Reason of Runoff Reducing through Zhengyixia Gorge on Heihe River and Countermeasures
Heihe is located in the west of arid Gansu and Inner Mongolia, and the largest inland drainage of the area. The area of middle reaches is the middle part of Hexi corridor plain in Gansu province, which is the most developed area of industry and agriculture economy within Heihe basin and the important commodity grain base. The area of lower reaches is Ejinaqi Plain and it is also the main natural grassland of Alashan Plateau and the important ecological barrier of Hexi corridor. The boundary of middle reaches and lower reaches is Zhengyixia. In the latest half century, especially the recent ten years, the diverted river resource increases because of sustainable growth of industry and agriculture. The Heihe streamflow which consists of river(flood) from mountain and spring passing through Zhengyixia to the area of lower reaches shows a decreasing tendency. It decreased from 10.50×108～10.99×108 m3*a-1 in 1970s-1980s to 7.81×108 m3*a-1 in 1990s, which led the vulnerable ecological environment in the lower reaches of Heihe to further deterioration.In addition, it caused serious ecological environmental problems, such as oasis retreated, lakes dried up and land deserted. The reasons of the streamflow decreased through Zhengyixia are as follows: The first one is that the diverted water in the area of middle reaches is increased continually. The second one is the runoff of spring gradually decayed in the area of middle reaches. The third is that the global climate is warming and precipitation is being reduced. When river water is mainly used, the groundwater is replenished in middle reaches of Heihe, which causes groundwater rising, soil salinization and the 0.11×108 m3*a-1 spring increased. The runoff of Heihe passing through Zhengyixia is decreased by 2.12×108 m3*a-1 to 8.28×108 m3*a-1 (average for many years) and 5.69×108 m3*a-1 (75% frequency), which further aggravates the elological environment in lower reaches of Heihe and discontentes “the principle of water allocated between Gansu and Inner Mongolia” (Ministry of water conservancy, 1992), that is water discharge of Heihe through Zhengyixia must be greater than 9.7×108 m3*a-1 (average for many years) and 7.3×108m3*a-1 (75% frequency). There is much more groundwater in the area of Heihe middle reaches. The natural groundwater resources is 16.87×108 m3*a-1, the reserves 3 850×108 m3, the permissive yield 7.16×108 m3*a-1. There are 12.3×108 m3*a-1 elastic regulation resources as reserves. The exploiting resources at the present status is 2.28×108 m3*a-1, which is 31.84% of the permissive yield, so the potential capacity is huge. The thick aquifers are distributed in the vast corridor pain, which is 80～200 m and the buried depths of groundwater are 2～100 m; water richness of the aquifers is better, generally 1 000～5 000 m3*d-1, especially in the middle of pluvial fan more than 5 000 m3*d-1. The water quality is good, i.e. mineralization less than 1.0 g*L-1 normally, therefore, the exploiting condition of groundwater is quite well. When groundwater is mainly used (the permissive mining yield) about 0.91×108 m3*a-1 regional spring resources is reduced. Meanwhile, the groundwater level is drawn down. At last, the runoff of Heihe through Zhengyixia is increased by 0.51×108 m3*a-1 to 10.91×108 m3*a-1 (average for many years) and 8.32×108 m3*a-1 (75% frequency). It plays an important role in improving the ecological environment and keeping it in balance. Addition to it, it can also contente “the principle of water allocated between Gansu and Inner Mongolia”. So it is relatively the optimized plan for using water resources.
NETL
NSTL
万方数据
维普
