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Summaries of case studies

Drainage water management in the Aral sea basin

By V. Dukhovny, K. Yakubov, A. Usmano and M. Yakubov


The Aral Sea Basin is located in Central Asia and covers an area of 154.9 million ha. Under farming conditions characterized by high evaporation and low precipitation, most crops are irrigated. The irrigated area covered 7.9 million ha in 1999. The main crops grown under irrigation are cotton, rice, wheat, maize and fodder crops.

Water resources in the region consist of renewable surface and groundwater as well as return flows in the form of agricultural drainage water and wastewater. The two major rivers in the basin are the Amu Darya River in the south and Syr Darya River in the north. The total mean annual river runoff is 116 000 million m3. The annual amount of groundwater that can be subtracted without damage is 13 100 million m3. Water use in the Aral Sea Basin ranges between 110 000 million and 117 000 million m3 annually depending on the actual water availability. The groundwater abstracted is about 10 000 million m3 per year. On average, the agriculture sector accounts for 95 percent of all water withdrawals.

Each year about 5 000 million m3 of water reaches the Aral Sea, compared with 54 000 million m3 before the large-scale expansion of irrigation. This has led to the gradual drying up of the Aral Sea, which has had severe adverse effects on the region's environment, health and economy. It has been estimated that at least 73 000 million m3 of water would have to be discharged to the Aral Sea each year for a period of at least 20 years in order to restore it to its 1960 level of 53 m above sea level. The riparian states consider this target to be unrealistic. Proposals have been made to restore part of the Aral Sea to a level of 38-40 m above sea level, requiring an inflow of at least 6 000-8 000 million m3.

Low irrigation efficiencies have resulted in rising groundwater levels and secondary soil salinization. Nearly half of the irrigated lands are affected by salinity. Salt balances show that especially in dry years in the middle and lower reaches of the Amu Darya River salt accumulation takes place amounting to 0.6-10 tonnes/ha annually. In the lower reaches, even in wet years salt accumulation amounts to 8 tonnes/ha annually. For the Syr Darya Basin this phenomena can be observed in its middle reaches with an annual salt accumulation of 5.3 tonnes/ha. In addition to salinity, on 30 percent of the irrigated lands shallow groundwater poses a major problem for agricultural production. To combat these problems, a collector drainage network has been developed on 4.45 million ha. Within this area, 1.8 million ha have been equipped with horizontal or vertical subsurface drains. The disposal of drainage water causes considerable problems in terms of downstream water quality. About 92 percent of the total return flow consists of agricultural drainage water. Most of this water, about 20 000 million m3/year, returns into the river systems and a slightly smaller part, about 15 million m3/year, is diverted to desert sinks. In total, 137 million tonnes of salt are discharged annually together with agricultural drainage water. Of this total, 81 million tonnes were originally present in the irrigation water and 56 million tonnes originate from the mobilization of salts from the subsoil.

The guiding principle in the planning and management of water resources in the Aral Sea Basin is to set targets for water use and conservation, and to establish mechanisms to reach these targets. A wide range of measures has been implemented to decrease the losses from irrigated areas (including replacing cotton with wheat, which requires less water). Extensive research has been undertaken to establish practices that reduce application, conveyance and operational losses. Research has shown that application efficiencies can be improved by furrow levelling and rescheduling the amount and timing of irrigation water applications. One of the main reasons for the present waterlogging and salinity problems is the high irrigation norms adopted in the past. Applying a larger number of irrigation turns with smaller amounts of water increases the efficiency. However, research results have not led to large changes in irrigation practices. The large-scale adoption of research results requires an effective extension service. Another obstacle is that the infrastructure and irrigation scheduling on former collective farms do not always allow individual farmers to apply the amounts of water that would be most efficient. In addition to on-farm losses, high distribution losses are a major concern. Following the breakup of the former collective farms, new allocation and scheduling rules have yet to come into existence. The establishing of water users associations could help reduce distribution losses within the former collective farms. However, such reductions can only be expected if irrigation supply from higher levels also improves.

Drainage water use for irrigated agriculture in its place of origin or in adjacent areas is one of the options for reducing the disposal problems in the Aral Sea Basin. For the Central Asian conditions, a water quality classification has been developed for the use of saline water and conditions for use in relation to its salinity and chemical composition. A soil classification for the use of saline water has also been proposed. It is estimated that drainage water use can be increased to up to 25 percent of the annual drainage flow in the Aral Sea Basin, compared with the current 11 percent. In addition, agricultural drainage water can be reused in wetlands and biodiversity development.

Along the Amu Darya River, desert depressions are found in which drainage effluent is disposed and left for evaporation. These desert sinks or drainage lakes are of various sizes. This practice is a feasible alternative to disposal into the river. Moreover, it avoids an increase in mineralization of the river. Specific forms of flora and fauna have become established around these lakes, and fisheries may become a possibility. The main problem is that most lakes along the Amu Darya River have reached their maximum capacity. If the inflow into the lakes is not controlled, there is a risk that the lakes will overflow and flood the surrounding areas.

There have been plans to construct an outfall drain to the Aral Sea since the 1980s. This drain would run parallel to the Amu Darya River for 900 km. Upon its completion, mineralization levels in the river could be maintained below 1 g/litre at all times. The drain would collect drainage water from an area exceeding 1 million ha. Construction work commenced in the early 1990s. However, due to a lack of funds, work stopped in 1994 with only 20 percent of the drain completed.

Drainage water reuse and disposal: a case study from the Nile Delta, Egypt

By N.C. Kielen


The Nile Delta in northern Egypt starts north of Cairo where the Nile River splits into two branches, the Domitta and Rozetta. Egypt's cultivated land amounted to 3.3 million ha in 1994, nearly all of it irrigated. In the absence of effective rainfall, the country's water resources consist of: surface water from the Nile River; shallow and deep groundwater; and drainage water. The main source of water in Egypt is the Nile River. The 1959 agreement with Sudan allocates 55 500 million m3 of the Nile discharge per year to Egypt. The annual recharge to the groundwater in the Nile Valley and Nile Delta is estimated to be between 5 600 million m3 and 6 300 million m3.

The gross water use in the mid-1990s was about 60 300 million m3 per year, of which 51 500 million m3 or 85 percent was extracted for irrigation purposes. The Ministry of Water Resources and Irrigation (MWRI) expects irrigation demand to increase to 61 500 million m3 per year by 2025. The projected total water demand cannot be met by developing new water resources. Besides increasing water use efficiency, drainage water reuse is the most promising immediate and economically attractive option to make more water available for agriculture. In the 1980s, the reuse of agricultural drainage water became a policy to augment Egypt's limited fixed freshwater resources and to close the gap between supply and demand.

Reuse is centrally organized with the pumping of water from the main drains into the main canals. In 1996/97, the amount of water pumped at the reuse mixing stations was 4 400 million m3 with an average salinity of 1.8 dS/m. The total quantity of drainage water released to the Mediterranean Sea and coastal lakes was 12 400 million m3 with an average salinity of 4.2 dS/m. The MWRI has committed another 3 000 million m3 of the drainage water for reuse within the new reclamation areas of the El Salam Canal and Umoum Drain projects. Another 1 000 million m3 of the drainage water will be reused in the near future to irrigate newly reclaimed lands in the Kalapsho area in the Middle Delta. Therefore, the volume of drainage water officially reused for irrigation is expected to increase to 8 000 million m3 per year in the near future.

Farmers also use drainage water directly by pumping it from drains close to their fields. This is termed unofficial reuse. Estimates of the amount of drainage water unofficially used for irrigation range from 2 800 million m3 to 4 000 million m3 per year. Unofficial reuse in illegal rice fields in the Bahr Hadus area is of concern to the MWRI as it competes with the El Salam Canal drainage diversion.

A central issue in water resource management in Egypt is how much of the annual drainage discharge can be reused. In theory, 13 300 million m3 of drainage water with a salinity of less than 4.7 dS/m is available for reuse. This amount is equivalent to 84 percent of the generated drainage in 1993/94. Taking leaching requirements and deteriorating drainage water quality due to municipal and industrial pollution into consideration, the total estimated reuse potential is 9 700 million m3 with a maximum salinity of 3.5 dS/m, of which 8 000 million m3 can be used effectively. This is 5 000 million m3 more than the reuse level in 1993/94.

The Northern Lakes located adjacent to the Mediterranean Sea, comprising lakes Maruit, Edko, Burrulus and Manzala, are economically important as they support a large fishery and many fish farms. For continued fish production, the salinity levels in the lakes should be maintained between 5.5 and 6.25 dS/m. Based on maintaining these salinity levels, the drainage outflow to Lake Manzala and Lake Edko can be reduced by a maximum of 50 percent of the outflow level in 1993/94. The outflow to Lake Burrulus is already on the low side and cannot be reduced any further. The additional drainage reuse potential based on sustained freshwater lake fisheries is 4 000 million m3 per year, which is 1 000 million m3 less than the reuse potential based on maintaining a favourable salt balance in the Nile Delta.

The official strategy for drainage water reuse has not caused major increase in soil salinity levels on a large scale. In terms of maintaining a favourable salt balance in the Nile Delta, drainage reuse in Egypt has been successful. Factors that have contributed to a sustainable implementation of reuse are that drainage has been implemented on 90 percent of the irrigated lands, and that reused drainage water after mixing with freshwater has a low salinity content. Salinity levels of the water in the main drains increase from south to north, which is the general flow direction. Therefore, drainage water with favourable salinity levels is intercepted for reuse while drainage water with a high salinity content is disposed in the coastal lakes and Mediterranean Sea. However, soil salinity levels might be high locally especially in tail end areas where irrigation water is inadequate and groundwater salinity is high.

Since the 1990s, pollution of the drains as a result of large-scale urbanization and industrialization has received increased attention. Due to the increasing deterioration of water quality in the main drains and the increasing concern about how to manage unofficial reuse of drainage water, it appeared that it would be difficult to expand official reuse. The MWRI explored new opportunities for drainage water reuse. Between the centralized official reuse and the localized unofficial reuse, there is the option of capturing drainage water from branch drains and pumping it into the branch canals at their intersections. This level of reuse is termed intermediate reuse. It offers two main advantages. First, relatively good-quality drainage water is captured before discharging into the main drains where it is lost to pollution. Second, with the poor level of the current delivery system, water shortages often occur at the tail end of canals. At intermediate level, drainage water is pumped into the tail end of the branch canals, so making water available to water shortage areas.

Two alternative modes of reuse have been tested on an experimental basis. The first involved the application of freshwater separately from drainage water in the so-called cyclic mode. The other option tested was deficit irrigation in which irrigation was withheld during a certain period. In this period, the crops took up shallow groundwater to satisfy their water requirements. This strategy seemed to offer considerable scope in water shortage areas. Additional reported advantages are: it saves on engineering and energy costs for pumping; it avoids farmers having to come into contact with contaminated water; it prevents the application of saline water to the upper rootzone layers; and it reduces nitrate pollution of drainage effluent. Leaching should be applied periodically to guarantee long-term sustainable salinity levels. The alternative drainage reuse strategies tested yielded reasonable results in terms of soil salinity and crop yields.

Drainage water reuse and disposal in northwest India

By N.K. Tyagi


Northwest India encompasses two major river basins (the Indus and the Ganges) and lies in the states of Punjab (south), Haryana and Rajasthan (northeast and northwest). Although it is a water deficient region, the introduction of canal irrigation has reduced the gap between supply and potential demand to a certain extent. Irrigation is the mainstay of agriculture in this area. As irrigation development took place without the parallel development of drainage, water and salt accumulation has occurred in most canal command areas. Salinity has already affected an area of 1 million ha. This area might expand to more than 3 million ha in the next 20 to 30 years unless remedial measures are taken.

In Punjab and Haryana, surface drains were constructed and groundwater development and flood control were initiated in order to overcome waterlogging and salinity problems. In areas where surface drains do not have a natural drainage outlet, low-head high-discharge pumps dispose the drainage effluent into major canal systems. Horizontal subsurface drainage has been developed on a small scale in the region. Vertical drainage in the form of shallow tubewells is widespread throughout the region. The density of the tubewells varies with the groundwater quality and recharge. In areas located in the saline groundwater zones, the annual groundwater recharge from the extensive canal network continues to exceed groundwater abstraction. As a result, the rise in the water table and subsequent salinization has continued in these areas. If national food security is to be ensured, this problem needs to be addressed. Efforts to date have consisted of lining irrigation channels up to watercourse level and sinking public tubewells for irrigation. Water testing facilitates have been improved and the technology for the use of tubewell water has been disseminated to farmers.

The reuse of saline effluents is an important option for Northwest India as it could supplement scarce irrigation water supplies and also help to alleviate disposal problems. Reuse can take place by applying the drainage water directly to the crop, blending it with canal water and using it intermittently with canal water. The last form of reuse is most common for private tubewell water use as farmers receive canal water for only a few hours per week. The scope for reuse is highest during the winter season when evaporative demands are low and the initial soil salinity is low due to the leaching which occurs during the monsoon rains between June and September. During the winter season, the soil salinity will increase slowly. When summer starts, the crops are at maturity stage and are able to tolerate higher levels of salinity. The subsequent monsoon rains will leach the salts that have accumulated during the winter and early summer. If the monsoon rains are not sufficient, a heavy pre-irrigation might be given to ensure that the salinity is reduced to acceptable levels for a good germination of the subsequent winter crop.

In addition to drainage water reuse, shallow water table management is an important mechanism for the use of soil water in lands provided with drainage. Experiments showed that on a sandy loam soil with a water table at a depth of 1.7 m and with a salinity of 8.7 dS/m, the water table contributed up to 50 percent of the water requirement when irrigation was withheld. Similarly, at another site, a shallow water table at a depth of about 1.0 m and with a salinity of 3.0-5.5 dS/m facilitated the achievement of potential yields even when the surface water application was reduced to 50 percent. The salinity buildup was negligible and the small amount of accumulated salts was leached in the subsequent monsoon season.

For the maintenance of a favourable salt balance in soil and groundwater, the salt outflow from the system should at least equal the salt inflow plus any salt generation in the system itself. For Northwest India, the possible methods of disposing of the drainage effluents include: (i) disposal into the regional surface drainage system that links the major rivers flowing through the region; (ii) pumping into the main and branch canals that carry high flow discharges for most of the year; and (iii) disposal into evaporation ponds.

During the monsoon period, the Yamuna River carries a very high flow discharge. The salinity of the river water during the monsoon is less than 0.2 dS/m. The high flow and low salinity of the water during the monsoon period indicate the potential for the disposal of saline effluents into this river. In Haryana, an area of 1 633 000 ha drains into the Yamuna River. An extensive surface drainage system to evacuate floodwaters has been constructed. Projections regarding the amount of subsurface drainage water that could be disposed through the surface drains into the Yamuna River were made on the basis of a study covering a period of five years. In the basin, waterlogging and salinity affect 183 000 ha. The study shows that the entire amount of subsurface drainage water could be disposed into the Yamuna River during the monsoon period, whereby the river water salinity would remain below 0.75 dS/m. In the winter months, low river flows reduce the disposal capacity considerably. However, in this period, the disposal requirements can be reduced through the implementation of shallow water table management and the reuse of generated drainage water.

As the need for saline water disposal is increasing, evaporation ponds might need to be constructed. The performance of an evaporation pond constructed in a sandy area at Hisar was not encouraging, probably the result of locating the pond in a slightly higher area. It may be necessary to construct a series of ponds in the lowest-lying areas.

It will be necessary to maintain a fine balance between reuse and disposal in order to establish a favourable salt regime in the region. The existing experience from small pilot projects is only indicative of the feasibility of reuse, shallow water table management and disposal requirements. The large-scale drainage disposal and reuse programmes planned for Northwest India will need to give due weight to maintaining a favourable salt regime at basin level.

Drainage water reuse and disposal: a case study on Pakistan

By M. Badruddin


The Indus River and its tributaries are the main sources of water in Pakistan. Under the Indus Water Treaty of 1960 between India and Pakistan, Pakistan is entitled to all the waters of the Indus and to that of two out of the five eastern tributary rivers, the Jehlum and Chenab. Since then the annual inflow has averaged 171 460 million m3. The quality of the water in the Indus River and its tributaries at their entry points into Pakistan is characterized by a low salt content ranging from 0.16 to 0.47 dS/m. Apart from surface water, groundwater is an important source of supplemental irrigation supplies in the irrigation system of Pakistan. Estimates of the early 1990s indicate that 44 520 million m3 is pumped annually within the canal commands both from private and public tubewells. The salinity content of groundwater varies considerably. About one-third of the irrigated area has groundwater with a high salt content.

Irrigation in Pakistan is based on the water supplies of the Indus River and its tributaries and is essentially confined to the Indus Plain. The surface irrigation system consists of the command areas of 43 main canals and covers the largest contiguous irrigated area in the world extending over a gross command area of 15.8 million ha. Due to the absence of any entrenched waterways in the flat plains (which could provide natural drainage), the introduction of irrigation caused a gradual rise in the water table. This has resulted in widespread waterlogging and salinity problems with serious adverse impacts on agricultural production. Under the Salinity Control and Reclamation Programme (SCARP), initiated in the early 1960s, vertical subsurface drains, i.e. deep tubewells, were installed in large tracts of affected lands, while horizontal subsurface drainage has been used for smaller areas.

As a result of the low water allowances and the corresponding low design cropping intensities, there has been constant demand for more irrigation water in order to cultivate the available farmland more intensively. This demand has continued to grow with the increasing population and land pressure. Alongside the need to implement water conservation measures to increase farmgate water availability, drainage water represents a source of additional irrigation water.

Government policies encourage the maximum use of groundwater pumped for drainage for irrigation in conjunction with the canal supplies. Where groundwater is saline, drainage effluent is allowed to be disposed into the canals for reuse after dilution or it can be conveyed to the rivers through drains at times of high river flows. Alternative disposal measures have been provided only where the groundwater effluent is too saline.

Groundwater reuse in SCARP areas has had a significant impact on agricultural production. With the increased irrigation supplies, the cropping intensities in these areas rose from an average of 80 percent in the 1960s and early 1970s to an average of 116 percent in the mid-1980s. The drainage relief provided in conjunction with increased irrigation supplies through groundwater reuse has had a positive impact in terms of reducing salt-affected soils. However, the irrigation technology chosen may not have been the most suitable as the high O&M costs of the deep tubewells placed a heavy burden on the limited budget of the Irrigation Department. To ensure sustained drainage, tubewells in the fresh groundwater zones have been transferred to private sector undertakings, which use the effluent for irrigation purposes.

In zones where groundwater salinity exceeds 4.5 dS/m at a depth of 38 m, the effluent cannot be used for irrigation and needs to be safely disposed of. This might cause problems in certain areas. However, in large areas within the saline groundwater zones, shallow layers of usable groundwater lies on top of the saline groundwater. In these areas, skimming wells or horizontal subsurface drains could be used to provide the required drainage relief without disturbing the deeper saline groundwater. Research has also shown that the effluent of horizontal subsurface drains improves with time. Thus, the drainage effluent from skimming wells and horizontal subsurface drains could subsequently be used for irrigation, so also alleviating disposal problems.

The case study also focuses on the reuse of water whose quality would be regarded as poor or marginal. A number of local research institutes have investigated the effect of marginal and poor-quality tubewell waters on crop production and soils. Based on their findings and experiences elsewhere, a case is made for saline agriculture. It shows that a number of salt tolerant crops and grasses can be commercially grown using water with a salinity of up to 27 dS/m with only a moderate reduction in yield. Similarly, salt tolerant trees for fuel and forage production have been identified which can be irrigated with waters with a salinity of 19 dS/m. Salt bushes, which can tolerate high levels of salinity, have also been identified as a supplementary source of animal feed.

Evaporation ponds have been provided for the disposal of highly saline drainage effluent from irrigated areas bordering the desert towards the southeast of the country. These areas are located 500-800 km from the sea and they are characterized by interdunal depressions with highly sodic soils lying between longitudinal sand dunes 4-9 m high. In order to develop the evaporation ponds, dykes were provided across the saddles and channels cut across the dunes to form a series of connected ponds. Soon after the ponds became operational, some irrigated areas close to the ponds were severely affected by waterlogging. This could be due to significant seepage losses from the ponds generating a zone of high groundwater that obstructs or retards the natural subsurface drainage from the irrigated lands. In the space of four years, the affected area had grown to 4 200 ha.

A spinal drain has been constructed for areas located close to the sea. The outfall drain is 250 km long and has a capacity at the outfall of 113 m3/s. It has been constructed to convey highly saline subsurface drainage effluent from 577 000 ha and the rainfall excess from in and around the area to the sea. As the vertical method of subsurface drainage predominates, the operational plans provide for the tubewell pumping to be stopped at times of heavy rain storms in order to make room in the tributary surface drains for the evacuation of the excess rainfall. Experience to date suggests that the lower fringes of the irrigated area are not at risk although the gradients of the drains at the outfall are as low as 1:14 000.

Drainage water reuse and disposal: a case study on the western side of the San Joaquin Valley, California, the United States of America

By K.K. Tanji


This case study focuses on the western side of the San Joaquin Valley, California, the United States of America. This area comprises the subareas of Northern, Grasslands, Westlands, Tulare and Kern. In the western side of the valley there is about 938 000 ha of irrigated land which receives imported canal water from the Sacramento Valley. Water delivery to irrigated agriculture is based on water rights and water availability. The principal crops are cotton, almonds, grapes, tomatoes, feed grains, alfalfa hay, sugar beets, oilseeds, onions, garlic, lettuce, melons and broccoli.

The western side of the San Joaquin Valley is affected by worsening waterlogging and salinity problems. In 1990, water tables less than 1.5 m from the land surface were found on about 20 650 ha in Grasslands, 2 020 ha in Westlands, 17 000 ha in Tulare, and 4 450 ha in Kern. The estimated volume of collected subsurface drainage waters in 1990 was 46.854 million m3 in Grasslands, 4.932 million m3 in Westlands, 39.456 million m3 in Tulare, and 9.864 million m3 in Kern. The extent of waterlogging and volume of subsurface drainage waters that need to be managed under a no-action scenario up to 2040 is expected to result in an increase of 138 percent in waterlogging and an increase of 143 percent in drainage water volume.

The soils on the western side of the valley are derived from marine sedimentary rocks of the mountains of the Coast Range and are thus naturally saline. The rise in the water table does not only cause waterlogging, it also brings salts into the rootzone. Shallow groundwater and rootzone drainage intercepted by tile drains is of poor quality. At the valley level, the salinity levels in these waters are elevated with a geometric mean of 13 073 ppm. The geometric means for boron and selenium concentrations are 14.9 ppm and 12.3 ppb, respectively. Currently, there is a salt imbalance in the western side of the valley based on the salt content of the water inflow and outflow. More salts need to be discharged out of the basin to achieve a salt balance to sustain irrigated agriculture.

The Sate of California promotes efficient water use through policies and legislation. Government policies exist for the reuse of reclaimed wastewater but not for the reuse of irrigation subsurface drainage water. However, there are constraints on the discharge of irrigation return flows to public water bodies. These constraints on drainage water discharges serve as an incentive for improved water management practices.

For the western side of the San Joaquin Valley, eight drainage water management practices were identified. As the principal constraint is subsurface drainage water disposal, the management options are broader than merely reuse and disposal. Drainage water management options include: source reduction, drainage water reuse, drainage water treatment, disposal in evaporation ponds, land retirement, groundwater management, river discharge, and salt utilization.

A study from the Grasslands subarea shows that source reduction is considered to be the preferred drainage water management option. This is because it is comparatively easy for many growers to implement, contributes to managing water more efficiently and reduces the volume of drainage water that needs to be disposed. A combination of source reduction and drainage water reuse is a natural follow-up to reduce irrigation return flows and to meet water disposal requirements for river discharge. Moreover, source reduction and drainage water reuse will reduce the volume of drainage water and thus help reduce the need for evaporation ponds, drainage water treatment, groundwater management and land retirement. However, drainage water reuse could degrade the soil physically and chemically if the loading rate is too large. Moreover, deep percolation may eventually degrade groundwater if the concentrated drainage water is not intercepted and removed. Implementing a real-time drainage water disposal programme could expand the possibilities for river disposal.

For drainage water treatment, the flow-through wetland system appears to be the most promising option. It is relatively inexpensive yet fairly effective at reducing aqueous selenium concentrations. However, this form of drainage water treatment has been implemented mainly on a pilot scale to date. Other technologies, such as reverse osmosis, do not at present appear to be more viable economically. Land retirement will set aside land for wildlife habitat and as resting areas for migratory birds. However, alternatives to land retirement (including active land management) may yield the same results and thus should be considered. When retiring land, if water formerly used for the irrigation of those lands is merely conveyed to nearby lands for irrigation, then little improvement will be achieved in terms of reducing drainage water quantity. Evaporation ponds would decrease the volume of drainage water which would otherwise be disposed into rivers. However, the mitigation measures and other measures necessary to meet the water disposal requirements might be expensive, especially where selenium concentrations are high. Although groundwater management can play a major role in addressing drainage problems, the management options available for groundwater are all of a long-term nature and may be expensive. Salt utilization offers good long-term potential for helping to meet the salt balance in the valley. However, the conditions of a profitable market and economic harvesting and transport arrangements are not in place.

The current drainage water management options being practised, such as offsite drainage water disposal, source reduction and drainage water reuse, are perceived to be inadequate to sustain irrigated agriculture in the western side of the valley. For example, less than 50 percent of the salts imported with irrigation water is discharged from the western side. Additional out-of-valley disposal of salts through ocean disposal or inland salt sinks is constrained by environmental concerns and costs. However, a concerted effort is underway to sustain agriculture with other drainage water management options. If waste discharge requirements for the disposal of drainage waters cannot be met after implementing many of the drainage water management options, it may be necessary to modify the waste discharge requirements, export evapoconcentrated drainage waters (brines) to the ocean or a designated salt sink, or limit the importation of water for irrigation. The sustainability of irrigated agriculture in the western side of the San Joaquin Valley is a public policy question.

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