26321 Water Resources and Environment Technical Note E.1 Irrigation and Drainage Development Series Editors Richard Davis Rafik Hirji WATER RESOURCES AND ENVIRONMENT TECHNICAL NOTE E.1 Irrigation and Drainage: Development SERIES EDITORS RICHARD DAVIS, RAFIK HIRJI The World Bank Washington, D.C. Water Resources and Environment Technical Notes A. Environmental Issues and Lessons Note A.1 Environmental Aspects of Water Resources Management Note A.2 Water Resources Management Policy Implementation: Early Lessons B. Institutional and Regulatory Issues Note B.1 Strategic Environmental Assessment: A Watershed Approach Note B.2 Water Resources Management: Regulatory Dimensions Note B.3 Regulations for Private Sector Utilities C. Environmental Flow Assessment Note C.1 Environmental Flows: Concepts and Methods Note C.2 Environmental Flows: Case Studies Note C.3 Environmental Flows: Flood Flows Note C.4 Environmental Flows: Social Issues D. Water Quality Management Note D.1 Water Quality: Assessment and Protection Note D.2 Water Quality: Wastewater Treatment Note D.3 Water Quality: Nonpoint-Source Pollution E. Irrigation and Drainage Note E.1 Irrigation and Drainage: Development Note E.2 Irrigation and Drainage: Rehabilitation F. Water Conservation and Demand Management Note F.1 Water Conservation: Urban Utilities Note F.2 Water Conservation: Irrigation Note F.3 Wastewater Reuse G. Waterbody Management Note G.1 Groundwater Management Note G.2 Lake Management Note G.3 Wetlands Management Note G.4 Management of Aquatic Plants H. Selected topics Note H.1 Interbasin Transfers Note H.2 Desalination Note H.3 Climate Variability and Climate Change Copyright © 2003 The International Bank for Reconstruction and Development/THE WORLD BANK 1818 H Street, N.W., Washington, D.C. 20433, U.S.A. All rights reserved. Manufactured in the United States of America First printing March 2003 2 CONTENTS Foreword 5 Acknowledgments 7 Introduction 9 Why Irrigate or Drain Land? 10 The primary reason for irrigating and draining land has been to improve or sustain agricultural productivity in Authors areas where surface soils are naturally dryer or wetter Walter Ochs and than desired. Irrigation and drainage can also make Hervé Plusquellec rural areas more habitable and improve accessibility. Technical Adviser Water Quality Issues 11 Stephen Lintner Salinity is the key water quality parameter of concern for irrigation water. This is almost always a problem in Editor arid and semi-arid regions. Increasingly, there are is- Robert Livernash sues arising from the use of wastewater for irrigation. Other water quality issues associated with drainage Production Staff management include pesticides, toxic trace elements, Cover Design: Cathe Fadel nutrients, and sediment. Design and Production: The Word Express, Inc. Irrigation: Environmental Consequences and 12 Solutions Notes Environmental problems caused by irrigation can be Unless otherwise stated, avoided or considerably mitigated by proper plan- all dollars = U.S. dollars. ning and design of irrigation projects. All tons are metric tons. Drainage: Environmental Consequences and 17 Cover photo by Solutions UNESCO Drainage is often necessary to prevent waterlogging Irrigation fields, Mexico and to dispose of saline water in irrigation areas. Un- less properly designed, drainage systems can have This series also is available on the environmental consequences, including leaching of World Bank website natural soil elements; leaching of applied materials (www.worldbank.org). such as fertilizers and pesticides; hydraulic and hy- drologic problems; and water quality problems down- stream. Institutional Considerations 22 Institutional considerations include irrigation and regu- latory agency role, structure, and mandate; stake- holder participation during all project phases; the availability of technical education and assistance; and institutional mechanisms for downstream/upstream me- diation or cooperation. 3 WATER RESOURCESANDENVIRONMENT · TECHNICAL NOTE E.1 Quantifying impacts of I&D Schemes 25 Methods for quantifying impacts include environmental assessment during plan- ning to identify potential problems; monitoring and evaluation; water and salt- balance calculations for specific basin and sub-basin areas; and modeling of potential impacts prior to project development. Case Studies 27 Case studies are presented in the Lop Noor Lake region, Xinjiang Province, China, and the Indus River basin, Pakistan. Further Information 30 Boxes 1. Egypt's Nile Delta 14 2. The Aral Sea 16 3. Favorable habitat for aquatic snails 16 4. Damage from drainage: Kesterson National Wildlife Refuge, California 18 5. The Uttar Pradesh Sodic Lands Reclamation Project, India 18 6. Acid sulfate soil drainage 22 7. Usangu Plain in Tanzania 24 8. Liguasan Marsh in the Philippines 26 9. Items to be considered in monitoring programs for irrigation and drainage 26 Figures 1. Flow toward depressed groundwater table under plantations 13 2. The process of waterlogging and salinization 13 3. Indicative groundwater and surface-water balance in the Tarim River Basin 27 4. Example of salt balance and distribution ­ Pakistan portion of Indus River Basin 28 Tables 1. Degrees of restriction from salinity and SAR for irrigation uses of water 11 4 IRRIGATIONANDDRAINAGE: DEVELOPMENT FOREWORD The environmentally sustainable development and priority in Bank lending. Many lessons have been management of water resources is a critical and learned, and these have contributed to changing complex issue for both rich and poor countries. It attitudes and practices in World Bank operations. is technically challenging and often entails difficult trade-offs among social, economic, and political con- Water resources management is also a critical de- siderations. Typically, the environment is treated velopment issue because of its many links to pov- as a marginal issue when it is actually key to sus- erty reduction, including health, agricultural tainable water management. productivity, industrial and energy development, and sustainable growth in downstream communi- According to the World Bank's recently approved ties. But strategies to reduce poverty should not lead Water Resources Sector Strategy, "the environment to further degradation of water resources or eco- is a special `water-using sector' in that most envi- logical services. Finding a balance between these ronmental concerns are a central part of overall objectives is an important aspect of the Bank's in- water resources management, and not just a part terest in sustainable development. The 2001 Envi- of a distinct water-using sector" (World Bank 2003: ronment Strategy underscores the linkages among 28). Being integral to overall water resources man- water resources management, environmental agement, the environment is "voiceless" when other sustainability, and poverty, and shows how the 2003 water using sectors have distinct voices. As a con- Water Resources Sector Strategy's call for using sequence, representatives of these other water us- water as a vehicle for increasing growth and re- ing sectors need to be fully aware of the importance ducing poverty can be carried out in a socially and of environmental aspects of water resources man- environmentally responsible manner. agement for the development of their sectoral in- terests. Over the past few decades, many nations have been subjected to the ravages of either droughts or floods. For us in the World Bank, water resources man- Unsustainable land and water use practices have agement--including the development of surface and contributed to the degradation of the water resources groundwater resources for urban, rural, agriculture, base and are undermining the primary investments energy, mining, and industrial uses, as well as the in water supply, energy and irrigation infrastruc- protection of surface and groundwater sources, pol- ture, often also contributing to loss of biodiversity. lution control, watershed management, control of In response, new policy and institutional reforms water weeds, and restoration of degraded ecosys- are being developed to ensure responsible and sus- tems such as lakes and wetlands--is an important tainable practices are put in place, and new predic- element of our lending, supporting one of the es- tive and forecasting techniques are being developed sential building blocks for sustaining livelihoods and that can help to reduce the impacts and manage for social and economic development in general. the consequences of such events. The Environment Prior to 1993, environmental considerations of such and Water Resources Sector Strategies make it clear investments were addressed reactively and prima- that water must be treated as a resource that spans rily through the Bank's safeguard policies. The 1993 multiple uses in a river basin, particularly to main- Water Resources Management Policy Paper broad- tain sufficient flows of sufficient quality at the ap- ened the development focus to include the protec- propriate times to offset upstream abstraction and tion and management of water resources in an pollution and sustain the downstream social, eco- environmentally sustainable, socially acceptable, logical, and hydrological functions of watersheds and economically efficient manner as an emerging and wetlands. 5 WATER RESOURCES ANDENVIRONMENT · TECHNICAL NOTE E.1 With the support of the Government of the Nether- The Notes are in eight categories: environmental lands, the Environment Department has prepared issues and lessons; institutional and regulatory is- an initial series of Water Resources and Environ- sues; environmental flow assessment; water qual- ment Technical Notes to improve the knowledge ity management; irrigation and drainage; water base about applying environmental management conservation (demand management); waterbody principles to water resources management. The management; and selected topics. The series may Technical Note series supports the implementation be expanded in the future to include other relevant of the World Bank 1993 Water Resources Manage- categories or topics. Not all topics will be of inter- ment Policy, 2001 Environment Strategy, and 2003 est to all specialists. Some will find the review of Water Resources Sector Strategy, as well as the past environmental practices in the water sector implementation of the Bank's safeguard policies. useful for learning and improving their perfor- The Notes are also consistent with the Millennium mance; others may find their suggestions for fur- Development Goal objectives related to environmen- ther, more detailed information to be valuable; while tal sustainability of water resources. still others will find them useful as a reference on emerging topics such as environmental flow assess- The Notes are intended for use by those without ment, environmental regulations for private water specific training in water resources management utilities, inter-basin water transfers and climate such as technical specialists, policymakers and variability and climate change. The latter topics are managers working on water sector related invest- likely to be of increasing importance as the World ments within the Bank; practitioners from bilateral, Bank implements its environment and water re- multilateral, and nongovernmental organizations; sources sector strategies and supports the next gen- and public and private sector specialists interested eration of water resources and environmental policy in environmentally sustainable water resources and institutional reforms. management. These people may have been trained as environmental, municipal, water resources, ir- rigation, power, or mining engineers; or as econo- mists, lawyers, sociologists, natural resources Kristalina Georgieva specialists, urban planners, environmental planners, Director or ecologists. Environment Department 6 IRRIGATIONANDDRAINAGE: DEVELOPMENT ACKNOWLEDGMENTS The Bank is deeply grateful to the Government of Jan Hoevenaars and Roel Slootweg of Geoplan of the Netherlands for financing the production of this the Netherlands. It was reviewed by Safwat Abdel- Technical Note. Dayem and Doug Olson of the World Bank. Helpful comments were also received from Ashok Technical Note E.1 was drafted by Walter Ochs and Subramanian of the World Bank. Hervé Plusquellec, building on the earlier work by 7 IRRIGATIONANDDRAINAGE: DEVELOPMENT INTRODUCTION An estimated 270 million hectares of irrigated land-- ogy and, in many instances, government subsidies about 18 percent of the world's cropland--generates for power and pump installation. At present, about about 40 percent of the world's food production.1 175 million hectares are irrigated by surface water, Among regions, there are great disparities in the and about 95 million hectares are irrigated by distribution of irrigated land and its contribution to groundwater. The increasing use of groundwater food security. Around 65 percent of the world's irri- has led to the overexploitation of groundwater re- gated lands are in Asia, while Africa and South sources in some arid and semiarid regions, where America have less than 5 percent each. Compared water tables are falling at an alarming rate--often 1 to other water uses, irrigation is a high volume, low to 3 meters a year. The point has been reached in quality, low cost use. Given the large demands placed some areas where the exploitation of groundwater on water resources by irrigation, the extent of irri- is posing a major threat to the environment, health, gation development has major implications for other and food security. For example, about 10 percent of water uses, including water needs for cities, indus- the world's agricultural food production depends tries, and hydropower, as well as for national parks, on mined groundwater, or water that is extracted wetlands, instream uses, and estuaries. faster than it is replenished. Globally, about 150 to 200 million hectares are Consequently, proper use of water for irrigation and drained, including 100 to 150 million hectares of drainage (I&D) is essential for sustainable water rainfed land and approximately 50 million hectares resources management. This Technical Note is one of irrigated land. This land contributes 10 to15 per- of three dealing with irrigation and drainage. Tech- cent to global food production (Smedema 2002). nical Note E.2 deals with issues arising from the Drainage developments generally are intended to rehabilitation of existing I&D systems. Technical improve agricultural productivity, but can have sig- Note F.2 discusses issues, concepts, techniques and nificant environmental effects, including both ben- methods involving water conservation for I&D efits--such as control of salinization and schemes. This Note contains six sections. The first waterlogging--and costs--such as reduction in wa- two discuss the reasons for irrigation and drainage ter quality for downstream uses. and irrigation water quality issues. The following sections review potential environmental conse- The global irrigated area increased by more than 2 quences and solutions related to irrigation and percent a year in the 1960s and 1970s, slowing down drainage, methods for quantifying impacts of irri- to 1.6 percent in the 1980s. The area under irriga- gation, and drainage and remedial programs. The tion is currently increasing at an annual rate of about Note concludes with two case studies. 1.4 percent, largely because of a considerable slow- down in new investment combined with the loss of some irrigated lands as a result of salinization and urban encroachment. India and China accounted for about two-thirds of the global expansion during the 1990-98 period. Bank orld W, The area irrigated by groundwater has been grow- ing at an exceptional rate in recent decades because Plusquellec of greater certainty of supply, advances in technol- vé Her by Photo 1Schultz, B. (2001). Proportional flow divider, Pakistan 9 WATER RESOURCES AND ENVIRONMENT · TECHNICAL NOTE E.1 WHY IRRIGATE OR DRAIN LAND? IMPROVE AGRICULTURAL (although there can also be increasing pollution PRODUCTIVITY AND SUSTAINABILITY from excessive use of agricultural chemicals). MAKE RURAL AREAS MORE HABITABLE The primary reason for irrigating and draining land is to improve or sustain agricultural productivity in areas where surface soils are naturally dryer or Irrigation and drainage systems can improve the wetter than desired. Semiarid regions often have habitability of rural areas through: higher agricultural productivity if irrigated, while I Improved domestic water supply, which is of- naturally wet regions are often habitable at a higher ten associated with irrigation water supply density, accessible with less effort, or have higher I Reduction of mosquito breeding areas to help agricultural productivity when drained. The reduce malaria and other diseases normally sustainability of these I&D systems, however, is associated with drainage systems questionable if a sound operation and maintenance I Reduction, through drainage, in salt crusts (O&M) program is not carried out or if poor irriga- which can become windblown tion practices are used by the farmers and opera- I Extension of drainage into villages to provide tors of the system. Poor irrigation and agronomic improved storm water control and better foun- practices have led to salinity, sodicity, and water- dation strength for buildings. logging, which affect 40 to 50 percent of the 270 million hectares of land currently under irrigation.2 These factors can be important because of the im- Systems that do not have proper and continuous proved living conditions they bring to the rural com- O&M programs eventually require extensive reha- munity. bilitation due to reduced system performance over time (Note E.2). Over-abstraction of water for irri- IMPROVE ACCESSIBILITY gation has also degrated entire ecosystems and created conflicts with downstream uses. Other rea- Rural areas in the developing world often have poor sons for system modernization or rehabilitation transportation facilities for marketing agricultural include upgrades in technology to improve services and other products, for accessing larger cities for and efficiency, or because environmental conse- health care and social experiences, and for educa- quences need to be addressed. tional opportunities. The development, expansion, or improvement of I&D areas often provides oppor- The explosive increase in the use of groundwater tunities to improve accessibility and contributes to for irrigation is largely because groundwater offers the improvement of other rural infrastructure such greater certainty in the supply of water than sur- as energy, health, and communications. face sources of water. On average, agricultural yields in groundwater-dependent irrigation areas in In- Canals and drains sometimes provide the opportu- dia are 30 to 50 percent higher than yields in areas nity for parallel roads to be built without taking irrigated from surface sources. With an adequate much additional land out of production, thus re- and assured water supply from groundwater ducing the destruction of wetlands or lakes. How- (whether the supplemental or primary supply ever, these developments have to be planned and source), farmers are more confident in making in- executed carefully to ensure that environmental vestments in items such as fertilizers, pesticides, degradation, such as drainage of wetlands and shal- and improved crop varieties, leading to higher yields low lakes, does not occur--and if it occurs, that it is minimized or mitigated 2Szabolcs, I. (1994). 10 IRRIGATIONANDDRAINAGE: DEVELOPMENT POTENTIAL ENVIRONMENTAL Deciding how to balance these on-site and off-site BENEFITS RELATED TO IRRIGATION benefits with the costs to the I&D districts involves policy decisions that need to be taken by each coun- AND DRAINAGE try in the light of its own development needs. For example, establishing high water quality standards Social and economic improvements are the key rea- for the discharge of drainage waters will lead to sons for irrigation and drainage, but with careful downstream environmental benefits. The decision planning other benefits can often be realized. In on whether these benefits are great enough to war- Case Study 1, for example, water saved through con- rant the costs to the irrigators is a social decision servation efforts was allocated to a downstream taken by each country. Sometimes countries will green corridor. The control of waterlogging and elect to establish national water quality standards salinization for agricultural productivity reasons can that apply equally to all I&D schemes; other times also benefit the environment. With water table man- they will use a case-by-case approach to estab- agement and water level control in open drains, lishing discharge standards (see Notes D.1 and eutrophication can be mitigated by removing ex- D.2). cess nitrogen through denitrification. WATER QUALITY ISSUES WATER QUALITY REQUIREMENTS excessively, it can cause complete salinization and FOR IRRIGATION WATER elimination of all vegetative cover. FAO guidelines indicating the degree of plant growth restriction are Arid and semiarid climates. Salinity is the key wa- given in Table 1. ter quality parameter of concern for irrigation wa- ter. This is almost always a problem in arid and Another key item related to water quality for irri- semiarid regions. Salinity problems develop if salt gation is the sodium adsorption ratio (SAR), which accumulates in the crop root zone to a concentra- describes the tendency for sodium ions to be tion that causes yield loss. If allowed to accumulate adsorbed onto soil particles in preference to other TABLE 1. DEGREES OF RESTRICTION FROM SALINITY AND SAR FOR IRRIGATION USES OF WATER Potential Restriction None Slight / Moderate Severe Salinity Electrical Conductivity (dS/m) < 0.7 0.7 to 3.0 > 3.0 Total Dissolved Solids (mg/l) < 450 450 to 2000 > 2000 SAR 0­3 EC > 0.7 EC 0.7 to 0.2 EC < 0.2 w w w 3­6 EC > 1.2 EC 1.2 to 0.3 EC < 0.3 w w w 6­12 EC > 1.9 EC 1.9 to 0.5 EC < 0.5 w w w 12­20 EC > 2.9 EC 2.9 to 1.3 EC < 1.3 w w w 20­40 EC > 5.0 EC 5.0 to 2.9 EC < 2.9 w w w Source: FAO, 1985. 11 WATER RESOURCES AND ENVIRONMENT · TECHNICAL NOTE E.1 ions (particularly calcium and magnesium). At any extensive dry periods during each year. Irrigation given SAR, infiltration rates increase as water sa- extends the growing season and provides an op- linity (measured as electrical conductivity, ECw) portunity to grow crops that cannot be grown dur- increases. Thus SAR, together with the salinity of ing wet seasons. Water quality is often poor during the applied water, gives an estimate of potential these dry periods in surface waters, but groundwa- infiltration problems (Table 1). ter quality is normally better, especially if it is taken from deeper aquifers. If treated wastewater is to be used for irrigation (see Note F.3), tests should also be run for patho- WATER POLLUTANTS RELATED TO gens, heavy metals and nitrate (NO ). Excessive nu- 3 IRRIGATION AND DRAINAGE SYSTEMS trients (NO -N >30 mg/l) and bicarbonate (HCO 3 3 > 8.5 me/l)3 often reduce crop yield or quality Both surface and subsurface drainage effluents con- through unsightly deposits on fruit or foliage and tain substances that are potential pollutants, which can cause corrosion of equipment. If there is ap- may be purposely introduced into the irrigation preciable runoff, high nutrient levels can also lead water, mobilized by the practice of irrigation and/ to eutrophication of surface water bodies and ni- or drainage, or concentrated as a result of evapo- trate contamination of groundwaters. transpiration. Humid, temperate, and tropical climates. Water qual- The pollutants include salts, nutrients, pesticides, ity for irrigation is normally not a great concern in trace elements, sediments, pathogens, acids and humid, temperate, and tropical climatic areas. When elevated temperatures. The processes causing irrigation is used in these areas, it is often on the these pollutants to be released and methods for more porous soils and as supplemental irrigation, managing them are described in the next two particularly when high-value crops are grown. sections. Tropical areas are sometimes irrigated because of IRRIGATION: ENVIRONMENTAL CONSEQUENCES AND SOLUTIONS TECHNICAL PROBLEMS AND SOLUTIONS tion, and performance of irrigation and drainage systems, both on- and off-farm. Some government Environmental problems caused by irrigation can and donor-supported projects do not address these be avoided or considerably mitigated by proper plan- issues adequately because of a lack of expertise in ning, design and operation of irrigation projects. modern design. Waterlogging and salinity are caused by over-irri- gation and by not constructing drainage works be- It is important to note that the effective implemen- fore the problem is evident. Water losses from tation of modern policy approaches to irrigation canals, reservoirs, and on farmland are often un- requires the appropriate physical environment. Only derestimated because of unrealistic expectations a combination of appropriate physical infrastruc- about the efficiency of these phases of an irrigation ture, proper policy instruments, adequate institu- system, including the long-term effectiveness of tional capacity, and committed management measures such as canal lining using rigid materi- (including enforcement of regulations) will lead to als (see Note F.2). high performance of irrigation systems. Good design requires a sound understanding of the 3Reported in milliequivalent per liter (me/l) (mg/l / relationship between design, construction, opera- equivalent weight = me/l) 12 IRRIGATIONANDDRAINAGE: DEVELOPMENT WATERLOGGING OF SOILS farm and off-farm) is a priority. Control of sources of seepage water from canals and reservoirs is also Waterlogging occurs when soil pores fill with wa- important (Note F.2). In many cases, these actions ter because the soils either have few interstitial will not be able to cure waterlogging quickly or com- spaces (low porosity) or do not drain well (poor pletely enough. Although drainage is the usual so- hydraulic conductivity or presence of impervious lution to removing excess water, excess groundwater layers), thus reducing the air content. Oxygen defi- can also be removed through bio-drainage, i.e. tran- ciency results and carbon dioxide accumulates to spiration by vegetation. Bio-drainage has not been toxic levels. This directly impairs root growth and used extensively in large-scale projects, but has the ability to absorb nutrients for most crops ex- promise if used under the right conditions. The tran- cept rice, which can transfer air through its stomata spiration capacity of the landscape is enhanced by to its roots. Consequently, rice and wetland vegeta- introducing high-water-use vegetative types in large tion are able to grow well when the roots are sub- enough areas to maintain groundwater balances merged for long periods. below the root zone of the crops or vegetation that is to be protected.4 Figure 1 illustrates the bio-drain- As a result of poor irrigation practice, waterlogging age concept. problems occur on about 50 million hectares of ir- rigated land. High water tables can develop in ar- SALINIZATION OF SOILS eas where excess water is applied, leading to waterlogging a considerable distance from the source Soil salinization, illustrated in Figure 2, is a con- areas. Farmers in the low parts of a command area cern in irrigation projects located in most arid cli- are vulnerable if farmers on the higher parts do not mates, some semi-arid climates and in a few project carry out good irrigation water management prac- areas in temperate or tropical climates that are close tices. Waterlogging also occurs along irrigation sup- to oceans or salt water tidal areas. In these climates, ply canals and downstream from reservoirs. salt can accumulate in the soil and groundwaters and be brought up to the root zone of crops as Waterlogging problems need to be addressed at their source. Improving irrigation water management (on- 4 FAO (2002). FIGURE 1. FLOW TOWARD DEPRESSED GROUNDWATER TABLE FIGURE 2. UNDER PLANTATIONS THE PROCESS OF WATERLOGGING AND ALINIZATION S Transpiration Transpiration Transpiration Rainfall irrigation Evaporation Transpiration Salt Trees Crops Trees accumulation Salt infusion Salt infusion Water table Water table Brackish groundwater 13 WATER RESOURCES ANDENVIRONMENT · TECHNICAL NOTE E.1 BOX 1. EYGPT'S NILE DELTA Agriculture in Egypt depends almost entirely on irrigation from the Nile River. With the year-round availability of water, two or three crops a year can be grown. Under the present cropping pattern, the quantity of irrigation water applied to a representative area in the southern part of the Nile Delta is about 1,240 mm/year. Although the irrigation water has low salinity (0.3 dS/m), it brings salts into the soils at a rate of 8.0 tons/ha/year. Egypt has had great success in control- ling this salinity. Until the Aswan High Dam was constructed in the 1960s, the Nile flooded every August and September, causing natural leaching of the salts from lands in the delta area. Salinity increases were evident soon after the frequency of natural floods dropped following the completion of the dam. Salinity and waterlogging are considerably more serious in the northern part of the delta since that area is further downstream and the close proximity of the agricultural lands to the Mediterranean Sea causes a shallow watertable. Six subsurface drainage pilot projects were installed between 1961 and 1969. The results showed that this drainage has reclaimed the salt-affected soils and maintained a high level of productivity. The Government of Egypt, in partnership with the World Bank, has invested about $3 billion since the 1970s to provide drainage systems to 2 million hectares. The program is expected to continue until the irrigated area (about 2.7 million hectares) is fully covered by the year 2017. Both the government and farmers have shown great commitment to the program by adopting appropriate technologies, improving the irrigation system, transferring management to water user associations, and adopting a well functioning system of cost recovery. There has been a remarkable 230 percent increase in crop intensity, and the yield of crops in Egypt stands now among the highest in the world, especially for wheat, rice, and cotton. Improved drainage accounts for 15 to 25 percent of the yield increase. Reuse of drainage water has contributed to an overall water use efficiency that is one of the highest in the world. Source: ILRI 1994; Safwat Abdel-Dayem, 2000, World Bank Drainage Portfolio Review, internal document. groundwater tables rise with excessive water ap- water to infiltrate into the soil. Plant roots and soil plications. In extreme cases, the salts can accumu- organisms may be starved of oxygen. Adding gyp- late on the surface forming salt scalds. In most sum is the common solution to sodic soil problems. temperate and tropical climates, salts have been leached from soil profiles over time and salinity is Irrigation water also contains a mixture of salts not a problem. When an irrigation and drainage from the catchment area of the water supply or the area is developed in many arid climates and some recharge area of an aquifer. In coastal areas, semi-arid climates, often soils must be artificially overexploitation of groundwater resources can lead leached before cropping can begin. In these climates, to saltwater intrusion and consequent increases in it may take 4 to 8 years before sufficient salt is the salinity of irrigation water. The extent to which leached for the soils to be used productively. these salts accumulate in the soil will depend upon the irrigation water quality, irrigation management, About 23 percent of the world's cultivated land has and the adequacy of drainage.6 Land salinization saline soils and another 37 percent has sodic soils.5 initially is noticeable as a reduction in crop yields Sodic soil is closely related to saline soils. The ap- or vegetative growth. It can gradually progress to a plication of irrigation water to areas with abundant complete sterilization of the landscape if manage- salts and more than 15 percent exchangeable so- ment interventions such as drainage are not applied dium leads to the formation of sodic soils (some- to leach excessive salts from the soil. Box 1 describes times called alkaline soils). If soil has a low chloride the management of salinization problems in the Nile and calcium content, or if irrigation water has abun- Delta in Egypt. dant exchangeable sodium bicarbonate or sodium carbonate, the clay particles in the soil adsorb the sodium and magnesium salts and swell. The soil 5 Szabolcs, I. (1989). loses its permeability, which hinders the ability of 6 FAO (1985). 14 IRRIGATIONANDDRAINAGE: DEVELOPMENT Soil salinization can cause environmental problems HABITAT LOSS that have direct economic impacts. Not only will crop productivity decline, but soil biodiversity, wet- Water-source areas include the catchment area for lands, and areas of natural vegetation such as tree water supply, surface water stored in reservoirs be- belts will all be affected. hind dams, and sometimes in-stream storage. There can be significant habitat losses in all these areas USE OF TREATED WASTEWATER during irrigation development projects. In these cases, World Bank policies require environmental Wastewater from municipalities is increasingly used assessments prior to development, as well as moni- for irrigation (Note F.3). This reuse benefits both toring during and after project implementation. De- municipal sources and irrigation by reducing the forestation in particular can cause serious problems quantity of wastewater discharges to waterways as in and below the catchment areas. Soil conserva- well as providing water, nutrients, and organic matter tion practices should be undertaken in catchment to irrigation areas. In arid and semi-arid climates, areas to minimize downstream sedimentation prob- wastewater irrigation may significantly increase farm lems. Habitat loss can be kept to a minimum in the production. At a flow of 140 liters per capita per day, catchment if proper environmental planning is in- 100,000 people would generate about 5 million cu- cluded in the soil conservation plans. Habitat losses bic meters of wastewater per year, enough to irri- and changes are often significant during the devel- gate about 1,000 ha, using efficient irrigation opment of water storage and transmission facilities. methods. Irrigation of parks and green-space with Reservoirs inundate extensive areas and create a wastewater is becoming increasingly attractive to habitat that is difficult to manage for fisheries if the improve the environment in and around municipali- changes in water depth are too fast or severe. ties. Irrigation of grasslands and forestlands or wind- breaks can be used to develop greenbelts to control Habitat changes will also take place within the irri- desertification and for reforestation as well as ero- gation command area and the area receiving drain- sion control. The ability to generate income from age waters. These habitat changes may not be great the wastewater stream improves the efficiency of in- if an existing system is being restored or modern- vestments in wastewater treatment and contributes ized (see Notes E.2 and F.2). If the I&D system is to the conservation of freshwater sources. being significantly expanded or a new system is being developed, there are likely to be major changes in However, the reuse of wastewater can be limited habitat values, including the loss of wetlands. Sound by inadequate water resources legislation and an environmental assessments are critical in these situ- inability to control effluent quality. For example, ations; mitigation needs to be undertaken if there wastewater can be unsuitable when it contains sig- are significant impacts on important habitat. nificant loads of industrial effluent. The effect of wastewater irrigation on public health is the pri- Both water quantity and quality (see next section) mary concern, although there are also significant can be affected downstream of an I&D development. environmental risks through oxygen depletion Fisheries, wetlands, estuaries and, in cases like the caused by the breakdown of organic contaminants Aral Sea (Box 2), even air quality can all be adversely and the introduction of toxic chemicals into sus- affected. Water flows will inevitably be reduced down- ceptible ecosystems. Adequate pathogen removal stream of an irrigation scheme because of the in- can be achieved with a low-cost, multicell waste- creased transpiration from crops and canal vegetation stabilization pond system with about 20 days of de- and evaporation from fallow areas and possibly tention. Monitoring and evaluation of systems drainage from water disposal basins. Additionally, involving wastewater use are critical, and care must the downstream flow hydrograph will be affected by be taken to promptly correct developing deficien- the timing of releases from upstream reservoirs to cies before they become serious problems. irrigation areas. In extreme cases, the flow regime can be reversed with maximum flows occurring dur- 15 WATER RESOURCES AND ENVIRONMENT · TECHNICAL NOTE E.1 BOX 2. THE ARAL SEA The problems in the Aral Sea region were caused by the rapid expansion of irrigated agriculture in the Amu Darya and Syr Darya River basins. The waters of these rivers were diverted from reaching the Aral Sea with the result that its surface level dropped by 17 meters over 40 years, and its surface area was reduced from 66,000 km2 to less than half that size today. Disposal of polluted drainage water back to the rivers triggered adverse water quality and environmental problems for downstream populations. Major inter-basin diversions were planned from rivers flowing to the Arctic Ocean to limit the expected shrinking of the Aral Sea, but were not carried out due to environmental, political, and financial concerns. The drying out of the Sea has not only seriously affected the livelihoods of those previously dependent on the re- sources of this major water body but has severely reduced the extent of adjacent wetlands. Dust storms are now a common feature of this area, as winds transport the soils of the now dry lakebed long distances. In addition, wind blown salts from irrigation-induced salinity pose a health hazard to rural populations. ing the crop-growing season (late spring-summer) The type of water preferred by mosquitoes for egg- after the development of an irrigation scheme instead laying varies between species, but the following of, say, during winter-spring. Triggers for fish and conditions are generally suitable: waterbird migration and breeding, plant habitat, and I Edges of reservoirs and rivers, shallow pools floodplain regeneration will all be affected, impact- with emergent vegetation ing downstream communities who are dependent I Small pools of ponded water, as in ungraded on these resources (see Note C.1) road ditches I Stagnant drains or watercourses INCREASED DISEASE TRANSMISSION I Paddy rice fields, if control measures such as stocking larvivorous fish are not used. Irrigation systems can provide habitat for the vec- tors transmitting water-related diseases such as Irrigation project areas can provide these sets of schistosomiasis (Box 3), malaria, encephalitis, and conditions. Planners, designers, operators, and dengue fever (mosquitos). maintenance staff need to be aware of these habitat BOX 3. FAVORABLE HABITAT FOR AQUATIC SNAILS Schistosomiasis, also known as bilharziasis, is a parasitic disease that leads to chronic ill health. Despite efforts to control this disease, caused by flatworms that reside in the bloodstream, it is estimated that 200 million people, mainly in rural areas, are infected. The majority of these cases occur in Africa. Individuals are infected when they come into contact with water containing the worms, which can penetrate through skin within seconds. Using freshwater snails as a host, the larvae of the worms go through several cycles. The snails eventually produce thousands of new parasites, which are then excreted by the snail into the surrounding water. Irrigation canals provide excellent habitat for these snails. The conditions that favor them include: Moderate light penetration Water velocity < 0.3 m/s Little turbidity Gradient < 0.2m/km Partial shade Temperature 0-37oC Slight pollution with excreta Optimal temperature 18-28oC Firm mud substrata Aquatic weeds in excess Gradual change in water levels Source: Birley, M. H. (1989). 16 IRRIGATIONANDDRAINAGE: DEVELOPMENT factors and develop drainage designs that minimize wildlife habitat, result in breeding areas for dis- these conditions. Disease monitoring and response ease-causing vectors, and interfere with efficient programs should be developed in susceptible ar- crop production. Sediment can also be deposited eas. These programs are usually carried out on a at downstream locations, where the water velocity community or regional basis. The Further Informa- slows. Many of the environmental problems caused tion section contains references to documents on by siltation have economic dimensions, such as loss the management of these diseases. of reservoir capacity or depth of channels, loss of bird nesting or fish spawning locations, or stimu- SOIL LOSS BY WATER AND lation of algae growth or other ecological imbal- ances in canals (see Note G.4). WIND EROSION Project areas with surface soils lacking cohesion, Soil loss by both water and wind erosion can be a such as sandy soil, are susceptible to wind erosion. significant issue in both the catchment area and in This can become a serious issue when long and the command area of I&D schemes, primarily be- flat open stretches are exposed to prevailing winds. cause of the removal of the natural vegetation cover. Barriers such as tree belts planted perpendicular Erosion from catchment areas can seriously im- to prevailing winds are necessary in these project pact both the natural habitat of upland species and areas. In desert environments, green belts compris- the productivity of upland croplands. Water ero- ing trees, shrubs, and grasses often need to be de- sion is less likely within the command area because veloped to serve as a buffer between the desert of the generally flatter terrain. However, there can environment and the I&D scheme. In China's Tarim be local erosion due to poor irrigation practices on- Basin II Project (see Note F.2), green belts were es- farm, leading to sedimentation problems within the tablished using drainage water. These green belts fields or in tail-water recovery systems and open were found to improve habitat value in the desert drains. These sediment accumulations impose ex- environment. cessive maintenance costs, cause deterioration of DRAINAGE: ENVIRONMENTAL CONSEQUENCES AND SOLUTIONS Drainage in relation to agricultural and irrigation enter drainage systems. Salt (NaCl) is the most com- interests is the removal of excess surface and sub- monly leached compound that can degrade water surface water from land, including removal of quality if disposed of in freshwater systems. Some soluble salts from the soil to enhance crop growth. metals and metalloids, such as arsenic (As), lead (Pb), At farm level it is an environmental mitigation mea- and selenium (Se), are toxic when present in suffi- sure for the waterlogging and salinization problems cient concentrations and pose a threat to agricul- associated with some irrigation schemes. While the ture, aquatic flora and fauna, and human health. purpose of drainage schemes is to enhance the pro- Toxic concentrations can arise from their collection ductive and environmental capacity of irrigation ar- in drainage waters as well as a result of evapora- eas, the disposal of the drainage water can impose tion in ponds or wetlands. Even if water concentra- significant environmental impacts on off-site and tions are low, the elements can bioaccumulate in downstream areas. the food chain. Selenium pollution of the Kesterson National Wildlife Refuge in California was perhaps LEACHING OF NATURAL SOIL ELEMENTS the most famous case of damage from naturally oc- curring ions (Box 4). Box 5 provides a summary of Numerous natural soil elements and compounds can lessons learned from a successful drainage project be leached from soil profiles during irrigation and to reclaim sodic lands in Uttar Pradesh, India. 17 WATER RESOURCES ANDENVIRONMENT · TECHNICAL NOTE E.1 BOX 4. DAMAGE FROM DRAINAGE : KESTERSON NATIONAL WILDLIFE REFUGE, CALIFORNIA (USA) In 1982, scientists found that selenium concentrations were increasing in the ponds of the Kesterson National Wildlife Refuge, the temporary terminal point in the drainage system for a large block of agricultural land in the San Joaquin Valley. Plans called for the ponds to eventually drain to the San Francisco Bay Delta and Pacific Ocean, but other funding priorities, environmental concerns, and other process delays caused the drainage system to remain incom- plete. It is still incomplete. Selenium and other potentially harmful, naturally occurring elements such as arsenic and molybdenum were being leached from soil and bedrock in upstream-irrigated areas and transported to the reservoir, where they were accumu- lating. Thousands of waterfowl and fish died outright from these contaminants, while others produced young that had severe birth defects. The concentrations of these substances at the pond inlet were probably not high enough to cause these problems. However, the concentrations were increased by evaporation in the closed ponds. Eventually, drainage from the Westlands Irrigation District and other contaminated sources was closed by court order. A $100 million case for compensation of farmers is still under consideration. The National Research Council eventually concluded that drainage system design must not only account for salt accumulation in soil and salt disposal in downstream water bodies, but also for potentially toxic effects of trace elements that may leach from soil and rock underlying the irrigated lands. Sources: Skaggs, R. et al. 1994; National Research Council. 1989. Irrigation-Induced Water Quality Problems. Washington, D.C.: National Academy Press. Once they occur, these problems with toxic trace LEACHING OF APPLIED MATERIALS elements are difficult to manage. Areas proposed SUCH AS FERTILIZERS AND PESTICIDES for new or expanded irrigation schemes should be checked for their presence. If these elements are The two primary nutrients in drainage water are present in nuisance concentrations, then water ap- nitrogen and phosphorus, both of which contrib- plication rates should be designed to minimize ute to eutrophication of surface waters (Note G.4). drainage and hence reduce the risk of leaching into If these nutrients are present in high concentrations, drainage waters. BOX 5. THE UTTAR PRADESH SODIC LANDS RECLAMATION PROJECT, INDIA Poorly managed irrigation of inherently sodic soils in Uttar Pradesh has rendered 1.25 million ha barren because of sodicity. Uttar Pradesh's weather, which alternates between heavy monsoons and prolonged dry periods, makes sodification worse. Where drainage is blocked, either naturally or by roads or canals, surface water accumulates and evaporates, leaving behind sodium ions, which form an electrochemical bond with clay particles in the soils, creating toxic salts. The World Bank funded a project in 1993 to help solve this problem. By tackling environmental protection, land tenure and improved agricultural production, the project was able to provide an integrated and sustainable solution to a complex situation. Extensive farmer participation was essential. The farmers took the major decisions and did virtually all the work. Smallholders were helped to gain clear title to land; this was critical in providing the motivation for technical improvements. The technical improvements involved soil testing, digging surface drainage, building tubewells, apply- ing gypsum, leaching and flushing with good quality groundwater, good crop husbandry, and regular flushing of salts from link drains. An area of 68,400 ha of sodic land (152 percent of the SAR) was reclaimed and 36,000 ha of barren land was brought under green cover for the first time. There was a significant increase in cropping intensity because of the successful land reclamation. Evaluations indicated that all objectives were met and the re-estimated economic rate of return was 28 percent against the appraisal estimate of 23 percent. Source: Agriculture & Rural Development Project Profiles, World Bank. 18 IRRIGATIONANDDRAINAGE: DEVELOPMENT they can fuel algal blooms in either drainage chan- OFF-FARM PROBLEMS nels or downstream waterways, which leads to deoxygenation of the water, the release of toxins Most hydraulic and hydrologic problems down- into the water, and the physical blocking of water stream from irrigation and drainage projects are off-takes. Nitrogen in surface drainage flow is pre- avoidable if the drainage system is properly designed dominantly ammonium, since it is readily adsorbed and maintained. Sources of water in drainage sys- on clay particles. The nitrate form is found in sub- tems include: surface drainage flow, since this form is very I Surface flows in excess of crop needs or due to soluble. Phosphorus can be found in drainage wa- excessive rainfall collected by surface drains ter in both organic and inorganic forms. Little phos- I Seepage water from canals or reservoirs col- phorus is found in subsurface drainage water lected by surface or subsurface drains because of its strong adsorption to clay soil par- I Flows from subsurface drains that control wa- ticles as it leaches through the soil. terlogging and salinity in the crop root zone I Baseflowsfromopendrainsandstreamswithin Most pesticides are synthetic organic compounds. the project area that intersect a high water table Surface runoff, in particular, can carry pesticides I Leaching water from deeper surface and sub- that cause toxicity problems in aquatic organisms surface drains. (such as invertebrates) in downstream areas. This can adversely affect higher levels of the food chain. Hydraulic problems are often caused by sediment High pesticide concentrations in subsurface drain- and excessive weed growth that reduces flow ca- age water are less likely because of the filtering pacity by clogging channels. These conditions also action of finer textured soils present in most irri- place significant demands on maintenance opera- gation schemes, although pesticides such as atra- tions such as dredging and cleaning of the outlet zine have been discovered in some groundwater channels. Off-site impacts from dredged sediments, systems. and other materials such as accumulated vegeta- tion, are a strategic environmental issue. Dredging The relative emphasis on surface and subsurface itself can release pollutants into the water such as drainage in the conceptual design can have signifi- phosphorus. Improper disposal of dredged materi- cant environmental implications, and should be als is also a concern because pollutants may leach carefully evaluated in any new construction, as well from the dumped material into surface or ground- as expansion or rehabilitation work on existing I&D water. Ideally, the dredged material should be used schemes. Although there are techniques to trap nu- in construction related to rehabilitation or modern- trients and pesticides before they enter down- stream waterbodies, it is most cost efficient to control them at the source. This means that farmers should be educated in the most effective application rates; perverse incen- tives such as subsidies should not exist to encourage their use; and methods for trans- porting nutrients and pesticides via both water and eroded soils should be minimized. Bank The introduction of integrated pest manage- orld W, ment programs and the possible adoption of genetically engineered crop varieties in Carnemark the future are likely to lead to reduced use Curt of pesticides. by Photo Dam, Tunisia 19 WATER RESOURCESAND ENVIRONMENT · TECHNICAL NOTE E.1 ization needs in the project. This option can be iden- flow. In addition, sediments (particularly colloidal tified through a strategic environmental assessment sediments) can block light penetration into the early in the project cycle. However, this is not al- water, thus affecting the productivity of food chains. ways feasible, and the dredged material must be Benthic fauna and flora will be particularly affected. disposed of with full regard to its possible impacts. Other problems can arise from the pollutants (pri- marily nutrients and pesticides) attached to the sedi- Hydrologic problems downstream are related to the ments. effect of drainage water on river flows and the tim- ing of peaks and troughs. Low flows are a particu- Drainage waters that contain salts can affect aquatic lar problem because concentrations of pollutants biota and human uses of the water, particularly are considerably higher during these periods. Hy- drinking water. Being a solute, salt is very difficult drologic basin-wide studies are important to ascer- to remove once it has entered drainage waters, so tain the impact of discharges (quantity, peak it is important to manage water applications to mini- drainage flows, and the time of the peak flow) from mize salt mobilization and drainage of saline wa- a specific project area on the flows of the basin. ters in these environments. This may require a Drainage flows can affect the proper ecological func- change in the technology used in the I&D scheme. tioning of downstream river reaches, floodplains, For example, in Pakistan, it was found that many of wetlands, and estuaries in the same way that up- the drainage tubewells mobilized excessive salts stream abstractions for irrigation can affect the flow because they leached too deep in the soil profile. regime of a river. During preparation of the National Drainage Pro- gram, a decision was made to correct some prob- WATER QUALITY PROBLEMS lem areas by changing the drainage system to horizontal pipe subsurface drainage, which would Surface and subsurface drainage effluent contain mobilize less salt. substances that are potential pollutants. These pol- lutants may be: Surface flows can pick up pathogens from villages, I Purposely introduced into irrigation or drain- animal yards, and septic fields, creating health haz- age water ards to downstream users of the water. Canals and I Mobilized by the practice of irrigation and/or main open drainage systems often receive partially drainage treated or untreated industrial wastewater from I Concentrated as a result of evapotranspiration urban and heavily populated rural areas. Design- (ET). ers need to anticipate the possibility of pathogen and heavy metal contamination from increased Common downstream water quality contaminants population densities from new or expanded I&D include sediments, salts, pesticides, pathogens, schemes. Minimization of runoff and proper con- heavy metals and increases in water temperature. tainment of surface flows together with enforcement of standards for disposal of polluted wastewaters Erosion and sediment transport problems are com- will reduce this problem. mon with open drains used to remove surface wa- ter runoff. Coarser sediments eroded from irrigation It is common for water temperatures to increase areas and channels are subject to rapid deposition below shallow reservoirs--as well as within irriga- in the slower flowing reaches of rivers or outlet tion and drainage systems--because of exposure to channel systems, blanketing habitat as well as caus- the sun. While elevated drainage water tempera- ing hydraulic problems. Finer sediments will be tures are unlikely to affect downstream aquatic life carried through to downstream bodies of water, in tropical and many sub-tropical areas, they can where they will cause physical problems such as cause problems in cold-water streams or those sup- blanketing of in-stream habitat and changes in river porting anadromous fisheries. 20 IRRIGATIONANDDRAINAGE: DEVELOPMENT WATER QUALITY MONITORING Water table management systems. These are also be- ing used in humid climates (particularly in East- Water quality monitoring should be included in the ern Canada and the United States) to help reduce design of all drainage systems. Points where drain- the concentration of chemicals (primarily nutrients age water should be monitored vary with each sys- and pesticides) in agricultural drainage water by tem, but in general the following locations should minimizing runoff. Since pesticides usually attach receive consideration: to soil particles, the reduction of surface runoff from I The ultimate disposal point for drainage water fields reduces the transportation of pesticides to the from the entire project area to ensure that down- drainage waters. stream water quality requirements are met (see Acidification. Rich tropical coastal wetland environ- Note D.1) ments are sometimes severely damaged by improper I Upstream and downstream from any waste reclamation of soils containing pyrite. These soils water treatment system to monitor the perfor- are usually called acid sulfate soils. When drain- mance of the treatment facilities and to facili- age systems are deep, subsoil layers are exposed to tate operational or management changes air and become oxidized. This leads to the forma- I At the ends of major drains in the system to tion of sulfuric acid from the pyrites. The pH levels determine if excessive loads of pollutants are in water draining from these areas can drop below being contributed by specific parts of the sys- 3, seriously harming plant and animal life, includ- tem ing the death of mangroves and fish kills. Iron and I At specific locations where there is the poten- aluminum can also be mobilized from soils when tial for point-source pollution such as below in- pH levels drop, causing human health problems if dustries, villages, and animal lots the downstream water is used for drinking purposes. I Upstream of any off-take point for drainage Maintaining a high water table to prevent the py- water reuse, particularly when mixed with ca- rite from oxidizing will control this problem. Box 6 nal water. describes two examples of problems with acid sul- fate soils. SPECIAL CONSIDERATIONS Reuse of drainage water. Downstream users inevi- There are a number of special issues that can arise tably reuse irrigation drainage water in an un- with drainage development projects. The following planned way because these waters find their way paragraphs provide an introduction to these issues to watercourses through surface and sub-surface and their solutions. More details can be obtained pathways. However, the planned reuse of drainage from the references in Further Information. water is increasingly being introduced in water scarce regions through constructed water reuse Organic soils. Peat and muck are two common terms schemes. Because pollutants tend to become more often associated with organic soils. Subsidence of concentrated as water is reused, water quality moni- the land surface is an irreversible result of draining toring and adequate management capacity should organic soil. The subsidence is caused by oxidation be important components of these reuse schemes. as water is removed. The rate of oxidation is related Some salinity management specialists promote the to the depth of the water table and the temperature. concept of reusing drainage water on successive The oxidation rate is lower if a high water table is crop types with increasing salt tolerance to maxi- maintained and in cooler climates. In spite of the mize the volume transpired and minimize the vol- problem of subsidence, organic soils can be very ume of drainage water. An interesting example of productive, and in humid climates are often used this approach, known as the serial biological con- for growing high-value crops such as vegetables and centration concept, has been tested in an agricul- flowers. Such I&D schemes can be sustainable if the ture-forestry system since the early 1990s in level of the water table is maintained. California. 21 WATER RESOURCES AND ENVIRONMENT · TECHNICAL NOTE E.1 BOX 6. ACID SULFATE SOIL DRAINAGE Acid Sulfate Soil Drainage in the Barito River Delta of Indonesia Pulau Petak, an island in the delta of the Barito River in South Kalimantan, Indonesia, contains mainly acid sulfate soils. Before reclamation, the water table was high. Soils were protected from the air so that no oxidation and subsequent acidification took place. The area was covered by mangrove forest along the coast and by freshwater swamp forest inland. About 150,000 hectares have been systematically reclaimed since 1920. Of the originally reclaimed area, however, 75,000 hectares have been abandoned again because of acidification that resulted from the drainage. Fish Deaths From Acid Sulfate Soil Drainage in Australia Acid sulfate soils emerged as a significant environmental concern for Australia's sugar industry following a major incident in the Tweed River in New South Wales in 1987. Heavy rains occurred, following a long drought. Some days later, a 23-kilometer stretch of the river became clear and devoid of aquatic fauna for several months. The river was found to have become very acidic, with aluminum concentrations of 2.5 mg/l. The problem was traced to acid sulfate run-off from major drainage works from extensive sugarcane fields. It is believed that acidic waters accumulate in the soils and drains during dry periods, and are flushed into the river when heavy rains occur. Similar problems have reoccurred at regular intervals since. Acid sulfate soils in the region have now been mapped and priority management areas have been identified. Different management actions are being tested in different parts of the area. In some parts, lime and organic mulch are being applied to neutralize the acidity; in other areas, the aim is to minimize the displacement of acidic ground- water to the river by laser leveling, planting in mounds, reducing the length of the drainage ditches to reduce the acid sourced from the drain banks, and liming drainage banks. After significant rain, pH still falls to around 3.5 for 3-4 days, before returning to about pH 8.0. Previously, acidic discharges would continue for some weeks. The discharge of acid has now been reduced by up to 80 percent. Sources: ILRI, 1994; Tulau, M.J. 1999. Acid Sulfate Soil Management Priority Areas in the Lower Tweed Floodplains. Sydney: Department of Land and Water Conservation. INSTITUTIONAL CONSIDERATIONS There has been widespread institutional reform in are remote from water users, inflexible and not the irrigation sector in many countries in the last business oriented. In developing countries, these 15 years, primarily driven by a need for govern- agencies are also often underfunded for O&M, lack ments to reduce their expenditure on irrigation transparency and accountability, and are either schemes. Both the methods for implementing these overstaffed or lack motivated staff. reforms and the results achieved have been mixed. REGULATIONS AND ORGANIZATIONS Institutions for I&D planning and management include both the rules (laws, regulations, cus- Bank toms) and the organizations that put those rules orld into practice through operations and mainte- W, nance activities (O&M). In many countries, both developing and developed, these institutional Plusquellec arrangements are not well designed for effec- vé Her tive O&M. For example, water management is by often dominated by government agencies that Photo Weir under construction 22 IRRIGATIONANDDRAINAGE: DEVELOPMENT There is no single model for effective planning and Otherwise, the basin's water resources might not management of I&D schemes but some general be allocated to their socially best use. The impor- principles are now widely recognized as being im- tance of this IWRM approach is widely recognized portant (see Note B.2). First, there need to be clear by international agencies, and is incorporated into responsibilities established in law for the planning the World Bank's 1993 Water Resources Manage- and management of water resources. In particular, ment Policy and its recent Water Resources Sector the regulation and operation of I&D schemes need Strategy. The difficulty lies in implementing this to be separated, so that one agency is not respon- concept. Sectoral interests are reluctant to give up sible for both operating an I&D scheme and enforc- their power; identifying the best allocation of wa- ing the laws governing the allocation of irrigation ter resources across a basin is technically difficult; water and the discharge of drainage waters. Ide- and incorporating the concerns of end users can ally, the planning and development of I&D should be difficult when they have not traditionally had a also be separated because in many countries de- voice in decisionmaking. However, there is now sign and construction of I&D schemes is a source enough experience to show that the benefits of an of pride that drives the development of irrigation IWRM approach make it worthwhile overcoming beyond what is necessary. these difficulties. Second, to minimize the potential for conflict when STAKEHOLDER PARTICIPATION water resources are scarce, the right to water use for irrigation needs to be clearly established. In many Stakeholder participation is a critical component of countries, there are locally understood but poorly all stages in the development of I&D systems, in- recorded systems of water rights. Whether these cluding planning, design, implementation, operation, rights need to be established in law or left to local and maintenance. Water users in irrigation systems custom is a decision that will depend on circum- are particularly important stakeholders, since they stances. The important principle is that the rights normally receive direct benefits from the project and are widely understood and accepted. pay for system operation and maintenance upon its completion. But other stakeholders--such as those Third, laws and rules governing I&D need to be having concern for impacts on municipalities or vil- enforced impartially. There are many instances lages, and those having interests related to the en- where a well thought-out set of rules exist, but are vironment--also need to be involved. All stakeholders not enforced because of lack of high-level support need to be involved from the beginning, since it is and the interference of influential land owners. Con- through their early involvement in the planning that sequently, irrigators take surface and ground water they develop the ownership that is necessary for beyond their allocations and discharge contaminated projects to be successful. Box 7 provides a good ex- drainage water to receiving bodies of water. ample of participatory planning in an area where Fourth, an increased emphasis needs to be put on water resources are heavily used. drainage where it does not exist. Under-investment has contributed to a loss of productivity in very large Promoting management transfers and the partici- areas. pation of water users in the operation of irrigation systems has provided great opportunities for im- Fifth, concerted policies and actions are needed to proving the performance of irrigation and drain- reduce the perverse subsidies for groundwater age systems in many countries, including Turkey, pumping. Phasing out such subsidies is both an India, and Mexico. There are many models for par- economic and an environmental necessity. ticipation, ranging from privatization of irrigation and drainage districts to participatory involvement. Finally, the planning of I&D needs to be carried out Mexico has transferred ownership of entire irriga- as part of integrated water resources management. tion districts to water users. Typically, a positively 23 WATER RESOURCES AND ENVIRONMENT · TECHNICAL NOTE E.1 BOX 7. USANGU PLAIN IN ANZANIA T There were far fewer people in the Usangu Plain of Tanzania in the 1950s compared to today. The initial people (Wasangu) were primarily livestock keepers. At that time, there were only small areas of rainfed cultivation and about 5,000 hectares of irrigated land. The natural vegetation was largely untouched, and the whole of the central grassland area of the plain was flooded every year. Since the 1950s, people from all over Tanzania have moved to the Usangu Plain, and over 26 different ethnic groups are now living there. Irrigation has been developed in parts of the southern plains, and cultivation of maize and sorghum has been developed in the western wetland areas. Meanwhile, a large national park has been declared in the north that is dependent on water from the river. Downstream from the park is Mtera Dam, a structure that regulates water for over 50 percent of the nation's hydropower production. Consequently, there is now intense competition for the limited water available. Village and ward-level people were involved in participatory planning for the "Sustainable Management of the Usangu Wetland and its Catchment" water resource project. Development teams were set up and helped identify the re- sources available to them, issues of concern, and their ideas for the future. From these, village action plans were developed that made use of the local knowledge, skills, and resources to develop community-based and community- led solutions to village issues. Many of the issues in the village plans were concerned with competition over the use of limited natural resources. One solution was to make village land use plans, which required bringing together the different resource users to resolve conflicts over future use of the resources. Numerous tradeoffs were reviewed due to the multitude of resource uses, which included land uses for irrigation (45,000 ha), wetlands (1,800 km2), grasslands (210,000 ha), catchment areas (20,811km2), woodland/forest areas (1.085 million ha), and rainfed cultivated areas (430,580 ha). A great deal of effort went into managing conflicts related to water and other resources, as well as developing subcatchment resource management programs. This is part of an ongoing effort to manage the water resources of Usangu. Source: The Sustainable Management of the Usangu Wetland and its Catchment, Project report 1998-2002. Ministry of Water and Livestock Development, Tanzania. reinforcing cycle occurs. Through involvement and The organization controlling a drainage system's a sense of ownership and control over the opera- operation and maintenance is usually formed at the tions of the water distribution system, irrigators local level. When other stakeholders, such as down- become more willing to pay water user fees. Con- stream communities dependent on the waterbod- sequently, the operational budget of the supply and ies receiving the drainage waters, are not involved distribution authority is expanded and a higher level in the important decisions about drainage infrastruc- of service is provided. ture, there can be conflicts because of the off-site impacts of drainage. The management of water and Clearly, to be effective, stakeholder participation the environmental conditions in the project area are needs to be accompanied by other reforms, includ- a concern of many more people than the direct ben- ing capacity building, reorganization of agencies, eficiaries, and all need to be involved if such projects and technical improvements. Nevertheless, these are to have long-term success and stability. improvements seldom succeed to the point where the irrigation district is able to operate independent of government or donor subsidies. The most suc- cessful examples occur where the political economy provides an enabling environment and the coun- 7 Shah, T., B. van Koppen, D. Merrey, M. de Lange and M. try has an advanced irrigation sector (Mexico, New Samad, 2002. Institutional Alternatives in African Small- Zealand, Turkey, the United States) or where there holder Irrigation: Lessons from International Experience is a highly unequal distribution of land (South Af- with Irrigation Management Transfer. Research Report rica, Colombia).7 60. Colombo, Sri Lanka: IWMI. 24 IRRIGATIONAND DRAINAGE: DEVELOPMENT QUANTIFYING IMPACTS OF I&D SCHEMES ENVIRONMENTAL ASSESSMENT (EA) and Bolton, 1993. This list was developed to iden- DURING PLANNING tify environmental effects of irrigation, drainage, and flood control projects. Some parameters, such as An EA is required for lending operations that have hydrologic and salinity changes, can be predicted potentially significant environmental impacts. Drain- from existing models, but many items require pro- age portions of projects can cause particular con- jections that must be based on similar projects else- cerns in relation to drinking water supplies and fish where where monitoring programs have been and wildlife habitat values, and thus should receive carried out properly. Models should not be prepared careful attention in EAs. Wetlands in particular are for project planning and then forgotten. They should important to consider when drainage is involved, be retained and improved as the project is imple- since drains located too close to wetland areas can mented and the system is operated. Data from moni- severely degrade their functions and the services that toring efforts need to be added to the model; they they deliver to local communities. Natural wetlands should be used to evaluate project operations and in tropical, temperate, and humid climates are the predict future impacts as well as to suggest improve- normal areas of concern; in arid and semiarid ar- ments in management of the system. eas, irrigation-induced wetlands are more common. MONITORING AND EVALUATION The more humid climatic areas often do not have salinity concerns; waterlogging of soils is the nor- Baseline studies should be undertaken before new mal reason for draining them. Detailed informa- I&D schemes are developed so the monitoring re- tion on wetlands can be found in Note G.3. In any sults can be interpreted. The monitoring, includ- arid or semiarid area, EAs should be used to de- ing the parameters to be measured, the data velop insights into the drainage needed to mitigate interpretation, and the dissemination methods, the waterlogging and salinization impacts of irri- should be specified in Environmental Management gation projects. System design and management to Plans that are developed in response to the EA. reduce the mobilization and transfer of pathogens However, it is often difficult to find funding to con- and toxic trace elements are also critical compo- tinue monitoring programs when the project is com- nents in EAs for projects involving drainage. pleted. Long-term monitoring is more successful with program-type approaches where longer-term In all such projects, the irrigation and drainage commitments for funding are available. Some of the development should be considered as part of the key items to monitor are noted in Box 9. development of a larger region or river basin. Box 8 provides an example. Monitoring should feed into decision making pro- cesses (see Note D.1). Analysis and interpretation For major I&D developments, the extent and sever- needs to be carried out properly, and the results ity of environmental impacts should be modeled must be shared with stakeholders and management, prior to project development. A comprehensive list alerting everyone to developing problems in time of parameters to model can be obtained from Mock to correct them or plan for the consequences. 25 WATER RESOURCES AND ENVIRONMENT · TECHNICAL NOTE E.1 BOX 8. LIGUASAN MARSH IN HE T PHILIPPINES The Liguasan Marsh is one of the significant features in the Mindanao River Basin in the Philippines. The marsh region covers approximately 220,000 ha (of which 140,000 ha is cultivable during the dry season) in the central and lower reaches of the basin. The actual area of marshland is about 89,000 ha. A special area of 43,930 ha, the "Liguasan Marsh Game Refuge and Bird Sanctuary," was proclaimed as a protected area in 1940. In the dry season, the inundated region consists of numerous interconnected areas that are well distributed throughout the central marsh. The soil is rich and the vast land and water resources provide tremendous potential for growth of wildlife habitat, fisheries production, and agricultural production. Within the marsh area, about 112,000 families use the area for fishing when the water levels are high, and agriculture when the water levels are low. During the dry season as much as 80 percent of the protected area is planted to crops such as corn and rice which are sustained by irrigation. By absorbing the floodwaters from different tributaries, the marsh minimizes flash floods in the low-lying areas of the Mindanao River as it approaches the basin exit point in Illana Bay of Moro Gulf. Residents in the lower marshlands are dependent on the aquatic harvest as well as agriculture for their livelihood. Deforestation is one of the most pressing problems in the upstream watershed areas, leading to soil erosion and the continuous deposition of silt in different rivers of the basin. There is only limited environmental information available for the marsh. However, the area is known to support about 20 species of fish, 3 species of reptiles, and over 20 species of waterfowl, notably herons, egrets and ducks. It is also one of the last strongholds for the endangered Philippine Crocodile (Crocodylus mindorensis), and the Monkey-eating Eagle (Pithecophaga jefferyi) is reported to be present in the forested areas of the marsh. The marsh area is particularly rich in orchids. The main threat to the marsh in the past has been drainage for rice cultivation and threats involving conversion of large areas to fish ponds. A development scheme has been proposed to create additional agriculture infrastructure and convert more of the lands surrounding and within the marsh area to irrigation. The scheme includes drainage, flood protection, irrigation, roads, and fisheries development. Some estimates indicate that with good flows in the rivers of the basin during the dry season, the extension of irrigation could be carried out to achieve 200 percent irrigated cropping intensity without the need for storage dams. Moreover, mangrove area rehabilitation and stabilization, improvement of wildlife habitat, and better access for development of tourism could possibly be part of the develop- ment framework. A comprehensive plan needs to be drawn up to balance the potential benefits of the scheme with the potential losses in wetland function (flood protection, biodiversity) and livelihoods for existing residents. However, planning for the development has not progressed because of the security problems in the region. Source: Internal World Bank Preparation Documents for The Philippines River Basin and Watershed Management Program BOX 9. ITEMS TO BE CONSIDERED IN MONITORING PROGRAMS FOR IRRIGATION AND DRAINAGE I Water volumes, surface water levels, and water quality changes for water flowing into the project area--at selected locations throughout the project area and at all discharge points over time. I Shallow groundwater levels throughout the project area, particularly in low areas where waterlogging is most likely to occur. I Aquifer piezometric levels and water quality to monitor changes and alert stakeholders to any degradation in water supply or potential drainage problems due to piezometric pressures. I Soil qualities, to ensure that the measures carried out are not degrading the soil within or outside the project area. Characteristics such as acidification (acid-sulfate soils), surface sealing, compaction, subsidence (organic soils), consolidation (collapsible soils) and salinization (coastal, arid and semi-arid areas). I Salinity changes in soil with time to check for sustainability of the area's agricultural system and problems related to developing salinization. I Air quality in locations where wind erosion or pollution from industries or municipalities is a concern, since they affect agricultural production and health. I Biological and ecological changes related to fish and wildlife habitats. I Human health and incidence of disease, particularly waterborne diseases. 26 IRRIGATION AND DRAINAGE: DEVELOPMENT CASE STUDIES CASE STUDY 1. 1970s, leaving behind a vast expanse of salt depos- its. The lower reaches of the Tarim River have also THE LOP NOOR LAKE IN been affected. Herdsmen and farmers have been left XINJIANG PROVINCE, CHINA without their livelihoods and the "green corridor", a 200-km-long area of natural riverine forests along The Lop Noor Lake is situated in the eastern re- both sides of the river, has been damaged. gion of Xinjiang Province in China. The Lake was the center of the kingdom of Loulan, a strategic stop- Since then, better water management has been in- ping point on the Southern route of the Silk Road stituted. In six out of the seven sub-basins of the during the Han and Tang periods. The lake's sur- Tarim River, total irrigated area has increased by face was highly variable because its water source, 45 percent, from 753,000 to 1,060,000 hectares since the Tarim River, depends on snow melt from moun- 1980, but the volume diverted for irrigation has in- tain streams for water. The flow in the upper Tarim creased by only 13 percent due to better manage- River was reduced following the intensive devel- ment and lining of canals. Water balance studies opment of irrigation in several oases of the Tarim for the five sub-basins in the on-going World Bank River basin. The lake progressively dried up dur- Tarim II project are depicted in Figure 3. The low ing the 1960s and was completely dried up by the efficiency is largely attributed to the high canal FIGURE 3. INDICATIVEGROUNDWATER AND SURFACE WATER BALANCE IN THE ARIM T RIVER BASIN (BILLION M3 YEAR / ) Inflow into sub-basins Evapotranspiration Diversion for irrigation 23 14 Diversion to fields Crop use 6 4 8 1 Canal losses Groundwater Inflow from rivers to groundwater 1 Recharge: 12 Discharge: 12 4 Drainage return flow to rivers 3 Non-beneficial capillary flux Outflow from sub-basins to Tarim river 0.5 Capillary Flux to non-irrigated 9 vegetation Note: The diagram shows only the major water flows and 0.1 to Green Corridor so the water balance is not closed. 27 WATER RESOURCESAND ENVIRONMENT · TECHNICAL NOTE E.1 losses, nearly 60 percent of the total diversion. Some cluding storage reservoirs, barrages, canals, and nu- part of these losses to groundwater is re-used by merous unlined watercourses) to form the largest capillary flux to irrigated crops and nonirrigated irrigation area in the world, covering about 15 mil- vegetation, such as pasture and trees. Another part lion hectares. The efficiency of the distribution sys- is lost by nonbeneficial capillary flux and some re- tem, however, was very low, with less than half the turn flow to the rivers. water diverted from the rivers actually reaching the farmers' fields. Field irrigation efficiency was even Canal lining is one of the most important compo- lower--possibly about 30 percent. Since the natural nents of the Tarim II project (see Note F.2). Canal groundwater drainage is inadequate and artificial lining will save water for downstream use, and will drainage was not provided when the irrigation sys- benefit irrigated agriculture through a re- duction in nonbeneficial evaporation. Some local environmental losses due to the re- FIGURE 4. duction of canal seepage will occur, since EXAMPLE OF SALT BALANCE AND DISTRIBUTION ­ PAKISTAN PORTION OF some canal-fed wetlands will dry out, and INDUS RIVER BASIN (SALT INMI (MILLION TONS )) recharge to the Tarim River will be reduced. INDUS The objective of the project is not to restore NORTHERN ZONE the Lop Noor Lake but to preserve the green corridor to provide a vegetation barrier WESTERN RIVERS against progression of the desert. Half of the 3 17 water saved in the project will be delivered downstream, with a minimum of 150 mil- 13 lion m3 being assigned to the green corri- 2.8 dor. The remaining water will be 0.7 IRRIGATED consumptively used by grazing land, forest 2.5 CROPS areas, irrigation and through non-benefi- IRRIGATED CROPS cial evapotranspiration. 19 2.2 CASE STUDY 2. EVAPORATION 1.5 0.7 POND WATERLOGGING AND SOUTHERN ZONE SALINIZATION IN THE 1.7 3.2 INDUS RIVER BASIN 4.3 IRRIGATED 5 CROPS The Indus River Basin lies in Pakistan and parts of India, stretching from the foothills 0.6 of the Western Himalayas to the Arabian Sea. IRRIGATED 2.8 Before region-wide irrigation was initiated, CROPS the groundwater table lay scores of meters deep and the aquifer was in hydrologic equi- 8.6 2.8 5 librium. ARABIAN SEA When large-scale irrigation was introduced early in the 20th century, an extensive wa- Note: Details are from the Drainage Sector Environmental ter distribution network was established (in- Assessment for the Pakistan National Drainage Program. 28 IRRIGATIONANDDRAINAGE: DEVELOPMENT tem was developed, percolation from the canals places where the groundwater was of good quality. coupled with over-irrigation led to a rapid rise of As a result, the water table ceased rising in large the water table. areas, and is even being lowered in some. In other areas, however, the rise continues. Waterlogging occurred first in areas along the ca- nals and later spread to form contiguous areas. By The disposal of drainage water is particularly diffi- 1960, the watertable was within 3 meters of the soil cult and expensive, since many of the problem irri- surface under about half of the canal command area, gated areas lie great distances from the sea, and and within 1 meter of the surface over a tenth of the land surface is extremely flat (less than 1:5,000). the area, causing salt infusion to the root zone. Salt The problem of drainage and effluent disposal is accumulations resulted in the salinization of about common to both the Pakistani and the Indian sides 1 million hectares. By 1980, the groundwater rose of the Punjab. Some evaporation basins have been to within less than 3 meters on the surface under- used, but leakage back to the rivers during dry pe- neath 55 percent of the total irrigated area. Salin- riods are problematic. The World Bank has been ization then affected an estimated 5 million hectares. helping India and Pakistan develop plans for solv- ing these long-term waterlogging and salinity prob- This alarming trend led the Pakistani government lems.8 An example of a salt balance related to the (with international assistance) to implement the Pakistan portion of the Indus River Basin is given Salinity Control Reclamation Projects (SCARP) pro- in Figure 4. gram. Under SCARP, a regional drainage canal has been constructed and private users have been en- couraged to install tubewells to pump water from 8Hillel, D. (2000). 29 WATER RESOURCES AND ENVIRONMENT · TECHNICAL NOTE E.1 FURTHER INFORMATION Information about irrigation systems can be found Information about water quality can be found in: in: FAO. 1985. Water Quality for Agriculture. FAO Irrigation Hoffman, G. J., T. A. Howell, and K. H. Solomon, eds. 1990. and Drainage Paper 29 Rev. 1. Rome: FAO. Management of Farm Irrigation Systems. St. Jo- FAO. 1997. Management of Agricultural Drainage Water seph, MI: American Society of Agricultural En- Quality. ICID & FAO Joint Report. FAO Water gineers. Report 13. Rome: FAO. Jensen, M. E., ed. 1980. Design and Operation of Farm Irrigation Systems. ASAE Monograph Number 3. Information about salinity can be found in: St. Joseph, MI: American Society of Agricultural Engineers. Christen, E.W., and J. E. Ayers. 2001. Subsurface Drain- age System Design and Management in Irrigated Information about drainage systems can be found Agriculture: Best Management Practices for Re- in: ducing Drainage Volume and Salt Load. CSIRO Land and Water, Australia Technical Report 38/ 01. (Available on the web at www.clw.csiro.au/ International Land Reclamation Institute (ILRI). 1994. publications/technical/2001). Drainage Principles and Applications. Publica- Hillel, D. 2000. Salinity Management for Sustainable Irri- tion 16, 2nd Edition. Wageningen, The Nether- gation: Integrating Science, Environment, and lands: ILRI. Economics. Washington: World Bank. Skaggs, R. W., and J. van Schilfgaarde, eds. 1999. Agricul- Umali, D. 1993. Irrigation-Induced Salinity. World Bank tural Drainage. Number 38 in the series Technical Paper No. 215. Washington: World "Agronomy." Madison, WI: American Society of Bank. Agronomy. FAO. 1997. Management of Agricultural Drainage Water Quality. ICID & FAO Joint Report. FAO Water Information about health effects from I&D schemes Report 13. Rome: FAO. can be found in: FAO. 2002. Biodrainage ­ Principles, Experiences and Applications. IPTRID Knowledge Synthesis Re- Birley, M. H. 1989. Guidelines for Forecasting the Vector- port No. 6. Rome: FAO. borne Disease Implications of Water Resource De- Stirzaker, R. W., R. Vertessy and A. Sarre, 2001. Trees, Water velopment. WHO, FAO, and UNEP - PEEM and Salt. Canberra, Australia: Rural Industries Guideline Series 2. Geneva: WHO. Research and Development Corporation. FAO. 1997. Management of Agricultural Drainage Water Quality. ICID & FAO Joint Report. FAO Water Information about environmental assessment can Report 13. Rome: FAO. be found in: The following are useful website links: Food and Agriculture Organization of the United Nations (FAO). 1995. Environmental Impact Assessment www.clw.csiro.au of Irrigation and Drainage Projects. FAO Irriga- www.fao.org tion and Drainage Paper 53. Rome: FAO. www.icid.org Mock, J.F. and P. Bolton. 1993. The Environmental Check- www.iwmi.org list to Identify Environmental Effects of Irriga- www.rirdc.gov.au tion, Drainage and Flood Control Projects. www.worldbank.org Wallingford, UK: HR Wallingford. World Bank. 1991. Environmental Assessment Sourcebook, Volume II ­ Sectoral Guidelines. World Bank Tech- nical Paper Number 140. Washington: World Bank. 30 IRRIGATIONAND DRAINAGE: DEVELOPMENT Other references in this Note: Subramanian, A., N. Vijay Jagannathan, R. Meinzen-Dick, eds. 1997. User organizations for sustainable water services. World Bank Technical Paper No. 354. Schultz, B. 2001. "Irrigation, Drainage and Flood Protec- Washington: World Bank. tion in a Rapidly Changing World." Irrigation and Szabolcs, I. 1989. Salt-Affected Soils. Boca Raton, FL: CRC Drainage 50: 261-77. Press. Skaggs, R., et al. 1994. "Hydrologic and water quality Szabolcs I. 1994. "Soils and salinization." In M. Pessarakli, impacts of agricultural drainage." Critical reviews ed., Handbook of plant and crop stress.New York: in environmental science and technology, 24(1): Marcel Dekker. 1-32. World Bank. 1993. Water Resources Management. World Smedema L K. 2002. Land Drainage: An Instrument for Bank Policy Paper. Washington: World Bank. Agricultural and Rural Development. Interna- tional Commission for Irrigation and Drainage. Proceedings on CD. 31