HYDROLOGICAL CLASSIFICATION OF THE BESEASE INLAND VALLEY BOTTOM IN GHANA FOR CROP PRODUCTION USING THE WATER TABLE FLUCTUATION METHOD

Abstract

The shapes and forms of piezometric hydrographs arising from the recharging and discharging of unconfined aquifers offer a hydrological tool for the classifications of inland valley bottoms in Ghana for crop production. A two-year measured water table fluctuations at Besease wetlands were plotted on a reference scale of time in months on the x-axis and hydraulic head on the y-axis. The water table fluctuation method was used to evaluate the seasonal and annual variations in the water level rise and to estimate the groundwater recharge. The monthly slopes segment of the water table fluctuations were used as a base for the classification of the heads. Results from the study showed that the estimated recharge for the study area ranged from 133 to 467 mm for the fourteen (14) piezometers, representing 9 to 31% of 2009 annual rainfall and 47.6 to 427.9 mm in 2010 representing 4 to 34% of the annual rainfall. The Results also showed that most of the piezometers had their monthly slopes dominated by the acute segment followed by the obtuse segment, flat segment and right-angled segment in that order. It can be inferred that most of the piezometric areas dominated by acute forms become relatively dry during the dry season; however, these areas may still have some water to support crops. The hydrograph representation of the monthly slopes were employed to classify the studied Inland Valley Bottoms into three hydrological regimes as a management tool for developing wetlands for crop production. The regimes were Water table fluctuation (WTF) Class I - acute slopes segment varying from 0 to 30%, WTF Class II - acute slopes segment varying from 30 to 45% and WTF Class III - acute slope segment > 45%. It is concluded that a controlled water table offers a distinguishing criterion for the development of Inland Valley Bottoms for year round crop production in Ghana.