| Huaihe River Basin is located in the climate transitional zone which is between the north subtropical zone and the south extra tropical zone of China. Under the influence of the global climate change, human activities and social development, Huaihe River Basin has been facing with more and more serious problems such as lacking of water resources and water pollution, which threaten the ecosystem and water resource security of the basin. Hence, it is pretty essential to carry out the research about the eco-hydrology mechanism and to calculate the ecological water requirement of Huaihe River Basin.The condition of eco-hydrology is typically different between the midstream wetland and downstream plain in Huaihe River Basin. On the basic of analyzing the current status of hydrology, water environment and the water ecosystem, this paper discusses the eco-hydrology mechanism of the middle reaches and lower reaches. With the goal of preserving the stability of water ecosystem, the improved method of calculating ecological water requirement adapted to different districts has been brought up in this paper. The main research conclusions are as follows:(1) The water ecology problem of Huaihe River Basin is analyzed in this research. The precipitation in the midstream has been increasing at the rate of1.85mm/a, the evaporation has been decreasing at the rate of2.23mm/a. The average measured annual runoff was reduced by hydraulic engineering regulation, but there is a rising trend in dry seasons. The water environment has been turning better in this century, but the water pollution is still serious. The species and biomass of phytoplankton, zooplankton and benthonic animal have been cutting down in the midstream. In the period from1982to2006, the area of wetland in the middle reach has reduced by20%. The lakes on the lower reach have been seriously shrivelled. For instance, the area of lakes in Lixiahe was only0.38%of that in the1950s.In conclusion, Huaihe River Basin has the following two ecological problems:(a) The water recycle period has lengthened as a result of dams, which weaken the self-cleaning capacity,(b) The ecological integrity has been destroyed owing to the condition of hydrologic condition, damage of spawning site and degradation of water environment.(2) On the basic of the assessment theory and model of hydrologic process, the research has not only built the classification assessment model of the river hydrologic process, but also brought up the method of caculating ecological water requirement based on the flow regime of river ecosystem. Hydrologic process is a tipycal element of river ecology system, because it controls the whole vital process. Take Runheji gate as example, the model shows that the flow under the nature condition could guarantee the water ecology requirement during the dry and flood season. And in the spawning period, the natural flow could control the high pulse discharge to satisfy both fish spawnind channel ecology system stability. Therefore, the calculating result of hydrologic process method has following advantages:(a) It satisfies the biological growth and bankfull discharge,(b) It conforms to the growth machanism of aquatic orgainisms.(c) It satifies the requirement of flood control and drought relief, so that it is better to apply to ecological vegulation.(3) With the goal of keeping aquatic ecosystem stability, the method of calculating ecological water requirement of plain river network is established in this research. In plain river network, the ecological process is complex. After analyzing the structure of food chain and influencing factors in biochemical reaction process, the research ascertains that velocity is the major control element of aquatic ecosystem stability in plain river network and the value ranges from0.09m/s to0.3m/s. Take Jianhu county in the lower reach as an instance, its ecological flow of main stream is60.87m3/s. |
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