Assessing The Performance Of Flood Recharged Aquifer Storage And Recovery Technology For Dry Season Irrigation In Northern Ghana

ABSTRACT Bhungroo, a floodwater harvesting Aquifer Storage and Recovery technology, piloted in Northern Ghana for dry season irrigation, was assessed to determine its environmental and technical performance. The study evaluated the recharge, storage and recovery potentials of three Bhungroos, and their impacts on groundwater resources. Due to the limited time available for data collection, a multi-method approach was used. Water quality samples from rainwater, community boreholes, monitoring wells, Bhungroos and floodwater were characterized to determine the effect of Bhungroo artificial recharge on groundwater systems and irrigation water quality. Pump tests coupled with continuous water level monitoring were undertaken to determine aquifer storage characteristics and behaviour. Bhungroo aquifer recharge was estimated using chloride mass balance, water table fluctuation and infiltration rate methods, while end-member mixing analyses was used to estimate Bhungroo recovery potential. The sustainability of the Bhungroos were determined from sustainable yields and potential irrigable area. The findings indicated that artificial recharge had significantly changed Bhungroo groundwater from a shallow fresh water and deep groundwater character type of Ca-Mg-HCO3 (67 %), Na-HCO3 (31 %) and Ca-Mg-SO4-Cl (6 %) with minimum anthropogenic influence towards floodwater character of Ca-Mg-HCO3 (72 %) and Ca-Mg-SO4-Cl (28 %) with a relatively higher anthropogenic impact. Microbiological differences between Bhungroos and surrounding groundwater systems, however, were found not be wholly attributed to the influences from floodwater recharge since E. coli had previously been observed in surrounding groundwater systems prior to Bhungroo operations. Generally, changes in Bhungroo groundwater character did not affect its suitability for dry season irrigation since all indicators showed no hazard; except for SAR, EC and bicarbonate which showed a slight to moderate effect of sodium hazard on soil water infiltration. Bhungroo recharge and recovery performances were found to be limited by available well/aquifer storage characteristics and behaviour. Hence, Bhungroos with transmissivities of 8.4 – 13.1 m2 /d, storativity of 0.0011 and specific capacities of 14.7 - 37.4 m2 /d increased mean annual recharge between 8 – 13 % but recovered between 0.17 – 0.41 for dry season irrigation due to the effect of well collapse and clogging. Thus, the loss of recharge proportion between 0.22 – 0.46 for Bhungroos with sustainable yields between 0.7 - 1.5 l/s implied a maximum of 14,000 m2 (1.4 ha) of vegetable farm could be irrigated. However, considering the high costs of the Bhungroo technologies visa-vis the low potential irrigable area, it is recommended that the economics of the Bhungroo Irrigation Technology in Ghana should be carefully evaluated before upscaling to ensure sustainability.