans of models

...

^{3 8 1} Chapter 9

.

^P?thods t o control and combat saltwater intrusion

...

³⁹⁶

(E

.

^Cuçtodio) 9.1 9.2 9.3 9.4 9.5 9.6 9.7 9.8 9.9 9.10 General considerations t o prevent se2 water intrusion

..

³⁹⁷

Construction and o p r a t i o n o f abstraction works

...

^{3 9 8} Exploitation o f coastal springs

...

⁴⁰²

Methods t o improve or renedy sea water intruded

...

⁴⁰⁵

aqui f e r s &th& t o maintain the existing aquifer exploitation

..

⁴¹²

....

⁴²²

Use o f coastal saline zquifers t o store fresh water

....

⁴²³

and t o dispose o f waste a t e r Combatting sea water salir, i z a t i o n through surface water.424 A l t e r m t i v e s t o <eveloping coastal aquifers

...

⁴²⁵

Plan f o r çroundwater exploitation i n a coastal aquifer

. .

⁴²⁷

Active control of upconing under a fresh wzter w e l l

aafler 1 0

.

^Case h i s t o r i e s

...

⁴³⁴

10.1 Introduction

...

⁴³⁵

10.2 Oeltas and a l w i a l q u i f e r s

...

⁴³⁶

1 0 . 4 Carhnate rocks

...

⁵¹⁶

10.5 I s l m d s

...

⁵⁶⁶

10.3 Coastal plains

...

⁴⁷⁴

1 O

.

^{6 S a l t balances.} surf ace-grounhiter

...

⁵⁸²

Introduction

Çeneral SCOR

This nonograph began w i t h the f i r s t session (9-17 A p r i l 1 9 7 5 ) o f the Interna- t i o n a l Hydrological P r o g r m e I n t e r g o v e r m n t a l Council, a f t e r considering the guidelines f o r the 1975-1980 period approved by the Unesco General Conference a t i t s 1 8 t h Session. Project 5 was established t o deal w i t h the evaluation o f hydrological and ecological e f f e c t s of rran's a c t i v i t i e s . Point 6 refers t o the estiniation o f chanqes in the s a l t water-fresh water balance in coastal areas due t o hydraulic works and grounihater exploitation. A s p c i a l focus i s PLI on the study of hydrological studies related t o new eneray sources.

A t the second meeting o f the Intergovernmental Council, held i n Paris on 20-27 June 1977, i t was decided t o re-establish the Working Group on evalua- t i o n of the changes on s a i t water-fresh water balance (surface and under- ground) i n deltas, estuaries and coastal zones, due t o the construction o f structures and t o grouncfwater exploitation (1977-1979) t o prepare a technical note (1975-1977) t o include a general description of the problems, studies and methods t o be used t o evaluate and foresee the changes i n the saltwater-fresh water balancees i n coastal zones as a consequence of human a c t i v i t i e s , w i t h a deadiine o f 1978. Subsequent delays prevented f i n i s h i n g put of the work u n t i l 1982.

A t the t h i r d meeting o f the Working Group, i t was decided t h a t the papr t o be w r i t t e n was t o tx a monograph w i t h wider coverage t o deal w i t h the d i f - ferent a s p c t s needed t o understand coastal water resources. The t i t l e

'Costal water problems' was ado@zed, but the contents s t i l l follow the main s c o p set by the Unesco Council.

O

The Working Group was i n i t i a l l y formed by A. El-Mugrin (Riyadh, Saudi Arabia, groundwater); E. Custodio (Barcelona, S p i n , groundwater); K.G. Lubanirova

(Moscow, USSR, surface water); and K. Sannuganathan (Reading, U.K., surface water). Later G.A. Bruggerran was added (the Ketherlands, groundwater).

a d was entrusted w i t h the a a i m s h i p of the group. Due t o unforeseen circumstances K.G. Lubomirova and A. El-Nugrin could not a c t i v e l y p r t i c i p t e i n the Working Group, and i t was thus reduced t o three people, plus the t e c h i c a i sectre- t a r i a t . V. Cotecchia (Bari, I t a l y , groundwater) was called upon t o h e l p the group as an observer, and p r f o m d a p r t o f the task. Some a i d was also

Only E. C u s t d i o was able t o attend the f i r s t meeting i n Paris,

received from R. D i j o n (Lnited Nations, New York) and J.C. van Can ( C e l f t , the Ketherlands) acting as advisors rrainly on the cjromhater aspects. P.e techn- i c a l secretariat and the Chaiman lcoked f o r a wite spxtrum o f case h i s t o r i e s and information, w r i t i n g t o IHP National Cornittees and t o a broad l i s t o f worla e x p r t s . The ansiers received are analysed i n chapter 10, and hâve also been u e d as background m t e r i a l f o r the other &apterS.

the Working Group establishec, a detailed o u t l i n e and shared among i t s merbers the task o f w r i t i n g the d i f f e r e n t chaflers. This task was cnly p a r t i a l l y accom- plished due t o d i f f i c u l t i e s and delays, and i n the f a i l o f 1 9 8 1 , since the surface water p r t proved t o be the nmst incoqdete and d i f f i c u l t t o f i n i s h , i t was decided t o handle only the gromdw;rter part.

A t the second meeting i n FJallingford, and l a t e r the t h i r d i n Paris,

For t h i s volurr,e, the C h a i m a took the task o f nodifying t h e octline, reorganizing the existing m t e r i a l , q d a t i n g i t , and w r i t i n g the parts n o t yet contributed by one of the groundwater experts.

Acknowledgements

The Chainnan o f the Working Group i s hicjhly indebted f o r the help received from the Cornisaria de Aguas d e l P i r i r i o Oriental (Eastern Pyrenees k:ater Authority) o f the General Directorship o f Public Works, the Pidustriai Engineers H i g h Technical School o f Barcelona, and Earcelona's Polytechnic University, and f o r p r m i s s i o n t o devote much time t o the task o f w r i t i n g and reviewing the present monograph. Also he i s indebted t o the crganizations above and the International Groundwater Eydrology Course o f Barcelona f o r the manpower and f i n a n c i a l h e l p in typing much of the d r a f t anà drawing half of the tigures, and also f o r providing the required secretariat f a c i l i t i e s and the exrpnses involved.

Thanks are also due t o the C i v i l Engineering Faculty o f the B a r i Univer- s i t y f o r the a i d received f r o m Mr. Vincenzo Cotecchia, and t o the Cutch R i j k s i n s t i t u u t voor Dinkwater Vorziening f o r the collaboration o f Ilr. G.A.

Brugcjerran

.

Acknowledgements must also be made t o those who have contribEted case histories, whether a p p a r i n g i n chapter 1 0 or not, and t o those who have con- tributed other material, especially Mr. Robert D i j o n o f the United Nations

(New York), Mr. J.C. van Dam of the Celft Technical University (the Rether- lands), Y ! . Josd-Ignacio Garcia-Bengochea o f Florida, Francis A. Kohout o f the U.S. Geological Survey (Washington), and Arthur Bruigton of the Los Angeles County Flood Control D i s t r i c t (California).

The Spnish, Dutch and I t a l i a n National Corranittees f o r the international Hydrological Programme have helped i n solving various problems, and have a i l encouraged the work. IU1 contributors are mentioned i n the contents.

Most o f the f i r s t typing o f the manuscript was accomplished by Ms. Enaria E'elisa Zurbano, and the drawings done by Ms. m a r 0 Aiaiz, both o f them working f o r the Eastern Pyrenees Water Authority and the international Groilndwater

Hydrology course. N e i l Grigg w i t h

the a i d o f his. Verdia Johnson and Mr. Gabriel Sabadell o f Colora20 State University.

The f i n a l e d i t i n g was carried out by Prof,

h i l i 0 Custcdio

C h a i m of the Working Group Barcelona, August 1 9 8 2

1. General considerations

E. Custodio

Coastal zones often contain m e of the most densely p p u l a t e d areas i n the world. The a v a i l a b i l i t y o f f l a t land, c m u n i c a t i o n s arteries, easy sea tran-

s p r t a t i o n , good s o i l s , and high productivity o f organic matter e,xplains t h i s f a c t . The areas close t o r i v e r s or deltas generally present the best condi- tions.

The demand f o r fresh water resources resources in areas not d i r e c t l y fed by rivers, and c o m n

.

easily exceed available water supply shortages are Man's a c t i v i t i e s i n t e r f e r e w i t h M t u r a l processes and many physical and biological changes are produced or expected, such as sea water intrusion, the destruction o f the natural habitat or shore modification through erosion and sedimentation.

Also c m n i s the progressive occupation o f w r i o d i c a l l y flooded lands, as w e l l as the desiccation or drainage o f wetlands. I n order t o pro- t e c t these settlements, many types o f c i v i l works are constructed. Tnese easily a l t e r natural processes and have a wide s p c t r m of i n d i r e c t effects.

Many o f these e f f e c t s are not considered or anticipated when the c i v i l works or modifications zre done, and i n mny instances they produce unexpected changes that need new corrective measures or impair existing uses o f natural resources.

The coastal zone i s subject t o more severe and complex issues than most other land and water resources, and must be viewed as an important com- ponent of a water resources system. The coastal zone, as the t r a n s i t i o n area from land t o sea, and from fresh water t o s a l t water, contains sone o f the world's most b i o l o g i c a l l y productive units, the estuaries being the key ele- ment, as shown by the following data (Teal and Teal, 1 9 7 1 ) :

Production rate

source t 1 h 2 / year

Arid agriculture 0.5

-

^{3 . 5}

3 . 5

-

^{1 2}

Estuarine zone 1 2

-

²⁴

Coastal water 2.5

-

^{3 . 5}

Moist agr i c u i t u r e

Open ocean

-

^1.0

Fresh water f l W J both surface and Imderground, has an important impact u p n the characteristics and q c a l i t y of the productive estuarine, coa- s t a l laqcon and wetlands waters, and upon sedimentary d e p s i t s along the coast.

Associated w i t h man's a c t i v i t i e s are h i s uses, and i n m y instances abuses, o f coastal resources. Tnese w i l l continue t o grow since man w i l l con- centrate h i s a c t i v i t i e s and urban establishmnts along the coasts. By the year 2000 i t i s assumed t h a t more than three quarters of the world's p p u l a - t i o n w i l l be a t or near the mast, and w i l l draw heavily on the already stressed coastal environnent.

The main uses o f coastal areas, including dry lands, marshes, sub- merged land, the surrounding waters and the natural resources, may be classi-

f i e d (üSGR3, 1 9 6 9 ) as:

-

urbanization and developnent (industry, housing, p o r t and harbor)

-

water supply (municipal, agricultural, r e c r e a t i o m l and indus- trial)

-

waste d i s p s a l ( m u n i c i p a l , dorriestic, industrial, a g r i c u l t u r a l )

-

transportation (land, sea, a i r )

-

extraction o f mineral resources ( o i l , gas, sand and gravel)

-

biological resources (fisheries, aquaculture)

-

recreation (beaches, swimming, boating, fishing, scenery, hunting)

-

w i l d l i f e , estuarine and wetland preservation.

Ey f a r , the major impact comes from urbanization and developnent.

The present monograa covers only water resources and the effects of t h e i r exploitation, but the other a s w c t s must be borne i n mind.

Estuarine and groundwater outflow areas have a d i l u t i o n e f f e c t o f sea water salinity t h a t a f f e c t s aquatic l i f e . River use, groundwater exploi- tation, urbanization impact on surface runoff and groundwater recharge niodify the d i l u t i o n p i t t e r n and & f e c t aquatic l i f e accordingly. Surface-groundwater r e l a t i o n s h i p cannot k neglected. Also marshes p s e interesting problems of s o i l s , cultivation, w i l d l i f e , and disease control where groundwater outflow may have a dominant role.

Not only i s water a major compnent of the ccastaï zone, but sand and gravel are also important elements. Dam construction, reforestation and cleforestation, a g r i c u l t u r a l Zevelopnent, urbanization, land erosion control programs, water transportation, r i v e r channelization, sand and gravel extrac- t i o n , etc., have a great e f f e c t on the s o l i d trclnsport and equilibrium i n cca- s t a l areas, e s p c i a l l y i n beaches. Sedimentology i s as imprtant as hydrology and hydrâuics.

Since uses are v a r i e d and often conflicting, i t i s necessary t o have coastal zone planning and xranagement i n order t o have a r a t i o m l way t o rranage m u l t i p l e coastal resources. Fresh water resources conservation and exploita- t i o n need w e l l established planning so future generations can use them.

The outline of a r a t i o n a l public p l i c y f o r a c o a s t i i zone nust con- si3er d i f f e r e n t factors:

-

&ysical, chemical and biological characteristics

-

urbanization, agriculture, t r a n s p r t a t i o n , industry and develop ment

-

governmental c a p c i t y f o r a6equate p l i c y developent and imple- rnentation.

After Dzurik ( 1 9 7 3 ) , one m u s t consider t h a t neither complete exploi- t a t i o n nor t o t a l preservation i s appropriate or feasible. A balance i s needed and m u s t be m i n t a i n e d i n order t o maximize long-term as w e l l as inmediate benefits through correct and adequate management o f coastal resources w i t h i n the framework o f water resource systems.

Management o f coastal resources cannot be separated f r o m the rrianage- ment o f inland water resources, and the converse i s also true. Although a narrow s c o p i s frequently necessary i n dealing w i t h resource and water prob-

l e m ~ , the subsystem should be understood w i t h i n the framework of the larger resource system. The Aswan High Dam i s now a classic example o f the great changes and damages which can occur t o coastal resources through disregard or i n s u f f i c i e n t consideration o f the interaction o f r i v e r and coastal waters.

But unfortunately i t i s not the only example, and a long l i s t o f f a i l u r e s , t o t a l or p a r t i a l , can be easily gathered both i n developd high technology countries and i n developing countries under colonial or n a t i o r d r u l e .

Not a i l changes i n inland waters are damaging t o coastzd resources or the whole system. When changes and uses are necessary, they should include the evaluation a€ the t o t a l possible effects and the correction of the nega- t i v e a s p c t s , without impairing others.

Pollutants generated by m ' s a c t i v i t i e s gather i n the Oceans as a final receptacle, and they are frequently t r a p p d and physically or biologi- cally concentrated i n estuarine zones. The long-term e f f e c t s can be serious and irreversible. Along many urban centers, coastal waters are used as a sump f o r i n d u s t r i a l and domestic waste d i s p s a l , and thus has k e n ruined f o r most other uses. Prime ecological systems, recreation areas, natural surface and underground storage systems have been eliminated needlessly through lack o f adequate planning and management. ?he Mediterranean area has been subjected t o many such negative a s p c t s .

Acute problems may appear i n developing countries, especially in those subject t o t r o p i c a l climates, i n islands and when the population density and b i r t h rate are very high. The recent acquisition of independence or broad aLtonony has generated great hopes among the p p u l a t i o n s f o r the improvemtnt

o f l i v i n g conditions, e s w c i a l l y as regards water supply (Dijon, 1 9 7 8 ) . Water d m m d f o r i r r i g a t i o n , p o r t i n s t a l l a t i o n s and related industries, and water uses

--

e s p c i a l l y tourism

--

have also increased dramatically, as a r e s u l t of the drive of the countries tcwards economic self-silfficiency.

As a sunnnary, Unesco's Man and the Bios@,ere Programme ( M I , 1974) enunerated the follcwing characteristics of t h e coastal environment t h a t make i t vulnerable t o hurrian i m p c t :

-

land-sea interactions, both c y c l i c a l and unidirectional;

-

productivity and the n u t r i e n t t r a p effect. Nutrient l e v e l s are usually enhanced due to. intensive r e q c l i n g processes, but those factors are also r e s p n s i b l e f o r t h e i r conversion t o p l l u t i o n sinks ;

-

fod-web structure;

-

v u l n e r a b i l i t y o f coastal zone organisms;

-

sedimntation control i n the environment;

-

w r t a n c e of freshwater i n f l o w ;

-

epidemiological characteristics. Human and animal pathogens find favorable conditions f o r t h e i r m u l t i p l i c a t i o n i n d e l t a i c coastal areas, such as malaria, noxious mosquitoes, arbviroses, ame- biosis, choleria, enterobacterioses, leptospiroses, schisto- somioses, oncocercoses, etc.

These a s p c t s are beyond the scope o f the present monogram and w i l l not be considered further.

only fresh groundwater resources w i l l be considered from the hydro- l o g i c point o f view.

Sea water encroachment problems i n coastal aquifers have been recog- nized since the f i r s t quantitative studies a t the turn of the century, and have not teen considered an important separate aspect of groundwater hydrclcgy u n t i l recently. A good h i s t o r i c a l discussion on what i s known about s a l t water i n t r u s i o n can be found i n Kashef ( 1 9 7 2 ) , and same a s p c t s of the developnent w i l l be given i n section 3 . 1 .

Probably the f i r s t classical book t o inclu& a chapter on quantita- t i v e aspects of sea water encroachment i n coastal aquifers i s t h a t o f Todd ( 1 9 5 8 ) . The U.S. Geological Survey Water-SuFply Paper 1613-C (Cooper e t a l . 1 9 6 4 ) was also an b n p r t a n t k n c h r k .

Perhaps one of the f i r s t international meetings t o include sea water i n t r u s i o n problems expressly was the Haifa Sympsim orgznized by the Interna- t i o r a l Association of S c i e n t i f i c Hydrology (Pub 92)

.

In Europe, i n i t i a l l y r e s t r i c t e d t o Nordic Europan Countries, the Sea Water I n t r u s i o n Meetings (SWIM) have been convened every two years, each t i m e w i t h a wide coverage o f problems, areas and countries. The most recent meetings have keen:

1975 IV

-

^{Ghent, Belgium}

1979 V I

-

Hannover, Federal Republic o f Germany 1981 VI1

-

Uppsala, Sweden

1983 VI11

-

Bari, I t a l y 1977 V

-

Mechrienham, U.K.

There i s no f o m a l organization f o r these meetings, but an agreement o f a national organization

t o

i n v i t e experts t o discuss-their a c h i e & w t s , the publication of the proceedings being handled by the host Organization.

1.1

References

Coopr, H.H. Jr.; Kohout, F.A.; Henry, H.R.; Glober, R.E. ( 1 9 6 4 ) . Sea w a t a U.S. Geol. Survey, Water-Supply Faper 163-C, 84 pp.

t i v i t i e s

I d s . Selected Water Problems i n Islands and

Dijon, R. ( 1 9 7 8 ) . A review of United N a t i w water resources ac

Coastal Areas. Seminar of Malta, 1978, United Nations Economic Corn- mission f o r Europe. Perganmon, 1979, pp.87-98.

Dzurik, A.A. ( 1 9 7 3 ) . The coastal zone as an i n t w i e l m e n t o f w a t c

-

.

Water Resources B u l l e t i n , AWRA. Vol. 9, N0.4, pp.733-745.

Kashef, A.A.I. ( 1 9 7 2 ) . do we know about s a l t water jritrus ion? Water Resources B u l l . AWRA. Vol. 8, No. 2 , A p r i l , pp. 282-293.

. . .

MAB ( 1 9 7 4 ) . -cal e f e c t s of h w a c t i v i t i e s on the value and resources d coastal zones:

1 report. Programme on Man and t h e Biosghere (MAB): Unesco.

MAB R e p r t Series No. 21, 80 pp.

R e p r t of the Workshop on Global Ecological Problems. The i n s t i t u t e o f Ecology.

USA.

. .

Teal, J.M.; Teal, M. ( 1 9 7 1 ) . i n the l i v i n u e n v i r o m n t .

Todd, D.K. (1958)

.

^{-ter hvdrolow}

.

^{John Wiley and Sons, New York.}

USGFû ( 1 9 6 9 ) . Pcience and e n v i r o m & ( 1 9 6 9 ) . Panel Reports o f the c0rruni.s- sion of Marine Science, Engineering and Resources. UçGFû. Washing- ton, 340 pp.

2. Coastal aquifers

E. Custodio

2 . 1 General

...

⁶

2.3 Sources of s a l t

...

^{1 0}

2 . 4 References

...

^{1 3}

2.2 TyIps o f coasts

...

⁷

2 . 1 General

The great length o f coasts requires t h a t a srrial1 but s i g n i f i c a n t p a r t of the continental water discharged t o the oceans outflows d i r e c t l y from the ground.

A much greater p r t discharçes t o the lower t r a c t s of rivers, i n areas where coastal conditions prevail.

The t o t a l d i r e c t discharge of groundwater i n t o the oceans i s a speculative f i g u r e since no &rect rreasures can be made. Frequently the discharge in a given coastal area i s obtained from the residual t e r m i n the groundwater balance, and i t accumulates a l l the errors. The resulting figure, generally small r e l a t i v e t o other terms i n the balance, i s not reliable.

Since the hydroqeological and hydrodynamical data along the ccast are generally inaccurate, Zekster and Czhamalov (1981b) mde an e s t i m t e by applying t o the discharcje. along the coast the same s p c i f i c figures obtained for the lower t r a c t s of the rivers. Most of the fresh groundwater discharge correspnzs t o the shaîïow aquifers. The values, i n i/s/km2 of surface con- tributing t o the ccast, vary from as high as 1 4 l/s/km2 i n very permeable materials i n areas w i t h normal-to-high r a i n f a l l . t o as l o w as l e s s than 0.2 l/s/km2 i n cold or warm a r i d arecis. !$‘he results are reproduced i n table 2.1.

The t o t a l f i g u r e i s close t o 2460 x 10 m3/year (about 1 5 d y e a r ) , similar t o t h a t obtained from other rwthods by the same au ors. It must be compared i o v e t a ï . , 1 9 7 4 ) .

w i t h the t o t a l r i v e r outflow o f &ut 45000 x

l o 9

m

5h

^{/year (300 mm/year) (Soko-}

Direct groundwater outflow i s ?.bus about 5% of t h e t o t a l continental fresh water o&flow, although due t o i t s greater s a l i n i t y , i t contributes about 1 / 3 o f t o t a l continental s a l t s trcinsprted by water from the continent t o the oceans, and thus i t has a s i g n i f i c a n t e f f e c t on the sea s a l t balances and on m y geochemical process leading t o rock and mineral formation.

The importance o f that a p p r e n t l y mll 545 appars when considering i t s d i s t r i b u t i o n along the coast, thus k i n g more d i r e c t l y susceptible t o the intense hman a c t i v i t i e s i n those areas. Also t h e i r s u s c e p t i b i l i t y t o easy degra2ation by sea water intrusion p s e s h l i c a t e problems f o r the use of the s o m t i m s great groundwater reserves i n highly porous coastal f o m t i o n s .

Table 2.1

-

Gromdwater discharse t o the World Ocean. Modifiez f r o m Zekster and Dzhmalov ( 1 9 8 1 a ) .

G r our?dwat e r d i scba r ge Contributin

Ocean Continent area 103

kmq

^{1 0 9 m3/yeâr l/s/km2}

A t l a n t i c E u r o p

North America South h r i c a Africa

Main islands Mediterranean E u r o p

Asia A f r i c a

Main islands Pacific

Indian

Asia

North America South America Austral i a Main islands Asia

A f r i c a Austral i a Main islands Arctic E u r o p

5 4 1 1 9 3 2 1 9 4 0 1713 555

2 94 1 0 8 404 6 5

1683 93 6 5 53 200 1693

1227 1 2 6 6 23 50 733

46 1

7 1 22 9 1 8 6 2 1 6

77

4.2 3.8 3 .O 4.0 4.4 7 7 9

49 8 5 6 6 8 2 5 4 1 6 3 2 0 1 7 713

5.3 2.4 0.4 2.8

4

4.7 ( 2 - 1 1 ) * 5.5 (1-13) 11.5 (11-15)

1.1

11.4 (4-33) 133 8

65 2 2 1 6 1 1 7

1.7 0.5 0.2 5.1 220

5 1 3.5

5 1

*

Range

9 3

T o t a l general, 2456 x 1 0 m /year

A 3% sea water percentage can render the water too s a i t y f o r many and 5% p r a c t i c a l l y renders i t useless, except i f very expnsive desalt- e s ,

i n g processes are used.

2.2

The masurenent and c l a s s i f i c a t i o n o f coasts and shores can help i n the uncier- standing o f t h e i r importance. The t o t a l length of the p r i m e t e r o f the e n t i r e

\?or12 Ocean hcts been calculated t o be a b u t 777,000 km (Luk'yanova and Kholo- d i l i n , 1 9 7 5 ) . This f i g u r e must be used w i t h caution. Due t o the shaps of f i o r d and r i a shores and coasts, the length of t h e i r shoreline increases shar- ply, i n f a c t they do not occur frequently by canparison w i t h other t y p s of shores.

but

The above f i g u r e refers t o the shoreline, which has a macroscopic aspect given by the i n i t i a tyFe o f dissection, and a microscopic aspect t h a t depnds on the sinuosiw, produced mainly by wave action. The n m k r o f micro and macro elements of the shoreline i s described by a rLqcedness or sinuosity index (Auphan, 1971) , t h a t relates the lexgth of the shoreline t o the length o f the corresponding seqents o f the shore and coast.

The shore can be considered as the zone bounded by the seâward and the landward water l i m i t i n g lines. The length i s measured by the smoothed median curve. ^An allowance i s mde f o r the microelements i n plan, mainly due t o wave action.

The coast i s defined similarly, but the d e f i n i t i o n must consider the such as heads o f f i o r d s and r i a s , o p n lagoons and continental macroelemnts,

islands.

When considering the shore and the coast lengths, the perimeter of the World Ocean i s reduced t o 469,000 and 413,000 km, r e s p c t i v e l y . Tables 2.2 and 2.3 show the importance and ruggedness of the d i f f e r e n t types of shores (according t o the abrasion-accretion process) and coast (according t o t h e i r mormologicaï o r i g i n ) , given by the work of Luk'yanova and Kholodilin

( 1 9 7 5 ) .

Table 2.2

-

^Length prcentage and ruggedness of the shore types along the

Shore t y p s ^%J length Ruggedness

World Ocean. Modified from Luk'yanova and Kholodilin ( 1 9 7 5 ) .

1. Unchanged or s l i g h t l y changed by the sea

lb. E l a t 7 1

l a . Ingressional, deeply dissected ( f i o r d ) 1 5 3 2. Denuational-abrasional

2a. Ingressional, deeply dissected ( r i a ) 3

2b. Ingressional bay 0.5

2c. F l a t 0.5

3. Abrasionaï

3a. ingressional abrasional (bay) 3b. Planate

3c. Dead c l i f f and accretion terrace

1 6 6 1 4. Abrasional-accretional

4a. ingressional, deeply dissected ( l o w r i a ) 2 4b. Ingressional, secondarily dissected 1 5

4c. Planate ⁴

5 . Accretional

5a. Ingr essional

5b. Secondarily dissected 5c. Planate lagoon

5d. Planate w i t h accretional terrace

2 7 1 0 11

4 1 1.5

1 1 1

1 1 1

2 2 1.5 1 T o t a l length o f shores 469,000 km

m b l e 2.3

-

^Length prcentage and ruggedness o f t h e coast tyFes along t h e

Coast types 4e length Rugaedness

World Ocean. M d i f i e d f r o m Luk'yanova m d Kholodilin ( 1 9 7 5 )

.

1.

2.

3 .

4.

5.

6.

Mountains

l a . Techtonically and erosionally dissected i b . Mainly block-techtonic dissection

1c. Dissection o f volcanic forms Tablelands and plateau

2a. Strongly dissected r e l i e f 2b. S l i g h t l y dissected r e l i e f Glaciated

3a. Present i c e sheets ( i c e coasts)

3b. Glacial aggradational and denudational 3c. Eluvioglacial and glacial-lacustrine

-

subject t o g l a c i a t i o n ( f i o r d s )

-

others (including r i a s )

(plains, elevations 1 aggr adational p i ains

1 2 6 2 . 5 2 5 9

1 0 7 2 Allwial

4a.

4b. Plains 8

4c. Alluvial-marine plains 2 1

Marine

5a. Aggradational and abrasional-aggradational 8

5b. Abrasional 1

Plains w i t h p n n a f r o s t or vein i c e

(also marine) 1 . 5

Others

6a. Eolian and eolian-marine plains 6b. Plains of varying o r i g i n

T o t a l length of coasts ^413,000 lan 3 2

2 1

1 3 2

1.5 1 1 2 1 . 5 1 1

The coast c l a s s i f i c a t i o n i s more adaeed t o t h e description o f the different r e l a t i o n s h i p ktween f r e s h and s a l t groundwaters i n coastal areas.

However i t i s necessary also t o consider hydrodynamic conditions (water table, confined systems, SerniconEining layers, l o w lands, etc.), t h a t can greatly influence relationships. Sea b t t o m sediments also can play an imprtant role.

From the hydrcgeolcgical p i n t of view not all coast t y p s have the sane importance, since those of hard, l c w fractured rocks (granites, gneiss) are a l m s t imprductive, while terrace d e p s i t s and great recent sedincntary k s i n s have a c l e a r l y overwhelming interest.

The f o l l w i n g c l a s s i f i c a t i o n i s adoned:

(a) Unconsolidated materials (glaciated, a l l u v i a l , marine an2 eolian), mainly accretiorial, a b u t 25% of t o t a l coast.

( a i ) water table (a21 s r d l islands (a31 confined (a4 semiconf ined (a 5 ) multilayered (a61 young deltas

(b) Consolidated materials (sane mountains, tablelmds and pla- teau), mainly abrasioml or denudational, a b u t 2 M of t o t a l coast ⁰

b i ) fissured hard rocks b2) k a r s t i f i e d rocks

Other factors t o te considered i n subclassifications are:

-

sea behavior ( t i d a l regime, storm surges, wzve action, sea bottom sedimnts 1

-

c l i m t e (wet tropical, semi-arid, t a n p r a t e , mediterranean;

predcminant win&; r a i n i n t e n s i t y )

-

recharge regime

-

rian interventions (desiccation, p l d e r i n g , r i v e r basin modifica- tion, agriculture, urbanization)

-

long-term evolution (sea water tranqressions or regressions, sub- sidence).

n-ie min source of s a i t i n coastal areas i s sea water. Sea water has a rather constant chemical composition except f o r mal1 changes due t o the variable e v a p r a t i o n rates (higher i n the tropics and the Pediterranean ) or great con- t i n e n t a l fresh water contributions (Caribbean ) . Greater differences can be found i n closed or half-closed seas such as the B a l t i c , the Caspian, the Black Sea, etc.

?Lpical sea water analyses are (from Custodio and Llmas, 1976, p.

Oceanic Mediterrm.ean

1080) ( q / l ) :

0.07

-

0 . 1 4 0.07

-

0.17

2.4

-

^{2.7 2 . 9}

-

^{3 . 2}

c l

^17.5

-

^{19.0 20.5}

-

^21.5

Na 9 . 7

-

^{10.5 11.7}

-

^11.8

K 0.36 0.27

-

0 . 5 0

ca. 0 . 3 8

-

^{0 . 4 0 0 . 4}

-

^{0 . 5}

Elg 1 . 0

-

^{1 . 3 1.1}

-

^{1 . 4}

H033

TES 3 3

-

^{35 36}

-

⁴³

The &nsity ( s w c i f i c mass) varies w i t h salinity and terrrperature as shokin i n f i g u r e 2.1. It can be calculated by the formula:

= 1000 + ^0.8054s

-

0 . 0 0 6 5

(e -

⁴ + 0.2214s) 2 i n which

P = density in kg/m 3

S = salinity i n pFt (parts p r thousand 2 g / l )

e

⁼ t m p r a t u r e ^(OC)

Other sources o f s z l t can be found i n coastal areas and m u s t be taken i n t o accomt when considering the d i f f e r e n t processes that lead t o fresh water salinization.

W a t e r d e n s i f y g / c r n 3 I O0 I O 1 I O 2

I l I

O 5 10 I 5 20 25 30 35 ( 0

Toial dissolved s o l i d s , p a r t s p e r t h o u s a n d

Fig. 2 . 1

-

Relationship among total. dissolved s o l i & i n water (abscissae), water t m p r a t u r e (ordirates) and water demity (curves).

O l d sea water w i t h d i f f e r e n t degrees G f chenical changes, d i l u t i o n , or concentration, can be found i n sediments, e s p c i a l l y i n l c w p r m e a b i l i t y formatiom (clay and s i l t lenses and s t r a t a ) , confined aquifers and the bottom of coastzl sedirrents presenting a very f l a t surface. The o r i ç i n o f o l d sea water i s not always known i n detail, but can be related t o sea transgressions and regressions ( w e l l studied i n the Netherlands, see Meinardi, 1 9 7 5 ) and entrapped (connate) sea water i n the sedimnts depsiteCi i n estuaries, coastzï lagoons, advancing coasts, etc. ( w e l l known i n the Llcbregat area, see Custo- dio, 1 9 8 1 ) . Chemical reactions w i t h the sediments ( i o n exchange, c a l c i t e and dolomite p r e c i p i t a t i o n and dissolution, intense reducing conditions), d i l u t i o n by fresh water ( d i f f u s i o n and d i s p r s i o n ) , or e v a p r a t i o n while on the surface

(lagoons) lead t o s a l i n i t y and c h m i c a l chançes. ?he complexity of sedimenta- t i o n i n deltas and coastal basins, and the m v m e n t o f pre-water due t o load and compctation gradients, c m p l i c a t e even more the entrappd s a l t water dis- t r i b u t i o n . I n some areas fresh brackish or s a l t water may be under geopres- surized conditions.

Old sea water only mans s a l t water not i n a d i r e c t relationship w i t h present ocean water, and can be as young as a few hundred years old, or older than m y ten thousands o f years, even m y hundred thousand years. For o l d sea water the name ' r e l i c t ' s a l t water was propsed i n the Uppsala 1 9 8 1 SWIM meeting.

m a p r a t i o n from surface water bodies or d i r e c t l y from the ground when the m r e a t i c table i s a t a shallow depth produce saline water, even from fresh continental water without any previous mixing w i t h sea water. It a p p a r s i n very f l a t and l o w l y i n g coastal areas i n dry climates (e.g. the coast north of Mar &l Plata in Argentina).

Since the sea i s the lowest drairage area of many great continental basins, regional f l a w systems w i t h very l o w flow and very long resiilence time can discharge brackish and even s a l t y water near the coast. This s i t u a t i o n i s n o t related t o the sea water salinity and must not be confused w i t h a n oceanic influence.

Other sources of s a l t such as the dissolution of e v a p r i t e deposits They are only s i g n i f i - are less important and only o f very l o c a l importance.

cant in s p x i a l situations, generally localized ones.

2.4 Referenceç

Auphan, E. ( 1 9 7 1 ) . J J o u c t

.

Norois, Vol. 1 8 , No.

71.

near Barcelona (Catalonia, S r i a i n ) . Intruded and R e l i c t Groundwater Custodio, E. ( 1 9 8 1 ) . Sea water encroachnaent i n the JJobreaat and Res& areas,

of Marine Origin. V I 1 S a l t Water I n t r u s i o n Meeting. WIN-81. Upp- sala. Sveriges Geologiska Undersbhing, r e p p r t e r cch reddelanden Custcdio, E., Llamas, M.R. ( 1 9 7 6 ) . Uidrologia P u b t e a (Groundwater

hydrology). Ediciones Omega, Barcelona. 2 vols, 2350 pp.

Luk'yanova, S.A., Kholodiiin, N.A. ( 1 9 7 5 ) . Lenuth o f the shoreune o f the World Ocean and o f v a r w s o f shores and coasts

.

^Soviet

Hydrology: Selected Fâprs. No. 2. Am. Geophysical Union, Wash- ington.

27, pp. 120-152.

d '

Meinardi, C.R. ( 1 9 7 5 ) . Brackish aroundwater bo i e s as a result o f ueoloqical R i j k s i n s t i t u u t voor Drinkwatervoorziening. The Hague. Also in, Symp. on Brackish Water as a factor i n Developrent. Beer-Sheva, Israel.

V and hvdroloaical c m d i t i a

. .

R.I.D. Mededeling 75-1,

Sokolov, A.A. e t al. ( 1 9 7 4 ) . dlx& water -ce

.

Studies and R e p r t s on Hydrology 2 5-Unesco. Paris.

Zekster, I.S., Dzhamalov, R.G. (1981a). G r o G

,

- Unesco. Nature and Resources. v o l . X V I I , 3 , pp. 20-22.

. .

Zekster, I.S., Dzhamalov, R.G. (1981b). Uoundwater W u e t o the Pacific We& Hydrological Sciences B u l l . V o l . 26, No. 3 , September,

1981, pp. 271-279.

3 . Salt-fresh water interrelationships under natural conditions

E

.

Custodio

contents

3 . 0 Introduction

...

^{1 5}

3 . 1 Basic 3 . 1 . 1 3 . 1 . 2 3.1.3 3.1.4 3.1.5 3.1.6 3 . 1 . 7 3 . 1 . 8

concepts

...

^{1 5}

The s a l t groundwater wedge. the interface and the mixing zofie

. .

^{1 5}

The hydrostatic approach: E a b n Ghyben-Berzkrg p r i n c i p l e

....

^{1 6}

Fqplicability and l i m i t a t i o n s

Dynamic freshwater f l o w on a stationary s a l t water wedge

...

^{1 9}

True dynamic e q u i l i b r i u m

...

²⁰

aie d i f f e r e n t i a l equations o f groundwater flcw i n a coastal

...

²²

aquifer

Water heads i n water of variable density

.

Fovement insi2e

....

^{2 5}

the mixing zone

Respnse o f the fresh-salt grounhater body a d the interface

..

^{3 0}

t o water head changes and t i d a l o s c i l l a t i o n s

Unstable situations

...

^{3 8}

3 . 2 Coastal conditions

...

⁴⁰

3 . 2 . 1 Saline wedge penetration

...

⁴⁰

3.2.2 Nonhomogeneity effects

...

⁴²

3.2.3 Anisotropy e f f e c t s

...

⁴³

3 . 2 . 4 Sea bottom conditions

...

⁴³

3.2.5 The thickness o f the mixing zone

...

⁴³

3.2.6 Unstable situations

...

⁴⁷

3.2.7 Sea l e v e l conditions

...

⁵⁰

3.2.8 Water table coastal aquifers

...

^{5 1}

3 . 2 . 9 Confined coastal aquifers

...

^{5 1}

3 . 2 . 1 0 Semiconfined coastal aquifers

...

⁵³

3 . 2 . 1 1 Multilayered coastal aquifers

...

^{5 5}

3.2.12 Natural unsteady situations

...

⁵⁶

3.2.13 Entrappd o l d sea water

...

⁵⁷

3 . 3 Application t o several t y p s o f coastal, areas

...

^{5 8}

3 . 3 . 1 h p o r t w c e o f geologic conditions

...

^{5 8}

3 . 3 . 2 k l t a s and ccastal a l l w i d f o m t i o n s

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3 . 3 . 3 Coastal plains

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3 . 3 . 4 Iiard rccks

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3.3.5 Special situations i n k a r s t i c f o m t i c n s

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3.3.6 L i t t o r a l and s d x x i r i r e sprir.gç

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⁷⁷

3 . 3 . 7 srral1 p r v i c u s islands

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⁸²

3 . 4 Mixed cjround-scrface water conditicns

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⁸⁸

3 . 4 . 1 Effects i n c o a s t d sea water

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3 . 4 . 2 Estizries

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⁸⁸

3 . 4 . 3 Low 1 X : C S

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^~9

3 . 5 F?.eferences

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