Application of SWAT and MODFLOW models for characterization of surface–groundwater interaction in the Modjo River catchment, central Ethiopia

Assessing the relationship between Surface Water (SW) and Groundwater (GW) is an important aspect of hydrology, as it aids in the conjunctive and effective management of water resources. This study characterized the surface–groundwater interaction in the Modjo River catchment, central Ethiopia using the Soil and Water Assessment Tool (SWAT) and MODFLOW models. The SWAT model adequately simulated the hydrology of the study area for the calibration (2007–2011, R2 = 0.83) and validation (2012–2015, R2 = 0.7) periods. The semi-distributed average GW recharge from the SWAT model simulation with other hydrogeologic parameters and boundary conditions was utilized to construct the GW flow model using the MODFLOW–NWT version. The integrated modeling result showed that about 43Mm3 of water leaks to the groundwater system annually, whereas the flux from GW to rivers is about 165Mm3/yr. Most reaches of the Modjo River in the northern and central areas of the catchment are gaining, with fluxes reaching up to 4940 m3/day. The downstream part of the catchment is characterized by a losing-disconnected river, with a lower flux of up to 675m3/day. In general, most reaches of the Modjo River are interconnected with the GW system and the GW inflow to streams is higher. Based on these findings, future exploitation and management of both SW and GW resources should consider the nature of their interconnection for sustainable utilization of the water resources in the catchment.