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|Title: ||NUMERICAL GROUNDWATER FLOW MODELING OF THE KOBO VALLEY: NORTHERN ETHIOPIA|
|Authors: ||Getaneh, Kinfu Hailu|
|Advisors: ||Tenalem Ayenew (Prof.)|
|Copyright: ||Jun-2010 |
|Date Added: ||10-May-2012 |
|Abstract: ||The study aims to get better understanding of the groundwater flow system of the Hormat-
Golina basin using numerical groundwater flow modeling under steady-state condition. The
basin comprises inter-mountain valley (Kobo Valley) which is the most fertile irrigable land.
The basin is part of the western escarpment of Afar Rift and measures about 811 km2.
The study was ambitious in the sense that the modeling was conducted with limited data
particularly for the highland volcanic part of the basin. Two aquifer units: the fractured basalt
and the valley fill sediments aquifer were identified in the basin. The fractured basalt aquifer
forms the highland part and underlies the alluvial sediments aquifer. The two-aquifer systems
were assumed to be hydraulically connected. Deep groundwater circulation was assumed for
the highland volcanic aquifer, because of the absence of shallow groundwater features such as
springs and base flow of the rivers.
The groundwater flow system in the two aquifers of the basin was modeled using PMWIN
Pro (Chiang et al., 1998) as pre-and post processor for MODFLOW (McDonald and
Harbaugh, 1988). The model was run for steady-state conditions in unconfined aquifer. The
grid cell size of the model was taken 250 x 250m and 500m x 500m for the valley part and the
highland volcanic aquifer respectively. Model area and the layer top elevation were delineated
by the ASTER DEM processing and use of topographic maps. The hydraulic conductivity
values were determined from pumping test data analysis and literature review for the alluvial
sediment aquifer and the fractured volcanic aquifer respectively. Recharge was estimated
from water balance method.
The model was calibrated using observed hydraulic heads from 37 wells. The model was
calibrated to the root mean square error (RMSE) of about 6m and it was sensitive to recharge
and hydraulic conductivity. The model simulated water budget showed that the basin receives
a total recharge of (in-flow) 48mmy-1 and discharge it to the river for steady state condition.
Similarly, the model generated total in-flow for the highland volcanic aquifer and the alluvial
sediments aquifers were 54mmy-1 and 52mmy-1 respectively. The model result showed that
the valley fill sediment receives more in-flow from horizontal flux (40mmy-1) than other
recharge sources. In this study, the model was calibrated but not verified. Thus, the model
results obtained should not be interpreted as a perfect simulation rather as system response for reasonable model input parameters.|
|Appears in:||Thesis - Earth Sciences|
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