Quantification of Groundwater Recharge in the Midstream Area-Gash River Basin Using the Water Table Fluctuation Method

Abstract

Abstract Quantification of groundwater recharge differs in their methods of estimation and therefore gives variable recharge estimates whenever a groundwater system is evaluated. Quantifying the fraction or the percentage of infiltrated water which reaches the water table is a key factor in any sustainable planning scheme for groundwater resource management. The water table fluctuation method was used to evaluate the seasonal and annual variations in water level rise and to estimate the groundwater recharge. The method used in this study includes monitoring of groundwater level measurements to estimate groundwater recharge using Water Table Fluctuation “WTF” to determine sustainable withdrawal. The average annual discharge of the River Gash is estimated to be 1,031×106 m3 at El Gera gage station (upstream) and 711× 106 m3 at Kassala bridge gage station (downstream). The annual loss mounts up to 29% of the total discharge. The water loss is attributed to infiltration and evapotranspiration. The present study showed that the monitoring of groundwater level measurements indicates that the water table rises during the rainy season by 9 m in the upstream and 6 m in the midstream areas. The average rise in groundwater table (ΔHn) in the period from 1999 to 2013 found to be 8.36 meters. The average annual groundwater recharge during the period 1999 to 2013 is 107 × 106 m3 whereas average difference in Gash river discharge at Kassala Bridge during the same period is 320 × 106 m3.