Groundwater Environment Change And Its Impact Mechanism In Typical Ecological Water Supplement Areas Of Hutuo River

Hutuo River alluvial fan plain is located in the central part of Taihang Mountain in North China Plain.With the increase of water demand and the impact of human activities brought by water conservancy project construction,industrial and agricultural development,urban expansion and so on,the imbalance of supply and demand and deterioration of water quality of groundwater resources have appeared in this area,which has formed a typical shallow groundwater depression area in North China Plain.In Hutuo River,the mode of"dual source water supply"is carried out through reservoir water supplement and external water diversion.The decline of regional groundwater level can be controlled to a certain extent.However,whether the groundwater environment will change in different degrees after the groundwater in the two areas is recharged by different water sources needs to be studied.Based on field monitoring and field sampling,134groups of samples were collected from 6 phases during the period of water supplement from 2018to 2020 for analysis.With the help of hydrochemical analysis,mathematical statistical analysis and PHREEQC simulation methods,the characteristics of groundwater environment change in the two typical areas in the early stage of recharge and the internal change mechanism of groundwater environment in the process of recharge are comprehensively expounded:In the early stage of recharge,the groundwater level and flow field changes in the two typical areas are affected by hydrogeological conditions and recharge methods,and the groundwater dynamic response is different:in the upstream intermittent recharge area,the channel infiltration recharge mode is intermittent,the average increase of groundwater level is 3.14 m,and the groundwater flow field has not changed significantly;The average increase of groundwater level is 3.34 m.The groundwater mound is formed with poor permeability in the downstream.The groundwater flow field in the area changes from northwest to southeast to northeast to southwest.In addition,the change characteristics of groundwater hydrochemical behavior in the two areas are also different at the initial stage of recharge.The recharge water source in intermittent recharge area and the local groundwater is HCO₃·SO₄-Ca·Mg type.The hydrochemical characteristics of groundwater have not changed significantly in a short time,and the regional hydrogeological conditions are the main controlling factors of groundwater environment change;The groundwater in the continuous recharge area is HCO₃·SO₄-Ca·Mg type.On the basis of hydrogeological conditions(contribution rate of action:33.95%),the mixed action(contribution rate of action:24.84%)and human activities(contribution rate of action:10.24%)in the recharge process jointly affect the groundwater environment changes in this area.Finally,the reaction path simulation and mixed simulation of the two areas before and after recharge are carried out by PHREEQC software.The results show that dolomite and calcite in the upstream intermittent recharge area change from supersaturated state to equilibrium state.The results show that calcite,dolomite,gypsum and fluorite in the downstream continuous recharge area are all in the trend of transition from saturated state to unsaturated state.The overall p H of groundwater environment will be close to the recharge source.The saturation index of calcite and dolomite in the two recharge sections will change from saturated state to unsaturated state when the mixing ratio is 6:4(groundwater:recharge water).Although the influence mechanism of the downstream area after receiving recharge water is more complex,the hydrogeological condition plays a major role in controlling the groundwater environment in the process of two areas.