Numerical Groundwater Flow Modeling of Tisabalima Sub- Basin, South Wollo Zone, Northern Ethiopia

Mulugeta Asrat

dc.contributor.author	Mulugeta Asrat
dc.date.accessioned	2023-06-30T08:23:46Z
dc.date.available	2023-06-30T08:23:46Z
dc.date.issued	2022-11
dc.identifier.uri	http://ir.bdu.edu.et/handle/123456789/15422
dc.description.abstract	Tisabalima sub-basin is part of the Awash Basin and is found in South Wollo zone, Amhara National Regional State. The sub-basin has a surface area of approximately 788 km i 2 . The study targets mainly steady-state groundwater flow modeling of Tisabalima sub-basin with a single layer of average 200m aquifer thickness. The major purpose of this study was to evaluate the current conditions of the aquifer system based on the known level of exploitation in the model area, simulate one or more future scenarios of water exploitations, and their effect on the sub-basin aquifer system. The chloride mass balance (CMB) and soil water balance (SWB) methods were employed to estimate the annual recharge of the sub-basin. The result was 172.2 and 124.29 mm/year respectively. Therefore, the average result of the above two methods was 148.26 mm/year. MODFLOW which is the USGS modular three-dimensional finite-difference groundwater flow model was selected, to simulate the system behavior under different stress conditions for the sub-basin. Model calibration was carried out by trial-and-error method using groundwater contours constructed from heads collected in thirty head observation points. The model domain was discretized into 230 rows by 182 columns with a grid size of 200 m by 200 m and contains a total of 41,860 cells. Considering the boundary conditions of the sub-basin the northern, western, southern, and southeastern parts are groundwater divides and were represented by no-flow boundaries. The northeastern part of the sub-basin was represented by a general head boundary. The water balance of the sub-basin under steady-state conditions reached equilibrium conditions with recharge from precipitation 3.1935079E+05 m 3 /d, well abstraction 3.7126080E+04 m /d, and outflow through the general-head boundary 2.2343695E+04 m 3 /d. The recharge conditions in Tisabalima subbasin are characterized by two sources of water that is recharged from precipitation and seepage from Hayk and Ardibo lakes. On the other hand, outflow from the aquifer are characterized by baseflow, well abstraction, and outflow through the general head boundary.  25 percent change in recharge which will bring a significant effect on the simulated results of the model. On the other hand, parameters like pumpage, and increase in hydraulic conductivity especially up to 25 % can be varied, with minor effects on the model simulation results. The steady-state withdrawal rate was increased by 50% and 75%, these increases are equivalent to withdrawing an additional 18563.04 The model is most sensitive to a decrease in hydraulic conductivity by 50 percent and beyond 3 m 3 /d or 214.85 l/s, and 27844.56 m 3 /d or 322.27 l/sec over the whole catchment respectively, and the increased withdrawals were distributed among the existing wells. Increasing the existing pumping from the aquifer by 50% resulted in a corresponding reduction of 2.54 % in outflow through the general-head boundary and a 5.9 % reduction in groundwater discharge to streams from the sub-basin. In addition to that, increasing existing aquifer pumping by 75% results in a 22,839.86 m 3 /day decrease in base flow, which is around 8.87 % of the base flow of the calibrated steadystate model. Generally, the groundwater level declined by 14.24 m on average up on an increase in pumping by 75 %	en_US
dc.language.iso	en	en_US
dc.subject	Hydrogeology	en_US
dc.title	Numerical Groundwater Flow Modeling of Tisabalima Sub- Basin, South Wollo Zone, Northern Ethiopia	en_US
dc.type	Thesis	en_US