Abstract:

Sustainable groundwater management requires knowledge of recharge. Recharge is an important factor in evaluating groundwater resources but difficult to quantify. Hence estimation of groundwater recharge requires modeling of the interaction between all the important processes in the hydrological cycle. In this study the long term seasonal and annual groundwater recharge of Modjo river catchment (2,202 km²) was estimated and recharge map were developed through a grid based physically distributed model, WetSpass. Long term average hydro-meteorological data and spatial pattern of watershed physical grid maps were used as main inputs for the model. All input maps for the model were prepared using ArcGIS 10.2 spatial analysis tool. Soil, land use and runoff coefficient parameters in data base files, season independent gridded base map of topography, slope, and soil were used in the model; whereas precipitation, potential evapotranspiration, temperature, wind speed, groundwater depth and land use map were prepared and employed by the model, in ASCII grid format of 120m cell size with 647 numbers of row and 425 numbers of columns for both winter and summer seasons. From the result, it is found that the long-term temporal and spatial average annual rainfall of 933 mm was distributed as: surface runoff of 164 mm (17.6%), evapotranspiration of 686 mm (73.5%), and recharge of 83 mm (8.9%). Thus an average of 183Mm³ of groundwater will be recharged per year or 5,802 liter/second from the catchment area. Flood control dams (artificial recharge) practice was recommended in this study area to harvest the excess water (simulated annual surface runoff of 361Mm³) which is helpful in one way to reduce soil erosion and in the other way to enhance more recharge to groundwater