Use of chloride mass balance method for estimating the groundwater recharge in northeastern Ghana

This study uses the chloride mass balance (CMB)method to estimate the recharge to the groundwater aquifers in the upper east region (UER)in north- eastern Ghana. In addition, the recharge is compared with water demand to understand the potential of groundwater for improving water supply. The UER is one of the most densely populated areas in Ghana and depends heavily on groundwater for domestic water supply as well as for dry season vegetable farming and livestock watering. The CMB method, basically, requires three data sets: the amount of precipitation, the concentration of chloride dissolved in rainfall, and the concentration of chloride dissolved in groundwater. Data were obtained from 12 rain gauges, 8 rain collectors, and 11 groundwaterwells, for a period of 10 months (March-December 2006). Monthly chloride concentration in rainfall in the UER ranged from 0.2 to 2.3 mg/l. Chloride concentration in groundwater was measured to be between 4.0 and 23.8 mg/l. The estimated annual groundwater recharge over the UER ranged from 34.0 to 182.0 mm, representing 3-19 percent of the long-term mean annual rainfall. Water demand in the region was estimated to be less than 14 percent of the recharge, indicating a huge groundwater potential.