Groundwater Flows Modeling of the Upper Catchment, Abbay Basin, Eastwollega Zone, Oromia Regional State, and Western Ethiopia.
No Thumbnail Available
Date
2019-05-05
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Addis Ababa University
Abstract
The problematic area selected is finding in the East Wollega Zone, Western Ethiopia called
upper Anger River Catchment of Abay Basin. The total surface area of the catchment is 7159.21
Km2. The purpose of this study has to understand the Regional Groundwater flow and the
response of groundwater system to different scenarios with the help of numerical groundwater
flow modeling. One layer and unconfined Aquifer system simulated under steady state flow
condition by using MODFLOW.
The boundary of the study area delineated from ASTR DEM with the 30m resolution by using
Arc SWAT (Soil Water Assessment tool) software. The input parameters for the model gathered
from the well completion reports. SWAT software used to calculate the regional recharge rate of
the upper Anger River Catchment. Annual recharge to the deep and shallow aquifer calculated
by the model is 388.84 mm/year.
The general Groundwater flow direction is from the north- east to south- west by following the
topographical trend and structural orientation. The model calibrated by Trial and Error method
using groundwater contours produced from different heads collected from 7 observation wells.
The calibration shows that about 97.75% of the simulated heads with the calibration targets and
the overall water of the simulated model result show 8889163.3130. Model sensitivity analyses
conducted with changing of the hydraulic conductivity and recharge the model is more sensitive
to them. Change in the hydraulic head by 20%, 30%, 40%, 50% result for the RMSE changes in
the head from the calibrated value. In addition, the same change happens in the recharge like the
difference in hydraulic head.
The result of the numerical simulations indicates while increasing well withdrawals by 25%,
50%, 75% and 100% respectively it also resulted to the change of RMSE heads by 8%. Water
Budget results of the model shows that the reviled groundwater recharge comprise by 0.5% and
97.75% by river leakage of the total water input for the total study area. The spatial distribution
of groundwater decline is limited towards the river. However, there is hydraulic connection
between the sediment bed and Anger River.
Description
Keywords
Anger Catchment, Agro Ecological Zone, Water Balance, Nekemte, Ethiopia