Assessment of the effectiveness of dams on the recharge of the shallow aquifer in the northern area of UAE

The United Arab Emirates is located in an arid region where the surface water is almost absent and the groundwater resources are mostly nonrenewable. Groundwater in the shallow Quaternary aquifers constitutes the only available water resource in the northern Emirates of UAE. The Quaternary aquifer has been heavily exploited since 1980 to meet the increasing water demands. Present extraction rate is more the 14 times the rate of its recharge. More than one hundred dams were constructed in the last three decades with the purpose of augmenting groundwater recharge in the Quaternary aquifer. Several local scale numerical groundwater flow models have been developed, calibrated, and used to investigate the hydrodynamic impacts of different groundwater management options on the potentiometry of the aquifer. In this paper, MODFLOW is used to assess the effectiveness of the dam of Wadi Tawiyaen on groundwater recharge. For a reliable analysis and accuracy purposes, the grid cells were refined near recharge and well field areas in the calibrated regional model. The results indicated that the evaporation loss from the storage in the ponding area is generally in the order of 30 of the total storage. The total water recharge to the system during the period January 1999 to the end of March 2005 was about 4.22 MCM. The recharge from the ponding area was 2.97 MCM. The groundwater recharge from the ponding area represents about 70 of the total recharge during this period. The efficiency of the dam, calculated as the ratio between the total recharge from the ponding area and the total storage during a specified period, is estimated around 22.