University of Twente Student Theses


Hydrogeological conceptualization and numerical modeling of groundwater resources in the Zamra catchment, Northern Ethiopia

Mihiret, Mr. Ayisheshum Walle (2022) Hydrogeological conceptualization and numerical modeling of groundwater resources in the Zamra catchment, Northern Ethiopia.

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Abstract:Due to the short rainy season and high rainfall variability, water scarcity remains a significant issue in the semi-arid region of Ethiopia, including the Zamra catchment (ZC). Groundwater evaluation and management are the most crucial aspects of groundwater in the areas where groundwater is the primary source of potable water. Groundwater resources can be successfully evaluated by applying a numerical model. A reliability of such models primarily depends on the adequately built hydrological conceptual model (HCM). The study's main aim was to build a realistic HCM by integrating numerous datasets and converting it to a steady-state numerical model. To create HCM of the ZC, the hydrologic system's lithology, stratigraphy, hydrostratigraphy had to be well understood. This was done through development (applying Rockworks 3D modelling software) of the 3D hydrostratigraphic model presented through a series of cross-sections. In that model, the sequence of seven hydrostratigraphic units (layers, none of them fully covering the whole ZC) consisted of (from top to bottom): 1) unconsolidated sediment, 0–27 m thick; 2) flood basalt, 0–69 m thick; 3) Agulae shale, 0–76 m thick; 4) Antalo limestone, 0–76 m thick; 5) Adigrat sandstone, 0–49 m thick; 6) Enticho sandstone, 0–45 m thick; and 7) metavolcanic, 0-45.5m thick. The groundwater flow pattern and direction were defined by interpolation of the available hydraulic head records. As the first aquifer was unconfined and the topography of the study area complex, the interpolation was carried out using regression kriging accounting for topographical relief variability. The obtained head pattern: i) showed eastward groundwater flow direction aligned with the main river course; ii) defined catchment no-flow boundaries along groundwater divides; and iii) allowed to roughly quantify groundwater flow rate. Based on HCM, a steady state numerical model was developed using MODFLOW 6 code, applying unstructured grid (originally 500x500 m), densified around streams and head observations. The numerical model consisted of five spatially discontinuous layers, obtained from seven hydrostratigraphic units, merging the two sandstone layers, Adigrat and Enticho into one sandstone layer and the Agulae shale and Antalo limestone into one limestone-shale layer. The steady-state ZC model was calibrated using hydraulic heads as a target parameter. The water budget showed the annual mean ET (38.65% of P), annual mean total stream discharge q (61.20% of P) and a very small amount of lateral groundwater outflow qg (0.16 %of P). There is mean gross recharge of 517.54 mm year-1 (78.38 % of P) and a net recharge of 33.90 mm year-1 (5.47% of Pe) with a substantial amount of groundwater exfiltration and groundwater evapotranspiration. The total groundwater exfiltration (66.78% of q) and the rejected infiltration (25.09% of q) were routed to the stream using the water mover (MVR) package and contributed a significant value to the total river discharge (q). This q (61.19% of P) covers the most significant value of the catchment outflow.
Item Type:Essay (Master)
Faculty:ITC: Faculty of Geo-information Science and Earth Observation
Programme:Geoinformation Science and Earth Observation MSc (75014)
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