Study Of Precipitation Recharge To Groundwater

Estimation of precipitation recharge is very important for regional water resources evaluation because it is a primary source of groundwater resources and is very useful for reasonable groundwater exploitation.The main techniques that have been used for groundwater recharge estimation include: physical technique, tracer technique and numerical modeling method. In this study, following three techniques used for quantifying precipitation recharge have been investigated: determination of the precipitation recharge coefficient, the water flux technique and unsaturated zone numerical modeling. The calculation results of the three techniques were validated based on observed data from the lysimeter in two hydrological observation stations.In this study, the precipitation recharge coefficients for different rainfall magnitudes were calculated directly using the observed precipitation recharge amount from the lysimeters at the Wudaogou Hydrological Experiment Station in Huaibei Plain, Anhui Province. Then, statistical relationships between the coefficient and the depth to groundwater table were established and tested by using the regression analysis methods. Study results demonstrate that the relationships for precipitation in a short time of a day and several days do not hold, and therefore, estimation of precipitation recharge amount based on this method may lead to a large error. However, for a long period of a month, a year or multi-years, the relationships between the mean coefficient and the mean depth are exist, and thus it is able to accurately used for estimation of the precipitation recharge amount.The methods of zero flux plane (ZFP) of soil moisture potential and fixed flux plane (FFP) were used to determine the precipitation recharge amount by using the observation data of the Hanwang Hydrological Experiment Station in Xuzhou, Jiangsu Province. Further estimation based on combing ZFP with FFP was proved to be more accurate than that from ZFP and FFP, respectively.A numerical model for simulating soil moisture content based on Richard equation was used to estimate the precipitation recharge. In the simulation, the key parameter of the unsaturated-zone conductivity was determined from the relationship between the conductivity and soil moisture content which is developed by FFP using the observation data of the Hanwang Hydrological Experiment Station. Other parameters were calibrated by comparing soil moisture contents between the observation and the simulation. The model was further validated by comparing the model calculated precipitation recharge and the lysimeter observation at the Hanwang Hydrological Experiment Station. The validation results demonstrated that the model is able to accurately estimate the precipitation amount.