Analysis of Rainfall-Infi l tration Recharge to Groundwate r

Understanding the recharge process and i ts relationship with rainfall is of critical importance t o the management of groundwater systems. In this research, in-situ lysimeter experiments, statistical methods, and numerical simulations were used t o study the process of rainfall-infiltration recharge to the groundwater. With a shallow groundwater table, each recharge process corresponds t o an individual rainfall event. Therefore, the infiltration-recharge can be predicted directly from rainfall events through a statistical correlation. The advantage t o use the statistical correlation for estimating the recharge is a minimal requirement of input data and computation effort, compared with numerical simulations. As the depth t o groundwater increases, the degree of correspondence between rainfall and recharge processes decreases. Below a certain depth, only the correspondence between relatively large rainfall events and peaks in the recharge processes may be observed. A technique was developed t o separate the recharge process corresponding t o rainfall events, and a concept of effective rainfall events was introduced t o analyze the rainfall-recharge relationship. I f the water table is further deep, there will be only one peak in the annual recharge process, and the processes of different years may overlap. Only a correlation between the annual precipitation and infiltration-recharge can be obtained. For a very deep water table, the variation of the infiltration-recharge rate becomes quite small, which can be approximated as a constant. The recharge rate may be determined using an annual or multi-year water balance