One Layer Transient Groundwater Flow Modeling at Becho Plain
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Date
2019-05-03
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Addis Ababa University
Abstract
The study focused on assessment of groundwater level responses and its spatial and temporal variability of the Becho plain using transient state flow following from steady state Modeling. Nowadays most of the water for domestic, irrigation and industrial within the study area is from the groundwater. Despite of this, the effect of abstraction with respect to recharge is not well assessed.
The groundwater recharge of the study area is mainly from direct rainfall. WetSpass modeling and Base flow separation was employed to estimate the recharge of the study area. The groundwater recharge was estimated with WetSpass modeling and Base flow separation is 120 mm/year and 85.78 mm/year (10.65% &7.8% of the annual rainfall) respectively.
The finite difference schematization of the modeled area was discretized into a uniform squared grid size 400m by 400m, comprising 265 rows and 226 columns. The transient model was simulated with MODFLW pm8 for a period of one year for one layer aquifer of 500 meter thickness. The initial aquifer parameters (hydraulic conductivity and initial hydraulic heads) were used from the steady state model.
The model was calibrated with trial and error by adjusting hydraulic conductivity and groundwater recharge by comparing the observed and simulated values. In MODFLOW, average groundwater recharge was simulated 97.72 mm/year which is within the range of recharge estimated by WetSpass model and Base flow separation methods. The water budget of the transient model shows that the aquifer storage declines from 148mm/year to 59.8 mm/year. After abstraction of groundwater with 275376 m3day-1 for ten years, the groundwater declines with an average 90.87m.
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Keywords
Abstraction Rate, Becho Plain, Groundwater Recharge, Groundwater Flow Modeling, Groundwater Monitoring, Model Calibration, Transient State Flow Modeling