Groundwater Recharge from Rainfall in Wadi Ham, United Arab Emirates

Mohsen Sherif1 Mohamed AlMulla2 and Abdel Azim Ebraheem2

1Civil and Environmental Eng. Dept., College of Engineering, UAE University, Al Ain, UAE
2Department of Water Resources, Ministry of Environment and Water, Dubai, UAE

Abstract

Rainfall constitutes the main source for natural groundwater recharge. However, in arid and semiarid regions, rainfall events are scare and infrequent and, in most cases, do not provide sufficient recharge to substitute for the excessive pumping. To enhance the groundwater recharge from rainfall events and improve the groundwater quality in arid regions, recharge dams are constructed across the main wadis to intercept surface water runoff. About 120 retention and detention dams of different scales and types have been constructed across the main wadis in the northern Emirates of UAE to protect the downstream area and improve the groundwater recharge.

This paper elaborates the experience of groundwater recharge through dams in United Arab Emirates. To that end, the dam of Wadi Ham in Fujairah Emirate was considered. Groundwater records were analyzed to determine the direct recharge from rainfall events in Wadi Ham. New boreholes and observation wells were drilled and pumping tests were conducted. Soil samples were analyzed and infiltration tests were conducted. A comprehensive geophysical investigation, including eleven sections, was completed.

MODFLOW was used to simulate the groundwater conditions in the area of Wadi Ham and assess the efficiency of the dam in recharging the groundwater system. The model was calibrated for a duration of 5 years to produce the measured groundwater levels in the observation wells. The model was then validated for 11 years and the resulted groundwater levels were compared with the measured ones. It is concluded that the dam has enhanced the groundwater recharge but it could be more effective by removing the upper silty layer in the ponding area periodically.   

Keywords

Groundwater recharge, rainfall, dams, numerical modelling, Wadi Ham, UAE