Calculation of minimum ecological flow in dewatering section of small hydropower stations:Taking Panxi cascade hydropower stations as an example
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Abstract:
The hydropower resources of small and medium-sized rivers account for a large proportion of domestic hydropower distribution .There is a large space for development and utilization.The development and operation of hydropower inevitably bring adverse effects to the ecological environment,such as the reduction of river runoff,dewatering of local river reach,and the damage to the local ecological environment.To reduce the negative impact of the construction and development of small hydropower on the ecological environment of the downstream river,it is a key method to ensure the minimum ecological discharge of small hydropower.At present,the researches referring to the domestic and overseas ecological discharge mainly concentrate on big rivers.However,the research related to the ecological discharge of small and medium-sized rivers,especially small hydropower stations are few.The available methods for calculating the ecological discharge also lack scientific analysis.A considerable number of small hydropower stations have not yet determined the minimum ecological discharge.Based on this situation,the related research was carried out on the minimum ecological discharge of small hydropower stations. At present,domestic and overseas calculation methods of ecological flow can be roughly divided into the hydrological method,hydraulic method,habitat norm method,and integral method.The hydrological research method is the most commonly used,convenient,lowest cost of ecological flow calculation method and is one of the classic calculation method.This study uses the improved Tennant method,the annual distribution method,the Q90 method,the improved frequency method,and the NGPRP method to calculate the minimum ecological flow of the leading reservoir.Taking 95% guarantee rate of the runoff data from the recent 30 years as a protection target,this study analyzes the satisfaction degree of the five methods and evaluates the rationality of the calculation results.This shows the evaluating results of calculation in the process of natural runoff of the section with satisfying the degree of 95 percent guarantee rate.If the degree of satisfaction exceeds or is lower than the requirement of the due guarantee rate,this method is considered not suitable for Dayang reservoirs.Finally,by comparing various methods,the calculation method of the minimum ecological discharge of the Dayang reservoir is selected,and the inner envelope of the calculated minimum ecological discharge is taken as the minimum ecological discharge of the reach.Finally,the minimum ecological flow process of Panxi cascade Ⅰ~Ⅳ power stations is obtained. According to the calculation,the lower limit of the minimum ecological discharge of the Dayang reservoir is 0.152 m3/s,and the minimum ecological discharge of 0.182 m3/s guaranteed between the second and third stage hydropower stations,and 0.102 m3/s guaranteed between the third and fourth stage hydropower stations.The discharge also guaranteed in the dry months.The minimum ecological discharge of each hydropower station can be satisfied with the water inflow from each hydropower station.This results have a reference value for the study of the minimum ecological flow of small hydropower stations in China.
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