GROUNDWATER POTENTIAL ZONE MAPPING AND MODELLING IN TEMCHA CATCHMENT: A CASE STUDY IN UPPER BLUE NILE BASIN, ETHIOPIA

Abstract

Groundwater is the most valuable source of freshwater on earth. For groundwater development, conservation, and implementing management plans efficiently, groundwater potential identification is important. In Temcha catchment, groundwater is being misused and management is weak. The purpose of part of this study is to assess and identify the groundwater potential zones using GIS and remote sensing approach. The relative weights of the influencing factors (lithology, slope, geomorphology, soil, lineament density, rainfall, drainage density, and land use and land cover) were assigned using the Analytic Hierarchy Process (AHP) based on Saaty’s 1–9 scale. The delineated potential zone has been divided into five categories: very poor (1.189%,), poor (19.188%), moderate (40.452%), high (28.559%, and very high (10.612%). As the sensitivity analysis shows lithology and slope are sensitive and influential and drainage density is the least sensitive. The validation result shows a good agreement with 73.33%. The developed groundwater potential zone will simplify the identification of locations for wells to be drilled and be helpful for development and water resource management. The goal of groundwater flow modelling in this study is to describe the groundwater quantitatively and to investigate the aquifer response for external hydrologic stresses in the Dijil catchment. A single layer unconfined aquifer two-dimensional conceptual model has been developed and simulated by MODFLOW-NWT code under steady state. The manual trial and error method was used to calibrate the model based on 18 observation points and its performance was evaluated through summary statistics and graphical techniques. The calibration result shows that the RMSE is 6.013m which satisfy the criterion. The scenario analysis indicates that Adisna-Gulit well site (DMTW#1, 2 &3) show large drawdown up to 45.20m. The river leakage and subsurface outflow also investigated. As the withdrawal rate increases, the river leakage increases linearly and subsurface outflow increase highly as the withdrawal rate increases. Additionally as the withdrawal rate increase and recharge rate reduced, the flow from the river to the aquifer increased and from the aquifer to the river was reduced. The sensitivity analysis result shows that hydraulic conductivity and recharge rate are more sensitive. From the simulated water budget, the total inflow-outflow is 1.4872m 3 /s with zero budget discrepancy.