Characterization of Potential Direct Recharge in the Gold Mining District of South-Western Ghana Using the Hydrus-1D Computer Code

The mean annual potential recharge rate to the ground water system in the Tarkwa gold mining district of South Western Ghana, has been estimated for the period 1977 to 2001 by analyzing precipitation recharge in response to rainfall pattern and distribution for the four main soil types; Huni, Tarkwa Phyllite, Banket and Kawere. Using the Hydrus-1D infiltration computer code model, simulation results of recharge-precipitation exhibited a linear relationship, and gave correlation coefficient values R2 ranging from 0.39 to 0.55 for the four soil types and 0.72 for the composite soil. Variability of annual recharge was assigned to various reasons, including the variation in the weather pattern (rainfall, temperature, evapotranspiration etc), topography and hydraulic properties of the aquifer system. The potential direct recharge rate was estimated to range from 269 mm/yr to 611 mm/yr, with an average value of 385 mm/yr. This is as a result of infiltration of about 18% to 36% (average 27%) of the mean annual precipitation. The high average value of 385 mm/yr is reasonable on the basis that it represents the potential maximum value of the actual recharge value of 299±72 mm/yr.