中国新彊省の水源「カレーズ」

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This is a report of field research on Karezes in Turpan and Hami in 1988. Both districts are inXinjiang, China. The research was conducted by the Xingjiang Institute of Biology, Pedology and Desert Research Chinese Academy of Sciences (XIBPDR) and an exploratory party from Japan sponsoredby the Japanese Ministry of Education. Much information was obtained on Karezes. For example, how to excavate them, the equantityof ground-water, how to maintain them, how to use their water for fields and present their troubles inTurpan and Hami. This abstract shows the troubles of Karezes, their vitalization and mentions conservation of water-resources in the future. We appreciate Xinjiang Bureau of Water Conservancy (XBWC) for their important information and suggestions. But this briefing is private and the first author takes the responsibility for mistakes. 1. Lowering of the Ground-water Table The biggest problem of the Karezes in Turpan and Hami is lowering of the ground-water table.The Karezes depend on ground-water but many Karezes excavated when the ground-water table wasmoderate high. Lowering of the ground-water table can not keep this condition and serves poor waterresources. The construction of open channels in 1960-1970s to get snow-melt water from the Tien ShanMts., was possibly due to lowering the ground-water table. Snow-melt water flow in many rivers infiltrates the desert land from the river beds. This infiltration has enriched the ground-water of Turpanand Hami for a long time. But new open channels convey water to fields directly and do not give theriver-flow enough time to infiltrate the desert land. The ground-water has thus decreased considerably. Today, thousands of small pump stations pump ground-water for irrigation in Turpan and Hami butthey also lower the ground-water table. The ground-water table is thus not available for manyKarezes. The great success of agricultural and industrial development in Turpan and Hami is due to waterresources development and conservation by those pumps and open channels. But the Karezes are suffering from little water due to modern water facilities. 2. Breakdown of the inner walls of Karez Most outlets of the Karezes are near villages or vegetable fields, i.e. oasis. The soil around anoasis is silty. Silty soil is good for vegetable growth but not for the structure of Karezes. When siltysoil becomes moisture, it becomes loosely. Flow of a Karez gives moisture to the inner wall andmakes erosion continuously along the watered lower part of the wall. After a moderate time, the wallsbecome weak and falls down. This situation has continues for a long time. The diameter of a Karez becomes bigger and biggerunder a silty soil area. This is very dangerous for the people of a village, because big diameter thinstop soil of a Karez near the outlet. In fact, there are many big hole-rows in some villages caused bydropping of top soil. When soil deposits on the bed of a Karez, flow is dammed up leading to greater depth. Thiscauses water loss through infiltration by high water depth pressure.3. Possibility of Water Pollution The success of agricultural development in Turpan and Hami depends also on popularization of chemical fertilizer. But this may lead to ground-water pollution, because some Karezes get seepage water from vegetable fields. If water contains excess chemical fertilizer, pollution will eventually result.4. Vitalization To lessen the decrease in ground-water flow, the bureau and farmers try to extend a Karez toward the up-stream to obtain more water but without success in some cases. The basic problem of Karezes is the lowering of ground-water. So, the bureau has recommendedfarmers to keep their pump stations away from the under-ground way of a Karez. This is good policyto conserve the ground-water table. But to farmers who want to get much water and produce much food, the pump station is moreconvenient and reliable. Pumping ground-water will be more popular and facilities larger in next tenyears possibly. But this may lead to serious problems for Karezes. XBWC is trying to recharge the ground-water by flood flow every year. When heavy rain falls inthe Tien Shan Mts., they forecast the time that the flood water will reach the desert. This will lead togood results provided the farmers work here. Vitalization of Karezes depends on recharging the ground-water over a long period. In a shortterm, extension of their length and protect work for seepage from inner wall of Karez are good policies. In any case, the vitalization must be a part of the strategy of water resources development andconservation for the Tien Shan Mts., in the near future.5. Renovation of the Water Delivery System Farmers in the vicinity of an oasis share water from Karezes very strictly. They have a conventional water delivery system for villages and fields. The system is very good, because all farmers can obtain water easily and equally. Only the quantity of water may be inadequate. To improve the system, field research for unit water requirement of crops and vegetables isneeded. The results of this research and appropriate improvement of form and dimensions of fieldsmay save water for fallow irrigation. Most delivery channels from Karezes are made by soil. Sometimes a channel breaks and waterflows into roads and other places. To prevent spillover and seepage, seal materials for channel bedsand walls are needed. Attention should be directed to the fact that when a channel is covered by seal, flow conditionchange. If the new design discharge for sealed channel is equal to old one, flow velocity will increasecauseing water depth to be low. These improvement, research and work have already been started and strongly supported byXIBPDR and XBWC. But the difficulty is not research but money.6. Observation of Ground-water To vitalize Karezes, we need more precise data on ground-water moving in the desert. LAND-SAT clearly showed the ground-water or soil moisture everywhere on the earth. Unfortunately continuous data are not available on it. We must create an observation system for ground-water and onwhich the future supply of water for the Karezes will depend. The Tien Shan Mts., await future development of water resources and water power generation.Some Karezes will obtain water from the Tien Shan Mts., as a result. Some inner walls will be sealedto become under-ground reservoirs for excess flood water.

中国新彊省の水源「カレーズ」

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