Spatial Variability Of Sediment Permeability Coefficient And River-Groundwater Interaction In Bahe Rubber Dam Area

The interaction of river and groundwater is an important part of hydrological cycle and a common phenomenon in nature.The permeability coefficient of river bed sediment is an important hydrogeological parameter of river and groundwater interaction,which directly affects the exchange capacity of river and groundwater.Urban water storage projects have increased the water area,improved the urban ecological environment,and had a profound impact on the urban hydrological cycle,but also brought a series of problems about water resources,water environment and environmental geological.In order to reveal the influence of water conservancy construction on the permeability coefficient of riverbed sediments,and further explore the influence of water storage projects on regional groundwater flow field and the interaction of river and groundwater,this paper took the rubber dam of Chanba ecological zone in Xi'an as an example.Depending on data collection,field tests and laboratory experiments,the spatial variation of the coefficient of the riverbed sediments in the rubber dam area was analyzed,the underground water flow field and the interaction between river water and groundwater were studied under the condition of filled dam and collapsed dam,by means of statistics,empirical formula and numerical simulation.The results are mainly as follows:(1)The average permeability of riverbed sediments in Bahe reservoir area was 1.06m/d,the maximum was 3.12m/d and the minimum was 0.08m/d.The permeability coefficient calculated by Beyer's empirical formula was closest to that measured by the standpipe method.(2)It is found that the permeability coefficients of A-33 and B-23 reach obeyed the normal distribution,and the other sections that didn't obey the normal distribution,when removing the abnormal value,also approximately obeyed the normal distribution.GIS software was used to fit the Semi variogram.The optimal model of the A-5 reach was the exponential model,and the other reaches were spherical model.The coefficient of permeability showed strong spatial correlation in space,and the coefficient of variations wereall larger than 1.Sediment permeability coefficient of every reach showed spatial variation between 5 to 10 m,mainly due to the deposition structure of the aqueous medium.It was found that the permeability coefficients of each reservoir area calculated by Kriging interpolation were increasing along the upstream direction.(3)According to the experimental analysis and the permeability coefficients of riverbed sediments,it was found that the permeability coefficients vary greatly before and after rubber dams impound water.The average permeability coefficient of sediments before construction was 31.86m/d,but after construction was 1.06 m/d.And the permeability coefficients varied greatly before and after the dam,the permeability coefficient of the sediments before the dam was between 7.45 and 30.2m/d,while after the dam was between 0.08 and 3.12m/d,and the permeability coefficient before the dam was less than that after the dam.The main reason for the change was that the sedimentation in the reservoir area,which resulted in fine particle precipitating,but after the dam water was washed down,so the sediment particles were coarse and the permeability coefficient was larger.(4)The hydrogeology conceptual model and the groundwater mathematical model of the study area were established.The model was identified and verified by Modflow software.It showed that the groundwater flow model,hydrogeological parameters and source and sink items were basically in line with the actual situation,so the simulation analysis of the operation of rubber dam in the study area was practicable.(5)The coupled model of surface water and groundwater was established by adding the measured surface water data into the model.The 3 rubber dams of Bahe and 2 rubber dams of Chanhe were taken as the research object,from three aspects,including the groundwater level observation hole,the groundwater flow field and the water balance in the reservoir area,the paper analyzed the change of the flow field and the interaction between the river and the groundwater under the condition of completely filled dam and collapsed dam.The water level in each reservoir area when completely filled water was about 1.26 m ~ 3.17 m higher than that in the condition of completely collapsed.The groundwater flow in the reservoir area didn't change obviously,and the groundwater flow in the reservoir area was from southwest tonortheast.The simulation results were positive balance both in the two conditions;it means the river recharge is greater than the river excretion.(6)According to the measured surface water and groundwater data,combined with the established model,the interaction between river water and groundwater in Bahe River Basin was obtained: the transformations of river and groundwater in rubber dams were uniformity whenever the dam was filled or collapsed.In the left bank of Bahe,the river recharged groundwater,while in the right bank,the groundwater recharged river;in the both banks of Chanhe,the groundwater recharged river;in the downstream area after Chanhe joining in Bahe,the river recharged groundwater.