| In recent years,with the gradual advancement of sponge city construction the effective utilization rate of urban rainwater resources has been improved to a certain extent.In order to explore the impact of low-impact development on groundwater level and water quality,this article lakes a single low-impact development facility seepage well and multiple groundwater monitoring wells in the sponge city pilot area of Fengxi New City in Shaanxi Province as the research objects.Through long-term groundwater level water quality monitoring and groundwater numerical simulation,the impact of rainwater infiltration from seepage wells on groundwater level and the changing laws of groundwater level and water quality in Fengxi New City under the action of a certain scale of low-impact development facilities are studied.The main research contents are:(1)Affected by the unstable operation of the facility and the delayed recharge of rainfall,the groudwater burial depth of the observation well J1 in the seepage well was maintained at 12.35m in the early stage from the end of 2017 to the beginning of 2019,and the buried depth was about 12m after stable operation in the later stage;Since agricultural irrigation requires a large amount of groundwater extraction,the groundwater burial depth of J1 and observation well J2 gradually increased from April 2019 to August 2019,reached the maximum depth of 14-14.3m around August,and then gradually decreased.(2)During the 2018 rainfall the SS concentration removal rate of seepage wells was 35%-80%,followed by NO3-N,and the removal effict of other pollutant concentration was unstable.In 2019,COD,TN and TP cconcentration removal rates of seepage wells reached 24.948%,13.277%and 22.078%,respectively.The removal rate of Zn in seepage wells is about 30%,and the removal rale of Cd is between 1%-20%.The removal effect of Cu is unstable.(3)After a large amount of pollutants carried by roof and road runoff are purified into the aquifer through seepage wells,the concentration of TP,NO3-N and TN in the groundwater at J1 will increase for a short time,and their average values will reach 0.151mg/L,1.097mg/L,and 1.587mg/L respectively.As the rainfall decreases,the concentration gradually decreases to 0.13mg/L,0.845mg/L,0.97mg/L;the seepage well has a good purification effect on NH3-N,COD,Cu,Zn,and Cd,and has minimal impact on groundwater quality.(4)The low-impact development and construction of Fengxi New City is conducive to groundwater recharge,and its average groundwater level in 2017 has increased by nearly 0.6m compared to 2016.Affected by groundwater exploitation and lagging recharge of rainfall during the year,the groundwater level slowly decreased from January to April,the decline increased from April to July,and the water level gradually rose from July to October.(5)The low-impact development and construction of Fengxi New C ity has improved the quality of groundwater to a certain extent.The inter-annual water quality poor rate has changed from 33.3%to 66.7%,and the extreme rate has changed from 58.3%to 25%.During the year,the quality of groundwater was reduced during the flood season.(6)When the scale of low-impact development is small,it will have a greater impact on the local groundwater level.When it reaches a certain scale,the impact on the overall groundwater level will increase;the combination of rainwater garden+infiltration paving+grass ditch facilities has a significant effect on groundwater recharge;The construction of low-impact development facilities at a depth of 10-12m in the study area can replenish groundwater to the greatest extent;The main factors affecting groundwater recharge in the study area are rainfall and groundwater exploitation. |
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