Ecological Flow Calculation And Value Assessment Of Dawen River

River is an important natural resource,with the functions of social services such as flood control,water supply,power generation,shipping,landscape,etc.,and is also an important channel for material circulation and energy flow,and is the basic guarantee for maintaining regional ecological balance.Affected by the rapid economic and social development,the contradiction between the supply and demand of river water resources has intensified,resulting in a serious shortage of water to maintain the ecological health of the river,ecosystem degradation and other problems in the river basin,and the ecological security of the river basin is threatened.Taking the Dawen River Basin as the research area,this paper analyzes the hydroecological status of the river basin from the hydrological changes and biological perspectives,calculates the ecological flow in the study area from the perspectives of ecological security and economic optimality,and finally analyzes the degree of guarantee of ecological flow at different levels,and puts forward the management opinions of ecological flow.The main conclusions of the paper are as follows:(1)According to the hydrological data of Beiwang,Dawenkou,Daicunba and Lude hydrological stations in the study area from 1956～2021,and using trend analysis,cycle analysis and hydrological change indicators,the overall annual runoff in the study area showed a decreasing trend;The degree of hydrological change of Daicunba station was higher than that of Dawenkou station,among which the indicators with greater hydrological index change of Dawenkou station were the average flow in March,the average flow in May,the annual minimum 30-day flow and the number of fluctuations,and the average flow in April,May and June,the annual minimum flow of 1,3,7 and 30 days.According to survey data,fish in the Dawen River Basin belong to 25 species in 4 orders,16 families,of which cyprin is the largest,accounting for 68%of the total number of fish species.From different time periods,the number of fish species,biomass and individual number in October were higher than in April,and based on the analysis of the relative importance index,it was found that the dominant species in the study area were crucian carp,black snakehead and dong.(2)Taking the river section from the north to Daicunba as the research river section,a hydrodynamic model was established based on the daily water level and flow data of Beiwang Station,Daicunba Station and Loude Station,and the daily water level data of Dawenkou Station was selected for model rate verification,and the spatial distribution of water level and flow velocity in the river section under different discharge flows such as 1～20 m~3/s at Beiwang Station was simulated.When the discharge flow of Beiwang Station is 1-14 m~3/s,the water level and flow velocity of the river channel do not change significantly,and when the flow rate is greater than 18 m~3/s,the water depth flow rate changes significantly,and the maximum water level of the river channel rises from 100m to 105m,and the maximum flow rate increases from 0.4m/s to 0.78m/s.(3)Taking crucian carp as the indicator species,the ecological flow required for different growth periods of crucian carp was calculated by habitat simulation method and ecological hydraulics method from the perspective of ecological protection,and the rationality analysis of the results was carried out in combination with Tennant and other hydrological methods,and the ecological flow of Beiwang Station in the study area was 2m~3/s in April～June,6m~3/s in July～September,and 2.43m~3/s,0.79m~3/s,0.70 m~3/s,0.61m~3/s,0.52m~3/s and 0.41m~3/s.(4)Based on the principle of maximizing the value of the river ecosystem,the ecological flow in the study area was determined to be 13%of the multi-year flow.By comparing the perspectives of ecological protection and economic maximization,the ecological flow in January～December was determined to be 0.79 m~3/s,0.68 m~3/s,0.53 m~3/s,2.00 m~3/s,2.00 m~3/s,6.00 m~3/s,6.00 m~3/s,3.15 m~3/s,1.02 m~3/s,and0.91m~3/s.Further analysis of the degree of guarantee of ecological flow at different levels of years,it is found that the degree of protection in dry years and extreme dry years is low,about 50%～60%,in order to ensure the satisfaction of ecological flow,agricultural economy must have losses,the analysis found that the value of ensuring ecological flow is always greater than the resulting agricultural loss value,so the government needs to make corresponding ecological compensation for agriculture when ensuring ecological flow.