The irrigated area in the Aral Sea basin totals about 7. 5 million hectare. Part of the water supplied to this area is consumed by the irrigated crop; the remainder of the supplied water drains to the groundwater basin, to downstream depressions, or back to the rivers. During its use, however, this drained part of the water accumulates salts and chemicals. The disposal of this polluted water causes a variety of (environmental) problems. If the percentage consumed water of the total water supply to an irrigated area (the so-called overall consumed ratio) can be increased, less water needs to be drained. This alleviates part of the related (environmental) problems. Further, if the overall consumed ratio for the above 7. 5 million hectare is improved, less water needs to be diverted from the rivers. Hence, more water can flow towards the Aral Sea. As mentioned above, part of the non-consumed irrigation water drains to the groundwater basin. Commonly, the natural discharge capacity of this basin is insufficient to handle this imported water. As a result, the groundwater table rises towards the land surface causing waterlogging. In (semi-)arid zones this waterlogging triggers a soil salinity problem resulting to a significant reduction in crop yields. The artificial increase of the discharge capacity, and lowering of the groundwater table, solves the soil salinity problem.

Klappentext

The irrigated area in the Aral Sea basin totals about 7.5 million ha. Part of the water supplied to this area is consumed by the irrigated crops; the remainder drains into the groundwater basin, downstream depressions, or back into the rivers. But the water accumulates salts and chemicals during its period of use, causing environmental problems which this book discusses. The natural discharge capacity of the groundwater basin is inadequate to handle the unconsumed irrigation water, leading to a rise in the groundwater table and to waterlogging. In (semi-) arid zones, this waterlogging triggers a soil salinity problem, resulting in poorer crop yields. The problem is solved by artificially increasing the discharge capacity and lowering the groundwater table. Since the lands surrounding the Aral Sea have become independent republics, a number of missions have reported on the water-related environmental problems in the basin. Such reports have contributed to a plan of action for solving or alleviating some of the problems identified, high priority being accorded to improving the irrigation efficiency, artificial drainage, and the related environmental effects.

Inhalt
Conclusions and Recommendations.- The Interrelationship between Irrigation, Drainage and the Environment.- Environmental Benefits of Reducing Collector-Drain Runoff and Ways to Improve Irrigation Water Quality in the Rivers of the Aral Sea Basin.- Planning for Drainage Development in the Aral Sea Basin.- Impressions and Findings of a Study Tour to Karakalpakia in Central Asia.- Drainage Development in the Arid Zones of Central Asia.- Choice of Envelope Materials for the Rehabilitation of the Drainage Network in Uzbekistan.- The Construction and Effectiveness of Combined Drainage Systems.- The Contribution of Horizontal Subsurface Drainage to Solving the Aral Sea Economic and Environmental Problem.- Flow through Wetlands for Controlling Water Quality in Discharges from Irrigated Areas.- Comparing Surface and Subsurface Drainage in Rice Irrigation Systems of Kazakhstan.- Environmental and Economic Benefit of Subsurface Horizontal Drainage Construction.- Improving Drainage Water Quality by Constructing Wetland Ecosystems in the Catchment Area of the Amu Darya, Aral Sea Region.- Irrigation Systems, Water Use Efficiency and Environmental Impacts.- Measures to Increase the Efficiency of Irrigated Lands in Kyrghyzstan.- The Use of Decision Support Systems in Water Management.- Conjunctive Water Management for the Aral Sea Basin.- Drainage Problems and Solutions in the San Joaquin Valley of California, U.S.A..- The Use of Specific Environmental Publications for Local Capacity Building for Irrigation and Drainage Projects within the Aral Sea Basin.- Irrigation and the Environment of the Aral Sea Basin; an Annotated Bibliography.