Estimation of pumpage and recharge in a groundwater system considering multiple irrigation practices

This study applies groundwater hydrograph and isotope analysis methods along with area rainfall hydrograph and historical irrigation pumpage variations to estimating various pumpage and recharge with time distribution in a groundwater system considering multiple irrigation practices. While the purpose of pumpage include non-irrigation and irrigation uses, and the sources of recharge include rainfall, river, inflow through the boundary, and groundwater irrigation seepage. Pumpage is the product of pumping rate and pumping days. The annual pumping rate of non-irrigation pumping is assumed to be constant and can be estimated as the slope of the groundwater hydrograph during the consecutive non-rainy days within the non-irrigation periods of the dry season. Under multiple irrigation practices, the time distribution of irrigation pumping rate can be estimated by the slope of groundwater hydrograph during the consecutive non-rainy days within the irrigation periods of the dry season as well as the irrigation pumpage variations which is extracted from the pumping records of Irrigation Association. This study regards recharge as the difference between inflow and loss. Inflow can be estimated by groundwater hydrograph analysis; loss, groundwater balance equation; and various sources of recharge, combining the analysis results of groundwater hydrograph and isotope mass balance equation. This study uses Cho-Shui river alluvial fan as study area. Results show that the methodology of this study not only can settle the restrictions of groundwater hydrograph and isotope analysis which were proposed by previous studies, but also can estimate monthly various pumpage and recharge effectively and rationally.