Study On Determination Of Ecological Discharge And Eco-scheduling

The Fengshan Reservoir Project in Qiannan Prefecture of Guizhou Province is located in the upper reaches of the Chong’an River in Fuquan City,Qiannan Buyi and Miao Autonomous Prefecture,Guizhou Province.Through the development and utilization of water resources,comprehensive utilization of urban and rural life and industrial water supply will be realized,and power generation will be taken into consideration.After the operation of the reservoir power station,a reduced-water reach will be formed from the dam site to the downstream tail water.Besides,the water supply will have certain adverse effects on the original “three farms” of fish.In order to coordinate the project benefits of flood control,water supply,ecology,irrigation,shipping,and power generation,and to maximize the ecological benefits of the project,we carried out the study on determination of ecological discharge and Eco-scheduling plan.This paper uses numerical simulation methods to study the ecological flow and eco-scheduling plan of Fengshan Reservoir.Based on the river hydrodynamic model HECRAS,a model of the lower reaches of Fengshan Reservoir was established.Parameter calibration and model verification combined with the water level and discharge curve of the dam site section.Then combined with the natural hydrological process,a preliminary eco-scheduling plan was proposed.After the comparison of habitat indicators and the optimal design of the plan,the recommended eco-scheduling plan was finally given.The conclusions are as follows.(1)Investigation and research on the aquatic ecosystem of the reduced water reach under the dam shows that there are 106 species of phytoplankton in 7 phyla,78 species of zooplankton in 4 phyla,33 species of benthic animal in 3 phyla,and 27 genera of fish in 4 orders,8 families in the studied river section.Besieds,the spawning season of fish in the study river is mostly spring and summer,and most of them lay eggs in the bottom material such as pebble,gravel,sandy or rock cracks,such as yellow catfish,etc.A certain amount of water pulse stimulation is necessary in the spawning period(April to May each year);(2)Research on typical ecological habits of representative fish shows that the velocity index of fish spawning ground in Chong’an River Basin is not less than0.2m/s,the water depth index of fish spawning ground is not less than 0.5m,and the water temperature index of spawning ground is not less than 18℃ ～20 °C.This paper only considers the improvement of fish habitat hydraulic indicators through the release of ecological water.The temperature of the effluent under the reservoir is mainly affected by air temperature,radiation and water intake measures,so it does not focus on the analysis;(3)The one-dimensional unsteady model of the river channel,HEC-RAS,is constructed based on the conditions of the reduced water reach and cross section,and the river channel roughness is calibrated according to the water level and flow relationship of the dam site section,and compared with the simulated the water level and flow relationship curve Validation value,the fitting effect is relatively good,indicating that the model parameters and boundary conditions are basically reasonable;(4)Analyzing the socio-economic and ecological environmental requirements of the reduced water reach shows that the water demand of the reduced water reach of the Chong’an River is mainly the amount of water needed to maintain the stability of the aquatic ecosystem and the dilution of pollutants downstream.For this reason,using hydrology and hydraulic methods to calculate the ecological flow that needs to be supplemented by the reservoir,it is recommended that the minimum discharge flow at the Fengshan Reservoir dam site during the dry season(October to March)is1.82m3/s,which accounts for 27% of the multi-year average flow.During the wet season(April to September),the lowest discharge flow rate is 30% of the dam site’s multi-year average flow rate,which is 2.04m3/s;(5)The hydrological frequency drainage method is used to calculate the peak flow of ecological regulation,and the calculation is as follows: Select the maximum daily discharge frequency of the Fengshan Reservoir dam site section from 1958 to2014 from April to May year by year.According to the frequency of P=20%,that is,once every five years,the maximum daily discharge is determined to be 14.45m3/s(P= 20%)as the peak value of the artificial pulse process.(6)Eco-scheduling plan is carried out based on the maximum daily flow of14.45m3/s(P=20%)from April to May.Firstly,the hydrological processes of small floods with peak discharge greater than 14.45m3/s in April and May between 1958 and2014 were screened.It is suggested that the flow process on May 1974,May 1960,and April 3,1982 should be taken as the preliminary eco-scheduling plan.After comparing the habitat indicators and optimizing the plan,a recommended eco-scheduling plan is finally given.1)Recommended process 1: The ecological dispatch lasts for 3 days,the peak flow is 15.48 m3/s,and the corresponding water volume is 3,274,700 m3,which is mainly suitable for low water inflows such as dry years;2)Recommended process 2: The ecological dispatch lasts for 5 days,the peak flow rate is 16.72 m3/s,and the corresponding water volume is 5,432,800 m3,which is mainly suitable for normal water supply conditions such as normal years;3)Recommended process 3: The ecological scheduling lasts for 7 days,the peak flow rate is 17.63 m3/s,and the corresponding water volume is 7.911 million m3,which is mainly suitable for the abundant water conditions such as wet years.(7)Analyze the coordination relationship between eco-scheduling and other schedules and storage capacity water level,and clarify the priority of each water use object as: domestic water,water for ecological environment in rivers(ecological base flow)>> Industrial water > Ecological dispatch(flow pulse)> Water for power generation.When the amount of water is insufficient,clarify the priority of each water use object as: domestic water,water for ecological environment in river(ecological base flow)>> industrial water > ecological dispatch(3-day flow pulse)> power generation water > ecological dispatch(5-day or 7-day flow pulse).