Estimation of the groundwater discharge through the edge of Changma alluvial fan in the Shule River Basin, northwestern China

Abstract

In this paper, the groundwater discharge through the edge of Changma alluvial fan in the Shule River Basin is estimated. The Changma alluvial fan is generalized as an aquifer system including an unconfined aquifer, an upper semi-permeable layer and a confined aquifer. The vertical flow of groundwater in the unconfined aquifer and the elastic storage of the semipermeable layer are neglected. The flow in the semi-permeable layer is assumed to be vertical. Analytical solution of the model is derived. From the top of the alluvial fan to the intersection of the unconfined aquifer and confined aquifer, the groundwater level decreases gradually and then increases suddenly at the intersection. The groundwater flow velocity and flux decrease from the intersection of unconfined aquifer and confined aquifer to the edge of alluvial fan. The recharge of Changma irrigation area from the unconfined aquifer is 0.82 billion m3/a. The quantity of evaporation of groundwater for each year is larger than 0.56 billion m3/a, which indicates that large amount of salt accumulated on the surface.