Study On The Yalong River Basin Ecohydrological Process Simulation And Water Transfer Impact

Hydrological model is a valuable tool in water resources management and is a hot field in hydrology and water resources research. It has experienced three different states: experience model, concept model and physical model. The distributed hydrological model stands for the new development direction in this field which contains physical process in hydrology cycle. With the improvement of awareness of ecological environment and the needs of sustainable development of human beings, it is necessary to consider the interaction between ecology and hydrology, to integrate ecological process to the hydrological processes, and establish an ecohydrological model to solve the ecological problems associated with water become more attention from the researchers. With the precondition of understanding related research status, this study tried to analyze the connotation of ecohydrological process and the driving mechanism in basin scale, and puts forward the coupled model. Considered the Yalong River water transfer project, it used the ecohydrological model to analyze the influence of the project on the eco-environment in the water transfer district. Using principal factor analysis method and fuzzy optimization method, it discussed the scheme selection of water diversion project with the model. Main results and conclusions are as follows:(1) Statistics methods were used to analyze the characters of precipitation, flow and temperature in study area. The impacts of the Yalong River water transfer project on the downstream river and the marsh wetland were made further analysis by spatial analysis technique. The annual average precipitation is stable, and the range of precipitation is500-750mm, the multi-years annual precipitation is630.8mm without specific period character. The variability of annual runoff in four hydrologic stations is not big, but the distribution within year is unequal. The flow in Daofu hydrologic station has increase tendency, not the other three. The temperature is increased based on the data observed by the five meteorological stations. The range of annual average temperature is-6.7℃-9.1℃, and the temperature rises gradually from north to south, the variation characteristics is bigger in north than in south. After water transfer, the flow in four hydrologic station sections will reduce differently in different level year. If the transfer progress is homogeneous, the river will dry up in non-flood season, and more serious in low flow year. The discharge will keep large in flood season after water transfer. Due to few hydraulic connections with the river channel, the project will influence little on wetland.(2) The connotation and mechanism of ecohydrology in basin scale were analyzed. Based on the relevant basic theory and the coupled model of ecohydrology, an ecohydrology model was built. Yalong River basin was used to test the ecohydrology model. According to the series observed data from1976-2000, the data from1976-1990was use to calibrate8 parameters of the model, including the maximum retention water, Manning roughness, hydraulic conductivity, riverbed material permeability coefficient, relative humidity, stomatal aperture. The rest data was used to verify the model. Three indexes were used to describe the effect of model capability, and they are the relative error, the correlative coefficient, and the Nash efficiency coefficient. The relative error was between1.37%-7.83%, the correlative coefficient was0.91-0.94, and the Nash efficiency coefficient was0.82-0.93. The model was qualified, and it can be used to solve the actual problem in water resources field.(3) With the ecohydrology model the impacts of the project on the eco-environment of the water transfer district area were analyzed, especially the impact on the dry valley, KaSha Lake and the typical fish in the Yalong River. According the results in the sections in Ganzi, Zhuba and Daofu, the river width, river depth, flow and velocity would be effected with different degree. The impact on flow and velocity is more than on the river width and depth in flood season than in no-flood season. The range of influence on flow and velocity is24.33%-55.6%in flood season, while15.12-34.78%in non-flood season. And the range of influence on river width and depth is3.1%-28.16%. The ecological water demand of dry valley is20.88%-52.19%of annual average flow, and the dry valley is located in a gorge which is influenced seriously by the project. The value of net water loss of KaSha Lake is positive in low flow year, and the biggest value is193.5thousand cubic meter. The ecological water demand of KaSha Lake is only3%of the sink flow to KaSha Lake, which causes the impact on KaSha Lake is little. Schizothorax is kind of typical fish in Yalong River, which can indicate the environment of river. The habitat area of Schizothorax would be reduced much because of reduce of the flow and velocity after water transfer calculated by PHABSIM. The weighted habitat area of fish is reduced by58.23%-71.94%. It is necessary to consider the compensation biological habitat environment.(4) Fuzzy optimal theory and method were used to select the most suitable schemes among the different schemes set. The factors of environment were analyzed by principal factor analysis method to find out which one was the most sensitive factor to the environment. The index system was built from three aspects, hydraulics, hydrology and ecology. Through changing the quantity and process of water diversion, five schemes were set. The results suggest the less water transfer the better environment appears. The decision-making apartment should consider the scheme with5billion cubic meter, and the better ratio of water transfer in food season and in non-flood season is7:3.