Groundwater Recharge Estimation in an overexploited Alluvial Aquifer using a Combination Method; a Primary Tool for Sustainable Groundwater Management

Abstract

Estimating groundwater recharge is critical for groundwater management in semiarid settings. A basic groundwater balance equation calculates the total annual groundwater recharge in the Eshtehard aquifer, north Iran, for the water year (2013–2014). The goals of this study are to (1) understand and differentiate the aquifer inflow and outflow components, (2) explicit computation of groundwater storage with the water table fluctuation (WTF) method, and (3) estimate the amount of annual Recharge in an alluvial aquifer using the water balance equation. The application of the WTF method requires a large number of water level measurements throughout the unconfined aquifer. The advantage of the method is that groundwater recharge is estimated at the scale of interest to basin hydrologic studies and that the method requires no extensive in situ instrumentation network. According to the findings of the well-log analysis, the low and high permeability zones are discontinuous and vary in depth and thickness. In the overdeveloped basin of Eshtehard, when extraction exceeds Recharge, a drawdown trend in groundwater levels may persist for many years. The yearly groundwater balance has a negative water budget of roughly 14.77 million m3/year in the aquifer system for 2013-2014. Due to the lack of permanent surface water running in the basin on the one hand and the small amount of rainfall besides the thick vadose zone in almost all parts of the plain, on the other hand, main groundwater recharge and discharge in the Eshtehard aquifer are pumping wells and recharge from returned of groundwater used for irrigation, industrial and municipal purposes. Based on this study, the overall amount of artificial groundwater removal from the alluvial aquifer is approximately 56.91 million m3/year. At the same time, the Recharge from this water is 16.48 million m3/year, percolating into the aquifer.