| The mainstream of national nature reserve of rare and endemic fish in the upper Yangtze River is located in the downstream of the Xiangjiaba Hydropower Station. There are more than 190 species of fish distribution within the reserve, which is of great academic and economic value. But with the development and operation of Xiangjiaba Hydropower Station and other cascade hydropower stations in the upper reaches, the natural flow of mainstream of the reserve has an impact. However, certain flow conditions are necessary for fish to complete the spawning process during laying period. At this stage the survival rate is directly related to the annual recruitment, which is the main reason of changes of population and age structure. In recent years both fish species and fish stocks are declining in the reserve, meanwhile, exotic fish added up by 6. In this context, this article selects Coreius heterodon which has the rich monitoring data and maximum CPUE as the typical fish. Comprehensive analyses of the ecological flow during the laying period of Coreius heterodon have important practical significance as proteceting a kind of important commercial fish. At the same time, it has some scientific significance for scientifically understanding fish with pelagic eggs represented by Coreius heterodon the needs to ecological flow during the laying period and the effect of reservoir impoundment to spawn in the downstream channel.Based on the spawning data of Coreius heterodon in Jiangjin section from 2009 to 2015 and flow data in Zhutuo station from 1954 to 2015, this thesis statistics the breeding characteristics, compare the flow component and spawning population changes before and after impoundment, and analysis the correlation between flow component and spawning population by IHA software after the calibration. For the high flow pulses(including floods) process in the laying period of Coreius heterodon, this thesis comes up with appearing time, initial rising flow, initial climbing, average climbing, peak flow, duration, annual rate of occurrence in total 7 instrumental factors. This thesis analysis the characteristics of high flow pulses(including floods) form before impounding, different inflow conditions and ecologically significance in all three ways. The design approach of the ecological flow during the laying period of Coreius heterodon are made up with base flow and high flow pulses(including floods). Essential, suitable and optimized in all three different levels ecological flow plan are submitted by the annual rate of occurrence.The research findings show as follows: The ratio of spawning amounts of Coreius heterodon in the mainly rising discharge process to in the mainly drawdown is 11:17. Annually egg-laying days are form twenty to twenty-six. In the average daily spawning amounts aspect, high flow pulses and floods are greater than low flow component. The average annual spawning amounts has significantly reduced after impounding in 2012, form 16.395×107ind to 4.19×107ind. The average annual duration of high flow pulses(including floods) also has significantly reduced after impounding, form 17-day to 8-day. For different inflow conditions, the instrumental factor of appearing time through the significance test in the significance level of 0.01, and the instrumental factor of initial rising flow through the significance test in the significance level of 0.02. The variation range of main instrumental factors of high flow pulses(including floods) when have ever spawned as follows: appearing time, from early May to early July, initial rising flow, from 4010 m3/s to 10600 m3/s, initial climbing, from 300 m3/s to 6840 m3/s, average climbing, from 187 m3/s to 3940 m3/s, peak flow, from 4890 m3/s to 25900 m3/s, duration, from 3 days to 42 days. The spawning amounts of Coreius heterodon peaks when average climbing is 850 m3/s. The annual rate of occurrence is respectively once, no more than 3 times, no more than 5 times in three different ecological flow of essential, suitable and best. |
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