| The ecological water requirement of river is the minimum flow to maintain the basic ecological function of the river,and its main function is to prevent the destruction of aquatic communities in the river channel due to the degradation of river habitat.With the development of society of water resources has been continuously strengthened,the degree of water resources development has been strengthened,and the construction of water conservancy projects on river is more and more,and the hydrological situation of rivers has changed.In the process of water resources development,if the lack of proper ecological values guidance,river aquatic habitat will be destroyed.While improving the utilization of water resources,how to protect the river ecological environment has become an urgent need to study the subject.At this stage,it is believed that it is necessary to reserve enough water for the river to meet the water demand of the ecological environment,which is an effective way to protect the ecological stability of the river and to estimate the ecological water demand of the river.However,there are few studies on the ecological water demand estimation of small rivers in Guangdong Province.By measuring the river cross section,the investigation of large benthic invertebrates and fish,etc.,to improve the calculation method to estimate the hilly areas of Guangdong Province and small hydropower stations in the mountains of the ecological flow.The main conclusions are as follows:(1)According to Shuangqiao hydrological station 1980-2010 years of runoff and cross section data,the minimum monthly average discharge method,7Q10 method,NGPRP method,month-bymonthminimum ecological runoff method,wetted perimeter methods and R2-Cross method were used to calculate the minimum Ecological flow,and analyze the results.Six ways to use the same annual ecological water demand standards,the calculation of the minimum ecological flow in the proportion of the average measured flow for years: 9.6%-67.1%.According to the evaluation criteria of Tennant method,the minimum monthly average discharge method,NGPRP method,month-bymonth minimum ecological runoff method are reasonable,the habitat of non-flood season can be maintained in good condition,and the minimum level can be reached in flood season.However,throughout the year using the same ecolo gical water demand does not meet the natural laws that amount of water of flood season is more than the non-flood season and biological breeding habitat requirements of the flood season is higher than non-flood season habitat.According to the water demand of different life cycle,such as aquatic breeding and wintering,the actual flow rate of flood season and non-flood season will be sorted separately,and the ecological flow in two periods will be calculated respectively.Based on the improved NGPRP method,the minimum monthly average flow method,and the monthly minimum ecological runoff calculation method,the ecological flow of the Sihe River in the non-flood season is as follows: 10.2%-26.1%,the variation range of the flood season For 38%-67.4%,the proportion of annual average flow is greater than 10%,habitat to reach the minimum level.If the ecological water demand of flood season and non-flood season are calculated separately,can meet the natural law of river runoff and biological.The research can provide ideas and methods for the estimation of ecological water demand in Guangdong hilly area.(2)The development of small hydropower plants on rivers in mountainous regions results in many dehydration reaches,and further threatens ecological syste m there.A need is urgent to discharge some ecological flow for compensation.Due to the fact that these rivers are lack of hydrological observation and investigation to their aquatic habitats,it is a challenge to apply routed methods which are common used to evaluate ecological flows for rivers.By surveying in field some typical river reaches with small hydropower plants in mountainous regions of Guangdong province,the R2-Cross method was improved that the fishes living in a cold water,as indicating species of hydraulic standards,were replaced by the fishes living in a warm water and the dominant benthic macroinvertebrates additionally.The new hydraulic standards were obtained as average water depth 0.1m,average flow rate 0.8m/s,and the percentage o f wet perimeter to that of annual average flow 75%,which reflect well the habitat requirements of aquatic life in the invested rivers and provide a basis for estimating the ecological flow of small rivers in mountainous regions of Guangdong province.By using river width model and the relationship between river shape and its forming discharge,the rough river cross section was generalized as a regular geometry.As in the wet perimeter method of ecological flow estimation,the sectional hydraulic variables of a discharge are determined in open channel flow formula.The river runoff was calculated annually and seasonally in a rainfall runoff model which parameters were optimized using observed data in a neighbor basin.With these procedures and the improved R2-Cross standards,ecological flows in rainy season and in dry season were estimated respectively for the typical sections of three rivers on which small hydropower plants were constructed.In Tennant classification,with the estimated ecological flows,the habitat of aquatic life reaches the minimum level in Xiaojinhe river,but a good level in Meizishe river,and even an excellent level in Jiulianshan river because both rivers are smaller than Xiaojinhe river but the same hydraulic standards were applied in the estimation of their ecological flows.The corresponding ecological habitat in the rain and dry season can reach the minimum and above level,the river ecosystem can be stable throughout the year without degradation.At the same time,this can better reflect the rain,dry season changes,in line with the actual situation in Guangdong.The ecological flow estimated by the R2-Cross method ensures that the habitat of the river is not degraded,but to release the ecological flow would cause a loss to the power enterprise's profit.For example,the power generation loss would be 20.4% and 18.7% in a year,or as much as 63.7% and 55.7% in the most drought month,to the fourth and fifth plants respectively on Xiaojinhe river if the estimated ecological flows were released.Guangdong mountainous small hydropower station and more by the private fund-raising construction,under the current regulatory conditions,the power generation of the power plant caused by the loss is too large,requiring the power station administrator to discharge the ecological flow there is a certain degree of difficulty.Finally,three operational strategies of ecological flow release are suggested:(1)the flow estimated in the improved R2-Cross method to provide an enough satisfied hab itat for the aquatic life,(2)the flow to meet the minimum requirements of fishes and also to take account of the enterprise's benefits,(3)the replenishment flow to static water areas in the most drought month to survive the fish and other aquatic life. |
PDF Full Text Request