| Guide County in Qinghai Province is favorable areas for agricultural production. The insufficient water supply capacity of the present water supply engineering directly affects the agricultural production water for people and livestock, and other industry when irrigation water shortage is serious in February and March. So we need to increase agricultural irrigation water outlet to develop and construct Laxiwa irrigation areas on the right bank of Laxiwa Hydropower station. With the irrigation construction, it is bound to cause a certain impact on the groundwater quantity、level and quality. Researching the water quality status, forecasting the groundwater level、water quality and the influence on the environment, has the vital significance to the scientific construction and management for the irrigation areas.This paper conducted a series of environmental hydrogeology test. Through the establishment of pumping test site numerical model combined with the pumping test data inversion coefficient of permeability of aquifer. In-stiu dispersion tests were concudcted in the irrigation areas. The dipersion degree of the unconfined aquifer was calculated based on the hydrodynamic dispersion theory of radial convergent flow. By these action dispersion parameters of the unconfined aquifer in irrigation areas was decided. The vadose zone permeability coefficient, antifouling performance and the ability of aquifers was confirmed through the double loop infiltration test, permeability test, test the water. The above measures laid the foundation for the impact evaluation of irrigation district construction on groundwater level, water quality.Based on the analysis of geological and hydrogeological conditions, this paper established the hydrogeological conceptual model and mathematical model and applied Processing Modflow software to solve the numerical model of groundwater. The numerical model was identificated and verificated according to the measurement of underground water level and the East River, West River water infiltration. The solute transport model that selected total nitrogen, ammonia nitrogen as the simulation factor was established on the basic of flow model. By the application of numerical model of groundwater flow and solute transportmodel this paper analysis the evolution trend of groundwater level and water, total nitrogen, ammonia nitrogen in the different irrgations and water used or not. The results show that:water of mining in the area near the water level drawdown is obvious, but the scope is small. Even reduce gross irrigation quota, improve comprehensive utilization coefficient of canal water, with the increase of irrigation area, the groundwater storage capacity in the irrigation area are still increasing which makes water level rise. Most of the rise of region ground water level is less than2m in the irrigation area. The underground water level increases the maximum value in the newirrigation area and the highest increase in value is less than2.6m. The total nitrogen, ammonia nitrogen concentration increment are less than5mg/L,0.02mg/L in most area of the regional groundwater irrigation. Total nitrogen, ammonia nitrogen form a high value area in the newirrigation area and the incremental maximum value are less than6.2mg/L,0.022mg/L.This paper studies the groundwater environment impact in the irrigation area in the condition of different irrigation and water extraction by the application of numerical model of groundwater flow and solute transportmodel through the analysis of the hydrogeological conditions and environmental hydrogeological test.Research results provide a basis for reasonable allocation of water resources in the irrigation area and a reference model for similar groundwaterenvironment impact assessment. |
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