| Sanjiang Plain is an important commercial food production base in China,with a huge scale of agricultural production.Groundwater is an important resource for agricultural production in Sanjiang Plain,and an important maintenance factor for many wetland nature reserves.Since the 1990s,with the rise of large-scale groundwater irrigation,the groundwater utilization has been at a high level,and the exploitation of groundwater has been increasing year by year.Therefore,the issue of whether the regional groundwater is overexploited has attracted increasing attention.Therefore,the determination of the lower limit of water resources and the rational utilization of water resources have become important measures to ensure the agricultural production,ecological protection and the sustainability of water resources utilization in Sanjiang Plain.Songhua River&Naoli River Basin in Sanjiang Plain is typical study area in this study.Based on the data of topography,geomorphology,hydrology,meteorology in satudy area,overexploitation status of groundwater was analyzed,regional ecological groundwater level and ecological river base flow wrere defined.The variation of groundwater resources in different water use projects were predicted by the groundwater numerical model.Specifically,it includes:(1)The groundwater overexploitation status was judged by the regime of groundwater level within a year,the variation trend of groundwater level between years,the regime characteristics of regional groundwater flow field and the variation of groundwater resource amount.The results show that the study area is in a status of mild overexploitation.However,due to the differences in hydrogeological conditions and the intensity of water resources development and utilization,the area of groundwater overexploitation mainly distributes in the middle and lower reaches of Naoli River.(2)According to the hydrogeological data of the study area,the use of preventing soil secondary salinization of critical depth of groundwater,the upper limit value of ecological groundwater depth is 0.08~4.03 m(wetland reserves don't be set the the upper limit of ecological water level).The critical value of preventing the land subsidence,the critical value of preventing the quaternary aquifer unwatering,the critical value of preventing the wetland degradation and the critical value of preventing the groundwater disconnecting from the surface water in Songhua River were considerated,the minimun of thses values was used as the lower limit value of the ecological water depth and the value is 2.20~19.68m.(3)Wetted Perimeter Method were used to calculate the ecological base flow of Songhua River and Naoli River in the study area,considering the navigation requirements of Songhua River.The ecological base flow of Kiamusze Hydrological Station,Baoqing Hydrological Station and Caizuizi Hydrological Station respectively were 601.90 m~3/s,6.34 m~3/s and 13.01 m~3/s.(4)Based on the data of meteorology,hydrology and hydrogeology,the groundwater numerical model in the study area was constructed by Visual MODFLOW,and the model was calibrated and verified in the time periods of 1 year and 5 years respectively.(5)The groundwater level and river discharge changes in the given scheme were predicted by the groundwater numerical model.The results show that if the groundwater is continuously exploitated at the current exploitation rate,a large number of groundwater depression cones will add in the study area,and the groundwater overexploitation status will be further deteriorated.If the project of partial groundwater replaced by surface water is adopted,the groundwater overexploitation status in local areas can be restrained,and the groundwater depression cones can be restored to a certain extent.On this basis,the projects of groundwater exploitation under the condition of no surface water diversion and the combined utilization of surface water and groundwater under the condition of surface water diversion were given respectively by model calculation. |
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