Preliminary Analysis On The Influences Of Groundwater Infiltration By Rain Garden And Rain Seepage Well In Xi'an Area

The influence of concentrated infiltration of rainwater facilities on groundwater has much attention because of its importance in the process of construction of sponge cities.Rain gardens and seepage well are considered to be two typical rainwater facilities.The impact of rainwater concentration infiltration on groundwater depth and quality is mainly studied by two methods of rain gardens and rain seepage well on-site monitoring and simulation prediction.First,meteorological,hydrological and geological conditions were collected in Xian,Water level in some wells(a control well J1 and three monitor wells J2-1?J2-2 and J3)were monitored from May through October,2016,and from June through December,2018.Groundwater samples were collected to determine the contents of NH4+-N,NO3-N,TN and TP.Second the conceptual model of groundwater was established by using the existing monitoring wells in rain garden,and the hydrogeological parameters were generalized,the source and sink terms were calculated and the sensitivity of parameters was analyzed.This paper establishes a numerical equation of groundwater flow in accordance with the actual situation of rainwater garden,and predicts the depth of water head in the future based on Visual MODFLOW.The meteorological,hydrological and geological conditions were collected in Xian Yang.Groundwater samples of J5 well and J6 well on the west side of seepage well were collected from June to December 2018,And groundwater samples were collected to determine the contents of COD,NH4+-N,NO3-N,TN and TP.Using Groundwater Level Online Monitor to Monitor the Groundwater Level Depth of J5 from October 2017 to December 2018.And then groundwater model of Fengxi New Town was established by using 14 groundwater observation wells and hydrogeological data,Through Kriging interpolation method in Google MAP,groundwater flow field and groundwater depth contour maps of the study area in wet season and dry season were obtained.The model was generalized to three-dimensional unsteady flow.Following conclusions can be drawn through monitoring results and the prediction results by Visual MODFLOW software simulation.First,the contents of NH4+-N,NO3-N,TN and TP in the wells J2 and J3 were increased after rainfall then declined rapidly.The contents of NH4+-N,NO3-N,TN and TP in groundwater were significantly different between 2016 and 2018,which is related to the thickness of aeration zone.The groundwater depth is between 1.5-4.3m,the variation range of water level was sorted as J2>J3>J1.Second,Groundwater depth in rainy season(August-October)is significantly lower than that in non-rainy season;The variation range of rainfall depth is within 0.5-1.5 meters;The removal eff-iciencies of COD,NH4+-N,NO3-,TN and TP are poor because of the instability of the initial operation of the system.Third,the simulated flow field is consistent with the overall trend of the actual groundwater level.The rainfall infiltration recharge is the main influencing factor for the change of the buried depth of the rain gardens and seepage wells.It can be known in the next year by simulating the depth of the groundwater level in the seepage wells at different levels.After that,the buried groundwater depth in the seepage area averaged 1.4 meters,and the maximum water quality spread was within 180 meters.