issn 0534-8293 · dams&theworld’swater 7 parts of the world. many of these dams are still in...

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NOTICE - DISCLAIMER:The information, analyses and conclusions in this document have no legal force and must not be considered as substituting for legally-enforceable official regulations. They are intended for the use of experienced professionals who are alone aquipped to judge their perti-nence and applicability and to apply accurately the recommendations to any particular case.This document has been drafted with the greatest care but, in view of the pace of change in science and technology, we cannot gua-rantee that it covers all aspects of the topics discussed.We decline all responsibility whatsoever for how the information herein is interpreted and used and will accept no liability for any lossor damage arising therefrom.Do not read on unless you accept this disclaimer without reservation.

The International Commission On Large Dams (ICOLD)was founded in Paris in 1928.

It is currently comprised of 88 countries and 10,000 individual members:Engineering Companies, Consultants, Builders, Development companies, Scientists,Researchers, Engineers, University Professors, Governments, Financial Institutions,Associations..

ICOLD is the world’s leading professional organization in the field of dams,advancing the technology of dam engineering and supporting the socially andenvironmentally responsible development and management of water resourcesto meet the worldwide demand.

ICOLD is a forum for the exchange of knowledge and experience in dam engineering.With an annual meeting in a different country each year and a Congress everythree years, it has built up nearly one century of knowledge.

This permanent search for progress is organized through 24 Technical Committeesand 500 experts on specific themes. ICOLD also promotes public awareness of thebeneficial role of dams in the sustainable development and management of theworld’s water resources.

ICOLD leads the profession in setting standards and guidelines to ensure thatdams are built safely and economically, and in an environmentall and sociallysustainable manner.

About ICOLDAbout ICOLD

3Dams&theWorld’sWater

Pre

face

During the coming century, water will continue to be a vitalresource for human civilization. An adequate and safe water supply is anessential component to our health, environment, communities and economy.But two major factors will increase the stakes: the incoming climatechange, making the water resources more irregular, with drying trendsnecessitating more water storage; and the world population growth,increasing the demand for domestic, agricultural and industrial waterwith emphasis on irrigation for food production. Therefore, the crucialrole dams played throughout human history will continue during the21st century.

ICOLD has played, since its inception in 1928, a key role in the spreadingof knowledge about dams and water. For a long time now, ICOLD is notonly open to engineers but also to the public. It is therefore natural forICOLD to explain to the younger generation what kind of challenges theywill face in the management of the world’s water. This booklet gives, in asimplified but rigorous way, the basic facts on the beneficial role of dams:

for water storage and management, food production, electricity generationand flood protection. It also delivers the essential facts about the world’s

water, its distribution and its cycle.

We are confident that this message will be useful to the generationthat will have the responsibility to lead human civilization to the 22nd century.

And we hope that they will use it efficiently to build their own future.

Mr Michel de VIVOSecretary General, ICOLD

Mr Art WALZ Vice President, ICOLD

Chairman of Committee on PublicAwareness and Education

Prof. Luis BERGAPresident, ICOLD

4 Dams&theWorld’sWater

1 Introduction . . . . . . . . p.6

2 The World’s Water . . . . . . . . . . . . p.8

3 How We Get Water - The World’s Water Cycle . . . . . p.11

4 Distribution of the World’s Water . . . p.13

4.1 Water-stressed and water-scarce countries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .p.13

4.2 Water for sanitation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .p.14

4.3 Integrated water management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .p.15

5World Population Data . . . . . . . . p.15

6Water Requirements . . . . . . . . . . . . . . . . . . . p.16

6.1 Domestic water requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .p.16

6.2 Combined domestic, agricultural and industrial water requirements . . . . . . . . . . . . . .p.16

7What is a Dam? . . . . . . . p.17

8 History of Dams in the World . . . . . . . . . . . p.17

9 Requirements, Purpose, Types,Features and Construction of a Dam . . . . . . . . . . . . . . . . . . p.19

9.1 Requirements of a dam . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .p.19

9.2 Purpose of a dam . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .p.19

9.3 Types of dams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .p.19

9.4 Features of a dam . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .p.22

9.5 Selection of the site and type of dam . . . . . . . . . . . . . . . . . . .p.24

9.6 Construction of a dam . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .p.24

10Dams of Today . . . . . . . . . . . . . . . . . . . . p.2810.1 The purpose of the current dams of today . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .p.29

Table

of Cont

ents

?

11 The Benefits we Receive from Dams . . . . . . . . . . . . . p.30

11.1 Water supply for domestic and industrial use . . . . . . . . . . . . . . . . . . . . . . .p.30

11.2 Meeting the agricultural demand for food supply . . . . . . . . . . . . . . . .p.32

11.3 Flood control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .p.33

11.4 Hydropower . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .p.34

11.5 Inland navigation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .p.36

11.6 Recreation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .p.36

11.7 Integrated water management in the river basin . . . . . . . . . . . . . . . . .p.36

11.8 Summary of benefits. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .p.38

12 Dams and the Environment . . . . . . . . . . . . p.42

12.1 Environmental conservation and enhancement . . . . . . . . . . . . . . . . . . . . . . . . . . . . .p.42

13 Looking to the Future - Dams of the 21st Century . . . . p.45

13.1 Planning process for a dam and reservoir project . . . . . . . . . . . . . . . . . . . . .p.45

13.1.1 Public involvement and coordination . . . . . . . . . . . . . . . . . . . . . . . . .p.46

13.2 Socio-economic issues associated with a dam

and reservoir project . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .p.47

13.3 Increased need of integrated water management

in the watershed or river basin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .p.47

13.3.1 Need for real time water management in the watershed or river basin . . . . . .p.49

13.4 Irrigation in the future . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .p.49

13.5 Hydropower in the future . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .p.50

13.6 Flood control in the future . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .p.52

13.7 Inland navigation in the future . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .p.53

13.8 The balance between project benefits and the environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .p.54

13.9 The need for public awareness and education on water resources . . . . . . . . . . . . . . . . . . . . . . . . . .p.56

14 The Role of ICOLD and the World’s Water . . . . . . p.57

15 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . p.58

Glossary of Terms . . . . . . . . . . . . . . . . . . . . . . . . . . . . p.60



Wateris the vital resource to sup-port all forms of life on earth. It is essentialfor the well-being of our civilization and isthe essential element for growth and develop-ment as well as the basic requirement for thehealth of the world’s environment. To assistthe readers in understanding some of theterms used in this book, a glossary of termshas been included as Appendix A.

In this book you will learn that there is afixed amount of water on the earth. Of thisfixed amount, only a small portion is freshand available for human consumption, irriga-tion of crops and industrial use. You will alsosee that we receive a fixed amount of precipita-tion or rainfall and only a small portionfalls on our landmass. A significant portion ofthis ends up as runoff to our streams andrivers and then into the oceans. This leaves asmall amount of rainfall for human use andinfiltration into the ground to replenish ourgroundwater, which highlights the need tocollect, store and manage water in reservoirs.

You will also see that this rainfall is not evenlydistributed by season or location, and sincethere is an imbalance between availabilityand demand, careful management is essen-tial. You will see the summary of the worldpopulation and the anticipated growth rate.Note that most of this growth in populationwill occur in the less developed countries -where the need for water is the greatest andthe current supply is limited. It is importantto recognize that careless use and contamina-tion of the water that is available is wide-spread. In some regions of the world, life isthreatened by the imbalance between thedemands and available supplies of water,food and energy.

You will see that throughout the history ofthe world, dams and reservoirs have beensuccessfully constructed across rivers tocollect and store vast amounts of water andthen manage releases to make daily riverflows to support civilization. For more than4000 years,civilization has used dams to providethe necessary water to sustain life in all

Introduction

Serre-PonçonDam - France amultiple purpose

dam

©2

(see

p.6

4)


parts of the world. Many of these dams arestill in operation today.

The demand for water as a resultof the expanding world popula-tion and economic growthhas increased the need tobuild dams for storing largeamounts of water. Today,dams and reservoirs continueto serve the same purposesof meeting the social andeconomic needs throughoutthe world and at the sametime are compatible withthe natural environment ofeach region. You will see thefull range of benefits that wereceive from dam and reservoirprojects - water supply, irrigation,flood control, hydropower, inland naviga-tion and recreation.

Introduction

1

Civilizationneeds water in

adequate quantitiesand quality to sustain

life and to supportgrowth and

development

The earthembankment of adam in Santa FeUnited States


This section explains where and inwhat form the world’s water exists and thenhow we get water - “the water cycle”. It mayseem surprising to most people that only2.5% of the water in the world is fresh water(located in glaciers, groundwater and ourlakes and rivers) and is available for thepeople and nations of the world.

Most of the world’s water is located in theoceans, the permanent snow and ice,glaciers of the Artic and Antarctic, rivers,lakes and groundwater. The actual distribu-tion of the world’s water is shown on thefollowing diagram.

Oceanscontain 97.5%of the water in

the world

The World’s WaterThe worldcontains a

large amountof water

© 3 (see p.64)

©4

(see

p.6

4)


A major portion of the world’s fresh water(68.9%) is in the form of glaciersand permanent snow cover inthe Artic and Antarctic regionsof the world. However, onlysmall portions becomeavailable each year.

Groundwater is a source ofusable fresh water. Its sourceis the rain, snow, sleet, and hailthat infiltrate or soak into theground.The water moves down intothe ground because of gravity, passingbetween particles of soil, sand, gravel, or rockuntil it reaches a depth where the ground is

filled, or saturated, with water. The areathat is filled with water is called the

saturated zone and the top ofthis zone is called the water

table (see diagram below).The water table may beclose to the ground's surfaceor it may be hundreds ofmeters below the surface.

Groundwater is a reliablesource in rural areas of the

world. Most of the groundwateris clean, but groundwater canbecome polluted,or contaminated.It is important that we protect it

from contamination.

The World’s Water

2

A typicalglacier in

NorthAmerica

It is importantto understand

where the 2.5%fresh water is

located

Groundwaterflows downhillto our riversand streams


To obtain groundwater, wells are installed towithdraw water for domestic, agriculturaland industrial use. This withdrawal must bemanaged so we do not lower the water tableand deplete it at some locations by heavy overpumping (from the center well).

It is essential to manage withdrawals ofgroundwater with respect to recharge orreplenishment to ensure that the localgroundwater is not depleted over time.

Over-pumping of groundwater will lower thewater table. This often requires pumpingwater from ever greater depth. Over time,this could lead to depletion of the groundwaterat that location. At present, over-pumping isknown to be occurring in parts of SaudiArabia, Israel, South Africa, India and thewestern parts of the United States. In theseareas of the world it is necessary to managewithdrawal of the groundwater and augmentit with reservoirs.

Today a large portion of the world’s popula-tion obtains its water from groundwater. Incomparison with surface water storage, suchas lakes, groundwater has the advantage thatit is often available locally and does notrequire transportation. In addition, invest-ments in developing groundwater resourcescan be made on an "as needed" basis. Sincegroundwater exists naturally, the locationand amount cannot be changed or expanded.In the arid regions of the world, groundwateris too scarce to provide adequate quantities.In and around Riyadh in Saudi Arabia, forexample, the groundwater is mined from adepth of 1200-1800 meters.During the develop-ment of the city of Phoenix, Arizona in theUSA, mined groundwater was relied on to thepoint of exhaustion. To meet today’s needs;

water from the Colorado River has beenpiped across the desert.

In section three, we will see that of all therain on the world, 19% of this rain falls on ourlandmass. Once the rain is on the land it caneither be absorbed into the ground, or it runsoff into streams and rivers to our oceans. Theamount of rainfall that is absorbed is thesource to recharge or replenish our ground-water. For open vegetated land with nodevelopment, absorption is the greatest - upto 75% of the rainfall. In areas with pavedparking lots and other development, runoff isthe greatest - about 75% of the rain fall. Inconclusion, it is important to realize that asdevelopment occurs, runoff is increased andabsorption decreases.

Theresult of heavy

pumping from thecenter well on the

water tableProduces a cone

of depression


Our lakes and rivers contain thesmallest portion of our freshwater. As it rains, some of thewater in these lakes flow intoour streams and rivers andthen the ocean.

Because of the relati-vely small amount offreshwater available

for consumption, it isessential that we manage

it and do not pollute orcontaminate our natu-ral lakes and rivers.This requires wastewater treatment plantsand managed landfill

sites for waste disposal.

The World’s Water

2

Water exists on earth as a solid (ice), liquid (water in the oceans, lakes and rivers) oras a gas (water vapor). The oceans, rivers, clouds and rain, all of which contain water, are in afrequent state of change (surface water evaporates, cloud water precipitates, rainfall infiltratesthe ground, etc.). However, it is important to understand that the total amount of the earth'swater does not change.The circulation and conservation of earth's water is called the "water cycle".

How we Get Water“The World’sWater Cycle”

... and inour rivers

Lessthan 1 % ofthe world’s

water supply isin our lakes...

©5

(see

p.6

4)

This World Water Cycle or Hydrologic Cycle asit is sometimes known refers to cycles theearth's finite and valuable water supply. Inother words, the water keeps getting usedover and over again. The sun’s energy in theform of light and heat causes water to evapo-rate from oceans, rivers, lakes and evenpuddles. Evaporation means the water turnsfrom a liquid to a gas, or vapor. Warm aircurrents rising from the earth's surface liftthis water vapor up into the atmosphere.

When the air currents reach the cooler layersof the atmosphere, the water vapor condensesaround and clings on to fine particles in theair. This step is called condensation. Whenenough vapor attaches itself to tiny pieces ofdust, pollen or pollutants, it forms a cloud. Asthe air absorbs more moisture, the dropletswhich form the clouds grow larger and larger.Eventually they will get so big that theswirling atmospheric winds can no longerhold them up. The droplets then fall from thesky as precipitation. This precipitation can bein the form of rain, snow, sleet or hail,depending on other atmospheric conditionssuch as temperature.

When precipitation reaches the ground,several things can happen to it. Much ofthe water will become run-off that goesinto streams and rivers as it flows back tothe ocean. Some of the precipitation willbe absorbed into the ground. This is calledinfiltration. Once in the ground, the watercan join the earth's ground water supply.Ground water is one of the world's largestsources of water. Unfortunately, it is notevenly located around the world. Thussome areas of the world have limitedaccess or no access at all to groundwater.

From the water cycle diagram above, it isimportant to understand that of the totalprecipitation or rainfall (577,000 km3)falling on the earth 79% falls on the ocean,19% on land and 2% on our lakes. Thismeans that only 110,000 km3 or 19% of ourrainfall goes to our landmass. It is essentialto understand that of this 110,000 km3 ofrainfall, 59% evaporates and 38% runs offinto our rivers and then to the ocean. Only2,200 km3 or 2% is infiltrated to ourgroundwater. This highlights the need tostore water in reservoirs.


How we Get Water“The World’s Water Cycle”

3


Floodsrepresent30% ofall naturaldisasters.Between1975 and 2000there were95 significantfloods inthe world.

Unfortunately, water is not always available exactly where and whenwe need it. Precipitation or rain is also not evenly distributed over the world by season andlocation. Development in the watershed increases runoff and loss to replenish groundwater.Landscape with natural groundcover has the smallest amount of runoff and the maximumabsorption for groundwater. A highly developed area results in most of the rainfall ending up asrunoff and then flooding. Some parts of the world such as Africa and Asia have severe droughtsmaking water a scarce and precious commodity. In other parts of the world water appears inlong periods of raging rainfall which cause loss of life and damage to crops, houses andbuildings. Sometimes within one country there can be devastating floods in one area, whileextreme droughts are occurring in other areas.

Distribution ofthe World’s Water

Dryand parched

river bed of theUsman SagarRiver in India

Floodingin China

4.1 Water-stressedand water-scarce countries

The United Nationsc h a r a c t e r i z e scountries with limit-ed availability ofwater as water-stressed or water-scarce dependingon the amount ofrenewable wateravailable. Water-stressed countrieshave fewer than

1,700 cubic meters of water available perperson per year (this volume is the same asa pyramid having a base on 25 metersand a height of 8.2 meters).This means that water isoften temporarily unavail-able at particular loca-tions, which requiresdifficult choices bemade for the use ofwater between per-sonal consumption,agriculture, or industry.Water-scarce countrieshave fewer than 1,000 cubicmeters per year (this isthe same pyramid with a25 meter base width and a heightof only 4.8 meters). In such cases, there

may not be enough water to provide adequatefood, the economic development may behampered and severe environmentaldifficulties may develop. This problem isdiscussed in detail in the section on waterrequirements.

For most purposes, river basins are a moreappropriate unit than countries for analyzingwater flows. However, many of the world'smajor river basins encompass more thanone country, a situation which requires coor-dination between the governments. Currently2.3 billion people live in river basins that areat least water-stressed; 1.7 billion live inbasins where scarcity conditions prevail. By2025 these numbers are projected to be

3.5 billion and 2.4 billion,respectively.

4.2 Water forsanitation

Lack of sanitation isa major public healthproblem causing dis-ease, sickness anddeath. More than2.6 billion people, or

40% of the world’spopulation, lack basic

sanitation facilities. As aresult, thousands of childrendie every day from diarrheaand other water borne,sanita-

tion and hygiene relateddiseases. Many more suffer and

are weakened by illness. In the past, progressin sanitation has suffered from limitedpolitical commitment and demand.

Today, water from reservoirs provides reliablestorage of water for treatment and toimprove sanitary conditions. However, simplyproviding access to improved water andsanitation does not guarantee the use ofthe services or the much expected healthbenefits to the people in the region. Thepromotion of fundamental behaviorchanges is key to integrating the appropriateuse of services into daily routine and needsto start in early childhood. Health andhygiene education programs provided byschools are an integral part of every waterand sanitation program.


Distributionof the World’s Water

4

Adry river

bed in a water-stressed

area

Landscapein a water-

scarce regionof Africa

Handwashing

prevents sickness- school children

in africa

©6

(see

p.6

4)

©7

(see

p.6

4)


4.3 Integrated watermanagement

There is a critical needfor integrated watermanagement in theriver basin or watershed.Dams and reservoirs thatare strategically located ina river basin allow for thestorage of water during rain-fall events and then manage thereleases to ensure that our rivershave a minimum daily flow at all times.Integrated water management means storing

water in all of thereservoirs in thewatershed dur-ing periods ofrainfall and thenmanaging thereleases of acoordinated and

predeterminedamount of water

from each dam tomaintain a consistentdaily flows in therivers downstream of

the dams.

WorldPopulation Data

With the current total growth, the world’spopulation will double every 54 years. Wecan expect the world's population ofapproximately 6 billion to reach 12 billion by2054 if the current rate of growth continues.

It is important to understand that thegrowth rate is much higher in developingcountries as shown on the chart. In thesecountries the supply of fresh water andelectricity is very limited.

In 2005 the world population was estimated to be 6.45 billion and it continues to grow atan annual rate of 1.3% or 77.3 million per year. The projection for the world populationthrough 2050 is as shown below. A large portion of this growth is in the arid portions of theworld - Africa and Asia. This growth continues to place a significant demand on water, food,energy and other infrastructure and services.

Worldpopulation

chart

Populationgrowth rate

chart showingsignificant growth

in developingcountries

Integratedwater management

ensures anaverage daily flow

in our rivers


6.1 Domestic water requirement

Water requirements are classified as domestic,agricultural and industrial. The recom-mended basic domestic water requirementin liters per person per day that has beenadopted as the world-wide standard is asfollows:

Purpose liters/person/day

Drinking 5Sanitation 20Bathing 15Cooking 10Total 50

this equates to 18.25 cubic metersor 4,821 gallons per person per year *

* This amount does not include lossesin the treatment process and distribution systems

For example, a city of 500,000 people requires25 million liters per day for the basic domestic

water requirement and about27 million liters per day

(this equates to an inter-national soccer field

with water 4.7 metersdeep) including los-ses. A town of1,000 people willneed 50,000 liters perday or 55,000 litersper day (equates to

a pyramid having abase of 8 meters and

a height of 2.6 meters)including losses. Even a

small village of 500 inhabi-tants will require 25,000 liters

per day or 27,500 liters per day with losses.

In 2000, there were 61 countries with a totalpopulation of 2.1 billion who can not getaccess to the minimum requirement of50 liters per person per day. With theanticipated population growth in less developedcountries this number of people will doubleto 4.2 billion by 2025.

6.2 Combined domestic,agricultural and industrialwater requirement

The combined water requirement includesdomestic, agricultural and industrial needs. Itis important to remember that the UnitedNations established three thresholds forcombined water requirements. The firstthreshold is countries that have more than1,700 cubic meters of water per person peryear (equates to a pyramid having a baseon 25 meters and a height of 8.2 meters)available and are considered to have anadequate supply to support the nation. Notethat the domestic requirement is about 1%of this total. The second threshold is countriesthat have less than 1,700 cubic meters ofwater per person per year available and areconsidered to be water-stressed. The thirdthreshold is countries that have less than1,000 cubic meters of water per person peryear (equates to a pyramid with the samebase width and a height of only 4.8 meters)available and are considered water-scarce. Atthis last level, there may not be enoughwater to provide adequate food, economicdevelopment is hampered and environmentaldifficulties will develop.

In the year 2000, there were 31 countries witha combined population of 508 million whowere considered water-stressed. By the year2025, it is estimated that the number of water-stressed countries will increase to 48 countrieswith a combined population of about 3 billion.River basins are a more appropriate unit thancountries for analyzing water flows. Many ofthe world's major river basins encompassmore than one country.This requires coordina-tion between countries.

Water Requirements

Many parts ofthe world lack

adequate quantitiesof water and distribution

systems


What is a Dam?A dam is defined as a barrier or structure across a stream, river or waterway to confineand then control the flow of water. Dams vary in size from small earth embankmentsoften for farm use to high massive concrete structures generally used for water supply,hydropower and irrigation.

History of Damsin the WorldRecent archaeological findingsindicate that simple earth dams andnetworks of canals were constructed asfar back as 2000 BC to provide peoplewith the reliable source of the waterthey need to live. The building of theMarib dam in Yemen began around750 BC and took 100 years to complete.It consisted of an earth embankment4 meters in height and stone sluices toregulate discharges for irrigation anddomestic use. In 1986, the existing damwas raised to a height of 38 meters thatcreates a reservoir of 398 million cubicmeters of water.

The construction of a dam usually requires therelocation of existing villages, individual houses,farms, highways, railroads and utilities fromthe river valley to a higher elevation above thereservoir. The principal types of dams in theworld are embankment, gravity and arch.Typical cross sections of each type are shownin section 9.3. The appurtenant or additionalstructures of a dam include a spillway, outletworks,hydropower plants and a control facility.

Dams are constructed to store and controlwater for domestic water supply, irrigation,

navigation, recreation, sedimentation control,flood control or hydropower. Some of ourdams serve one purpose and are thereforeknown as a "single purpose dam". Today,dams are being built to serve several purposesand are therefore called "multipurposedams". A multipurpose dam is a veryimportant and cost effective project fordeveloping countries because the populationreceives several domestic and economicbenefits from a single investment. It is thecornerstone in the water resources develop-ment of a river basin.

Aerial view ofSayamaike dam

built is the 7th centuryand still in use

today


Historically, dams have enabled people tocollect and store water when it is plentiful and

then use it during dry periods.Therefore, they have beenessential in establishing andsupporting towns and farms aswell as providing food throughirrigation of cropland.

One of the oldestdams that is stillin use today isan earth androckfill embank-ment dam builtaround 1300 BC

in what is now Syria. In China, asystem of dams and canals was con-structed in 2280 BC. Several ancient damsfrom the 13th to the 16th century in Iran are stillin use today.

In Sri Lanka, for example, ancientchronicles and stone inscrip-tions state that numerous

dams and reservoirs werebuilt as early as the6th century BC. Inter-basincanals augmented many

of these largereservoirs for irri-gation. One of theselarge dams, the Minneriyadam, was constructed duringthe rein of King Mahasen (276-303 AD), and was in tact when itwas discovered in 1900. It wasrestored in 1901 and is still in usetoday. More than 50 otherancient dams in Sri Lanka havebeen restored.

The main reason for the successful functioningof these reservoirs today is that thesluice structures, spillways andriprap that had been builtduring that early era arecompatible with themodern design principlesand criteria. Some of themasonry sluice towersand sluice gates constructedtwo to three millenniumsago have been repaired andconverted to working structuresduring the 1900’s.

The Romans built an elaboratesystem of low dams for water supply.The mostfamous was the Cornalbo earth dam insouthern Spain which had a height of24 meters (78 feet) and a length of 185 meters

(606 feet). After the Roman era, very littledevelopment in dam construction

took place until the end of the16th century when the Spanish

began to build largedams for irrigation.European engineersrefined the designand construction

knowledge in the19th century that gave rise

to the capability to construct dams to a heightof 45-60 meters or 150-200 feet.

Historically, dams have beenplanned and constructed for

the purpose of water supply,irrigation, and flood control. Inthe late 1800’s, hydropowerand navigation were added.Recreation has been a verybeneficial additional purpose

at many reservoir projects. Inmore recent times, dams have

been built to serve severalpurposes and are therefore called

multipurpose dams.

History of Damsin the World

8

The Sayamaike dam, one of theoldest dams in Japan, was built in

the early 7th century and afterseveral modifications and a

heightening is still in use today.

Inscriptionsin the sluice of

the original Maribdam, built in

750 BC

Ancientoutlet tower of

Minneriya dam thatwas built 276 -303 ADin Sri Lanka and wasrestored in 1901 forirrigation. It is still in

use today

Anearly irri-

gation damin Egypt

Handplaced rip-rapof Giritale dam

in Sri Lankaconstructed in608-618 AD

Ben-e-Golestan dam,

Iran - constructedabout 1350 AD

The newMarib dam,

Yemen - builtin 1968


9.1 Requirements of a dam

Because dams are a critical and essentialpart of our infrastructure, they must meetcertain technical and administrativerequirements to ensure safe, effective andeconomical operation. The design, constructionand operation of all dams must comply withthe following technical and administrativerequirements:

Technical requirements of a dam:◗ The dam, foundation and abutments must

be stable under all loading conditions(reservoir levels and earth quakes).

◗ The dam and foundation must be suffi-ciently watertight and have adequateseepage control measures to ensure safeoperation and to maintain storagecapacity.

◗ The dam must have adequate freeboard toprevent overtopping by waves and in thecase of an embankment dam must includean allowance for settlement of the founda-tion and embankment.

◗ The dam must have sufficient spillway andoutlet capacity to prevent over-topping bythe reservoir during an extreme flood.

Administrative requirements of a dam:◗ An operation and maintenance manual.◗ Adequate instrumentation to monitor

performance.◗ A plan for monitoring and surveillance of

the dam and structures.◗ An Emergency Action Plan.◗ Should support the natural environment.◗ A schedule for periodic inspections, compre-

hensive review, evaluation and modificationsas appropriate.

◗ Formal documentation of the design,construction and operational records.

9.2 Purpose of a dam

As is the case with all large public and privatestructures, dams are built for a specificpurpose. In ancient times, dams were builtfor the single purpose of water supply orirrigation. As civilizations developed, therewas a greater need for water supply, irriga-tion, flood control, navigation, water quality,sediment control and energy. Therefore,dams are constructed for a specific purposesuch as water supply, flood control, irriga-tion, navigation, sedimentation control, andhydropower. Recreation is sometimes addedto for the benefit of the population. A damis the cornerstone in the development andmanagement of water resources developmentof a river basin. The multipurpose dam is avery important project for developingcountries, because the population receivesdomestic and economic benefits from asingle investment.

9.3 Types of dams

Dams are classified by the material used toconstruct them. Dams built of concrete,stone, or other masonry are called gravitydams, arch dams or buttress dams. Damsbuilt of earth or rocks are called embank-ment dams.

Requirements,Purpose, Types,Features andConstruction of a Dam


Embankment dams are constructed ofeither earth fill or a combination of earthand rock fill. Engineers generally choose tobuild embankment dams in areas wherelarge amounts of earth or rocks are available.Embankment dams represent about 75%of all of the dams in the world. Some earthdams are constructed completely by earthand are known as earthfill dams, while others are rockfill dams, are constructedwith rock. Many embankment dams areconstructed with a combination of earthand rock and are know as earth androckfill dams.

Crosssection ofa gravity

dam

Crosssection ofan arch

dam

Crosssection of anembankment

dam


9

Gravity dams depend entirely on their ownweight to resist the tremendous force ofthe stored water. Some early gravity damshave been constructed with masonryblocks and concrete and are known as

masonry dams. Today gravity dams areconstructed by mass concrete or roller-compacted concrete (concrete placed inlayers and compacted by a roller) and arereferred to as concrete gravity dams.

Arch dams are concrete dams that curveupstream toward the flow of water. Most arebuilt in narrow canyons. As the water pushesagainst the dam, the arch transfers thewater's force to the canyon wall. Archdams require much less concrete thangravity dams of the same length. Theyalso require a solid rock foundation tosupport the weight of the dam.

Buttress dams depend for support ona series of vertical supports calledbuttresses. The buttresses run alongthe dam's downstream face: that is, theside facing away from the water's flow.The downstream face of a buttress damusually slopes outward at about a 45-degreeangle. The sloping face and the buttressesserve to transfer the force of the waterdownward to the dam's foundation.

Requirements, Purpose, Types,Features and Construction of a Dam

Aconcrete

gravity dam

Aconcretearch dam

A rockfilland earthfill

dam

Abuttress

dam

A large earthfill

embankmentdam

A rockfilland earthfill

dam

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9.4 Features of a dam

To operate properly, a dam must have severalfeatures. They are the reservoir, spillway,outlet works and a control facility. In thecase of a dam with hydropower, penstocks,generators and a switchyard are included.The reservoir is the feature that storeswater. The inflow must be continuouslymonitored and the outflow controlled toobtain maximum benefits. Under normaloperating conditions the reservoir level ismanaged by the control facility whichcontrols discharges in the outlet works, whichconsists of a large tunnel or conduit atstream level with control gates. Under flood

conditions the reservoir level is maintainedby both the spillway and outlet works.

The reservoir of a flood control dam is keptas low as possible during several months ofthe year to create the maximum amount ofstorage for use in the flood season. For anirrigation project, the reservoir is filled ashigh as possible in the winter and earlyspring and is maintained at that level formaximum release during the dry season.The reservoir of a hydropower dam will bemaintained at a constant level to create auniform head for use by the generators.Water quality is a very important aspectfor sustaining a balance in nature andmeasures to maintain good water qualityare incorporated into modern dams. Intakeports at various depths allow selectivewithdrawal and mixing to produce thedesired temperature and oxygen contentto enhance the downstream environmen-tal conditions. Fish ladders, a series ofelevated pools, are provided at many damsto allow free passage of fish upstream anddownstream of the dam. Screens are usedto prevent fish from entering the turbinesof the generators. Since most moderndams are multipurpose, the discharge mustbe managed carefully and continuously tooptimize economic and environmentalbenefits.

Exampleof an intaketower in the

reservoir connectedto the outlet

conduit

Crosssection of an

antake tower andoutlet conduit

through anembankment

dam


9

Exampleof a spillway foran embankmentdam in Idaho,United States


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A flowingspillway locatedin the center of

the dam


All of the features of a dam are monitoredand operated from a control room. Thisroom contains the necessary monitors,controls, computers, emergency equipmentand communications systems to allowproject personnel to operate the dam safelyunder all conditions. Weather conditions,inflow, reservoir level, discharge anddownstream river levels are also monitored.In addition, the control room monitors instru-mentation located in the dam and appurtenantfeatures that measure the structuralbehavior and physical condition of the dam.

9.5 Section of the siteand type of dam

The selection of the type of dam for a siteis dependent on technical and economicdata, along with environmental considera-tions. In the early stages of design, severalsites as well as several types of dams arecarefully considered. After a hydrologicsurvey is made, an exploration program, inthe form of drill holes and test pits is madeat each site to obtain soil and rock samplesto test the physical properties of thesematerials. In some cases field pumpingtests are performed to evaluate seepagepotential. Preliminary designs and costestimates are prepared and reviewed byhydrologic, hydraulic, geotechnical andstructural engineers and geologists.Environmental quality of the water, ecolo-gical systems and cultural data are alsoused in the site selection process.

Factors which affect the selection of thetype of dam are topography, geology, founda-tion conditions, hydrology, earthquakesand availability of construction materials.The foundation of the dam should be solid.Narrow valleys with shallow sound rockfavor a concrete dam, while wide valleyswith varying rock depth and conditionfavor embankment dams. Earth embank-ment dams are the most common typesince they accommodate all the materialfrom required excavation.

9.6 Construction of a dam

The construction of a dam is a major activityrequiring large amounts of materials,equipment and personnel. The construc-tion period or time to build the dam usuallytakes from 4 to 5 years and sometimes aslong as 7 to 10 years for very large multipurpose dam projects.

After the highways, railroads and the gasand electric utility lines have been relocatedfrom the valley floor to above the top ofdam or to another location; constructionof the dam can begin. The first step consistsof the site preparation or the clearing oftrees, vegetation and buildings. This isfollowed by diversion of the river so thatthe foundation can be excavated and theconcrete, earth, or rock placed. To divertthe flow of the river from the area, frequentlyhalf of the riverbed is excavated at onetime. The other half of the riverbed is usedfor the flow of the river. In some cases, it ismore economical to bore a tunnel throughan adjacent canyon wall. This tunnel maybe temporary or may become part of theoutlet works of the project and it permitsthe entire flow of the river to pass aroundthe dam site during the construction period.To accomplish this diversion, cofferdams(small dams placed temporarily across astream) are built upstream to divert theriver into the tunnel. After the dam hasbeen built high enough, the operatinggates for the tunnel are installed. After theoutlet works and main dam are completedto an appropriate level, the stream isdiverted into the outlet works by anothercofferdam of sufficient height to preventovertopping during construction in theother half of the river bed. A downstreamcofferdam may also be required to keepthe dam site dry. In the final part of theconstruction period the entire dam isbrought to full height.


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Nakai Dam(Nam Theun 2)- Laos - a roller

compactedconcrete dam

GanguiseDam - France -heightening anexisting earth

dam

Nakai Dam- Laos -

concretinggoing on

Dams&theWorld’sWater

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1

3

2

5 6 7

4

1 & 2 Chambon Dam - France - building a gravitydam in the 1930-35 years

3 Roselend Dam - France - the construction period

4 Construction of the Nam Them Dam - Laos

5 Potrerillos Dam

6 & 7 Potrerillos Dam - Argentine - upstream face

8 & 9 Katse Dam - Lesotho - concreting an arch dam

10 Ceyrac Dam - France - concreting a gravity dam

11 Construction of a roller-compacted concretedam - Penn Forest dam, USA (Delivery, placement,spreading and compaction by a roller)

12 Villerest Dam - France - building a gravity curved dam

13 Construction of the spillway of a mass concretegravity dam



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11

10

12 13


The International Commission on Large Dams (ICOLD)maintains a Register of Dams in the World. For a dam to beconsidered large and be included in the register it must havea height of 15 meters or 10 to 15 meters and store more than3 million cubic meters of water in the reservoir. The dams are listed by country and include datasuch as the dam name, year of completion, dam height, reservoir capacity, area of catchment(drainage area), the purpose, installed electric generating capacity, mean annual electricityenergy produced, irrigated area, volume of water stored for flood protection and number ofpeople affected by resettlement. The world data as of 2000 indicates that there are about50,000 large dams in operation. Embankment dams are the predominant type followed bygravity and arch dams. The planning process for a dam project and public involvement alongwith the local socio-economic issues are discussed in section 13.

Graphs showing when the world’s large dams were placed into operation, their distribution byheight and distribution by geographic areas are shown below:


Dams of Today


The primary type of dam is the earthfill embankment dam which represents 43.7% of thetotal. This is followed by gravity dams (10.6% of the total) and rockfill embankment dams(5.3% of the total).

10.1 The purposes of the current dams in the world

Most of these dams in the ICOLD register (71.7%) are single-purpose dams, but there is a growingnumber (28.3%) of multipurpose dams. Today, irrigation is the most common purpose of thedams in the ICOLD register. The distribution for each purpose among the single-purpose damsleads to the following results:

◗ 48.6% for irrigation◗ 17.4 % for hydropower◗ 12.7% for water supply◗ 10.0% for food control◗ 5.3% for recreation◗ 0.6% for navigation and fish farming◗ 5.4% others

Dams of Today

10


11.1 Water supply for domesticand industrial use

An adequate and dependable source ofwater is needed both to sustain existingcivilization and to support future growth. Inthe past and in many regions of the worldtoday, the main sources of domestic andindustrial water are groundwater or aquifers(layers of sandy gravels or rock beneath theground surface which contain and are capableof storing water). Today, the withdrawalfrom many of these aquifers exceeds thenatural recharge, which results in loweringof the water table. This situation can lead to

depletion of the groundwater both in timesof drought and permanently. It is importantto remember from section 3 that of the totalrainfall falling on the earth, only 19% fallson our land mass and a large portion endsup as runoff leaving only 2% is infiltratedto replenish our groundwater. Properlyplanned, designed and constructed andmaintained dams to store water contributesignificantly toward fulfilling our watersupply requirements. To accommodate thevariations in the hydrologic cycle, dams andreservoirs are needed to store water andthen provide more consistent suppliesduring shortages.

One of the fundamental requirements for socio-economic development throughout theworld is the availability of adequate quantities of water with the appropriate quality and anadequate supply of energy. Properly planned, designed and constructed and maintained damscontribute significantly toward fulfilling our water supply and energy requirements. Toaccommodate the variations in the hydrologic cycle, dams and reservoirs are needed to storewater and then provide a consistent discharge to maintain the required daily flow in our riversthroughout the year.

ChaudanneDam - France - is

an arch dam providingwater to a naturally dry

region for domestic,irrigation, industrialand hydropower

use

The Benefitswe Receive from Dams

© 26 (see p.64)


It is becoming essential that our watersupply obtained from groundwater be augmentedwith additional water from reservoirs. Largeurban areas depend heavily on water

stored in reservoirs during periods of highrainfall which is then used during dry periods.This is especially critical in arid regions ofthe world.

Water stored in reservoirs is also used forindustrial needs. These needs ranges fromthe direct use in manufacturing to chemicaland refining processes and for cooling at

conventional and nuclear power plants.Managedflows from reservoirs can be used to dilutedischarged substances by augmenting low riverflow to maintain water quality at safe limits.


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Anexampleof ench

dam

An exampleof industrial

water use - alarge pulp and

paper mill

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11.2 Meeting the agriculturaldemand for food supply

One of the biggest uses of water on a world-wide scale is irrigated agriculture. Since theearly 1990s, less than 1/5 of the land suitable foragriculture in the world has been irrigated, andit has contributed about 1/3 of world foodproduction. A popular saying amongthe people in arid regions of theworld is “Food grows wherewater flows”.

It is estimated that 80% of additional foodproduction by the year 2025 will need to comefrom irrigated land. This will put an additionaldemand on our fresh water supply.Most of theareas in need of irrigation are in arid zones,which represent a major portion of thedeveloping countries.Even with the widespreadmeasures to conserve water by improvements

in irrigation technology, theconstruction of more

reservoir projectswill be required.

Industryneeds

millions of litersper day

Providingwater for foodin developing

countries

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11.3 Flood control

Dams and reservoirs can be effectively usedto regulate river levels and flooding down-stream of the dam by temporarily storing theflood volume and releasing it later. The mosteffective method of flood control is accom-plished by an integrated water managementplan for regulating the storage and dis-charges of each of the main dams located ina river basin. Each dam is operated by aspecific water control plan for routing floodsthrough the basin without damage. This

means lowering of the reservoir level tocreate more storage before the rainy season.This strategy eliminates flooding. Thenumber of dams and their water controlmanagement plans are established bycomprehensive planning for economicdevelopment and with public involvement.Additional information on integrated watermanagement plans is in paragraph 11.7. Floodcontrol is a significant purpose for many ofthe existing dams and continues as a mainpurpose for some of the major dams of theworld currently under construction.


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Floodin a village

“FoodGrows

where WaterFlows”

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11.4 Hydropower

Water has been used as a form of power sinceRoman times. It was first used to drive waterwheels for various mechanical processes, suchas grinding corn, sawing timber or drivingtextile mills. In the early 19th century, thewater turbine was developed as a much more

efficient machine than the waterwheel,and bythe mid-19th century, water power was used toproduce electricity for the first time. Theconcept of using moving water to turn a turbineconnected by a shaft to a generator to createelectricity is known as hydropower.Since wateris the source, hydropower is a renewable andwidely used source of electricity.

Diagramof a dam andhydropower

plant

Aturbine

used forhydropower

Generatorsin the power

plant

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The greater the available force of water toturn the turbine, the more power can beproduced. The amount of electricity whichcan be produced thus depends on theheight though which the water has to fallto reach the turbine and the volume ofwater flowing through the turbine. A majoradvantage of hydroelectric power, comparedwith other sources of electricity (for exampleburning coal, oil or gas), is that the sourceis renewable. In other words, it is notconsumed by the process of creatingelectricity and is still available for otheruses when it is discharged from the powerstation. Also it is a clean source of power, asit does not involve burning fuel which canpollute the environment.

Some of the first countries to develop hydro-electricity on a large scale were Norway,Sweden and Switzerland in Europe, Canada,the USA, Australia and New Zealand. On a

smaller scale, projects were built many yearsago in some of the Asian countries withappropriate conditions; India’s first smallhydropower plant, for example, is more than100 years old.

Almost 200 countries in the world havesome kind of capability to develop hydro-electric power, whether on a large or smallscale. The best natural conditions are incountries which are mountainous or hilly,with plenty of lakes or rivers, or with bigriver systems. The largest hydro station inoperation is Itaipu, built on the Rio ParanaRiver between Brazil and Paraguay.Although this is an exceptionally largehydropower project (with power capacitiesof more than 14,000 MW (Mega Watt or1 million watts), there are hundreds ofthousands of medium-scale stations world-wide. Brazil produces more than 90% of itselectricity from hydropower projects.

Castillon Dam- France - showing

the plant at dam-foot,switch-yard and line

on the top right


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11.5 Inland navigation

Natural river conditions, such as changesin the flow rate and river level, ice andchanging river channels due to erosion andsedimentation, create major problems andobstacles for inland navigation. The advantagesof inland navigation, however, whencompared with highway and rail are thelarge load carrying capacity of each barge,the ability to handle cargo with large-dimensions and fuel savings. Enhancedinland navigation is a result of comprehensivebasin planning and development utilizingdams, locks and reservoirs which are regulatedto provide a vital role in realizing regionaland national economic benefits.

In addition to the economic benefits, ariver that has been developed with damsand reservoirs for navigation may alsoprovide additional benefits of floodcontrol, reduced erosion, stabilizedgroundwater levels throughout the systemand recreation.

11.6 Recreation

The attractiveness of reservoirs for recreationis often a significant benefit, in addition to theother purposes of a dam. This is verysignificant in areas where natural surfacewater is scarce or non-existent. Recreationalbenefits associated with lakes, such as boating,swimming, fishing, bird-watching and naturewalks, are taken into account early at theplanning stage and along with other objectivesachieve a balanced project. The operation ofthe dam and reservoir can enhance recreationalopportunities.

11.7 Integrated water management in the river basin

The availability of water in sufficient quantitiesand of adequate quality where it is neededremains the basic challenge. Thus, the waterobtained from groundwater, natural lakes,free flowing rivers and reservoir projects isused to meet the domestic, agricultural

Vaugrisstep on the

Rhône River: dam,plant and lock - amultiple purpose

equipment

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and industrial demands. Of these foursources, reservoir projects are the only sourcethat can effectively be managed to meet boththe water and energy needs in a state, regionand country. The inflow and outflow from areservoir must be managed. Integrated watermanagement in the river basin is the processby which the water stored in reservoirs andthe daily amount released is managed in thebasin to ensure that an adequate and dependablequantity is available. An example is storing thestorm flows for flood control. During a periodof drought gradual releases from each dam arecoordinated to ensure an adequate quantity isavailable over the entire basin. Each dam andreservoir in the basin has a water control planthat outlines discharges from that reservoirbased on inflow to the reservoir and down-stream needs. Each water control plan iscoordinated with other dam and reservoirprojects within the river basin. The overallcoordination and control is accomplished by abasin-wide organization such as a River BasinCommission. This organization has a criticalrole in controlling droughts and floods withinthe river basin.

Intakes located at different elevations on thecontrol tower of the dam allow the operatorsto make selective withdrawal of water atdifferent temperatures that, when combinedas discharge to provide the desired temperaturein the downstream river to enhance down-stream water quality. A properly managedreservoir project also maintains a predeter-mined reservoir level during the variousseasons of the year to maintain environmentalrequirements.

The objective of integrated water managementin the river basin is to satisfy demands forwater without sacrificing existing uses. Themajor issues to accomplish this in a riverbasin are:

◗ Formulating a strategy to provide adequatestream flow and at the same time maintainappropriate reservoir levels (flood anddrought management).

◗ Satisfying municipal, agricultural andindustrial demands without injury to theenvironment.

◗ Evaluating and improving water quality.


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Integratedwater managementfrom dams in the

watershed provides areliable average dailyflow over the year in

our rivers

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11.8 Summary of benefits

The benefits of dams and reservoirs must beviewed and weighed from all perspectives:

local, regional, national and global. Theentire range of benefits from a damproject are not always realized in theimmediate vicinity of the reservoiror by the population that livesthere. Generally the people of aregion and the whole nation receivethe full benefits of a dam and reservoir.An example is the Aswan High Damon the headwaters of the Nile Riverin Egypt. This dam stores and then

discharges water to maintain anaverage daily flow in the Nile. This

benefits the entire nation.

The value of integrated water managementin a river basin can best be seen in develop-ing and developed countries. For centuriesseveral countries of Southeast Asia, forinstance India and Indonesia, were periodicallyplagued by hunger. When the monsoon rainswere delayed or insufficient, the country

GambsheimDam, power-house

and locks on the Rhine river.A large multipurpose dam

manages river flow to providewater supply, electrical energy,navigation, flood control andrecreational use. A big fishpassage is being constructed

in the center partof the plant.

Industrialplant

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was affected bystarvation, frequentlywith a large number ofdeaths. When major reservoirswere built during the last five decades, theproblem was solved by storing of large quan-tities of water from the surplus during rainyseasons, for regulated release during periodsof drought.

An outstandingexample of the water

supply benefit in a water-stressed area is the Lesotho

Highlands Water Project. Situated in southernAfrica, it is a joint venture of theKingdom of Lesotho and the surroundingRepublic of South Africa. The projectprovides for storing water in several large


11

Maintainingfertile valleysby providingreliable river

flow

Aerial viewof Hungry Horse

Dam, Texas,United States

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reservoirs in the mountainous region ofLesotho where rainfall is relatively heavy.The water is then released through a nearly80 kilometer long tunnel system and suppliedto the arid central region of South Africa.Prior to this project, the Lesotho highlandswere under developed and almost inacces-sible. As part of this project new pavedaccess roads with bridges for heavy trafficwere built. The electricity and telecom-

munications networks in the whole countrywere substantially upgraded to modernstandards or built from scratch, schoolswere established at the construction sitesand in their surroundings and public healthservices and health care plans were intro-duced with hospital and medical emergencyposts. This basic infrastructure remains inthe area and continues to be a permanentbenefit.

Throughout the world, agriculture requiressignificant and reliable amounts water.Irrigation systems make this possible. In theUnited States, agriculture accounts for 49% ofthe fresh water consumption. In Africa andAsia, the United Nations estimates that 85% ofthe fresh water is used for agriculture. By 2025,the agricultural requirement for water willincrease by 1.5 times the current use.Dams andreservoirs are the tool to provide the largequantities of water to meet this need.

Industrial plants and operations require asignificant amount of water to operateefficiently. When fresh water is used, it mustbe treated before being discharged from thefacility, since the industrial processes usuallypollute the water.

Hydropower is the cheapest source of electricenergy, because water, the driving force isfree. So, hydropower can be a valuable meansto tackle the problem of poverty in many

Obtainingwater forirrigation

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parts of the world. Implementing a newhydropower plant can mean that some ofthe local population must be relocated fromthe reservoir area. Sao Paulo, Brazil is anexample is a city of 18 million and thelargest place of industrial concentration inSouth America. Of the total population,5 million are classified as low income.São Paulo’s electricity supply is almostentirely based on inexpensive hydropower.This has facilitated the creation of new jobsand improved the standard of living.

Inland navigation has the lowest fuel consump-tion and least amount of pollution of thebulk transportation modes. To move a givenload over a long distance, the transport byroad requires ten times, and by rail five

times the quantity of fuel, consumed whenshipping the load by barge. Since only fewrivers are readily navigable, natural obstaclessuch as rapids, shallow stretches of the riverbed or too a high velocity of the flowingwater have to be overcome or eliminatedby the construction of locks, dams andcontrol structures. Inland navigationcontributes to reducing the emission ofgreenhouse gases and thus to mitigatingthe worldwide effects of global warming.

Towboats push barges tied together to forma "tow". A tow may consist of four or sixbarges on smaller waterways up to morethan 40 barges on larger rivers. The bargesof a tow moving through a lock can be seenin the following picture.


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Largeshipments of

goods move thelocks and dams oninland waterways

such as thistow



In 1997, the International Commission OnLarge Dams (ICOLD) published a documentthat presents guidance for environmentalconsideration, assessment and mitigation:“Position Paper on Dams and theEnvironment”. It states:

Today we are mitigating the environmentalimpacts of dams. In many countries,governments have mandatory requirementsto take into account and plan to mitigatethe possible impact which dams may haveon nature and the environment whenselecting where a dam should be built, aswell as how it will be constructed andoperated. By taking these predictionsseriously, many possible consequences canbe addressed in a positive way.

The goal for a nation is to achieve clean andhealthy watersheds which support aquaticlife as well as their economic developmentand human needs. This goal is best met byencouraging and supporting comprehensive

water resource management that is tailoredto the regional and local needs. Watermanagement is essential to achieve bothwater quality and water quantity requirements.Environmental conservation includes mitiga-tion and enhancement for new projects,maintaining the existing conditions andrestoration where appropriate.

12.1 Environmental conservationand enhancement

Managing water resources in a river basinhas an impact on its natural water cycle.The scale of the impact depends on theactual size and natural condition of the areato be developed and the extent of develop-ment. Concerns about environmental issuesand implementation of mitigation meas-ures are essential elements in the planningof a project. This includes: clearing of vege-tation in the area to be flooded, multi-leveloutlet structures to optimize downstreamwater temperature and quality, provisionsfor the migration of fish and other aquaticorganisms,and operational rules for regulatingdownstream flows at critical times to protecthabitat for reproduction or migratoryroutes. Appropriate site selection, togetherwith the implementation of these techniques,

The economic recovery throughout the world following World War II was accompanied byphenomenal growth in infrastructure systems that included the world’s largest dam constructionperiod. Dam construction reached a peak in the 1970s. As this economic development andconstruction continued, the world population became aware of the environmental price thatwas being paid for this development. Today the people are looking for a balance between theeconomic benefits and environment benefits for water resources projects. They are also lookingfor an equal distribution of the benefits for the entire population in the region. People preferthat water resources development and management be accomplished on the entire watershedrather then in isolated areas.

Dams and theEnvironment

“Increased awareness ofthe natural environment and

its endangered situation is oneof the most important developments

of the late 20th century.”


will result in both new and rehabilitatedprojects that minimize unacceptableenvironmental impacts.

Encouraging and supporting a comprehensivewater resource management plan canaccomplish environmental conservationand enhancement for both existing andnew projects. According to the regional andlocal needs, the plan should include conserva-tion, mitigation and enhancement of theexisting conditions. An example of optimiz-ing the environmental conservation andenhancement is treatment of the areawhere the reservoir meets the land (reservoirrim), limiting access in the reservoir area,and providing small dams with outlets inthe headwaters. This is very effective formulti-purpose projects where the reservoir

level may fluctuate during operation. Partsof the reservoir area are restricted forwetland development, aquatic habitat andanimals. Islands and small dams areconstructed to protect the wetlands fromreservoir fluctuations. The dam in theheadwaters also serves to control sedimenta-tion. Uneven shorelines can be created forwetland development. Many existingprojects throughout Europe and Asia havebeen modified and changed to incorporatethese measures.

An example of the implementation of thistechnology can be seen at the Rottachreservoir in Bavaria, Germany. This sameenvironmental mitigation and enhance-ment can be incorporated in projectsworld-wide.

Dams andthe Environment

12

Conservationof the natural

habitat is part ofthe design of a

dam project

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Creatinga separate pond

and wetlands at theupstream end of theRottach reservoir in

Germany

Dams andthe Environment

12View

lookingdownstream -

showing shallowwater and wetland

development

Rivers naturally transport sediments. Sediment depositionoccurs as the river enters a reservoir and its sedimenttransport capacity decreases in the backwater created by thedam. Coarse sediment is typically deposited first while finerclay and silt fractions are transported much deeper into a reservoir.Most reservoirs trap nearly 100 % of the river sedimentloads that enter them, but sedimentation typically onlybecomes a significant problem 50 or more years afterconstruction of a dam, since dams are designed with extrastorage to allow for sediment deposition.

Due to the rapid growth in dam development during the1960s to 1970s, about 45 percent of the current storagecapacity in reservoirs would be seriously affected byreservoir sedimentation in 20 years time. Most existingdams would be seriously affected by lost storage due tosedimentation by the year 2065.

Sedimentation rates vary greatly with some of the highestyields being found in geologically active regions where earth-quakes occur. Sedimentation impacts on reservoirs are gener-ally however most severe in semi-arid regions where sedimentyields are relatively high and dam catchments large.Agriculture and afforestation, deforestation of natural forests,overgrazing and other human activities with help ofstormwater, are the main contributors to catchment erosion.

To limit soil erosion and reservoir sedimentation, humanorganisations have to deal with technical tools and regulatoryones, such as catchment management policies.The ideal solution is indeed to minimise the accumulationof sediment within reservoirs.◗ Build small (relative to the river flow) dams on rivers that

carry substantial sediment loads. These dams must beprovided with large low level gates to flush deposits outduring floods when necessary.

◗ Storage dams should be built in valleys with low sedimentyields and/or with small catchments, and should be sizedwith additional dead storage for future sedimentation of say50 to 100 years.

Once sediments have become deposited and consolidated,it becomes very difficult to remove and store them cost-effectively by mechanical means. Alternative solutions suchas dam heightening may be better than recovering loststorage capacity by dredging.

The riverbed directly downstream of a dam typicallyexperiences degradation (lowering of the riverbed) dueto the sediment being trapped in the reservoir, dependingon the existence of large tributaries downstream thedam location.

Sedimentation aspects

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Aerialview showing

a completed pondand wetlands for

ecosystem conser-vation

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At the 2005 World Summit of the UnitedNations General Assembly eight MillenniumDevelopment Goals (MDG’s) were presentedfor achievement by 2015 to eradicatepoverty, improve education, improvehealth, combat disease and ensure environ-mental sustainability. These MillenniumDevelopment Goals can be viewed atwww.un.org/millenniumgoals. The UnitedNations also states that management ofthe world’s water resources is an essentialingredient to achieving all of the MDG’s.They recognize that dams and reservoirswill continue to play a major role in themanagement of the world’s water resources.

As the world needs significant quantities ofwater for domestic, agricultural, energy andflood control to sustain development,multipurpose dams are the most realisticoption. Solar, wind and groundwaterschemes must be pursued for the purpose ofaugmentation, but again they do not offerthe quantities for viable alternatives.Conservation measures are a must - but theyare not stand-alone measures.

Effective management of the world’s waterresources in watersheds by dams and reservoirsin conjunction with other measures is essentialto sustaining both the existing and future popu-lation of the world. This is critical for thedeveloping nations and in the vast arid regions

of the world.Basin-wide planning for water man-agement is the key element to providing opti-mum water supply and other benefits. Whiledams provide significant benefits to our society,their impacts on the surroundings may include:

◗ Resettlement and relocation of the affectedpopulation.

◗ Socio-economic impacts.◗ Environmental concerns.◗ Sedimentation issues.◗ Safety aspects.

The challenge for the future will be the wiseplanning and utilization of dams and reservoirsin the watershed in conjunction with thegroundwater, climate, environment and landuse for the wise management of the world’swater resources as part of each nation’s socialand economic development goals.

13.1 Planning process for adam and reservoir project

The watershed or river basin is defined byhydrology and transcends national, political,social and economic boundaries making itthe basic element for the planning and manage-ment of water resources and the ecosystems.The planning for water resource developmentshould be accomplished on a watershed basisrather than a “project-by-project” basis. The

Today, the world is undergoing major changes in social and business practices as wellas vast economic development associated with the world globalization and the rapid advancesin technology and expanded communications associated with the continued unprecedentedincrease in population. At the same time, in many areas careless use of our water have acceler-ated pollution of the environment.

Looking to theFuture - Dams forthe 21st Century


planning process is a systematic and compre-hensive activity that considers all resourcesin the watershed. Therefore the size and loca-tion of reservoir projects is best determinedon this basis.

Once a dam and reservoir project is locateddetailed planning in the region can begin.Withregard to a specific dam project, every effort ismade to assure that an economic, social andenvironmental value is added to the water-shed. Ecosystem restoration is one of theprimary environmental objectives of a damproject. For the specified project goals andobjectives of a new dam project, this processcontains six individual steps and is a structuredapproach to identifying and then solvingissues and problems. It provides a rationalframework for sound decision making. Thisprocess is also applicable for many other typesof major projects. The six steps are :

◗ Step 1Identifying issues,problems and opportunities.

◗ Step 2Inventorying and forecasting conditions.

◗ Step 3Formulating alternative plans.

◗ Step 4Evaluating alternative plans.

◗ Step 5Comparing alternative plans.

◗ Step 6Selecting a plan that best meets the needs.

A successful project is generally based on theaccomplishment and documentation of all ofthese steps. It is essential that planners,economists and engineers conduct each step asa team. It is important that this be a repetitiveprocess that includes public and partnerinvolvement. As more information is acquiredand developed, it may be necessary to reiteratesome of the previous steps.

These six steps are presented in a sequentialmanner for ease of understanding, but one stepusually occurs several times and sometimesconcurrently. Iterations of steps may beconducted as necessary to formulate efficient,effective, complete and acceptable alternativesfor selecting the best. Wise planning with inputfrom all stakeholders is essential for successfuldam projects.

13.1.1 Public involvement andcoordination

The purpose and goal of public involvementand coordination is to open and maintainchannels of communication with the publicand local businesses in order to give fullconsideration of public views and informa-tion in the planning process. The objectiveof public involvement is to ensure that thedam projects and programs are responsiveto the needs and concerns of the public.Elements critical to a good public involve-ment and coordination process are dissemi-nating information about proposed activities,understanding the public's desires, needsand concerns, providing for consultationwith the public before decisions arereached, and taking into account thepublic's views.

All planning studies incorporate publicinvolvement, collaboration and coordina-tion with the public. This is initiated duringthe initial planning process, where issues,opportunities and problems are identified,and continue throughout the planningprocess. Involvement at the initial stage ofthe planning process not only helps toidentify the problems and opportunities,but also extends an invitation to the publicto have continued involvement and anopportunity to voice their concerns, ideasand suggestions in the planning anddecision making process.

Based on an initial public meeting, in theearly phases of the planning process, theproject team will determine, the extent ofpublic involvement required and willestablish an appropriate strategy for inte-grating public involvement into the plan-ning process. It is important to develop astrategy that creates relevant, quality publicinvolvement opportunities for those whohave, or may have, an interest in the study.The strategy shall reflect the scope andcomplexity of each particular study. Majorpublic involvement activities conductedduring the planning process are announc-ing the initiation of the study, identifyingthe public, and the scoping process. It isimportant for the public to see and haveinput to the alternatives being studies. At


the end of the planning process, thepublic should be briefed on the selectedalternative and the schedule for designand construction.

13.2 Socio-economic issuesassociated with a dam andreservoir project

In a national economic development plan,significant benefits are needed. Thisresults in the planning, design andconstruction of large dams that createsignificant reservoirs. The project cancreate local economic and social issuesthat if not addressed early in the planningcan result in impacts. Resettlementprograms for the local population andbusinesses must involve the identificationof the affected population as well as theaffected activities such as agriculture,irrigation, forestry, commerce and indus-try. Appropriate compensation, movementand actual rebuilding of communities forthe population and business activitiesabove the reservoir level are an essentialbudget item in the project cost.

In tropical areas of the world, sanitationmust be addressed. Reservoirs can create

an environment which is favorable for thetransmission of water-related diseases.The primary preventive measures aresanitation and health-care programs forthe population around the reservoir, inconjunction with appropriate operatingrules such as fluctuating lake’s waterlevel to discourage growth of disease-carrying insects.

In summary, one of the most importantobjectives of a dam is to ensure that anappropriate share of the benefits go to thepopulation directly affected.

13.3 Increased need of inte-grated water management inthe watershed or river basin

Water in adequate quantities and of adequatequality at the right locations will be the essen-tial ingredient to support expansion of theworld’s population and assist developingcountries in making progress to meet theirsocial and economic development goals.Dams which are properly planned, designed,constructed and maintained contribute signif-icantly toward fulfilling our water and energyrequirements. The primary source of freshwater supply is from rainfall. We must always

Looking to the FutureDams for the 21st Century

13

Maintainingconstant waterlevels to ensurereliable wetlands

for habitat

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Exampleof a river that

has integrated watermanagement

to provide a minimumand dependableflow throughout

the year

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Adry river anexample of

the need for watermanagement

An exampleof industrial

development: alarge pulp and

paper plant


be mindful that throughout the world thehydrologic cycle varies and is not predictable.Toaccommodate these variations in the hydro-logic cycle, we need to manage the fresh waterthat is available to us effectively.

Wise management of the water in ourreservoirs is essential to support the growingdemands.Dams and reservoirs are a useful toolfor the management process, since they canstore water and then provide more consistentsupplies during shortages. In short terms Damswill continue to enable us to manage water sothat we do not have dry streams for most ofthe year.The goals of regional integrated watermanagement in the watershed are:

◗ Improved management of the water supply.◗ Improved water quality in our rivers.◗ Improved environmental conditions

in the watershed.

Therefore, the traditional approach of waterresources development of water supply, irriga-tion, navigation, hydropower and recreationmust be expanded to include:

◗ Water quality.◗ Management of water quantity - (flood and

drought).◗ Sedimentation control.◗ Climate assessment.◗ Land use and zoning.◗ Groundwater management.◗ Maintaining the habitat.◗ Maintaining and enhancing the environment.

13.3.1 Need for real time watermanagement in the watershedor river basin

Water management in a river basin includesthe collection and evaluation of the criticalinformation so that decisions can be madeto achieve the optimum releases from reservoirprojects to meet domestic, industrial andagricultural demands in the river basin. Forexample, it takes 38 liters or 110 gallons torefine 3.8 liters or 1 gallon of gasoline. Tosatisfy the increasing demand for water, aswift, accurate and reliable data managementsystem is required. These real time decisionsare driven by observed and real time date

collection, modeling and forecasting of thecurrent weather and river flow conditions.The information and data used in thesedecisions relate to:

◗ Water quality in the river.◗ Managing river flows for both droughts and

floods.◗ Emergency planning and response for floods.◗ Planning,zoning,and land use by communities.◗ Improving the efficiency and benefits of

existing dam projects.◗ Planning in the river basin (modifying the

operation (storage and releases) of existing damsand new dam projects where and when needed).

The requirements for this type of system are :

◗ River basin wide network for real-time datacollection.

◗ Development of a dependable database.◗ Mathematical modeling within the river basin.◗ Detailed mapping.◗ A fast and reliable computer system .Watershed modeling is an important aspect ofthis system. It includes the hydrologic data,reservoir storage data and the systemhydraulics. The output is in the form offorecasts for various scenarios and appropriatereservoir operations to optimize benefits andminimize damage

13.4 Irrigation in the future

Irrigation will be necessary throughoutmuch of the world to ensure that agricul-ture production is possible to support theexpanding population. While people in thedeveloped countries enjoy prosperity andplentiful food, it is estimated that half ofthe people in the world, some three billionpeople, have insufficient food to sustainlife. These same people do not have accessto safe drinking water.

Management of water and efficiency ofirrigation will play a key role in the future.Successful irrigation requires a reliablewater supply throughout the growing season.Reduced losses in canals, improved meas-urement, monitoring and control systemswill help optimize the amount of waterused for irrigation. The use of water


13


soluble fertilizers willimprove the foodproduction from agiven field. Storageof water duringperiods of excessflow for use during

periods of storageby using dams and

reservoirs is the mostimportant factor for assuring

that a reliable water supplywill be available.

13.5 Hydropower in the future

Hydropower supplies about 20 % of theworld’s electricity today and there are hydrostations being built in virtually all parts ofthe world because it is a renewable source ofelectricity.

A country’s basic hydroelectric potential canbe worked out based on its annual rainfall, itsriver systems, and its topography (hilly ormountainous terrain). But not all of thispotential can ever be used, as there maybe areas where it is not technically possibleto build a dam or power station, becausegeological or other conditions may not beright, and may also be economic and politicalconstraints. There may be other priorities fora country’s budget, or reasons to avoid someareas because of other uses for the land, or alarge population living there.

Most remaining technically feasible sitesremain today in Africa, Asia and LatinAmerica, and in these regions there areoften economic constraints. But there arehydroelectric schemes being either built orplanned in about 180 countries. Currently,the leading countries at present for develop-ing their hydroelectric potential are:China, India, Iran, Brazil and Turkey.

The largest hydro station in full operationis at the Itaipú dam, built on a riverbetween Brazil and Paraguay producing14,000 MW. The biggest one under construc-tion is Three Gorges Project on the YangtzeRiver in China. When complete in 2009, itwill produce 18,200 MW plus provide floodcontrol and navigation. These are excep-tionally large projects. There are hundredsof medium-scale hydropower facilitiesworldwide.

Many countries have connections to a gridsystem at the national or regional level.Hydro stations very often feed power intothese systems. Often several neighboringcountries have interconnected grid systems,so water resources in one country might behelping to supply electricity to others.Sometimes agreements are made betweentwo countries whereby one will agree tobuy power from another, and will help tofinance and develop hydroelectricresources for its neighbor. Examplesinclude Thailand buying power from Laos,and India buying power from Bhutan, ineach case this is based on distribution ofpower in a region.

“Small-scale hydro schemes” can also playan important role worldwide. They gener-ally only involve the construction of verysmall dams, so they are cheaper to build,and they may supply isolated areas of thecountryside, or small communities, sometimesnot reached by a national grid system.Small hydro stations can sometimes beadded at dams which have been builtmainly for other purposes. The relativelyflat Mur River in Austria near the borderwith Slovenia has several low head smallhydropower projects.

The ThreeGorges Projecton the YangtzeRiver in China

Managedwater and

soluble fertilizerswill improvefood produc-

tion



13

Itaipu Dam,Brazil and Paraguay.In 2006 the world’slargest hydropower

project

Generators ina hydropower

plant

GabersdorfDam near Leibnitz

- Austria - is an exampleof small hydropower

The project has a headof 8 meters and

a capacity of14.5 MW

Details ofGabersdorfturbines andradial gates

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As part of the process to improve floodcontrol systems, governments will needto review the climate changes and thestandard level of protection to be provided.In many parts of the world this levelwill need to be raised. In addition,stricter zoning of land in and adjacentto the floodplain will have to beimplemented.

Significant difficulties in weather predic-tion arise from rapidly developing

climate changes in almost allparts of the world. Therefore,

greater use of weather radarmonitoring rainfall, hydro-logic models and computerforecasting will allow realtime forecasts for opera-tional discharges fromthe dams and forecasts

of all river stages in thebasin. Here is an example

of the components of a realtime water management in a

river basin.

13.6 Flood control in the future

As in the past, a significant portion of theworld’s population will continue to settlenear our rivers and streams. This situationwill require optimization of existing floodcontrol dams and projects as well as the

planning, design and construction of newprojects. It will be essential that the plan-ning for these flood control projects beaccomplished on a watershed basis toaccount for the anticipated amount ofrainfall and locations of populationgrowth.

Automatedstream gagesto obtain real

time stream flowand stage

Weather radarfor predictionof the amountand locations

of rainfall

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RochemaureDam - France - damsand flood protection

systems will continue tocontrol flood waters inour rivers to preventovertopping of the

levee systems

13.7 Inland navigationin the future

As economic development continues inthe world, there will be a significantincrease in the transport of raw materialsand goods as well as an increased demandfor products. Rising fuel costs will have animpact on the means of transportationused. Inland navigation is the most costeffective and least polluting means oftransportation. A principal value of theinland waterways is their ability to efficientlyconvey large volumes of bulk commoditiesmoving long distances. A 15-barge tow iscommon on larger rivers with locks. Suchtows are an extremely efficient mode oftransportation and can move about 22,500 tonsof cargo as a single unit. Two examples ofthe cost effectiveness on inland navigationare as follows:

The capacity of 1 barge= 15 jumbo rail cars= 55 normal trucks

The capacity of 1 tow (15 barges)= 21 four unit trains= 870 trucks


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Computerizedhydrologic models

to use real time inputfrom weather radar andstream gages to makeaccurate forecasts foroperational changes

in reservoirs

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DonzèreDam - France -

operationaldischarges tocontrol down-stream flooding


13.8 The balance betweenproject benefits andthe environment

The social and environmental impacts ofdams and reservoirs built today must beavoided, or mitigated. The operation ofexisting dams must be reviewed and if neces-sary modified to accommodate projectimpacts on the environment. Every effortmust be made to have the dam and reservoirproject enhance or support the environment.Today's water resources professionals areguided by environmental policy as well asby engineering and safety concerns.Planners and engineers, many of whom aremembers of the International Commissionon Large Dams, include the environmentamong their responsibilities. The teams ofengineers and specialists from manydisciplines - planning, engineering, environ-mental and social science - are involved in

the planning, design and construction ofdams. The following issues are consideredwhen developing modern water resourcesprojects:

◗ Dam and reservoir projects require systemplanning which recognizes the impact onan entire river basin and its ecosystems.

◗ Public consultation and input from all thepeople involved to obtain a consensus isnecessary for the most effective projectplanning, implementation and operation.

◗ Include the environment, both naturalconditions and social aspects, along witheconomic benefits in the initial planningfor the project.

◗ Many countries now require the formalidentification of environmental impactsduring the conceptual phase of a project.

◗ Environmental protection and enhance-ment are generally included in all phases ofthe project.

Looking to the future, if the cargo transportedon the inland waterways each year had tobe moved by another mode, it would takeabout 6.3 million rail cars or 25.2 million trucksto carry the load. Imagine adding this trafficwith the associated air pollution to thealready congested rail lines and highwaysthat pass through our communities.

The ability to move more cargo per shipmentmakes barge transport both fuel efficient andenvironmentally advantageous. On average, agallon of fuel allows one ton of cargo to beshipped 59 miles by truck,202 miles by rail, and514 miles by barge. Developing countries withrivers will need to use inland navigation as partof their national economic development plan.

Centrallock and dam

structures


◗ Rigorous economic analyses of the benefitsand costs for environmental mitigation forlarge projects provide critical information todecision-makers.

◗ With careful planning and implementa-tion, the people required to be resettledbecause of the reservoir project can andmust benefit first.

◗ Monitoring of the environmental impactsof existing projects provides a better under-standing of the true impacts rather thanprojected impacts.

◗ Research on the ecological aspects of themany existing dams and reservoirs canprovide important lessons for futureprojects.


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Sault-BrenazDam

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13.9 The need for publicawareness and educationon water resources

The world is in an era where vast amounts ofinformation are available through the all versionsof the media. The Internet, publications andother forms of media have a significant impacton the knowledge and perceptions of society.The issue of the expansion and rehabilitation ofthe world’s infrastructure and the debate aboutthe need for and use of dams is an excellentexample of this worldwide phenomenon.

It is important for the public be remindedabout the realistic facts about water as theworld’s vital natural resource. Most of thewater on the earth is located in the oceans.There is only a small of all of the water on theearth that is fresh and available on the earthfor human consumption - 2.5% of the total.While groundwater is a widely used source,withdrawals must be managed to guardagainst depletion. The public must be madeaware of the fact that the amount of waterfrom precipitation or rainfall on the worldremains constant and only 19% or 110,000 km3

falls on land. Of this amount, 65,200 km3 or

59% evaporates and 42,600 km3 or 39%becomes runoff to the ocean. There is only2,200 km3 or 2% infiltration for groundwater.As the world develops it becomes moreimportant that we capture some of the42,600 km3 of runoff in reservoirs to managethroughout the year. This has been a succes-sful strategy for more that 5,000 years.

It is important to become aware of thechallenges and opportunities that exist rel-ative to the world’s water and the benefitsfrom the storage and management ofwater in river basins. The public mustbecome aware of the beneficial role ofdams in the management of water inwatersheds or river basins to meet theincreasing demand for water and to pre-vent floods as well as the relationship ofdams and the environment.

ICOLD is a source reliable facts and informa-tion to the political decision-making bodies,financing agencies, environmental lobbygroups and organizations, and to the generalpublic, on the benefits of prudent utilizationof water, especially by storage in reservoirsand the proper operation of dams.


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Environmentalmitigation and

enhancement canbe effective

a river ecosystemin the USA


In summary, this book demonstrates thatwater remains the vital resource to sustaincivilization around the world, and that freshwater for human consumption and irrigationis only available in limited quantities.Sustainability of life in some regions of theworld is threatened by the imbalancebetween the demand for and availablesupplies of water, food and energy. We haveseen how the world gets its water from thewater cycle and the limited quantity of rainthat falls on the world’s landmass. We mustremember that this limited quantity is notevenly distributed in the world by season orregion. There is an imbalance between thedemand for water and its availability.

History shows us that dams and reservoirshave been used successfully in collecting,storing and managing water needed tosustain civilization for five centuries. As welook to the future, we must learn from thepast and project this knowledge to thefuture. ICOLD was established in 1928 andcurrently has 88 member countries withabout 10,000 individual technical expertsand has a long history of providing technicalguidance and standards for the use of damsaround the world. Today, ICOLD plays amajor worldwide role in advancing the artand science of building dams to produce themost efficient, effective and responsiblewater resource projects for the benefit ofsociety. This is accomplished by developingand promoting technically sound engineeringconcepts and guidelines that are compatiblewith the social, environmental, financialand operational requirements of a waterresources development project. Looking tothe future ICOLD is

“Preparing to meettomorrow’s challengesin the development

and management of theworld’s water resources”

This goal is being accomplished by theinternational exchange and transfer ofknowledge and experience about dams andtheir associated technology and functions.This process is very useful in passing informa-tion from those with long-term experienceto those who have major construction programsahead in their future. It is also important toensure that existing dams remain safe, andare operated in the most efficient andeconomic way. This is where big internationalassociations such as the InternationalCommission On Large Dams (ICOLD) areimportant. The Commission was establishedat a time when major dam building programswere beginning in places like Europe andNorth America.

As we look to the future, the planningprocess must carefully document the proposedbenefits as well as the concerns andimpacts that must be mitigated. The concernsand adverse impacts of dams can be minimizedor eliminated by careful planning anddesign that incorporate public involvementand input in the early stages of thisprocess. When the appropriate mitigationmeasures are identified early in the plan-ning and design process for a dam andreservoir, they can be efficiently and effectivelyincorporated into the design,construction andoperation of the project.

The Roleof ICOLD andthe World’s Water


ICOLD’s intent is to ensure that the dams andassociated structures required for waterresource development and managementaround the world are safe, economical,environmentally responsible, sociallyacceptable and are operated and maintainedfor sustained reliability. Dams and reservoirs

can and should be compatible with the socialand natural environment of the region. Thechallenge for the future will be the utilizationof dams and reservoirs for the wise manage-ment of the world’s water resources as partof each nation’s social and economicdevelopment goals.

SummaryIn the beginning of this book, we haveseen that there is a fixed amount of water inthe water cycle and that only a small quantityof fresh water is available for human consump-tion.We now understand that most of the rainfalls on the oceans and we understand that asignificant portion of the rain that falls onland evaporates or ends up as runoff thatgoes into our streams and then the ocean.This means that only a small amount of wateris available to replenish our groundwater. Thisemphasizes the need to collect, store and useintegrated water management to insureadequate river flows throughout the year.History shows us that generations before uswere quick to see the need for dams andreservoirs to store water for reliable distribu-tion of water throughout the year.

As in the past, the well-being of people of theworld in the future will continue to beclosely linked to reliable and sustainablewater supplies. The water shortages in manyregions of the world will increase significant-ly. Reliable supplies of water will be neededto improve the state of health in the worldand to increase the agricultural and industrialproductivity.

Throughout the history of the world, damshave played a major role in storing andmanaging water needed to support civiliza-tion. Today, the world is undergoing majorchanges in ethical values, business practices,and living conditions as a result of rapidadvances in technology and expandedcommunications associated with the continuedunprecedented increase in population.

At the same time there has been careless useof our natural resources and acceleratedpollution of the environment. As the popula-tion of the world continues to grow with theassociated economic and agriculturaldevelopment, so does the need for watersupply and more dams.

The watershed is the basic element formanaging water resources and the environ-ment. Therefore, in looking to the future,planning and development must be madeon a watershed basis. As the magnitude ofthe demand for water continues to increase,people will need to use wise planning andengineering in the successful six step plan-ning process to best meet these needs andthe goals and objectives of individual damprojects. With proper public involvementand coordination, the socio-economic issuessuch as resettlement and equal distributionof project benefits can be adequatelysolved. Then, dams of a proper size andlocation can be designed and constructed inthe watershed. This is particularly importantin the developing nations. The UnitedNations recognizes that water is theresource that is an essential ingredient toachieving their goals to eliminating povertyand hunger, improving health, and combat-ing disease by 2015. The mitigation of flooddamage to society will require increasedflood control storage in both existing andnew dams. More dams will be needed andwe must be mindful that these dams andreservoirs, when properly managed, are the


The Role of ICOLDand the World’s Water

15only viable option to provide the quantitiesof water needed. We must also recognizethat they can be operated in an environ-mentally responsible manner.

Since the environment is an importantaspect of our existence and is related toour streams and rivers, reservoir projectsneed to be managed on a watershed basisto optimize environmental mitigation andbenefits. The objective of water managementin the watershed remains unchanged:satisfy demands without sacrificing existinguses. The major issues with respect towater management in the watershedbasins are:

◗ Formulating strategies to provide adequate stream flow.

◗ Satisfying the municipal and agriculturaldemands without injury to theenvironment.

◗ Evaluating and improving water quality.

Watershed planning and water managementthat includes environmental mitigationand conservation are the key elements toproviding optimum water supply, flood control,hydropower and other benefits withoutharming the ecosystems. Successful integratedwater management must incorporate real-timedata collection, state-of-the-art spatiallydistributed rainfall-runoff flow forecastingcapabilities and reliable models to ensurethat adequate water quality and quantityis available to meet the regional andlocal needs.

Advanced technology is needed for theplanning, design, construction, operationand maintenance of large dams and theirrelated facilities so that they are economical,safe and environmentally responsible. Asin the past, ICOLD continues to advancethe state of the practice for the planning,engineering, construction, operation andmaintenance for dams. The increasinglyimportant role of ICOLD is to make surethat dams will be planned,designed,constructedand operated with maximum mitigation ofenvironmental impacts while maximizingsocial and economic benefits. This is thebest way to achieve sustainable develop-ment and management of the world’s waterresources. The goal is plan, design, constructand operate cost effective, efficient damsthat are socially, environmentally responsibleprojects of our infrastructure. The beststrategy is to use a wise planning processwith public involvement that considersall water resources in a watershed. Theconcerns and potential adverse impacts ofdams can be eliminated by this carefulplanning process.

Looking to the future, we must benefit andbuild on the successful experiences fromprevious generations for the managementof the world’s water. Wise planning for bothgroundwater and reservoirs in a watershedwill best suit the growing need for water.Dams and reservoirs will continue to beneeded to supply water in large quantitiesand adequate quality to meet the needsof a region.

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Gloss

ary

of T

erms The purpose of this glossary is to define the common

terms used for dams and in water resources developmentand management. The terms are generic and applicable toall dams, regardless of size, owner, or location. The termsare listed in alphabetical order.

Abutment That part of the valley side against which thedam is constructed. An artificial abutment is sometimesconstructed, as a concrete gravity section, to take the thrustof an arch dam where there is no suitable natural abutment.The left and right abutments of dams are defined with theobserver viewing the dam looking in the downstreamdirection, unless otherwise indicated.

Acre-foot A unit of volumetric measure that wouldcover one acre to a depth of one foot. It is equal to43,560 cubic feet or 1,233.6 cubic meters.

Appurtenant structure The other features of adam project such as the control rooms, outlet conduit,outlet tunnel, spillways, penstocks, power plants, etc.

Aqueduct Bridges built to carry water across a valley

Bedrock Any sedimentary, igneous, or metamorphicmaterial represented as a unit in geology; being a sound andsolid mass, layer, or ledge of mineral matter; and with shearwave threshold velocities greater than 2500 feet/second.

Borrow area The area from which natural materials, such asrock, gravel or soil, used for construction purposes is excavated.

Channel A general term for any natural or artificial facilityfor conveying water.

Cofferdam A temporary structure enclosing all or partof the construction area that construction can proceed in thedry. A diversion cofferdam diverts a stream into a pipe,channel, tunnel, or other watercourse.

Compaction The mechanical action that increases thedensity by reducing the voids in a material.

Concrete lift The vertical distance measured in feet ormeters between successive placements of concretedelineated by horizontal construction joints.

Conduit A closed channel to convey water through,around, or under a dam.

Core A zone of low permeability material in an embank-ment dam. The core is sometimes referred to as centralcore, inclined core, puddle clay core, rolled clay core, orimpervious zone.

Crest length The measured length of the dam alongthe crest or top of dam.

Crest of dam See top of dam.

Cross section The elevation view of a dam formedby passing a plane through the dam perpendicular tothe axis.

Dam An artificial barrier that has the ability to impoundwater, wastewater, or any liquid-borne material, for thepurpose of storage or control of water.◗ Arch dam A concrete, masonry, or timber dam with thealignment curved upstream so as to transmit the major partof the water load to the abutments.

◗ Buttress dam A dam consisting of a watertight partsupported at intervals on the downstream side by a seriesof buttresses. Buttress dam can take many forms, such asa flat slab or massive head buttress.

◗ Diversion dam A dam built to divert water from awaterway or stream into a different watercourse.

◗ Earthfill dam An embankment dam in which morethan 50% of the total volume is formed of compacted earth.

◗ Embankment dam Any dam constructed of excavatednatural materials, such as both earthfill and rockfill dams.

◗ Gravity dam A dam constructed of concrete and/ormasonry, which relies on its weight and internal strength forstability.

◗ Masonry dam Any dam constructed mainly of stone,brick, or concrete blocks pointed with mortar. A dam havingonly a masonry facing should not be referred to as amasonry dam.

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◗ Multiple arch dam A buttress dam comprised of aseries of arches for the upstream face.

◗ Rock-fill dam An embankment dam in which morethan 50% of the total volume is comprised of compacted ordumped cobbles, boulders, rock fragments, or quarriedrock generally larger than 3-inch size.

◗ Roller compacted concrete dam A concretegravity dam constructed by the use of a dry mix concretetransported by conventional construction equipment andcompacted by rolling, usually with vibratory rollers.

Divert To make go another way.

Drainage area or catchment area The areathat drains to a particular point on a river or stream(expressed in square miles or square kilometers).

Earthquake A sudden motion or trembling in the earthcaused by the abrupt release of accumulated stressalong a fault.

Erosion The wearing away of a surface such as the bank,streambed, embankment, or other surface by river flows,reservoir waves, wind, or any other natural process.

Evaporate The process of changing liquid into a gas orvapor which is incorporated into the air

Fertile The very rich soil which is best for producingcrops

Flood A temporary rise in water surface elevation of astream or river as a result of significant rainfall in thedrainage area. It results in inundation of areas not normallycovered by water.

Flood, Inflow Design (IDF) The flood flow abovewhich the incremental increase in downstream water surfaceelevation due to failure of a dam or other water impoundingstructure is no longer considered to present an unacceptablethreat to downstream life or property. The flood hydrographused in the design of a dam and its appurtenant works particularlyfor sizing the spillway and outlet works and for determiningmaximum storage, height of dam, and freeboard requirements.

Flood, Probable Maximum (PMF) The floodthat may be expected from the most severe combination ofcritical meteorological and hydrologic conditions that arereasonably possible in the drainage basin under study.

Flood plain The area adjoining a body of water ornatural stream that may be covered by floodwater. It is alsoused to describe the downstream area that would beinundated or otherwise affected by the failure of a dam or bylarge flood flows.

Flood storage The retention of water or delay of runoffeither by planned operation, as in a reservoir, or by temporaryfilling of overflow areas, as in the progression of a flood wavethrough a natural stream channel.

Foundation The portion of the valley floor that underliesand supports the dam structure.

Freeboard Vertical distance between a specified reser-voir surface elevation and the top of the dam.

Gate A movable water barrier for the control of water.◗ Radial gate A gate with a curved upstream plate andradial arms hinged to piers or other supporting structure.

◗ Slide gate A gate that can be opened or closed bysliding in supporting guides.

Generator The machine that produces electricity

Head The vertical distance between two elevations ofwater (expressed in feet or meters).

Headwater The water immediately upstream from adam. The water surface elevation varies due to fluctuationsin inflow and the amount of water passed through the dam.

Hydrology One of the earth sciences that deals withthe natural occurrence, distribution, movement, and proper-ties of the waters of the earth and their environmentalrelationships.

Hydrometeorology The study of the atmosphericand land-surface phases of the hydrologic cycle withemphasis on the interrelationships involved.

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Instrumentation An arrangement of devices installedinto or near dams that provide for measurements that can beused to evaluate the structural behavior and performanceparameters of the structure.

Intake Placed at the beginning of an outlet-works waterway(power conduit, water supply conduit), the intake establishesthe ultimate drawdown level of the reservoir by the positionand size of its opening(s) to the outlet works. The intake maybe vertical or inclined towers, drop inlets, or submerged,box-shaped structures. Intake elevations are determined bythe head needed for discharge capacity, storage reservationto allow for siltation, the required amount and rate ofwithdrawal, and the desired extreme drawdown level.

Integrated water management in the riverbasin The process by which the water stored in reservoirsand the daily amount released is managed in the basin toensure an adequate and dependable quantity is available.Each dam and reservoir in the basin has a water control planthat outlines discharges from that reservoir based on inflowto the reservoir and downstream needs. Each water controlplan is coordinated with other dam and reservoir projectwithin the river basin.

Length of dam The length along the top of the dam.

Low level outlet An opening at a low level from areservoir generally used for emptying or for scouringsediment and sometimes for irrigation releases.

MW or Mega Watt A unit for measuring power.One MW equals 1 million watts.

Meteorology The science that deals with theatmosphere and atmospheric phenomena, the study ofweather, particularly storms and the rainfall they produce.

Minimum operating level The lowest level towhich the reservoir is drawn down under normal operatingconditions. The lower limit of active storage.

Multipurpose project A project designed for irrigation,power, flood control, municipal and industrial, recreation,and fish and wildlife benefits, in any combinations of two ormore. Contrasted to single-purpose projects that serves onlyone purpose.

Outlet An opening through which water can be dischargedfrom a reservoir to the river.

Outlet works A facility of a dam that provides for thecontrolled release of water from a reservoir.

Peak flow The maximum instantaneous discharge thatoccurs during a flood. It is coincident with the peak of a floodhydrograph (expressed in cubic feet per second - cfs orcubic meters per second - cms or m3sec).

Penstock A pressurized pipeline or shaft between thereservoir and hydraulic machinery.

Probable Maximum Flood (PMF) See Flood.

Probable Maximum Precipitation (PMP)Theoretically, the greatest depth of precipitation for a given dura-tion that is physically possible over a given size storm area at aparticular geographical location during a certain time of the year.

Reservoir The body of water impounded by a dam andin which water can be stored.

Reservoir regulation The process of the compila-tion of operating criteria, guidelines, and specifications thatgovern the storage and release function of a reservoir. It mayalso be referred to as the flood control diagram, or watercontrol schedule. These are usually expressed in the form ofgraphs and tabulations, supplemented by concise specifica-tions and are often incorporated in computer programs. Ingeneral, they indicate limiting rates of reservoir releasesrequired or allowed during various seasons of the year tomeet all functional objectives of the project.

Reservoir rim The boundary of the reservoir includingall areas along the valley sides at the water surface.

Reservoir surface area The area covered by areservoir when filled to a specified level (expressed in squaremiles - miles2 or square kilometers - km2).

Reservoir Storage The retention of water or delay ofrunoff either by planned operation, as in a reservoir, or bytemporary filling of overflow areas, as in the progression of aflood wave through a natural stream channel (expressed inacre-feet - ac-ft or cubic meters - m3). Definitions of specifictypes of storage in reservoirs are:

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Gloss

ary

of T

erms

◗ Active storage The volume of the reservoir that isavailable for some use such as power generation, irrigation,flood control, water supply, etc. The bottom elevation isthe minimum operating level.

◗ Dead storage The storage that lies below theinvert of the lowest outlet and that, therefore, cannotreadily be withdrawn from the reservoir.

◗ Flood surcharge The storage volume betweenthe top of the active storage and the design water level.

◗ Inactive storage The storage volume of a reservoirbetween the crest of the invert of the lowest outlet andthe minimum operating level.

◗ Live storage The sum of the active-and the inactivestorage.

◗ Reservoir capacity The sum of the dead andlive storage of the reservoir.

River basin or watershed The area drained bya river or river system or portion thereof. The watershedfor a dam is the drainage area upstream of the dam(expressed in square miles or square kilometers).

Single purpose project A project that providesa single purpose, such as navigation only

Slope Inclination from the horizontal. Sometimesreferred to as batter when measured from vertical.

Spillway A structure over or through which flow is dis-charged from a reservoir. If the rate of flow is controlledby mechanical means, such as gates, it is considered acontrolled spillway. If the geometry of the spillway is theonly control, it is considered an uncontrolled spillway.

Spillway capacity The maximum spillway outflowthat a dam can safely pass with the reservoir at its maximumlevel (expressed in cubic feet per second - cfs or cubicmeters per second - cms or m3sec).

Spillway channel An open channel or closed conduitconveying water from the spillway inlet downstream.

Spillway crest The lowest level at which water canflow over or through the spillway.

Stability The condition of a structure or a mass ofmaterial when it is able to support the applied stress fora long time without suffering any significant deformationor movement that is not reversed by the release ofthe stress.

Stilling basin A basin constructed to dissipate theenergy of rapidly flowing water, e.g., from a spillway oroutlet, and to protect the riverbed from erosion.

Tailwater The water immediately downstream from adam. The water surface elevation varies due to fluctua-tions in the outflow from the structures of a dam and dueto downstream influences of other dams or structures.Tailwater monitoring is an important considerationbecause a failure of a dam will cause a rapid rise in thelevel of the tailwater.

Toe of the dam The junction of the downstreamslope or face of a dam with the ground surface; alsoreferred to as the downstream toe. The junction of theupstream slope with ground surface is called the heel orthe upstream toe.

Topographic map A map with detailed graphicdelineation (representation) of natural and man-madefeatures of a region with particular emphasis on relativeposition and elevation.

Tributary A stream that flows into a larger stream orbody of water

Tunnel A long underground excavation with two ormore openings to the surface, usually having a uniformcross section used for access, conveying flows, etc.

Volume of dam The total space occupied by thematerials forming the dam structure computed betweenabutments and from top to bottom of dam.

Watershed or river basin The area drained bya river or river system or portion thereof. The watershedfor a dam is the drainage area upstream of the dam(expressed in square miles or square kilometers).


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Publishing Manager:Mr Michel de Vivo (Secretary General of ICOLD)Authors:ICOLD Committee on Public Awareness and Education chaired byMr Art Walz (Vice President of ICOLD) with the kind cooperation ofMr Andy Hughes (Vice President of ICOLD), Mr Patrick Bonnet(Secretary General of the French National Committee) andMr Gerrit Basson (President of the Sedimentation Committee)

Design & Production:Vlady France Conseil - VFC54bis, rue Louis Rouquier92300 Levallois-Perret - FranceTel: 33 (1) 40 89 23 23 - Fax: 33 (1) 47 58 80 95Layout: Benoît Lamy - VFCPrinted in the European UnionISSN N°0534-8293 - Dépot légal juin 2007

This book was prepared by the members of the ICOLD Committee on Public Awareness and Education. The photographs used have beenobtained from the ICOLD library or from some of the 88 member countries of ICOLD. The information contained in Dams of Today wasobtained from the ICOLD Register of Dams.

Photos:Front cover: © DR, © pmphoto/Fotolia, © Guillaume Beuls/Fotolia, © Julian Owen/FotoliaInside pages: © Eric Martinez/Fotolia: n°1,3 - © Guillaume Beuls/Fotolia: n°4 - © Julian Owen/Fotolia: n°5 - © Geoffrey Whiting/Fotolia: n°6, 40© Koldo Ruilope Gonzalez/Fotolia: n°7 - © Rudy Van Der Walt/Fotolia: n°14, 52 - © photo EDF: n°15, 16,18, 19, 20, 26 - © BRL i: n°17© pmphoto/Fotolia: n°27 - © Philippe Aurouz/Fotolia: n°30 - Sören Platten/Fotolia: n°32 - © Studios Villeurbannais: n°34 - © Zastavkin/Fotolia: n°35, 37, 54 © Philippev/Fotolia: n°38 - © Jennie Hall/Fotolia: n°41 - © Emmanuelle Combaud/Fotolia: n°42 - © Sean Mcfadden/Fotolia: n°43 - ©Les quatre vents: n°54© Sascha Felragel/Fotolia: n°45 - © CNR: n°46, © Matteo Natale/Fotolia: n°48 - © Micheal Andrey/Fotolia: n°49 - © photoeyes/Fotolia: n°50© Jonart/Fotolia: n°51 - © JoLin/Fotolia: n°53 - © Médiathèque EDF: n°2, 8, 9, 10, 11, 12, 13, 21, 28, 29, 30, 31, 33, 36, 39, 44, 47 - © Landscapingand publicity/Armin Rieg: n°55, 56, 57

References:

◗ ICOLD Position Paper on Dams and Environment, May 1997.◗ ICOLD Position Paper on the Role of Dams in Flood Mitigation,2006.

◗ ICOLD Paper - The Role of Dams in the XXI Century to AchieveSustainable Development, 2006.

◗ ICOLD, Technical Dictionary on Dams - Glossary of Terms, 1994.

◗ ICOLD Bulletin 128, Management of Reservoir Water Quality- Introduction and Recommandations, 2004.

◗ ICOLD Bulletin 125, Dams and Floods - Guidelines and CaseHistories, 2003.

◗ Dams, Dunn, Andrew, Thompson Learning, NY, 1993◗ World Book Encyclopedia, 22 Volumes, 2006 Edition, World Book,Inc., Chicago, IL.

◗ The New Encyclopedia Britannica: Macropedia, 15th ed., 2005

International Commission On Large DamsCommission Internationale des Grands Barrages151, Boulevard Haussmann - 75008 Paris - FranceTel: 33 (1) 40 42 68 24 - Fax: 33 (1) 40 42 60 71

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