Authors:Juan Antonio Lpez-GetaJuan Mara FornsGerardo RamosFermn Villarroya

MINISTERIO DE EDUCACINY CIENCIA

FundacinMarcelino BotnInstituto Geolgicoy Minero de Espaa

A natural underground resource

angmarRectngulo

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarRectngulo

angmarRectngulo

angmarRectngulo

angmarLnea

A natural underground resource

GROUNDWATER

01 a 10 ingls 13/2/06 11:02 Pgina 1

angmarRectngulo

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarRectngulo

angmarRectngulo

angmarRectngulo

AuthorsJuan Antonio Lpez-GetaJuan Mara Forns AzcoitiGerardo Ramos GonzlezFermn Villarroya Gil

This textbook corresponds to the English version of the book jointly published by the Instituto Geolgico y Minero de Espaa (IGME)and Marcelino Botn Foundation, on 2001, titled Las aguas subterrneas. Un recurso natural del subsuelo. This publication includes a newand long chapter about groundwater use in the world. Besides, authors have higtly modified the original structure to obtain a world-wide approach.

The book has been done with the special collaboration of Dr. Jos Javier Cla, valuable in his ideas, designs and treatment of texts comingfrom the different authors. His scientific knowledge and editing industry experience have been crucial for the final quality of this work.

Dr. Jos Manuel Murillo Daz and Dr. Carlos Martnez Navarrete contributed to the following chapters: Conjunctive use of surface waterand groundwater, Artificial recharge, and Wellhead protection areas for groundwater catchments.

The authors thank Dr. Emilio Custodio, Former Director General of the Spanish Geological Survey (IGME) and Professor of the TechnicalUniversity of Catalonia, for his unfailing attention and dedication to the publication of this book. The observations and suggestionsmade on the basis of his long experience were of inestimable help in achieving the desired quality for the contents of this book. We alsoexpress our gratitude to Dr. Ramn Llamas Madurga and Dr. Juan Jos Durn Valsero for checking the manuscript and for their valuablesuggestions. We thank, too, Dr. Jos A. de la Orden Gmez for the reviewing of the translation into English, and all those who gene-rously gave us permission to use the photographs illustrating the text, especially to Dr. Antonio Fernndez Ura, Marc Martnez Parra,Carlos Torres Minondo, Juan Jos Rodes Martnez, Juan I. Rozas, Vicente Fabregat Ventura, Carlos Mediavilla Laso, Diego Martn Sosa,the Provincial Council of Alicante, Crdoba City Hall, Rafael Nuche, Empresa Nacional de Residuos S.A., Aguas de Barcelona, Taylor &Francis Group and NASA.

TranslationGlenn Harding

TypesettingIbersaf Industrial, S. L.

INSTITUTO GEOLGICO Y MINERO DE ESPAA UNITED NATIONS EDUCATIONAL, SCIENTIFIC AND CULTURAL ORGANIZATION (UNESCO) FUNDACIN MARCELINO BOTN Legal deposit: M-8122-2006NIPO: 657-06-011-4ISBN: 84-7840-618-2

Printing and photosettingGrupo Industrial de Artes GrficasIbersaf Industrial, S. L.

01 a 10 ingls 13/2/06 11:29 Pgina 2

angmarRectngulo

angmarLnea

angmarLnea

angmarLnea

angmarRectngulo

angmarRectngulo

angmarRectngulo

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

Beneath its own image it springsand each drop on being bornforestalls the birthof one that nearsthe threshold of its life.

Absent activity becomes calm,tiring of movement,confines its energy in a narrow spaceand patiently awaits the succour of the rope,chorus of innocence.

However often the bucket breaks it,it never empties or depletes;this sweetness comes from somewhereundiminishable,that is, without being, where it always was.

Eternal fresh spring waterthat gathers in my hand in its deep primordial state.Water and rock, theres nothing else: no sky or gaze or light or mouth.

No tread splashes, raising foam,no voices break the calm.Circle of grace! Cold mineshaftof streamless water, silent,without current, banks, or reeds.

Skyscraper, underground well,subterranean dwelling,here the tree, craving water,put down a wayward root, and wedded its lifeto a wound.

Translated from Pozo mo,by Miguel Hernndez (1910-1942)

My wellMy well

01 a 10 ingls 7/2/06 17:08 Pgina 3

angmarRectngulo

angmarLnea

angmarLnea

angmarLnea

angmarRectngulo

angmarRectngulo

angmarRectngulo

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

To preface a book is always a satisfactory task as it permitsunderlining both the topic and content of the subjectedvolume. This satisfaction increases when the book dealswith dissemination of the scientific knowledge on a resour-ce that is critical for Man life and welfare, such as Water is.Moreover, the content of the book can help in a betterunderstanding on the behaviour and characteristics ofgroundwater for developing countries in which water avai-lability is scarce. One may wonder if problems derived fromthe scarcity of water in those countries is a result of real lackof the resource or maybe they came out from technologicalshortage and/or administrative deficiency.

In the last decades, many international meetings havebeen mainly concerned with the necessity of guaranteingbasic endowment of water resources to population. For ins-tance, the Conference of Mar de Plata, in 1977, and theEarth Summit of Ro de Janeiro in 1992 were centered onthis topic.

The integration of all aspects related to water as a resour-ce and social practices arises as a notorious necessity, such

as the former President of the International Council ofScientific Unions (ICSU) clearly addressed during theSymposium on The New Culture of Water held in Madridin 1998.

It is assumed that between 15% and 25% of the worldpopulation has problems to access drinkable water, andabout one-third of the population does not own appropria-te and safe sanitation systems. The Spanish GeologicalSurvey (IGME) is sensitive to this reality and deeply thankUNESCO-IHP the possibility to contribute with the presentbook to the dissemination of the basic knowledge ongroundwater. This is a hidden resource which supplies 50%of the world population, and in addition covers 40% of thetotal demand of water for industries and 20% of the waterrequired for agriculture.

JOS PEDRO CALVO SORANDODirector General of IGME

(Spanish Geological Survey)

4

Presentation

01 a 10 ingls 7/2/06 17:08 Pgina 4

angmarRectngulo

angmarLnea

angmarLnea

angmarLnea

angmarRectngulo

angmarRectngulo

angmarRectngulo

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

5The International Hydrological Programme (IHP) is anevolving programme, ready to adapt to the needs ofan ever changing society. In order to respond promptly andwith appropriate actions, the programme is implemented insix year phases, so as to identify new emerging problems,alert decision makers, raise public awareness and providethe necessary resources.

Today, integrated water resources management posesnot only scientific, but also technical, socio-economic, cul-tural and ethical challenges. IHP is a multidisciplinary pro-gramme at the forefront of research and development; andto this end is a prominent agent in meeting the UnitedNations Millennium Goals.

Since the seventies IHP has focused in particular onhydrogeology and studies related to groundwater resources.

The intention of this monograph is to contribute to abetter understanding of the crucial role played by ground-water resources in the support of both ecosystems andmankind.

A particular emphasis in this book is given to thecurrent challenges on groundwater issues such as the con-

junctive use of surface water and groundwater, the artificialrecharge and the wellhead protection areas for groundwa-ter catchments.

Because of the great importance of the contributionmade by this work to the groundwater knowledge disse-mination, UNESCO-IHP has encouraged its translationinto English. This book represents a splendid example oflearning material and a valuable educational tool ongroundwater, illustrated through a relevant national casestudy.

UNESCO-IHP is aware of the importance of providingessential support to the publication of such monographsand will continue to strengthen this kind of initiative.

We would like to express our deep thanks to all the aut-hors whose valuable contributions appear here.

ANDRAS SZLLSI-NAGYDivision of Water Sciences

United Nations Educational,Scientific and Cultural Organization

01 a 10 ingls 7/2/06 17:08 Pgina 5

angmarRectngulo

angmarLnea

angmarLnea

angmarLnea

angmarRectngulo

angmarRectngulo

angmarRectngulo

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

The phrase may be well worn, but it is still true that thepast fifty years have witnessed spectacular changes bothin the fields of science and technology and in the politicaland social structures of society. These changes have had agreat impact on the use made of underground water resour-ces during this period, an impact which has had many posi-tive aspects and some negative ones.

One of the most evident characteristics of present-daysociety in Spain and in many other countries is that lawsare ineffectual if people, if all those comprising civil society,do not understand and share their motivations and rules.This non-observance, due to a lack of education and infor-mation, is particularly serious with respect to the use ofgroundwater, a situation frequently found in Spain, as wasacknowledged in the White Paper on Water in Spain (LibroBlanco del Agua en Espaa), published in 2000. To justifythe publication of this small book, perhaps it is appropriateto remark that the progressively greater and more intensiveuse of groundwater has occurred over a short period of time(the last three or four decades) and has been carried out basi-cally by hundreds of thousands of individual users, mostlyfarmers of average economic means, and also by severalthousand small or median sized urban centres.

As is well known, crop irrigation makes up about 90% oftotal water consumption in Spain. Available data clearlyshows that irrigation with groundwater is more profitableand provides more jobs than does irrigation with surfacewater. This is true even though the land area irrigated withsurface water is more than twice that irrigated with ground-water, and despite the fact that the annual volume of surfa-ce water used for irrigation is about four or five times grea-ter than that of groundwater used for the same purpose.These figures reveal the notably greater efficiency of irriga-ting with groundwater resources.

Groundwater exploitation financed and put into practi-ce mainly by the users themselves, has been carried outwithout the necessary control on the part of water autho-

rities. These circumstances, together with the understanda-ble lack of hydrogeological training of such small andmedium-scale farmers, has given rise in certain areas tovarious problems, which are described in this book. Theseproblems are contributing to the birth of a certain awarenessthat the management of groundwater cannot continue inthe same way. The Spanish Water Act of 1985 comprised anattempt to rationalise the use of groundwater in Spain but,as recognised in the White Paper on Water in Spain, theimprovements achieved so far have been insufficient.

The law creating a National Hydrologic Plan, which cameinto effect in July 2001, also addressed this issue. Amongother goals, it advocated an intensive campaign of hydrolo-gic education aimed at wide sectors of society. The presentpublication is intended to contribute to this public aware-ness campaign.

A relevant aspect of the present book is that it has beencreated as a result of cooperation between government,represented by the Spanish Geological Survey (IGME), andthe private sector, in this case represented by the MarcelinoBotn Foundation. Preparation of the document was a jointproject carried out by staff of both institutions, who are ack-nowledged on other pages. We also acknowledge and aregrateful for the many hours dedicated by the formerDirector General of the Spanish Geological Survey, who is arenowned hydrogeologist, to reading and checking thevarious drafts preceding the finished work.

For the staff of the Marcelino Botn Foundation it hasbeen a gratifying experience to collaborate with the expertsof the Spanish Geological Survey. What is most important,however, is that we are convinced this book will be of greathelp in achieving a better management of the hidden trea-sure beneath our feet, the groundwater of Spain.

M. RAMN LLAMASDirector of the Groundwater Projectof the Marcelino Botn Foundation

7

01 a 10 ingls 13/2/06 11:05 Pgina 7

angmarRectngulo

angmarLnea

angmarLnea

angmarLnea

angmarRectngulo

angmarRectngulo

angmarRectngulo

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

The phrase may be well worn, but it is still true that thepast fifty years have witnessed spectacular changes bothin the fields of science and technology and in the politicaland social structures of society. These changes have had agreat impact on the use made of underground water resour-ces during this period, an impact which has had many posi-tive aspects and some negative ones.

One of the most evident characteristics of present-daysociety in Spain and in many other countries is that lawsare ineffectual if people, if all those comprising civil society,do not understand and share their motivations and rules.This non-observance, due to a lack of education and infor-mation, is particularly serious with respect to the use ofgroundwater, a situation frequently found in Spain, as wasacknowledged in the White Paper on Water in Spain (LibroBlanco del Agua en Espaa), published in 2000. To justifythe publication of this small book, perhaps it is appropriateto remark that the progressively greater and more intensiveuse of groundwater has occurred over a short period of time(the last three or four decades) and has been carried out basi-cally by hundreds of thousands of individual users, mostlyfarmers of average economic means, and also by severalthousand small or median sized urban centres.

As is well known, crop irrigation makes up about 90% oftotal water consumption in Spain. Available data clearlyshows that irrigation with groundwater is more profitableand provides more jobs than does irrigation with surfacewater. This is true even though the land area irrigated withsurface water is more than twice that irrigated with ground-water, and despite the fact that the annual volume of surfa-ce water used for irrigation is about four or five times grea-ter than that of groundwater used for the same purpose.These figures reveal the notably greater efficiency of irriga-ting with groundwater resources.

Groundwater exploitation financed and put into practi-ce mainly by the users themselves, has been carried outwithout the necessary control on the part of water autho-

rities. These circumstances, together with the understanda-ble lack of hydrogeological training of such small andmedium-scale farmers, has given rise in certain areas tovarious problems, which are described in this book. Theseproblems are contributing to the birth of a certain awarenessthat the management of groundwater cannot continue inthe same way. The Spanish Water Act of 1985 comprised anattempt to rationalise the use of groundwater in Spain but,as recognised in the White Paper on Water in Spain, theimprovements achieved so far have been insufficient.

The law creating a National Hydrologic Plan, which cameinto effect in July 2001, also addressed this issue. Amongother goals, it advocated an intensive campaign of hydrolo-gic education aimed at wide sectors of society. The presentpublication is intended to contribute to this public aware-ness campaign.

A relevant aspect of the present book is that it has beencreated as a result of cooperation between government,represented by the Spanish Geological Survey (IGME), andthe private sector, in this case represented by the MarcelinoBotn Foundation. Preparation of the document was a jointproject carried out by staff of both institutions, who are ack-nowledged on other pages. We also acknowledge and aregrateful for the many hours dedicated by the DirectorGeneral of the Spanish Geological Survey, who is a renow-ned hydrogeologist, to reading and checking the variousdrafts preceding the finished work.

For the staff of the Marcelino Botn Foundation it hasbeen a gratifying experience to collaborate with the expertsof the Spanish Geological Survey. What is most important,however, is that we are convinced this book will be of greathelp in achieving a better management of the hidden trea-sure beneath our feet, the groundwater of Spain.

M. RAMN LLAMASDirector of the Groundwater Projectof the Marcelino Botn Foundation

7

01 a 10 ingls 7/2/06 17:08 Pgina 7

angmarRectngulo

angmarLnea

angmarLnea

angmarLnea

angmarRectngulo

angmarRectngulo

angmarRectngulo

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

IndexPage

INTRODUCTION................................................................................................................................. 11THE WATER CYCLE ........................................................................................................................... 13WHAT IS GROUNDWATER? .............................................................................................................. 16WHAT IS AN AQUIFER? ..................................................................................................................... 19NATURAL COMPOSITION OF GROUNDWATER ............................................................................. 25HOW IS GROUNDWATER EXTRACTED? ......................................................................................... 29CONJUNCTIVE USE OF SURFACE WATER AND GROUNDWATER ............................................... 34ARTIFICIAL RECHARGE .................................................................................................................... 37WELLHEAD PROTECTION AREAS FOR GROUNDWATER CATCHMENTS................................... 41GROUNDWATER USER COOPERATIVES.......................................................................................... 44ECONOMIC VALUE OF GROUNDWATER ........................................................................................ 45ENVIRONMENTAL ASPECTS OF GROUNDWATER ......................................................................... 47DROUGHT ........................................................................................................................................... 53GROUNDWATER MONITORING NETWORKS ................................................................................. 54MAIN PROBLEMS AFFECTING GROUNDWATER............................................................................ 56

Intensive use of groundwater .................................................................................................... 56Contamination of aquifers ........................................................................................................ 59

GROUNDWATER IN THE WORLD ................................................................................................... 67Water and People ....................................................................................................................... 67Th policies .................................................................... 68G .................................................................................. 70

GROUN .................................................................................. 79Aq .................................................................................. 79G .................................................................................. 80Pu .................................................................................. 82

01 a 10 ingls 7/2/06 17:08 Pgina 9e development of international waterroundwater ............................................DWATER IN SPAIN..............................uifers and hydrogeological units.........

roundwater reserves and resources .......blic administration of water ................9

angmarRectngulo

angmarLnea

angmarLnea

angmarLnea

angmarRectngulo

angmarRectngulo

angmarRectngulo

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

10

Registry and Catalogue of water exploitations ......................................................................... 83Uses of groundwater .................................................................................................................. 85

THE FUTURE FOR GROUNDWATER................................................................................................. 90THEMATIC CARDS ............................................................................................................................. 95RECOMMENDED READINGS ................................................................................................................... 105INFORMATION OF INTEREST .................................................................................................................. 107

01 a 10 ingls 7/2/06 17:08 Pgina 10

angmarRectngulo

angmarLnea

angmarLnea

angmarLnea

angmarRectngulo

angmarRectngulo

angmarRectngulo

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

Numerous primitive civilizations were founded on siteswhere groundwater was available. In fact, many place-names incorporate words such as bir in Arabic, well in English,and pozo, fuente, hontanar, fontanar in Spanish.

Since prehistoric times, man has made use of the groundwa-ter surging from natural springs. At first, this water was only

taken for drinking, but asthe centuries passed, it wasapplied to other activities,such as agriculture andindustry, that were incor-porated into daily life andwhich required water. Thustoday in Spain, groundwa-ter is used to supply a thirdof the population (somethirteen million people), aswell as a significant propor-tion of the 60 million tou-rists who visit Spain each

year. One fact that demonstrates the importance of groundwaterin this country is that in 70% of urban centres, drinking water isobtained from wells, boreholes or springs.

Numerous primitive civilizations were foundedon sites where groundwater was available

An annual volume of 5500-6500 Mm3 of water is extracted fromaquifers in Spain. Of this amount, an average of 4800 Mm3 is dedi-cated to crop irrigation, with the rest required for urban and indus-trial use. Of the 3.5 million hectares of land currently irrigated inSpain, almost a third depend mainly on groundwater sources. Thevalue of the agricultural production of the 942,000 hectares irriga-ted with groundwater exceeds, in general, that of the 2,263,000hectares irrigated with surface water.

For many, little or nothing is known about where groundwa-ter comes from, which has given rise to myths and misunderstan-dings. Nevertheless, groundwater comprises an irreplaceable resourcefor large areas of the planet, a resource that is essential for publichealth and for economic progress. A good many people add tothe simple fact that the water is located below the surface of theearth, a whole package of properties more suited to superstition:it has been attributed with fabulous curative powers, for exam-ple. A halo of mystery surrounds everything concerning ground-water, to such an extreme that, even today, in order to find thesewaters, people resort to the geomantic art of the water-diviner*.This represents the darker side of the reality of hydrogeology,which is a science and a technique based on straightforward prin-ciples of physics and chemistry, which can be evaluated inmathematical and economic terms.

Introduction

11

11 a 33 ingls 13/2/06 11:07 Pgina 11

angmarRectngulo

angmarLnea

angmarLnea

angmarLnea

angmarRectngulo

angmarRectngulo

angmarRectngulo

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

Introduction

Enormous conurbations such as Mexico City,Lima, Dakar and Jakarta are supplied bygroundwater, as are countries like Denmark,Holland, Hungary, Italy, Barbados, Malta andCosta Rica, which depend almost entirely ongroundwater to meet their demands. In the USA,half the water supplied for urban use is ground-water, while in France and Great Britain morethan a third is obtained from aquifers.

It is often the case that the concept of water isrelated to the names of cities. Thus, the placena-me Madrid is derived from the Arab word mayrit,which in turn seems to have come from the Latinmatrix aquae (waters mother), which was appliedto describe what now is known as viajes de agua(water trips): galleries that drained and channe-lled groundwater to public fountains. Possibly,without this wealth of underground water, PhilipII would not have transferred the capital of hiskingdom to Madrid (Spain).

These scientific truths, together withthe development of drilling and extractiontechniques (the invention of the turbinepump) laid the foundations for the extra-ordinary expansion of hydrogeology, espe-cially since the mid-twentieth century.

WATER DIVINER: person said to have thepower to locate underground water byusing a wooden fork or pendulum, whichreveals the existence of effluvia supposedto be caused by the flow of water bene-ath the earth. However, there is no scien-tific evidence to support this notion.

For centuries,groundwater has beenused for economicadvantage

Ancient means of extracting water by means of an animal-powered water-wheel

12

11 a 33 ingls 7/2/06 17:12 Pgina 12

angmarRectngulo

angmarLnea

angmarLnea

angmarLnea

angmarRectngulo

angmarRectngulo

angmarRectngulo

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

zone* (groundwater runoff*). When the intensity of the precipita-tion exceeds the infiltration capacity of the soil, surface runoffoccurs. This, in conjunction with subsurface runoff comprises totalrunoff*, which then flows to the rivers and finally into lakes orinto the sea.

Water cycle refers to the constant movement of water, on theEarths surface, above it and below it. Understanding thiscycle is fundamental for the correct use and management of waterresources.

Water in the oceans, seas, lakes, rivers and reservoirs evapora-tes, and at a greater rate as the temperature rises and the air beco-mes drier. Vegetation also contributes to evaporation, by themechanism of transpiration. Water vapour rises into the atmosp-here and charges the air with humidity. When the water vapourcools it condenses into minute particles that form clouds andmist. The water returns to the Earths surface and to the oceansas precipitation (rain, snow, hail, dew or frost). Not all the preci-pitation reaches the Earths surface, as part of it evaporatesduring its descent and part is intercepted by plants or by the sur-faces of buildings, roads, etc., and is soon returned to the atmos-phere as water vapour.

Of the liquid water that reaches the ground, part is retained inpuddles or small undulations. Most of this returns directly to theatmosphere. Another part flows over the surface (direct surfacerunoff* and subsurface runoff or inflow*) and is concentrated intorivulets which then come together to form streams that later flowinto rivers. At the same time, part of the precipitation infiltratesinto the ground, depending on the soil type and humidity and onthe intensity and duration of the precipitation. The infiltrated*water first soaks into the soil and then slowly percolates* throughthe unsaturated* zone, producing the recharge* of the saturated

The water cycle

13

Zone avouring evaporation. Laguna de Caada del Hoyo,

province of Cuenca (Spain)

11 a 33 ingls 13/2/06 11:08 Pgina 13

angmarRectngulo

angmarLnea

angmarLnea

angmarLnea

angmarRectngulo

angmarRectngulo

angmarRectngulo

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

The water cycle

DIRECT SURFACE RUNOFF: the part deri-ved from the rain water that flows over theland surface into streams, rivers and otherbodies of water.

GROUNDWATER RUNOFF: the part of theinfiltrated water that recharges the satura-ted zone and flows through aquifers.

INFILTRATION: the quantity of precipitatedwater that penetrates the land surface andoccupies, partially or totally, the pores, fis-sures and gaps in the soil.

Mm3:equivalent to a million cubic metres orto a thousand million litres.

and flows through the upper part of thesoil without reaching the saturatedzone, subsequently reappearing on thesurface and rejoining the direct surfacerunoff.

TOTAL RUNOFF: the fraction of the precipi-tation that falls into a water basin, escapesevapotranspiration and flows both on andunder the surface.

UNSATURATED ZONE: The land lying bet-ween the land surface and the saturatedzone. In this sector the pores are occupiedby air and water.

PERCOLATION: the movement of wateror other liquids through the intersticesof the soil. Usually applied to the ver-tical flow through an unsaturatedmedium.

RECHARGE: The part of the infiltratedwater that reaches the saturated zone.

SATURATED ZONE: The layer of the landbeneath a certain depth where watertotally occupies the gaps between thesolid particles.

SUBSURFACE RUNOFF OR INFLOW: thepart of the precipitation that infiltrates

The different phases of the water cycle: evaporation of sea water, its transport in clouds, precipitation (as rain or snow), runoff into streams andrivers, recharge of aquifers, evapotranspiration, outlet to the sea and the cycle begins again

14

11 a 33 ingls 7/2/06 17:12 Pgina 14

angmarRectngulo

angmarLnea

angmarLnea

angmarLnea

angmarRectngulo

angmarRectngulo

angmarRectngulo

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

ESTIMATE OF THE DISTRIBUTION OF WATER IN THE HIDROSPHERE1

Volume (Mm3 x 106) % of the total water % of total Averageon the planet fresh water residence time

Oceans and seas.......... 1 338 000 97.5 2500 yearsGlaciers and polaricecaps......................... 24 064 1.74 68.7 9700 yearsFresh groundwater...... 10 530 0.76 30.1 tens of thousands of yearsFreshwater lakes.......... 91.0 0.007 0.26 17 yearsSaltwater lakes ............ 85.4 0.006 150 yearsRivers........................... 2.12 0.0002 0.006 15-20 daysBiomass ....................... 1.12 0.0001 0.003 a few hoursAtmosphere................. 12.9 0.001 0.04 8-10 days

How the water cycle is affected by mans actions: atmospheric pollution, contamination of rivers and reduction in the volume of water they carry,falling piezometric levels and entry of sea water into aquifers (red arrow)

1 Shiklomanov, I. A. (1997). Comprehensive assessment of the freshwater resources of the World. World Meteorological Organization

15

11 a 33 ingls 7/2/06 17:12 Pgina 15

angmarRectngulo

angmarLnea

angmarLnea

angmarLnea

angmarRectngulo

angmarRectngulo

angmarRectngulo

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

Groundwater comprises all the water below the land surfa-ce, and specifically, the water lying beneath the phreaticlevel*, completely filling all the pores and fissures in the ground.This water flows naturally out to the surface through springs,seepage areas and water courses, or directly into the sea. It canalso be channelled, artificially, into wells, galleries or other typesof catchments. Thanks to natural recharge, groundwater isconstantly renewed. This recharge is mainly derived from pre-

cipitation, but it can also be caused by surface runoff or comefrom surface water courses (particularly in arid climates), fromnearby aquifers or from use-returns (notably the irrigationreturns).

Groundwater passes through aquifers very slowly. Its normalvelocity ranges from less than a metre to a few hundred metresper year; only in the case of karstic aquifers* and severely frac-

Recharge and discharge areas, flow lines and the residence time of water in an aquifer from when it reaches the saturated zone until it emerges at the surface. This time variesaccording to the route taken (the times shown are merely indicative)

What is groundwater?

N

PHREATIC LEVEL: the upper boundary ofthe saturated zone in an unconfined aqui-fer. It is the geometric location of thepoints of an unconfined aquifer that are atatmospheric pressure. Its height withinthe unconfined aquifer is determined bythe altitude of the undisturbed water in ashallow well.

16

11 a 33 ingls 7/2/06 17:12 Pgina 16

angmarRectngulo

angmarLnea

angmarLnea

angmarLnea

angmarRectngulo

angmarRectngulo

angmarRectngulo

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

KARST: morphological term derived froma region of Slovenia, where the occurren-ce was first identified. It refers to landsca-pes, environments and processes that de-velop via a complex series of physical andchemical phenomena in which an essen-tial feature is the dissolution of rock bywater. Such phenomena are frequent invarious types of rocks, including gypsum,limestone, dolomites, detritic rocks con-solidated with clasts*, or soluble cement.However, carbonate rocks provide the re-ference model, because of the complexityof the process and the wide range offorms created. These rocks, therefore,best define a karstic landscape. Whenkarstification occurs there is continual in-teraction between surface water andgroundwater. The process develops through selective action on the weaknessplanes of the rock, on fractures and onstratification surfaces. Thus a group ofexokarstic and endokarstic forms arecreated, notable among which are sinkho-les and caves, thus determining the flowof water underground.

CLAST: rock fragment, of mineral or fossilorigin. May be loose or embedded withina rock. These fragments are classified bysize, from larger to smaller, as follows:blocks, pebbles, sand, silt and clay.

tured rocks may preferential conduits exist,through which the water can travel at speedssimilar to those of surface currents. Thus, adrop of water that falls onto a watershed loca-ted 200 km from the coast and that is incor-porated into a river current would take a fewdays to enter the sea. If the same drop, howe-ver, travelled underground (through a detriticaquifer), it would take hundreds or even thou-sands of years to reach the sea.

This slow movement by water throughthe unsaturated and saturated zones helps usmanage, exploit and protect groundwater.

In the latter case, itmeans we can actbefore a contamina-ting agent has time tospread through thewhole aquifer.

A significant pro-portion of what wecall surface water ori-ginates from ground-water. Groundwater isderived from rechargeand, after passingthrough the aquifers,

it may flow into rivers or out to the land sur-face through seepage areas, springs and areasof diffuse discharge.

Groundwater moves

very slowly through

detritic aquifers;

its average speed can

range from a few metres

to several hundred

metres per year.

In karstic aquifers,

it can travel at speeds

similar to those found

in surface currents

Natural outlet of groundwater in a karstic terrain

17

11 a 33 ingls 7/2/06 17:12 Pgina 17

angmarRectngulo

angmarLnea

angmarLnea

angmarLnea

angmarRectngulo

angmarRectngulo

angmarRectngulo

angmarLnea

angmarLnea

angmarLnea

angmarNotaAccepted definida por angmar

angmarNotaNone definida por angmar

angmarLnea

angmarLnea

angmarLnea

angmarLnea

Unsaturated zone: here, the porescontain air and water. The wateris subject to capillary tension thatholds it against the ground andwhich makes its effective pressureless than atmospheric pressure.

The zone comprises three sectors:

a) The soil subzone (or edaphiclayer), from the ground surface tothe depth of plant roots. This layer iscriss-crossed by roots, by the spacesleft by roots that have disappearedand by trails and tunnels opened byanimals (fast ones like mice andmoles, or slow ones like earth-worms). Here, the soil humidityvaries greatly, depending on the sea-sonal changes that affect vegetation.

b) The intermediate subzone,which varies in thickness conside-rably from one aquifer to another(from just a few centimetres to tensof metres) or which may not existat all. In this subzone, there ishardly any seasonal variation insoil humidity.

c) The capillary strip, characterisedby the existence of water-filled pores,channels and fissures that are main-tained above the phreatic level bycapillary tension. The finer the par-ticles and fissures, the greater is theheight of this subzone.

Saturated zone: here, the pores are completelywater-filled; the water pressure exceeds that of

the atmosphere and increases hydrostaticallywith greater depth. The water in this zone movesnaturally towards springs, rivers, lakes or the

sea, and can be channelled artificially towardsunderground extraction sites, by means such aspumping, draining and galleries.

What is groundwater?

Aquifer zones

18

11 a 33 ingls 7/2/06 17:13 Pgina 18

angmarRectngulo

angmarLnea

angmarLnea

angmarLnea

angmarRectngulo

angmarRectngulo

angmarRectngulo

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

Aquifers can be classified as follows:A) Depending on the hydrostatic pressure* of the water they con-

tain:

Free, unconfined or phreatic aquifer: defined as anaquifer in which the top of the water mass forms a real surfa-ce that is in contact with the air of the unsaturated zone and,therefore, is at atmospheric pressure. When a well is drilleddown from the land surface, water appears in it when the phrea-tic level is penetrated or reached (from the Greek phreatos =well) and remains at this depth. Recharge of this type of aqui-fer is mainly achieved by precipitation through the soil or bythe infiltration of water from rivers and lakes.

Confined or artesian aquifer: at the upper limit or roof*of this aquifer, the water pressure is higher than that of theatmosphere. This is typical when permeable materials are cove-red by a confining layer that is much less permeable (e.g. asandy layer lying beneath a layer of clay). If a well is drilled intoan aquifer of this type, when it penetrates the roof the waterlevel quickly rises until it stabilizes at a certain level. Water sur-ges from the well when the piezometric level* is above theheight of the well mouth. This phenomenon used to be calledartesianism, but nowadays this term tends to be no longer used.

An aquifer is a geological formation capable of storing andtransmitting water in significant quantities, such that thewater can be extracted by catchment systems. Its dimensions canvary greatly, from a few hectares* in surface area to thousands ofsquare kilometres, while the depth can range from several metresto hundreds or thousands of metres.

When these formations transmit water very slowly, and thewater is difficult to extract in any significant quantity by mechani-cal means, they are called aquitards. Nevertheless, the latter are capa-

ble of interchanging considerablevolumes of water with aquifersthat are in horizontal contact,as the interchange surface isvery large.

We use the term aquicludeto describe a geological for-mation that contains waterbut does not transmit it, andtherefore from which it can-not be extracted. When theaquifer contains no water atall, it is called an aquifuge. Inpractice, there do not existany geological formationsthat can, strictly spea-king, betermed aquifuges.

What is an aquifer?

The term aquifer

is used to describe

a geological formation

that is capable of

storing and

transmitting

groundwater in

significant quantities,

such that it can

be extracted by

catchment

works

19

11 a 33 ingls 7/2/06 17:13 Pgina 19

angmarRectngulo

angmarLnea

angmarLnea

angmarLnea

angmarRectngulo

angmarRectngulo

angmarRectngulo

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

The recharge of a con-fined aquifer is mainlycaused by rainfall infil-trating directly throughthe zone where the aqui-fer formation crops out,that is, where it behavesas an unconfined aquifer.Alternatively, it mayoccur where the aquiferis semi-confined andwhere conditions arefavourable.

Semi-confined aquifer:this may be considered a specialcase of confined aquifer, in whichthe floor*, the roof, or both, are nottotally impermeable, but allow thevertical movement of water. This verti-cal passage of water can occur towards oraway from the aquitard, and may even vary in time, depen-ding on the relative values of the piezometric levels.

B) Depending on the type of materials making up the aquifer

Unconsolidated deposits of loose materials: thesegeological formations are formed by the accumulation ofparticles that are transported by gravity, wind or ice; in lake-side or marine settings. They are usually comprised of sandsand gravels of varying geological origin: fluvial deposits aremade up of the alluvial materials of rivers and their terraces;

deltaic deposits accumulate at river mouths. In general, suchdeposits are recent, in geological terms. They are often verysuitable for exploitation and considerable volumes of watercan be extracted, given the appropriate means. Such is thecase of the Tertiary detritic aquifer that supplies Madrid andof the marshland of the Almonte-Marisma aquifer (in theprovinces of Huelva and Sevilla), the site of the DoanaNational Park (Spain).

What is an aquifer?

20

Types of aquifers depending on their behaviour

11 a 33 ingls 7/2/06 17:13 Pgina 20

angmarRectngulo

angmarLnea

angmarLnea

angmarLnea

angmarRectngulo

angmarRectngulo

angmarRectngulo

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

tone rocks. We must remember that if these rocks are notkarstified, then they are relatively impermeable. In Spain,there are many aquifers of this type, some of the best knownbeing the aquifers of Campo de Montiel (the site of the lakesknown as Lagunas de Ruidera), those of the western part ofLa Mancha (including the Tablas de Daimiel wetlands) andthe carbonate aquifer of Sierra de Cazorla. In fact, most ofthe aquifers in the Mediterranean area of the peninsula, aswell as those of the Balearic Islands, are of this type, made upof karstified limestones and dolostones. Sandstones (conso-lidated sands) and calcarenites (sandstones comprising car-

Consolidated sedimentary rocks: these are sedimentsthat have become consolidated by compaction or diagenesisprocesses. They are classified, according to their origin) asdetritic (conglomerates, sandstones, clays), chemical (limes-tones, dolostones, marls) and organic (carbons and naturalhydrocarbons). The most important of these are the limes-tones and dolostones. They vary considerably in density,porosity and permeability, depending on the sedimentationenvironment surrounding their formation and the subse-quent development of permeable zones caused by the disso-lution of carbonate materials, especially in the case of limes-

Detritic aquifer Fissured aquifer Karstic aquifer

21

11 a 33 ingls 7/2/06 17:13 Pgina 21

angmarRectngulo

angmarLnea

angmarLnea

angmarLnea

angmarRectngulo

angmarRectngulo

angmarRectngulo

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

changes in the structure of the rock itself, thus adjusting tonew pressure and temperature conditions and possible chemi-cal inputs (eg slates, schists, etc). The possibilities of an aquiferforming among such rocks are limited to the altered surfacezone or to areas fractured by faults and diaclases*, which ena-ble an appreciable degree of water circulation. This type ofaquifer is common in the NE of the Iberian peninsula and inSistema Central. It comprises an important source of water forsmall villages and for rural demand.

It is hard to define the hydrogeologic behaviour of volca-nic rocks, as they may or may not constitute aquifers. Theirbehaviour pattern is between that of porous consolidated andfractured rocks. The levels of scoria, pyroclasts and retraction

fissures play a sig-nificant role. Themain factors influe-ncing the flow ofgroundwater arethe composition,the age and, aboveall, the degree ofalteration. Theseaquifers are foundin practically allthe Canary Islands.

bonate grains) also constitute important aquifers, for exam-ple the calcarenites that outcrop near Carmona (province ofSevilla, Spain) or the Cretaceous sandstones known as faciesUtrillas. Consolidated sedimentary rocks contain abut 75% ofall the groundwater in peninsular Spain.

Igneous and metamorphic rocks: igneous rocks are for-med by the cooling and consolidation of magma. They can beextrusive (volcanic) or intrusive (plutonic), depending onwhether they consolidate on the surface or within the Earthscrust, respectively (eg granites, gabbros, etc).

Metamorphic rocks are those that have undergone pro-found physical and chemical transformations, giving rise to

What is an aquifer?

Types of aquifersdetermined by thehydrostatic pressureof the water theycontain

22

11 a 33 ingls 7/2/06 17:13 Pgina 22

angmarRectngulo

angmarLnea

angmarLnea

angmarLnea

angmarRectngulo

angmarRectngulo

angmarRectngulo

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

lie over the regional saturated zone. The groundwater in thesehanging aquifers both discharges towards the underlying regio-nal saturated zone and gives rise to small springs or to bogs.

The movement of groundwater within geological formationsis governed by two relatively simple physical laws: Darcys Law*and the Law of Conservation of Mass. The following three mag-nitudes are especially relevant in the corresponding equations:the permeability* or hydraulic conductivity, the porosity* andthe storage coefficient*.

In the presence of lenticles, or discontinuous low-permeabi-lity layers in the unsaturated zone, perched aquifers may someti-mes form. These layers retain part of the recharge for a certainperiod, and produce relatively widespread saturated zones that

DARCYS LAW: expresses the proportionalitybetween the specific flow volume (q) of aliquid travelling through a porous medium andthe hydraulic gradient (i)* q = k i It is onlyvalid when the flow is laminar.The speume (q)is the flow per section unit of the medium.The coefficient of proportionality k is calledthe permeability or hydraulic conductivity.

DIACLASE: a fracture in a rock with norelative displacement of any of its faces.

HECTARE: unit of surface area used in agro-nomy and equivalent to 10,000 m2.

HYDRAULIC GRADIENT: the variation in thepiezometric level per unit of movement inthe groundwater flow direction.

HYDROSTATIC PRESSURE: the pressureexerted by an undisturbed column of water.

PERMEABILITY: also termed hydraulic con-ductivity.This is a measure of the ease withwhich an aquifer transmits water.The mag-nitudes that determine permeability may be

intrinsic or extrinsic.The former are thoserelating to the aquifer itself and depend onthe size of the pores (all else being equal,the larger the particle size, the greater thepermeability of a medium). Extrinsic magni-tudes depend on the fluid, particularly itsviscosity and specific weight. The values ofboth these are temperature dependent.Permeability may be primary or secondary,according to whe-ther it is produced at themoment when the solid medium is formedor afterwards, caused by fractures, by mete-orisation of the rock or of the soil, or bydissolution of the rocks. The transmissi-vity is calculated as the product of thehorizontal permeability and the saturatedthickness of the aquifer.

PIEZOMETRIC LEVEL: the height of the columnof water necessary to produce a pressureequal to that of the aquifer at a certain point,calculated for a given altitude. It representsthe energy per unit of weight of water.

POROSITY: the storage capacity of anaquifer is determined by its porosity. Thisis defined as the ratio between the volu-me of spaces (occupied by air and water)and the total volume of the rock. Primaryporosity is created during the formationof the rock, while secondary porosityoccurs after the rocks formation, due tofracturing, meteorisation, dissolution ope-nings or crevices provoked by plant oranimal action. Primary porosity is influen-

23

11 a 33 ingls 7/2/06 17:13 Pgina 23

angmarRectngulo

angmarLnea

angmarLnea

angmarLnea

angmarRectngulo

angmarRectngulo

angmarRectngulo

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

What is an aquifer?

ced by the shape, degree of selection andconcentration of the clasts, while secondaryporosity depends on the distribution andnumber of fractures opened and on thedegree of alteration. Drainable porosity (alsoknown as efficient porosity) only takes intoaccount the quantity of water that a rock orsaturated soil liberates due to the effects ofgravity.The difference between total and drai-nable porosity is the specific retention of

water, which in agronomy is termed the fieldcapacity.

ROOF AND FLOOR: In a geological formation,the terms roof and floor, refer to the top andbottom, respectively, of a stratigraphic series,layer or seam.

STORAGE COEFFICIENT: water that can bereleased by the vertical prism of an aquifer with

a cross section equal to that of the unit andwith a height equivalent to the saturated thick-ness of the unit, when a unit fall in the piezo-metric level occurs. This value is unidimensio-nal. In unconfined aquifers, its value coincideswith that of the drainable porosity. In confinedaquifers, the value is related to the compressi-bility of the water and of the aquiferousmedium, a value that usually ranges between10-5 and 10-3.

Left, panoramic view of the outlet of the Almonte-Marismas aquifer (Spain), in the vicinity of Asperillo (Mazagn-Matalascaas), showing the drainagefront that extends along the cliff face. Right, enlargement of the circled area, where the drainage front is clearly reflected in the profusion of ferns

24

11 a 33 ingls 7/2/06 17:13 Pgina 24

angmarRectngulo

angmarLnea

angmarLnea

angmarLnea

angmarRectngulo

angmarRectngulo

angmarRectngulo

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

Water is a universal solvent, capable of dissolving a greatmany substances contained in the ground through whichit flows. Groundwater has more opportunities to dissolve mate-rials than does surface water, due to its prolonged contact withthe geological formations that is passing through, to the presen-ce of carbon dioxide and oxygen dissolved in the water and tothe slow velocity at which it moves. For these reasons, ground-water normally presents a greater ion concentration than doessurface runoff of the same origin (Card 1).

The natural chemical composition of groundwater resultsfrom the following processes: a) the evaporation and concentra-tion of atmospheric salts, incorporated in the form of a marineaerosol*, or as dust and salts dissolved in rainwater; b) the inter-action of water with minerals in the soil, whether by hydrolysisor by a state change via oxidation-reduction; c) the incorporationof residual saline waters (relicts), as yet unwashed.

The natural composition of groundwater can be affected bynatural causes or by anthropogenic factors*. The former causesinclude the climate, the temperature, the type of terrain

through which the groundwater flows, its residence time wi-thin the aquifer and the supply of reactive gases, mainly CO

2

and O2.

With respect to anthropogenic factors, human activity canaffect the chemical composition of the infiltrating water andthe recharge, (sometimes intensely so), by modifying its tem-perature, introducing solutes (salts, nitrates, etc.) and varioussubstances (such as hydrocarbons, pesticides and halogenisedsolvents) into the land and the water. Their presence may leadto a significant degradation of the natural characteristics ofthe water.

Moreover, the environment can be modified by other fac-tors, such as chemical precipitation, ion interchange (mainly ofcations) and reduction-oxidation reactions. These processesmay be intense when one body of water is displaced by anotherwith a different chemical composition (good examples of thisare found in coastal aquifers, in the mixing zone between fresh,inland water and salt seawater) or when the ground containsorganic matter.

Natural composition of ggrroouunnddwwaatteerr

25

11 a 33 ingls 7/2/06 17:13 Pgina 25

angmarRectngulo

angmarLnea

angmarLnea

angmarLnea

angmarRectngulo

angmarRectngulo

angmarRectngulo

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

Natural composition ofggrroouunnddwwaatteerr

An example of the evolution of the natural composition of groundwater within an aquifer: the recharge water containing CO2

of edaphic origin (from thesoil), dissolves the carbonate rock, which hardens the water and transforms it into a calcium bicarbonate type. In this initial stage, the water stillcontains sufficient oxygen dissolved to be able to oxidize both the organic matter in the medium and the metals in a reduced state, such as Fe (II),that it encounters. Most of the water discharges through the main spring and a minor proportion through the confined area, via the semi-confining roof.In the case illustrated, there is not sufficient potential for submarine discharge to occur, and a large part of the confined aquifer contains almostimmobile salt water. Further inland, this gives way to fresh water, via a large intermediate mixing area where the degree of salinity is variable. In thearea marked as A, all the available oxygen may have been consumed and the presence of organic matter may cause the reduction of sulphates and thesubsequent appearance of sulphides (SH- and SH

2) and/or the reduction of the Fe (III) in the medium to the soluble ion Fe++, with sometimes very

complicated structures; there could also be an increase in alkalinity and the possible precipitation of metallic sulphides. If the land previously containedsalt water, there would be a cationic exchange which would decrease the hardness of the water and make it evolve towards a sodium bicarbonate type.In the sector marked B, there is a mixing of fresh and salt water, presumably of a reductive nature, and cationic exchanges that depend on whetherthe salinity is increasing (water hardening and precipitation of carbonates)or decreasing (water softening, increase in Na+ and the possible dissolution ofcarbonates). In sector C, the composition of the water is close to that of the sea water, although it is only renewed very slowly (and thus is old) and ispresumably of a reductive nature (absence of SO4

=, presence of SH- and SH2, and perhaps that of CH

4, Fe++ and, sometimes, NH4

+).

AEROSOL: suspension of very fine, solid or liquid particles in a gas, normally air.

ANTHROPOGENIC FACTORS: processes, actions, materials and forms resulting from human activity. In this sense, man is considered a geological agent likeany other, with the capability to provoke phenomena that change the configuration of the geosphere.All resource-extraction activities, their commercia-lisation and use, civil engineering projects and agricultural activities are considered actions parallel to those of erosion, transport and sedimentation.Theyare all capable of transforming the landscape and its geological components.

EVAPORITIC MATERIALS: sedimentary rocks formed by the evaporation of water and, therefore, with components that are easily soluble.The main eva-poritic rocks are gypsum, anhydrite and common salt or halite.

26

11 a 33 ingls 13/2/06 11:09 Pgina 26

angmarRectngulo

angmarLnea

angmarLnea

angmarLnea

angmarRectngulo

angmarRectngulo

angmarRectngulo

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

Human activity can affect the chemical composition of thewater that recharges the aquifers, sometimes intensely or to aconsiderable degree, modifying the temperature and introdu-

cing solutes that may lead to a degradation of the natural cha-racteristics of the groundwater and of the land.

Example of amap based on

an anthropogeniccontamination

study: nitratecontents in an

area to the southof Madrid (Spain),

represented byisolines. The inset

map shows thesame situation butwith colour zones,so that the areasof highest nitrate

content are shownin deep red.

27

11 a 33 ingls 13/2/06 11:09 Pgina 27

angmarRectngulo

angmarLnea

angmarLnea

angmarLnea

angmarRectngulo

angmarRectngulo

angmarRectngulo

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

Natural composition ofggrroouunnddwwaatteerr

with a predominance of chloride and sodium, largely due to the ari-dity of the climate. In the central parts of the high-altitude islands(they can reach great heights), salinity is low. Emissions of carbon dio-xide of volcanic origin sometimes give rise to the occurrence of waterthat either has low pH or is highly mineralised, of sodium or magne-sium bicarbonate type.

The existence of evaporitic materials* in the land is associatedwith a high content of sulphates, chlorides and sodium in the water.These circumstances occur quite frequently in some parts of Spain,although they tend to be very localised.

The groundwater in carbonate aquifers is mainly of magnesium andcalcium bicarbonate type. It is mineralised to a slight or modera-te degree, with an electrical conductivity of 700 S/cm and concen-trations of principal ions that rarely exceed those permissible for thewater to be fit for human consumption. In Spain, this type of water ismainly found in aquifers in the Norte basin, in the northern part ofthe Duero valley and on the borders of Sierra del Guadarrama, in theTajo basin. It is also present in some aquifers in the Alto Guadiana,

Guadalquivir, Sur, Jcar andEbro basins and in the inlandbasins of Catalua.

Detritic aquifers are cha-racterised by a low level ofmineralisation and by the varia-bility of the chemical composi-tion of their waters.They maycontain both calcium and mag-nesium bicarbonate facies andthose of calcium and sodiumsulphates and chlorides.Examples of these in Spaininclude the detritic basins ofthe Duero and the Tajo, the lit-toral plains of the Levante

region and the alluvial aquifers of the Guadiana and the Guadalquivirbasins.The chemical quality is usually acceptable for all uses, although itmay sometimes present macroconstituent contents that exceed permis-sible limits for drinking water.

The composition of the groundwater in the Canary Island archi-pelago varies widely. In coastal areas, the water is highly mineralised,

Human activity can

affect the chemical

composition of the

groundwater, modifying

the temperature and,

what is more important,

introducing substances

both in the water and

in the land that may

lead to a degradation

of the natural

characteristics

28

11 a 33 ingls 7/2/06 17:14 Pgina 28

angmarRectngulo

angmarLnea

angmarLnea

angmarLnea

angmarRectngulo

angmarRectngulo

angmarRectngulo

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

wells have been excavated, with or without deep galleries andlateral drains to favour the acquisition of groundwater.Many towns and cities were founded where springs surgedfrom the ground or on alluvial plains where wells could

easily be dug. The appearance of the steam engine and the deve-lopment of pumps capable of raising water from great depths,together with technical advances in drilling machinery and techno-logy, enabled the drilling of numerous boreholes and wells duringthe nineteenth century and even more so in the twentieth.

The oldest ways of using groundwater were to take it directlyfrom springs or fountains, or to carry out pick-and-shovel work bydigging wells and constructing horizontal galleries. In general,wells had a circular cross-section, with a diameter of one to twometres, and were only a few metres deep. The equipment consistedof a pulley or an animal-powered system (for example, the waterwheels to be found all over the flatlands of La Mancha, in Spain)or a wind-powered mechanism (such as the windmills around thecity of Palma de Mallorca). Today, these manual means of creatingwells have been replaced by modern drilling machinery.

The ancient civilisations of the East constructed systems ofgalleries to channel water to where it was needed; a similar sys-tem supplied Madrid from the times of the muslims until themid nineteenth century, while Barcelona, too, had an extensi-ve, and very old, network of galleries. Similar arrangementshave existed in many parts of eastern Spain and in the Balearic Islands. In the Canary Islands archipelago it is verycommon to make use of groundwater by means of long, deepgalleries that drain volcanic formations. In many other areas,

How is groundwater extracted?

Drilling a well using the rotation system with recirculation of mud and slurry

29

11 a 33 ingls 7/2/06 17:14 Pgina 29

angmarRectngulo

angmarLnea

angmarLnea

angmarLnea

angmarRectngulo

angmarRectngulo

angmarRectngulo

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

Modern wells require sophisticated technology with appro-priate technical design, together with detailed knowledgeof the aquifer. Nevertheless, the importance of high quality welldesign and construction is frequently underestimated. The life-time of a well and the efficiency of its functioning dependdirectly on the quality of the materials employed and on that ofthe technology utilised. Some of the problems ascribed togroundwater supply sources are, in fact, often due to defectiveconstruction and/or maintenance of the well, and not to theaquifer. Nowdays, highly advanced technology is available anddrilling a well has become a civil engineering project that requi-res good design, management, maintenance and observation.

The drilling methods most often used today are percussion,rotation and roto-percussion.

Percussion drilling consists of repeatedly striking the rockwith a trepan* until the rock is pulverised. It can then be raisedto the surface surface by means of a tool called bailer andextracted. This system has been used to drill wells in all sorts ofgeological materials, although, depending on the type of rock,drilling may be more or less difficult. This method is particularlysuitable for drilling into consolidated aquifers (marbles, limesto-nes, dolostones and cemented sandstones, among others).However, many wells in unconsolidated formations made up ofgravels have also been constructed by this system; drilling resultslargely depend on the experience of the drill operator.

Rotation drilling consists of breaking up the rock bymeans of a cutting bit normally fitted with a giratory head thatbreaks through the rock. The rock fragments are extracted bypressure with water or mud. Two methods may be employed:

How is groundwatereexxttrraacctteedd??

A hydrogeological boreholeand its components

30

11 a 33 ingls 7/2/06 17:15 Pgina 30

angmarRectngulo

angmarLnea

angmarLnea

angmarLnea

angmarRectngulo

angmarRectngulo

angmarRectngulo

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

pressed air into the shaft. The simplicity, speed of executionand economy of this method (sometimes to the detriment ofconstruction quality and design) mean it is often used for othertypes of geological materials, too. This technique only allowsoperators to obtain an approximate description of the litholo-gical column that is being drilled into. Currently, the system iscombined with that of rotation.

direct or inverse circulation of the fluid. Rotation drilling iswidely used to create wells in unconsolidated ground, such asarkose, sandstone, silt and gravel.

For hard terrain such as quartzite, granite and slate, themixed method of roto-percussion, using a rotating percussorhead, is employed. The detritus* is extracted by injecting com-

Main drillingmethods andtechnology

31

11 a 33 ingls 7/2/06 17:15 Pgina 31

angmarRectngulo

angmarLnea

angmarLnea

angmarLnea

angmarRectngulo

angmarRectngulo

angmarRectngulo

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

Water extraction boreholes in Spain normally have a dia-meter of 300-500 mm and a depth of up to 300 m, althoughwith current technology, 1000 m or more may be reached.Filters are used when water must be passed through boreholessited over detritic aquifers. These filters can be of variousdesigns and materials (normally they are made of metal orPVC), and the filter mesh is sized depending on the granulo-metry of the detritic materials through which the boreholemust pass. The ring between the walls of the borehole and themain shaft is filled with siliceous gravel calibrated, amongother functions, to prevent the passage of small-grained parti-cles into the borehole.

Before the well is finished, it must be cleaned and stimula-ted. This is done by mechanical means (pistons or compressedair) or with chemical methods (dry ice, polyphosphates, acidsor ice) or by both. These techniques are used to clean off anyresidues that may have remained within the drill tube, such asthe silt within the mass of gravel, and to increase the efficiencyof the well by removing the silt from the first twenty or thirtycentimetres of the geological formation penetrated by the drill.

When constructing a well, it is very important that aWorks Manager should be present to ensure thework plan-ned and con-tracted isc o r r e c t l ycarried out.The correctdesign of anextractionsystem (well,

borehole, etc.) is a fundamental question indetermining its duration, or useful life, andwater output, without raising unwanted parti-cles from the geological formation. An opti-mum design maximises output and minimi-ses running costs. The project plan for aborehole should include the following:selecting the drilling method; determiningthe estimated depth to be reached, accor-ding to the prior hydrogeological survey;deciding upon the diameter of the drilland the main shaft; locating which sec-tions of tubing need to be equipped withfilter slots and meshes and which will beblind-tubed (with no slots); identifyingthe zones or sections that must be iso-lated, due to the presence of poor-qua-lity water or of materials with a high

percentage of fine sands andclayey silts suspended in thewater, etc. The project shouldalso include measures to pro-tect the well, such as thetipping (the cemented rein-

forcement) and sealing ofthe first few metres

and closures, wherenecessary to prevent

the undesirable mixing of water.When the well does not achieve the desired

objectives and the decision is made to abandon it, it must besealed (with cement or other products) to avoid the possiblecontamination of the aquifer and to prevent accidents.

How is groundwatereexxttrraacctteedd??

Developing a borehole with dryice or solid carbonic anhydrid

32

11 a 33 ingls 7/2/06 17:15 Pgina 32

angmarRectngulo

angmarLnea

angmarLnea

angmarLnea

angmarRectngulo

angmarRectngulo

angmarRectngulo

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

DETRITUS OR DEBRIS: the remains of asolid mass after it has disintegrated intoparticles due to the action of the cuttingelement of drilling machinery.

TREPAN: cutting instrument used in per-cussion. It consists of an extremely heavycomponent with cutting edges, that carriesout the task of breaking, disintegrating andcrushing the rock.

Portable pumping equipment used to determine the optimum water flow

extractable from a well (Ondara, provinceof Alicante, Spain)

Operator of well drilling machinery

33

11 a 33 ingls 7/2/06 17:15 Pgina 33

angmarRectngulo

angmarLnea

angmarLnea

angmarLnea

angmarRectngulo

angmarRectngulo

angmarRectngulo

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

greater guarantee when extraction from aquifers is incorporatedinto the supply system. The extra element provides a higher degreeof overall security.

In conjunctive use, groundwater is used when and whererecommended by water management strategies, but the basic prin-ciple is to use surface supplies in wet years and groundwater sour-ces in dry years.

In some conjunctive use schemes, the complementaritysought involves not just obtaining a greater quantity of wateror of improving the reliability of supply, but also of obtainingbetter water quality by mixing the two sources of water, surfa-ce and underground. This is done either at source, by means ofartificial recharge, or during delivery, using deposits andcanals.

The schemes set up in Spain correspond more to local expe-diency than to prior planning. These programmes have beenmainly promoted and established by the private initiative of users,both at the individual level and at that of communities and orga-nisations. Nevertheless, government bodies have subsequentlycollaborated with actions to improve the more or less spontaneousoriginal systems.

In many cases, the exclusive use either of surface water or ofgroundwater does not meet the objective of fully satisfying thedemands created by different uses, especially for urban areas, forcrop irrigation and for industry. Nor does it always sufficiently res-pect the water-related environments.

A conjunctive use system can contribute to improving or tofully satisfying a particular demand situation for water, throughthe coordinated use of surface and groundwater resources.

Such a system makes use of the complementary hydrologic fea-tures of surface reservoirs and of aquifers. The former are largeenough to retain the volume of runoff that may be caused in extre-me, short-term meteorological situations, while aquifers providelong-term storage of a volume of water that can be tens or evenhundreds of times greater than that of the average recharge.

The proportions in which the waters from one or the other sour-ce are combined vary depending on the current state of the annualwater cycle, on the reserves available in the surface storage systemand in the aquifers, and on the quality of the water stored in each.

By these means, it is normally possible to make use of a greaterquantity of surface water, as the exploitation of reservoirs enjoys

Conjunctive use of surface wateraanndd ggrroouunnddwwaatteerr

34

34 a 43 ingls 7/2/06 17:21 Pgina 34

angmarRectngulo

angmarLnea

angmarLnea

angmarLnea

angmarRectngulo

angmarRectngulo

angmarRectngulo

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

T he most significant programmes carried out in the fieldof conjunctive use have probably been those involvingMadrid and Barcelona, in Spain. Water supplies for the city ofMadrid and for most of its region are based on fifteen reser-voirs that store and regulate the surface water derived fromSierra de Guadarrama and Sierra de Somosierra, in conjunc-tion with about 120 wells. Annual demand for water is

approximately 600 Mm3. The strategy employed to satisfythis demand is based on extracting water from the aquiferduring dry years, to complement that stored in the reser-voirs. During years when rainfall is normal or abundant, sur-face resources are used almost exclusively. In such periods,then, water levels within the Tertiary detritic aquifer ofMadrid are allowed to recover.

A system of conjunctive use of surface water and groundwater, comprising a surface reservoir and two aquifers, one of which is located upstreamfrom the surface reservoir. The diagram also shows the different areas of water demand (urban, industrial and irrigation). Depending on theavailability of water in the reservoir, a certain level of demand is met either from surface reserves, or jointly with groundwater, or exclusivelyby the latter. This system can be complemented with artificial recharge operations so that river water may be stored in the aquifer

35

34 a 43 ingls 7/2/06 17:21 Pgina 35

angmarRectngulo

angmarLnea

angmarLnea

angmarLnea

angmarRectngulo

angmarRectngulo

angmarRectngulo

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

The system that is most widely used in Spain, and whichhas been most extensively developed, is that of Llobregat(province of Barcelona). This system has evolved throughvarious stages since the early twentieth century when watersupply to Barcelona and nearby towns was improved by theincorporation of groundwater sources. The successive cons-truction of the reservoirs of Sant Pon and La Baells on theriver Llobregat, the scarifying of the river bed, the extensionto Barcelona of the Ter transfer, the construction of theAbrera-Martorell radial wells and the artificial recharge ofthe connection zone between Valle Bajo and the Delta, allhave varied the relative importance of surface water andgroundwater in this conjunctive use scheme. A more recentinitiative is the addition of the management of the aquiferbeneath the river Bess.

Barcelonas water supply system, which has historicallyprevented the need for water restrictions, is an example ofhow the integration of surface water and groundwater is nota utopia but a reality that has been tried and tested. On theother hand, some cities that normally rely exclusively onsurface water supplies to meet demand have suffered restric-tions during periods of drought.

Other activities to integrate surface water and groundwa-ter into an overall management system have been developedin areas like the Guadalentn valley, the Sagunto plain, theriver Palancia, Marina Baja and the Adra delta, amongothers. The best known scheme, with an extensive biblio-graphy, is the exploitation system established for the aquiferon the Castelln plain and the rivers and reservoirs withwhich it is related.

Main diagram: Conjunctive use of surface water and groundwater in the system supplying Madrid managed by the Canal de Isabel II company (Spain)

Smaller inset: Extraction well site. Larger inset: El Atazar reservoir (Spain)

Conjunctive use of surface wateraanndd ggrroouunnddwwaatteerr

36

34 a 43 ingls 7/2/06 17:21 Pgina 36

angmarRectngulo

angmarLnea

angmarLnea

angmarLnea

angmarRectngulo

angmarRectngulo

angmarRectngulo

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

This technique, as part of a programmed intervention, enableswater to be introduced into an aquifer, either directly or indu-ced. By these means, the volume of water available is increased, asis the reliability of supply and the guarantee of water quality.

Artificial recharge is used, when it is technically and economi-cally justified, to achieve a more rational management of waterresources within a particular river basin or exploitation system.

From the operational view-point, the technique presents acertain degree of complexity,especially compared with thesimplicity of the technology thathas been applied to date in pro-ject planning and hydrogeologi-cal applications. The program-ming of interventions based onartificial recharge should be limi-ted, fundamentally, to the follo-wing areas: where water resour-ces are relatively unregulatedand where demand is high; areasof well developed and highlyproductive agricultural activity;areas where the profitability ofwater is high; areas (especially

coastal areas) where it is not possible to construct conventionalregulation structures because of topographic difficulties.

The most frequently used applications of artificial rechargeare:

Underground storage of unregulated surface runoff. Reduction or elimination of falls in piezometric levels. Support for conjunctive water-use plans.

Artificial recharge

is defined as a body

of techniques that

via a programmed

intervention enable

water to be

introduced directly

or induced into

an aquifer,

thus increasing

the reliability and

availability of water

resources and

guaranteeing water

quality standards Operation to scarify the bed of the river Llobregat (province of Barcelona,Spain) to enable the river flow to recharge the aquifer

Artificial recharge

37

34 a 43 ingls 7/2/06 17:22 Pgina 37

angmarRectngulo

angmarLnea

angmarLnea

angmarLnea

angmarRectngulo

angmarRectngulo

angmarRectngulo

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

zone, as a filtration or treatmenttechnique both for drinking waterand for waste waters.

A necessary condition for planning andconstructing any type of artificial rechargeoperation is the availability of sufficientwater resources, in the form of continuous ordiscontinuous surface streams, or of treatedurban waste water, or of water derived fromanother aquifer, among other possibilities.

Maintenance of water resources inareas of special ecological and envi-ronmental importance.

Reduction of transport, storage andpumping costs.

Corrective action against problems ofland subsidence.

Reduction or correction of problems ofseawater intrusion.

Exploitation of soil properties and thecharacteristics of the unsaturated

Artificial recharge of an aquifer using two different systems: the first favours the infiltration of river water by the constructionof dikes on the river bed to slow the river flow. The second system uses decantation and infiltration ponds constructed on the leftbank of the river

The goal of artificial

recharge is to contribute,

when it is technically and

economically justified, to

achieving a more rational

management of

water resources within a

particular river basin or

exploitation system

Artificial recharge

38

34 a 43 ingls 7/2/06 17:22 Pgina 38

angmarRectngulo

angmarLnea

angmarLnea

angmarLnea

angmarRectngulo

angmarRectngulo

angmarRectngulo

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

Recharge by retention dikes. Top left, system of dikes to retain the waterfor subsequent aquifer recharge. Bottom left, pilot construction on ariver bed

Recharge by infiltration ponds. Top right, diagram of operation insta-llation. Bottom right, pilot construction in an alluvial valley

SOME EXAMPLES OF SURFACE-TYPE ARTIFICIAL RECHARGE INSTALLATIONS

River bed

39

34 a 43 ingls 13/2/06 11:11 Pgina 39

angmarRectngulo

angmarLnea

angmarLnea

angmarLnea

angmarRectngulo

angmarRectngulo

angmarRectngulo

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

Artificial recharge

The USA is the country that has most developed andapplied the technique of artificial recharge. These opera-tions are mainly located in the arid southern states of Texas,Arizona and California. The importance of such projects isreflected, for example, in the fact that in California alone theDepartment of Water Resources has carried out artificialrecharge operations to introduce 1400 Mm3/year into aquifers.

Israel is another country where artificial recharge techni-ques are highly advanced. Recharge water is obtained from theriver Jordan, from Lake Kinneret (Sea of Galilee), from spora-dic runoff after heavy rain and from treated waste water.

In the European Union, Germany and Holland are thecountries that have carried out most artificial recharge opera-tions. In these countries, the main objective of the activity isto purify and improve water for urban consumption by soil-aquifer treatment, although in Holland it is also necessary tomaintain the height of fresh water within coastal dune sys-tems, in order to limit seawater intrusion.

The first artificial recharge installations in Spain were cons-tructed near Barcelona, in the alluvial valleys of the riversBess and Llobregat. In some years, up to 20 Mm3 have beenintroduced into the latter aquifer by means of wells sited in thevalley, using surplus water from the treatment plant in theriver Sant Joan Desp. This recharge operation is complemen-ted by scarifying treatment of the river bed upstream to favourthe infiltration of the flowing water. Other pilot experiments,set up on a temporary basis, have provided valuable data aboutthe technique. Examples of these include those of the Palmade Mallorca plain, the alluvial valley of the river Oja, theGuadix plain, the Esgueva valley, the calcarenite aquifer ofCarmona and the alluvial valley of the Bajo Guadalquivir.

Many and varied procedures have been used to put artificialrecharge into effect, although the classical techniques can be divi-ded into two main groups of methods, depending on whether therecharge is carried out by filtration through the land surface or bydirect introduction of the water into the aquifer by drilling a con-nection. The first-named method is used for unconfined aquifers,while the second is particularly suitable for semi-confined andconfined aquifers.

In areas that are intensively farmed or densely populated,where land is scarce and/or very expensive, surface artificialrecharge can be difficult to put into practice, because it generallyrequires the availability of large areas of land. In such cases, deep-level recharge is used, using boreholes. These are also employed forgeological formations where permeable and impermeable levelsalternate, or where there is an impermeable horizon between theland surface and the aquifer.

Pilot deep-level recharge plant in the Esgueva valley(province of Valladolid, Spain)

40

34 a 43 ingls 7/2/06 17:22 Pgina 40

angmarRectngulo

angmarLnea

angmarLnea

angmarLnea

angmarRectngulo

angmarRectngulo

angmarRectngulo

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

angmarLnea

Immediate or absolutely restricted zone: the definition criterionfor this zone is a water transit time* of 24 hours or a small, arbi-trarily determined area (100-400 m2). Within this zone, all acti-vities not directly related to water extraction are usually prohi-bited. A boundary fence preventing access to the area is recom-mended.

Proximal or maximum restriction zone: the limits of this zoneare generally fixed according to a water transit time of 50-60days, to provide a measure of protection against microbiologicalcontamination.

Distant or moderate restriction zone: the most appropriate parame-ter to decide the limits of this zone is that the period of water tran-sit should be several years; complementary hydrogeological criteriashould also be considered, to protect the well from long-lived con-taminating agents.Moreover, Spanish legislation contains variousprotection procedures: zones have been established to protect waterand the environment, to prevent contamination of what is termedthe Public Water Domain, to protect areas of special ecologic, lands-cape, cultural or economic interest, to reduce or eliminate over-exploitation and to guarantee the conservation of wetlands.

When protection planning is considered for a particularregion, it is a good way to do to establish wellhead protection

T he establishment of wellhead protection areas is intended tosafeguard the quality and quantity of groundwater obtainedfrom urban supply wells. They are of crucial importance becau-se of the risk posed by human activity in the vicinity of suchextraction points.

The wellhead protection area delimits an area around thewell in which graduated controls restrict or prohibit activities orinstallations that might contaminate groundwater or that couldaffect the flow of water intended for human supply.

Wellhead protection areas to protect groundwater and safe-guard drinking water supplies must at the same time be com-patible with the socio-economic activity in the area surroun-ding the well.

The protection system most commonly applied consists of divi-ding the area around the well into different zones, graduated fromhighest to lowest risk and importance, and on this basis determinethe restrictions applicable to other activities.

To delimit these zones, detailed knowledge is required of theaquifer over which the well is sited, and of the latters designand characteristics. To protect the quality of groundwater, threezones are normally considered:

Wellhead protection areas forggrroouunnd