Numerical Ground-Water Flow Modelling Of the Awassa Catchment

No Thumbnail Available



Journal Title

Journal ISSN

Volume Title


Addis Ababa Universty


Groundwater is of major importance to civilization, because it is the largest reserve of drinkable water in regions where humans can live, so it is very important to calculate the quantity and quality of this resource for better protection and management. Groundwater modeling is a result of careful understanding of hydrology, hydrogeology and dynamics of groundwater flow in and around the study area. The modeled aquifer is important water resource in the study area and is used extensively for irrigation, municipal, and domestic water supplies. This thesis describes a conceptual model of groundwater flow in the aquifer and documents the development and calibration of a numerical model to simulate groundwater flow. Data for a two year period (from 2004 to 2006) and other source without specified time were analyzed for the conceptual model. Regional steady state groundwater model was calibrated to average conditions from 2004 to 2006. A three-dimensional groundwater flow model, with one unconfined layer, was used to simulate groundwater flow in the Lake Awassa Basin. The study area was divided into uniform grid size of 200m by 200m, with 230 rows and 250 columns. Arial recharge to the Lake Awassa basin aquifer occurs from precipitation and initial recharge rates were given in five different zones ranging from 1.195 × 10-4 m2/day to 2.787 × 10-4 m2/day. Discharge from the aquifer occurs through discharge to perennial streams, well withdrawals and springs, and groundwater outflow to the next Ziway-Shalla Basin. Discharge rates in million cubic meters per year (MCM/year) for the steady state simulation were 111 for base flow including Tikur Wuha River and 3.03 for outflow through wells and springs. Outflow to the neighboring catchment is simulated using general-head boundary. Estimated horizontal hydraulic conductivity used for the numerical model ranged from 0.05 to 100 m/d, which were adjusted during model calibration. Model calibration was accomplished by varying parameters within plausible ranges to produce the best fit between simulated and observed hydraulic heads. The root mean square error for simulated hydraulic heads for all wells was 4.42 meter. Simulated hydraulic heads were within ±10 meter of observed values for all observation wells. A sensitivity analysis was used to examine the response of the calibrated steady state model to changes in model parameters including horizontal hydraulic conductivity, recharge, and pumpage. The model was most sensitive to recharge and relatively less sensitive to horizontal hydraulic conductivity. Three different scenarios were simulated to see the response of aquifer. Increased withdrawals decrease the groundwater outflow through river leakage and general-head boundary. Complete disappearance of Lake Shallo result in an increase in water level particularly in wells found around this lake, while decreased recharge result in more inflow from constant-head boundaries as well as lower streamflow and groundwater discharge through the general-head boundary



Groundwater modeling