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........ published in NEWSLETTER # 61

by Dr. M.G. Bos, DHV Consultants, Amersfoort (The Netherlands)

These proceedings of a NATO Advanced Research Workshop (NATO ASI SERIES 2-22) document the effects of drainage from irrigation of 7.5 million hectares of agricultural land on the environment in the Aral Sea Basin. Part of the water supplied to this irrigated area is consumed by the 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 which may cause a variety of (environmental) problems. If the percentage of consumed water of the total water supply (the so-called overall irrigation efficiency) can be increased, less (relatively saline) water needs to be drained. This alleviates part of the related (environmental) problems. Further, if the overall irrigation efficiency for the above 7.5 million hectares 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. Frequently, 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 water-logging. In (semi-)arid zones this water- logging triggers a soil salinity problem resulting in a significant reduction in crop yields. The artificial increase of the discharge capacity, and lowering of the groundwater table, solves the soil salinity problem within the irrigated area. Because of the capital cost of the needed artificial drainage system (up to US-Dollars 3.500 per ha), the exchange of know-how on the alternative methods of artificial drainage that can be used in the Aral Sea Basin may have a major impact on the total cost of drainage.

Since independence of the five Aral Sea republics a wide variety of missions have reported on the water-related environmental problems in the Basin. Several of these reports have contributed to a plan of action to solve or alleviate some of the identified problems. Within these plans, improving the irrigation efficiency, artificial drainage, and the related environmental effects receive high priority. The Workshop helped to plan the next step.

The environmental problems within the Aral Sea Basin have been well documented. All these problems are related to the shortage of irrigation water and to the quality (mostly salinity) of the drainage water. Because of the structural shortage of water, the problems cannot be solved completely. Their magnitude, however, can be reduced significantly by using up-to-date know-how on irrigation and drainage. Most of this know-how can be made available through NATO member states.

The proceedings contain 18 papers. About half are on the site- specific boundary conditions of the Aral Sea Basin, the remainder present up-to-date know-how that could be used to solve part of the drainage problems within the irrigated area. Ample time was available during the Workshop to discuss the (dis)advantages of various solutions. A list of conclusions and recommendations is included. The book also contains an annotated bibliography on irrigation and the environment in the Aral Sea Basin.
Reference books: 2-9, 2-17, C222, C224, 2-22

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