Cover Image
close this bookLong Distance Water Transfer: A Chinese Case Study and International Experiences (UNU, 1983)
View the documentForeword
View the documentChapter 1.Long-distance water transfer: problems and prospects
View the documentChapter 2. The river Nile: main water transfer projects in Egypt and impacts on Egyptian agriculture
View the documentChapter 3. Agricultural water management and the environment
View the documentChapter 4. Japanese water transfer: a review
View the documentChapter 5. The Texas water system: implications for environmental assessment in planning for interbasin water transfers
View the documentChapter 6. China's south-to-north water transfer proposals
View the documentChapter 7. Natural conditions in the proposed water transfer region
View the documentChapter 8. Land use and crop allocation in the proposed water transfer region
View the documentChapter 9. South-north water transfer project plans
View the documentChapter 10. Environmental implications of water transfer
View the documentChapter 11. Impact of water transfer on the natural environment
View the documentChapter 12. Impact of south-to-north water transfer upon the natural environment
View the documentChapter 13. Institutions and China's long-distance water transfer proposals
View the documentChapter 14. The Chang Jiang diversion project: an overview of economic and environmental issues
View the documentChapter 15. Water balance in the water transfer region
View the documentChapter 16. Integrated evaluation of the surface and groundwater resources of the Hai and Luan He basins
View the documentChapter 17. Preliminary estimation of natural runoff in the Huai He basin
View the documentChapter 18. Shallow groundwater resources of the Huang-Huai-Hai plain
View the documentChapter 19. Potential evaporation and field water consumption in the north China plain
View the documentChapter 20. Analysis of storage for the regulation of surface water in the Huang-Huai-Hai plain for south-to-north water transfer
View the documentChapter 21. Using ancient channels to regulate water through storage: the example of the Hebei plain
View the documentChapter 22.On the problem of water supply in the Hai-Luan plain
View the documentChapter 23. Some aspects of the necessity and feasibility of China's proposed south-to-north water transfer
View the documentChapter 24. The atmospheric moisture balance in the proposed water transfer region
View the documentChapter 25. The effect of south-to-north water transfer on saltwater intrusion in the Chang Jiang estuary
View the documentChapter 26. An investigation of the water quality and pollution in the rivers of the proposed water transfer region
View the documentChapter 27. Possible effects of the proposed eastern transfer route on the fish stock of the principal water bodies along the course
View the documentChapter 28. Effect of diverting water from south to north on the ecosystem of the Huang-Huai-Hai plain
View the documentChapter 29. An experimental study of improving the Saline-alkali soil in the Yucheng experimental area, Shandong province

Chapter 3. Agricultural water management and the environment

Gaylord V. Skagerboe
Department of Agricultural and Chemical Engineering Colorado State University, Fort Collins

INTRODUCTION

WHETHER THE GOAL is minimizing diversions to new croplands because of limited water supplies, reducing future diversions to irrigated agriculture to provide water supplies for new demands, maximizing the effectiveness of interbasin water transfers, minimizing water quality degradation in receiving streams resulting from irrigated agriculture, or maximizing agricultural production on existing croplands; the solutions are identical-improved water management practices.

Irrigation is one of the most important agricultural practices developed by man, utilized in some form since the earliest recorded history of agriculture and providing the economic base for many ancient civilizations. Irrigation farming not only increases productivity, but it also provides flexibility which allows shifting from the relatively few dryland crops to many other crops which may be in greater demand. Irrigation contributes to strengthening other facets of a region's economy in that it usually creates more employment opportunities than rainfed agriculture through intensive and diversified cultivation, the stimulation of important agribusiness and public institutions, the provision of products for export, and the creation of a healthy domestic market (Skogerboe, 1974).

History is replete with declining civilizations due to declining agricultural productivity, which has usually been the result of improper soil and water management practices. This potential danger is present today at many places throughout the world, coming at a time of dangerous food shortages in a hungry world, when the goal is to increase crop yields per unit of land.

To maintain agricultural productivity in irrigated agriculture-and we must do more than that today-salts applied to the croplands, which are dissolved in the irrigation water supplies, must be moved below the root zone in order not to retard plant growth. Therefore, it is mandatory that water supplied to a crop must exceed the actual water requirements of the plants to include evapotranspiration needs, leaching requirements, seepage losses and in most cases other transit or water conveyance losses which in most countries are substantial.

As is known, the quantity of irrigation water diverted from a river usually far exceeds the cropland water requirements. Data from many irrigation regions indicate that seepage losses from canals and laterals throughout the irrigation distribution systems are extremely high. Added to this problem is the excessive application of water on farm fields, which results in surface runoff from the lower end of the field (tailwater runoff) and/or large quantities of water moving below the root zone (deep percolation). The combination of seepage and deep percolation losses causes groundwater levels to rise (waterlogging). In many irrigated regions, the groundwater levels have reached the vicinity of the root zone which frequently results in the upward movement of groundwater due to capillary action. When upward moving water reaches the soil surface and evaporates, the salts contained in the moisture are left behind on the ground surface. This process of salinization has not only resulted in declining agricultural production, but has caused many lands to become essentially barren.

The quality of water draining from irrigated areas is materially degraded from that of the irrigation water applied as we have discovered along the Colorado River and other rivers. Agriculturalists have viewed this phenomenon as a natural consequence of several complex processes and only in the past decade has attention been given to the possibility that progress could be made toward controlling or alleviating this degradation of water quality.

Historically, some degree of salt concentration due to irrigation has been usually accepted as the price for irrigation development. In some areas, however, there has been so much laxity that quality degradation has become a serious matter. As pressure on water resources becomes greater, due to growth in population and the necessity to produce food in increased quantity and improved quality, there is mounting concern for proper control of serious water quality deterioration and soil salinization. The need then for more precise information as a basis for wise policy action is a matter of critical importance.

The major problems resulting from irrigation are due to the basic fact that plants are large consumers of water resources. Growing plants extract water from the supply and leave salts behind, resulting in a concentration of the dissolved mineral salts which are present in all natural water resources. In addition to having a greater concentration of salts in the return flow resulting from evapotranspiration, irrigation also adds to the salt load by leaching natural salts arising from weathered minerals occurring in the soil profile, or deposited below. Irrigation return flows provide the vehicle for conveying the concentrated salts and other pollutants to a receiving stream or groundwater reservoir. It is necessary then to examine the waterlogging and salinity problems resulting from this process and to develop and implement measures to control or alleviate the detrimental effects.

Impaired crop production resulting from salinity is not limited to the western United States, but is a major problem in many areas of the world. In fact, the more one observes problems in other countries, the more one is convinced that this is indeed an international problem. Unfortunately, the portions of the world now facing the greatest population pressures are the same areas which have the least amount of additional land available for agriculture and in some cases where waterlogging and salinization are a major problem. In such areas, increased food production must come from more intensive farming with consequent increased yields. On the one hand, there is a great need to increase the productivity of such lands, but on the other, agricultural production is continually being damaged due to rising groundwater tables (waterlogging) and increased salinity in the soils and groundwater supplies. Though there are estimates of the extent of these salt problems in the world, suffice it to say that it is a growing concern in many places.

Whenever water is diverted from a river for irrigation use, the quality of the return flow becomes degraded. The degraded return flow then mixes with the natural flows in the river systems. This mixture is then available to downstream users to be diverted to satisfy their water demands. This process of diversion and return flow may be repeated many times along the course of a river. In the case of the original diversion, if the increase in pollutants contained in the return flow is small in comparison to the total flow in the river, the water would probably not be degraded to such an extent that it would be unfit for use by the next downstream user.

If the quantity of pollutants (e.g., salinity) in the return flow is large in relation to the river flow, then it is very likely that the water is not suitable for the next user unless the water is treated to remove objectionable constituents. Since water is diverted many times from the major rivers, the river flows show a continual degradation of quality in the downstream direction. As the water resources become more fully developed and utilized, without control, the quality in the lower reaches of the river will likely be degraded to such a point that the remaining flows will be unsuitable for many uses, or previous uses of the waters arriving at the lower reaches of the river basin will no longer be possible.

MAJOR WATER PROBLEMS

Water Quantity

The purpose of irrigation is to increase crop production, but the real difficulty lies in sustaining increased crop production over a long time period. History is replete with hydraulic societies which flourished and then floundered or became extinct. Why?

Maintaining or increasing agricultural productivity in an irrigated area requires, first of all, that a salt balance be achieved in the root zone; and secondly, that not too much water is applied such that the groundwater levels rise until the water table is near the ground surface, thereby resulting in waterlogging and increased salinity levels in the root zone. Thus, a balance must be reached in order that sufficient water is applied to the croplands to leach salts from the root zone, but not so much water that groundwater levels nearly reach the ground surface. The history of hydraulic societies has been primarily one of applying too much water. And over-irrigation continues today in most parts of the world.

In order that water does not limit crop yields, the proper amount of water must be applied to the cropland at the proper times. The timing and quantity of required irrigation water is primarily a function of climate, soils, and the stage of crop growth.

In many regions and countries, increasing urbanization and industrialization requires the reallocation of agricultural water uses in order to meet these new water demands. In order to accomplish this water reallocation, improved water management practices must be instituted in the agricultural sector, thereby reducing agricultural water diversion requirements.

The real detriment in over-irrigation is that groundwater levels rise, thereby resulting in waterlogging of the soils and a continual decline in agricultural productivity until the land may finally become barren. In addition, over-irrigation results in water quality degradation of irrigation return flows and consequent detriments to downstream water users.

Interbasin transfers will be highly beneficial in overcoming periods of water shortages. However, an overabundance of water frequently results in inefficient irrigation practices and consequent waterlogging.

Water Quality

Usually, the quality of water coming from the watersheds is excellent. At the base of the hills or mountain ranges, large quantities of water are diverted to valley croplands. Much of the diverted water is lost to the atmosphere by evapotranspiration (perhaps one-half to two-thirds of the diverted water), with the remaining water supply being irrigation return flow. This return flow will either be surface runoff, shallow horizontal subsurface flow, or will move vertically through the soil profile until it reaches a perched water table or the groundwater reservoir, where it will remain to be pumped or transported through the groundwater reservoir until it reaches a river channel.

That portion of the water supply which has been diverted for irrigation but lost by evapotranspiration (consumed) is essentially salt-free. Therefore, the irrigation return flow will contain most of the salts originally in the water supply. The surface irrigation return flow will usually contain only slightly higher salt concentrations than the original water supply. Thus, the water percolating through the soil profile contains the majority of salt left behind by the water returned to the atmosphere as vapour through the phenomena of evaporation and transpiration. Consequently, the percolating soil water contains a higher concentration of salts. This is referred to as the "concentrating" effect.

As the water moves through the soil profile, it may pick up additional salts by dissolution. In addition, some salts may be precipitated in the soil, while there will be an exchange between some salt ions in the water and in the soil. The salts picked up by the water in addition to the salts which were in the water applied to the land are termed salt "pickup". The total salt load is the sum of the original mass of salt in the applied water as the result of the concentrating effect plus the salt pickup.

Whether irrigation return flows come from surface runoff or have returned to the system via the soil profile, the water can be expected to undergo a variety of quality changes due to varying exposure conditions. Drainage from surface sources consists mainly of surface runoff from irrigated land (there will be some precipitation runoff). Because of its limited contact and exposure to the soil surface, the following changes in quality might be expected between application and runoff: (a) dissolved solids concentration only slightly increased; (b) addition of variable and fluctuating amounts of pesticides; (c) addition of variable amounts of fertilizer elements; (d) an increase in sediments and other colloidal materials; (e) crop residues and other debris floated from the soil surface; and (f) increased bacterial content (Skogerboe and Law, 1971).

Drainage water that has moved through the soil profile will experience different changes in quality from surface runoff. Because of its more intimate contact with the soil and the dynamic soil-plant-water regime, the following changes in quality are predictable: (a) considerable increase in dissolved solids concentration; (b) the distribution of various cations and anions may be quite different; (c) variation in the total salt load depending on whether there has been deposition or leaching; (d) little or no sediment or colloidal material; (e) generally, increased nitrate content unless the applied water is unusually high in nitrates; (f) little or no phosphorus content; (g) general reduction of oxidizable organic substances; and (h) reduction of pathogenic organisms and coliform bacteria. Thus, either type of return flow will affect the receiving water in proportion to respective discharges and the relative quality of the receiving water.

The quality of irrigation water and return flow is determined largely by the amount and nature of the dissolved and suspended materials they contain. In natural waters, the materials are largely dissolved inorganic salts leached from rocks and minerals of the soil contacted by the water. Irrigation, municipal and industrial use and reuse of water concentrates these salts and adds additional kinds and amounts of pollutants. Many insecticides, fungicides, bactericides, herbicides, nematocides, as well as plant hormones, detergents, salts of heavy metals, and many organic compounds, render water less fit for irrigation and other beneficial uses. From this information, it can be concluded that increased salinity concentrations and salt loading result primarily from subsurface irrigation return flows, as shown in Figure 1 (Radosevich and Skogerboe, 1977).



Figure 1. Schematic Representation of Nonpoint Source Pollution from Irrigated Agriculture

DEFINITION OF AN IRRIGATION SYSTEM

An irrigation system can be subdivided into three major subsystems: (a) the water delivery subsystem; (b) the farm subsystem; and (c) the water removal subsystem. The water delivery subsystem can be further subdivided into two components, namely: (a) the transport of water and pollutants from the headwaters of the watershed to the cross-section along the river where water is diverted to irrigate croplands; and (b) the transport of water and pollutants from the river diversion works to the individual farm. The farm subsystem begins at the point where water is delivered to the farm and continues to the point where surface water is removed from the farm. Also, the farm subsystem is defined vertically as beginning at the ground surface and terminating at the bottom of the root zone. The water removal subsystem consists of: (a) the surface runoff from the tail end of the farm; and (b) water moving below the root zone. These subsystems are illustrated in Figure 2.

PLANNING FOR EFFECTIVE IRRIGATION WATER MANAGEMENT

The resource base for irrigated agriculture has not substantially changed since its inception thousands of years ago. Over the last century there has been little incentive for any major innovation to improve efficiency in the use of water which now fortunately is considered a scarce resource. The provision of irrigated water since ancient times has been considered a governmental or collective responsibility, and the direct charges made for water have usually not been high enough to encourage proper budgeting of water or other necessary innovations. This custom of undercharging for water has continued to this very day; few regions charge the farmer for the real cost of water. However, there are a few examples of extremely water-scarce areas in the world where considerable ingenuity has been applied in effectively utilizing water supplies.

Aggravating this situation of so-called "cheap water" is the fact that the development of irrigated agriculture in most places, even in the last few decades, has focused almost entirely upon the construction of water delivery subsystems. This preoccupation with the installation of "hardware" results from a naive singlediscipline approach to water management, and one discipline cannot begin to solve the complex physical, economic and sociological problems involved. Probably the greatest deterrent to improved water management in most irrigation systems today is the inordinate focus on the water delivery subsystem and the almost complete neglect of other problems of the system such as the need for improved soil-plant-water management techniques, improvements in cultural practices, farm machinery, agrarian structural reforms, roads, marketing systems, advisory services and input supply systems, administration of institutions, water laws, co-operatives and water users associations, and many other factors all of which must fit together in all their interdependencies and complementarities to form a most complex system. In reality, though, especially in irrigated agriculture, we come face-to-face with a wide gap which frequently exists between "hardware development" and the development of all the other requisites for increased agricultural production.



Figure 2. Definition Sketch of an Irrigation System

The approach which has been applied to irrigated agricultural development in the past is characterized by separating the development of water resources from the management aspects of water resource utilization. Therefore, the record shows development being emphasized greatly while management is most often neglected. This orthodox approach has been used almost exclusively in the western United States with reasonable success. However, as water resources become more fully utilized, the necessity for meeting new water demands (along with physical, socioeconomic, and political problems of water quality degradation) require that we reject much of the conventional wisdom of the past. It should also be obvious that many other countries have neither the time nor the resources that many western irrigated regions had to utilize in their development. Pressures created by rapidly rising population rates alone will force them at some point to re-evaluate their approaches.

In contrast to the mere development of water resources approach, the "management" approach attempts to achieve water development objectives by applying a variety of measures after studying the entire system, thereby attempting to modify the total system to meet new and changing demands as well as estimated future demands. Therefore, instead of constructing new engineering works to meet new demands, the focus should be upon water resource management, with construction works being considered only as a tool when necessary to meet water management objectives. Unfortunately, in most cases, water management and the many disciplines required to produce efficient management are relegated to the post-analysis of engineering works (e.g., much of the future emphasis will be geared towards improving existing irrigation systems), which aggravates not only the implementation of technology, but really constrains or makes extremely difficult the implementation of a host of services requiring strong institutional measures.

The above philosophy applies to interbasin water transfers. Such transfers should be considered as part of an overall water management programme, wherein improved practices will result in minimizing the quantity of water to be transported into the river basin.

DESIGN OF AN IRRIGATION SYSTEM

The "heart" of an irrigation system is the farm subsystem. The purpose of an irrigation system is to grow food and this "action" takes place in the root zone. The purpose of the water delivery subsystem and water removal subsystem is to support this "action". Therefore, the proper design of an irrigation system requires, first of all, that the farm subsystem be adequately designed so that the water delivery subsystem can be designed to provide the quantities of water at the times required by the plants. The most important constraint in the design procedure is the necessity for assuring adequate drainage through the root zone in order to maintain a root zone salt balance to ensure continued long-term agricultural productivity.

Farm Subsystem

The most important variables in designing the farm subsystem are climate, soils, and crops. The interrelationships between these variables dictate the capability of the land resource for producing food and fibre. We need to understand the interactions and relationships between water and management factors such as optimum rates of fertilizer, proper pest control measures, seeding and tillage practices, and other improved cultural practices. Much of this research is adaptive and protective, which due to its rather low level of sophistication is sometimes neglected.

The next important variable will be water and its physical availability. Frequently, in arid areas of the world, water is the most limiting factor. However, the capability of the available water supplies (precipitation, surface runoff, and groundwater) for plant production is highly dependent upon the efficiency with which the water is used, which in turn is a function of both economic and institutional factors. Besides physical limitations, the questions of economics in supplying water must be answered to ensure that costs are commensurate with planning goals.

Once the general scope of an irrigation project has been determined, then the more detailed design procedures can follow. The critical factor at this point becomes the infiltration characteristics of the soil. Unfortunately, infiltration is a complex phenomenon and the intake function of a particular field will vary during the irrigation season, as well as varying from season to season. There are a number of laboratory and field methods available for determining the intake characteristics of a soil.

Using climatic data, the potential evapotranspiration of the various crops can be calculated. These computations will provide the information regarding water consumption with time, provided sufficient moisture is made available in the root zone.

The next important step is designing the farm irrigation layout so that sufficient moisture will be available in the root zone when required by the plants. The root zone is capable of storing moisture for future plant use. Again, soil characteristics determine the amount of storage, as well as the capability of the plant to extract the moisture from this "reservoir". At the same time, the leaching requirement for maintaining a salt balance in the root zone must be kept in mind. Consequently, the farm irrigation layout must be capable of supplying not only the plant water requirement, but also the leaching requirement.

The proper design of the farm irrigation layout is crucial for: (a) uniformly distributing the necessary moisture throughout the field; and (b) minimizing deep percolation losses so as not to aggravate problems in the water removal subsystem (e.g., waterlogging and salinity).

Generally, the development of irrigation projects has not entailed the design of farm irrigation layouts suited to the individual characteristics of each field. Instead, only the general method of irrigation may be adopted (e.g., basin or furrow irrigation). The farmer is usually left to his own means in irrigating his field, without having the benefit of technical (or economic) assistance. The situation is further aggravated because, along with adopting a general method of irrigation, an average irrigation efficiency for this method is "pulled out of the air". If this socalled average water-use efficiency were even close to being correct it would be most fortunate-let alone taking into account the variability of this "magic" number on any specific field throughout the irrigation season, as well as the variability from field-to-field. Usually, the application of this average efficiency results in large quantities of deep percolation during the early part of the irrigation season, which in turn contributes to waterlogging of the soil and consequent poor crop yields (or eventual failure of the irrigation enterprise).

Water Delivery Subsystem

The design of the individual farm irrigation layouts should dictate the design of the water delivery subsystem. The irrigation layout design, if properly accomplished, will show the necessary quantities and timing of water deliveries at the farm inlets. The water delivery network must be designed to meet the farm water requirements. Except for alluvial channels conveying large sediment loads, the design of the conveyance works is rather "mechanical".

One of the essential facilities for successfully operating an irrigation conveyance network is adequate and numerous flow measurement devices. To begin with, since each farm has a particular water requirement, then the only means by which the proper amount of water can be delivered is by measuring the water at the farm inlet. After all, the farmer cannot be expected to use good water management practices if he does not even know the quantity of water being managed. Besides each farm inlet, a flow measurement structure should be provided at all division points in the water delivery subsystem.

The real problem in the water delivery subsystem is the institutional framework controlling the operation of this portion of the irrigation system. Generally, the operation of the conveyance facilities has not been related to the requirements for sustaining a long-term productive agriculture. In particular, institutional factors have acted as constraints to improved water management or increased agricultural production.

The primary requirement for sustaining an irrigation system is an institutional framework that is compatible with the design requirements for the water delivery subsystem, which in turn has been dictated by the proper design of the farm irrigation layouts, as well as any constraints imposed by the water removal subsystem. Thus, even if all three components of the irrigation system have been properly designed, the lack of an adequate institutional framework for operating the system in accordance with the design criteria will likely lead either to failure of the system, or at least to having agricultural production levels below (or far below) expectations.

Water Removal Subsystem

The principal function of the water removal subsystem is to allow proper drainage below the root zone so that adequate leaching of salts from the root zone will occur. The most satisfactory mechanism for ensuring adequate drainage is proper operation of the water delivery subsystem. By so doing, a drainage problem may not occur. This is much better than allowing the problem to occur, then constructing drainage facilities to correct the damage. Unfortunately, the usual solution consists of constructing additional facilities. Frequently, project reports will state-"drainage facilities will be designed after the project has been in operation for a number of years in order to more precisely ascertain drainage requirements". This is the same naive single discipline thinking referred to in the previous section, which is the rule rather than the exception. Perhaps the statement is correct that the history of irrigation systems teaches one that man often does not learn from history.

Another important consideration in the water removal subsystem is water quality. If canal seepage and cropland deep percolation losses result in water quality degradation of the underlying groundwater supplies, then the use of these supplies may become impaired. Also, the return flows to the river may limit the usefulness of the river water to downstream users. Numerous examples of this situation can be cited throughout the world. Again, this is the rule rather than the exception.

The proper functioning of an irrigation system is highly dependent upon an institutional framework which is compatible with the design criteria used in developing the system, as well as providing flexibility in achieving improved water management as the need arises. Satisfying on-farm water management objectives cannot be achieved without controlling water deliveries. Therefore, the administration of the irrigation system requires that satisfactory legal mechanisms exist that control water deliveries.

The failure of new irrigation developments to meet estimated production goals has largely resulted from the lack of follow-up in providing essential agricultural inputs and services to farmers. Again, the lack of training in farm water management and other farm practices by those responsible for the planning, design and construction of the irrigation development leads to the shortcomings in output. Also, the lack of co-operation between disciplines is certainly a detriment in any country. Interdisciplinary team research is a noble concept but it is seldom internalized by researchers and implemented effectively. Perhaps the most expedient solution is to expand the training of those personnel involved in the planning, design and construction of irrigation enterprises. Such training would then hopefully provide feedback into the planning and design of future irrigation developments.

The provision of adequately trained personnel for the operation and maintenance of irrigation systems may be understood, but it is sometimes difficult to accomplish. Much focus must be given to training not only the engineers and technicians, but those who work directly and indirectly with the farmer. Although agricultural experiment stations may exist, there is usually a severe limitation in accomplishing on-farm improvements because of insufficient adequately trained farm-level advisors capable of transferring applied research results directly to the farmers. In many countries, the components of research and advisory services have never been brought together in a carefully planned partnership.

We are all aware of the need for improved delivery systems for technology once it has been made available by research. How best can this transfer of technology in water management be made to the end user, the farmer? Here we need the help of the applied social sciences such as economics, sociology, anthropology, political science and even social psychology. Some extension system is required which will take the proven findings of research, along with utilizing the knowledge of the social sciences "package", in such a way as to convince the end user to move from the trial to the final adoption stage.

RIVER BASIN SALINITY PLANNING

An approach for defining technological solutions to the above-mentioned problems will be briefly described below (for a more complete description, see Skogerboe and Walker, 1980). This description applies to a combination of water quantity and salinity analysis; however, the salinity component can be deleted, or models for other pollutants can be substituted for the salinity models.

The majority of water quality planning efforts in irrigated agriculture are directed towards identifying measures required to control salinity in individually irrigated areas or subbasins. However, plans must also be developed for the entire river basin in order to determine the programmes to be implemented. Firstly, evaluation of alternatives for each area leads to management practices that can effectively control salinity from use of irrigation water. These plans should indicate optimum policies for reducing salinity by amounts ranging from the maximum potential control achievable to no control as prescribed by each specific area. The relationship between salinity control policies and their resulting effectiveness is usually expressed as a cost-effectiveness relationship for the area under examination. This relationship must be developed for each area with a significant salinity contribution within the basin. This subarea analysis is schematically illustrated in Figure 3 (Skogerboe, Walker and Evans, 1979).

In each subarea, the magnitude of the problem must be determined and the sources delineated. This should include the magnitude of subsurface irrigation return flows resulting from seepage losses and deep percolation losses, along with changes in chemical composition of these flows enroute to the groundwater reservoir and subsequently the river. Appropriate solutions should be demonstrated and evaluated on farmers' fields to develop alternatives that are acceptable to both the farmers and various regulatory agencies. In addition, cost-effectiveness analysis must be applied to the acceptable solutions to arrive at best management practices. Finally, the basis for implementation of the best management practices must be established.

The second step in establishing the most cost-effective salinity control programme is to define the best management practices by optimizing cost effectiveness relationships from individual areas into a single strategy. This planning function delineates the level of salinity control required in each individual subbasin to achieve the overall goal for water quality improvement with the least cost. Relative levels of implementation among the areas are also determined.

Finally, the third step assigns the required level of salinity control that should be implemented in each subbasin or irrigated area. The basin planning process for salinity control involves integration of planning studies at the local level into the total basin framework to define the best management practices on a basin-wide scale. By integrating the results outlined in the first step, the best management practices for salinity control in each area are identified. A summary of this process is shown schematically in Figure 4.



Figure 3. Planning Framework for Developing Best Management Practices in a Subbasin

If it is not possible or feasible to determine a basin-wide salinity control programme, the processes involved in alleviating salt pollution from an individual area must be determined as shown in Figure 5. These analyses are identical to the process outlined in the first step, but the scale is much smaller and the best management practices are tailored to that particular area only.

IMPROVING EXISTING IRRIGATED LANDS

Much of the emphasis in the future will have to be on improving what we have. In other words, water management will have to be improved, waterlogging and salinity problems alleviated, and crop production increased on existing irrigated lands. Technology alone will not usually bring about the necessary improvements. Instead, a combination of technological changes and institutional modifications will usually be required to effectively manage existing irrigated lands.

A "Development Process for Improving Irrigation Water Management on Farms", which is directed towards improving the productivity of existing irrigated lands, has recently been reported (Skogerboe, Lowdermilk, Sparling and Hautaluoma, 1980). This process has two important themes: (a) an interdisciplinary approach; and (b) farmer-client involvement. Physical scientists and social scientists work together with farmers in identifying major constraints to increasing agricultural productivity and conserving natural resources. Acceptable solutions are developed for priority problems in collaboration with farmers. Finally, acceptable solutions are implemented that utilize both the resources of the farmers and government. This process consists of three phases: (1) Problem Identification; (2) Development of Solutions; (3) Project Implementation. The three phases have also been subdivided into subphases as listed in Table 1.

Problem Identification

The Reconnaissance subphase begins with setting preliminary objectives, which will usually encompass at least one of three major objectives: (a) increased agricultural production; (b) increased equity of income distribution; or (c) resource conservation. To develop a general overview of the irrigation system involves the collection and reading of available written information, as well as visits with selected officials of organizations related to agriculture. Reconnaissance field investigations are conducted to develop a preliminary listing of problems for the four major components of the irrigation system:



Figure 4. Planning Framework for Developing Best Management Practices for Salinity Management in a River Basin



Figure 5. Planning Framework for Developing Best Management Practices for only one Irrigated Area

Table 1.Phases and Subphases of the Development Process for Improving Irrigation Water Management on Farms

Phase Subphase
Problem Identification Reconnaissance
Problem Diagnosis
Development of Solutions Identification of Plausible Solutions
Testing and Adaptation of Solutions
Assessment of Solution Package
Project Implementation Project Authorization
Project Organization
Project Operation

(a) plant environment; (b) farm management practices; (c) water supply and removal; and (d) institutional linkages. This preliminary listing of problems is then used to refine programme objectives.

The Problem Diagnosis subphase involves more detailed field studies and data analysis than occur in the Reconnaissance subphase. Interdisciplinary diagnostic studies are designed which involve field studies of the plant environment, farm management practices, water supply and removal, and institutional linkages. Analyses of field data for the plant environment involve: plant suitability to its environment; pest management practices; plant nutrient deficiencies; and physical, chemical and biological root-zone characteristics. Analyses of farm management practices involve: resources inventory; irrigation practices; cropping practices; and farm budgets. Climate analysis, water budgets and salt budgets are included in the analyses for the water supply and removal component. For evaluating institutional linkages, the analyses include: cultural values; cultural network; farmer behaviour; water, irrigation and agriculture infrastructure; and policies, laws and codes pertaining to agriculture and water. These analyses are then interpreted through a series of questions in order to develop a listing of problems and their probable causes. These problems are then ranked according to their expected impact in meeting programme objectives. The Problem Identification phase is completed by reporting priority problems and their apparent causes; however, more insight into the causes of priority problems will be obtained during the Development of Solutions phase.

Development of Solutions

The Development of Solutions phase has three subphases (Table 1). The Identification of Plausible Solutions subphase is essentially a "think tank" exercise which begins with generating potential solutions to the priority problems reported in the previous phase. These potential solutions, which include all solutions that could possibly be employed, are then screened against programme objectives, programme constraints, and strategic considerations to develop plausible solutions to the "site specific" problems previously identified. These plausible solutions are then ranked according to: groups affected; uncertainty; disciplines involved; time requirements; resource requirements; and complementarities with other plausible solutions.

The Testing and Adaptation of Solutions subphase primarily involves field activities. An integrated interdisciplinary work plan is developed for the testing of plausible solutions at experiment stations, if necessary, and definitely on farmers' fields. This is a time-consuming process because solutions acceptable to farmers must also be tested under a phased withdrawal of resources. This allows a determination of the degree to which farmers can help themselves in implementing solutions, which has many advantages in terms of minimizing government inputs and maximizing the effectiveness of the solutions.

The third subphase-Assessment of Solution Packages-is a quantitative and qualitative assessment of the plausible solutions after having been field tested on farmers' fields. Each plausible solution is assessed according to programme objectives as to: technical adequacy; social and political feasibility; and organizational adequacy. Those solutions passing these tests are considered acceptable solutions. Such solutions are then synthesized into alternative solution packages. The final product is a report that lists alternative solution packages and their impacts and costs in meeting programme objectives.

Project Implementation

The final phase of this development process is Project Implementation. The Project Authorization subphase begins with decision-makers reviewing the report on alternative solution packages and then identifying their preferred approach for a project. Based on these decisions, objectives for the selected project approach are prepared. Then, a project proposal is prepared, which is authorized when approved by the body of decision-makers. The final step in this subphase is making all of the legal arrangements that will be required for the successful implementation of the authorized project.

The Project Organization subphase consists of establishing the type of organization, selecting key project personnel, and developing institutional linkages. Considerable emphasis must be given to the mode of project management, as well as to the selection and training of project personnel.

The Project Operation subphase emphasizes the importance of working closely with farmers. A highly important aspect of operationalizing objectives and developing a work plan and schedule of events is obtaining farmer participation. Farmers must also be trained in the use of the solutions being implemented. Also, farmers must be organized, either informally or formally, for the long-term maintenance of collective facilities. A monitoring network should be established so that the impact of the implementation programme can be measured. Besides evaluating the monitoring data, it is usually necessary to do supplementary periodic evaluations. The refinement process is concerned with implementations resulting from the evaluation process, which involves a reassessment or "tuning up" of the project plan. The primary purpose of refinement is to continually readjust the mechanics of project implementation and the packages of solutions, which is a recognition that successful project planning and implementation is a reiterative and dynamic process.

continue