Modelling Surface and Ground Water Interactions of Borkena River Catchment, Ethiopia
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Date
2020-06
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Addis Ababa University
Abstract
Inadequate water resources supply among different water users can be viewed both from social and
economic dimension. The Borkena Catchment is affected by recurrent draught due to climate change in
every eight to ten years. To sustain the water security of the catchment understanding the groundwater
surface water interaction and management is necessary. The general objective of this study is to
analyze the surface and groundwater interactions; specifically to estimate the recharge, to identify the
regional and local ground water in the system and to asses if the borkena river is gaining or loosing
river. ArcSWAT was applied to understand the water balance components of the study. The SWAT
model result was calibrated by using SWAT CUP SUFI2 algorithm with daily stream flow data ranging
from 2000-2007 and validated with stream flow data ranging from 2008-2014. The groundwater and
management parameters are more sensitive (groundwater revap coefficient, groundwater delay,
threshold depth of water in the shallow aquifer vital for return flow to occur (GWQMN), deep aquifer
percolation fraction (RCHRG_DP)). The model goodness of fit was evaluated with coefficient of
determination and the Nash-Sutcliffe Coefficient on a monthly basis for both calibration and validation
periods and resulted 0.68 and 0.66 for calibration period and 0.64 and o.63 for validation periods
respectively. After calibration the ArcSWAT model was conducted and the result was good. From the
SWAT model the annual rainfall of the whole catchment is 1017.5mm. The recharge calculated is
found 12% of annual rainfall, surface runoff is 62% of the annual rainfall and evapotranspiration is
58% of the annual rainfall. Based on the produced hydrogeological cross sections, hydrogeological
map, and groundwater level map from deep boreholes water level and physico-chemical analysis water
types data, there is groundwater transfer from Abay basin (Gerado) to Awash basin (CombolchaKemisse). The water types at Gerado/Abay basin (KCTVW-01-19) are Na-HCO3-CO3), water type at
Combolcha/ Awash basin (KCVTW-02-19) is Ca-Na-Ca-Mg-HCO3 and water type at Kemisse/Awsh
basin (KCVTW-03-19) is Na-Ca-HCO3-SO4 which are similar but due to geo-chemical processes
evolution of compounds is identified. This indicated that there is regional groundwater flow (transfer)
from Abay (Gerado) to Awash (Combolcha-Kemisse) and from the NW-N-S or Kutaber-Desse to
Combolcha and Kemisse locally. The surface water and groundwater exchange is analyzed based on
the boreholes groundwater elevation and borkena river elevation data the positive values in each river
and borehole data indicated that there is river water seepage to aquifers and negative values indicated
groundwater flows from aquifer to river. The analysis result indicated that 41.66 % is effluent or
gaining river, 36.11 % is influent or losing and 22.22% is effluent or Influent River. This also
confirmed with the SWAT-MODFLOW model result for 7448 river cells. A further study to identify
Regional groundwater flow from Gerado/Abay to Combolcha/Awash basin and Surface water and
groundwater interaction using Isotope analysis method is recommended.
Description
Keywords
Groundwater-Surface water Interactions, ArcSWAT, SWAT-MODFLOW, Borkena Catchment.