ESTIMATION AND PREDICTION OF THE INTERACTION OF SURFACE WATER AND GROUNDWATER: A CASE STUDY OF AWASH SEBAT KILO AREA
Creators: name: YOSEF TAMIRAT SHIFERAW
Publisher: name: National Academic Digital Repository of Ethiopia
Year: 2019
Subjects: Groundwater-surface water interactions, QSWAT, SWAT-MODFLOW

description: Interaction of the surface and groundwater is one of the main processes of water exchange in the planet and estimation of these groundwater-surface water interactions is critical to modeling surface and ground waters. This thesis presents these interactions using hydrogeological survey, hydrochemistry study, QSWAT models and the coupled SWAT-MODFLOW models. QSWAT is applied here to understand the water balance components of the study. The same is also done using the SWAT-MODFLOW models. Calibration and validation of the QSWAT model was conducted after carrying out the sensitivity analysis. The groundwater and management parameters are more sensitive as compared with others. The SWAT model was calibrated with daily stream flow data ranging from 1999 to 2008 and validated with the same stream flow data ranging from 2009 to 2013. Two years were used for the model warm up or initialization. The model goodness-of-fit was evaluated using the Coefficient of determination and the Nash-Sutcliffe Coefficient on a daily basis both for calibration and validation periods and resulted 0.84 and 0.79 for the calibration period and 0.87 and 0.871 for the validation period respectively. From the QSWAT model the annual precipitation of the whole of the study catchments was averaged about 856mm over the entire basin, of which 201.4mm (23.52%) goes to the surface runoff, 459.07mm(53.62%) to the evapotranspiration, 77.9mm (9,1%) to be recharged to the aquifer. The SWAT-MODFLOW model also shows a good match with the QSWAT model results. The outputs of the SWAT-MODFLOW model are also ET= 54.32% of precipitation, surface runoff=24.71% of precipitation) and recharge=8.8% of precipitation. The result is therefore in good correlation with that calculated by QSWAT. The goodness of fit comparison using the coefficient of determination and the Nash-Sutcliffe Coefficient shows 0.8544 and 0.769 respectively. From the conducted hydrogeological survey, the conceptual model of the water system of the study area was developed. The two main regional groundwater flow directions of the basin are directed along the predominant anomaly axes (regional tectonic structures) of the area. These two regional flow directions are separated by a NNE-SSW trending horst structures which also act as a surface and ground water divide. The boundaries of the study area are bordered by ground and surface water divides along the western, eastern and northeastern directions. The most likely recharge types and areas of the study area are: the recharge from the perennial Awash River for a length of about 130kms, the groundwater inflow from the volcanic aquifer of the Southern part of the plain for a length of about 74kms, recharge from rainfall within the basin and the recharge from run off along the valleys of other perennial and intermittent rivers of the area. The groundwater leaves the system in the extreme north of the plain along the NNE direction. Both chloride and sulphate salinity increases along the ground water flow path of the study area. Therefore, from this we can conclude that the ground water evolves along the flow direction. This is in view of enrichment of the salinity due to dissolution of minerals. The study would have been better if the grid size of the SWAT-MODFLOW model was reduced and I recommend doing the model at grid size of 1000m by 1000m or lowering. The hydrogeological and hydrochemical analyses were done using scarce data at the western part of the study area and I recommend conducting test well drilling and physic-chemical analyses of these drilled wells to enrich the document in the future.