Inter-Basin Groundwater Transfer and Multiple Approach Recharge Estimation of the Upper Awash Aquifer System

Abstract

Multiple approaches have been used to estimate groundwater recharge in the Upper Awash river basin. The amount of recharge reaching the Upper Awash aquifer system from the Blue Nile sub-basins is also estimated. Water Balance, Chloride Mass Balance and HYDRUS 1D infiltration model are used to estimate recharge. A total of 29 sites were selected for the HYDRUS 1D multiple "at point" recharge simulations. Base Flow Separation (BFS) methods, using both River Analysis Package software Version 3.0.3 and Excel-based Time Plot program are also used as a proxy for recharge. Besides, overlay analysis in Processing MODFLOW, ArcGIS, and SURFER environments has been done to thoroughly consider spatial heterogeneity between any two point estimates and appreciate the effect of lineament density, topography, slope and major urbanized land on pattern of spatial distribution of recharge. Because of differences inherent in the assumptions and datasets used, the various methods employed give wide range of differences in recharge estimates. Recharge estimated for the Upper Awash basin ranges from 51.5 mm/year to 157 mm/year and for the two southern left-bank sub-basins of the Middle Blue Nile basin (Mugher and Jema) ranges from 86 mm/year to 239 mm/year. Consequently, annual average volumetric recharge in the Upper Awash and annual groundwater flux from portion of the Blue Nile sub basins to the Upper Awash aquifer system are estimated to be 983 Mm 3 and 365 Mm 3 respectively. The significant flux joining the Upper Awash groundwater system from part of the Middle Blue Nile basin, which is almost 37% of the total annual recharge to the Upper Awash basin makes this part of the Middle Blue Nile basin an important recharge zone for the Upper Awash groundwater. Estimating recharge using integrated approaches was found to be useful to identify range of plausible recharge rates in the two basins. Besides, the new methodological approach of superimposing recharge governing factors on interpolation of point 77recharge estimates helps to produce physical based spatial distribution of recharge.

Effects of climate change on water resources in the upper Blue Nile Basin of Ethiopia

“…The Muger sub-basin is located to the southeast of the Abay Basin. Studies ( Azagegn et al, 2015 ; Berehanu et al, 2017 ) show that the aquifer system is connected to the upper Awash basin, which drains towards the southeast. This singularity combined with a lack of data makes calibration of the Muger basin very difficult.…”

Spatial and Temporal Variability in Hydrological Responses of the Upper Blue Nile basin, Ethiopia

“…Annual precipitation of only 1200 mm is distributed over two rainy seasons, so we used the cropping calendar from the eastern part of the Blue Nile basin. Recent studies showed that the aquifer system of the Muger sub-basin has a hydraulic connection with the aquifer system of the Upper Awash basin, a basin which does not drain into the Blue Nile [37,38].…”

“…In the Muger sub-basin, this results from a very low measured base flow during the dry season, which could not be simulated properly. An explanation for this discrepancy is the aquifer system of the Muger sub-basin, which has a connection with the aquifer system of the Upper Awash basin [37,38]. These water losses were not included in the model setup.…”

Insights From a Multi‐Method Recharge Estimation Comparison Study

“…Following recommended approaches, for example, Scanlon et al (2002) and Healy (2010), several techniques were initially applied, and it was found that they gave a wide range of recharge estimates. This is commonly reported in the literature, for example, Berehanu et al (2017); Afrifa et al (2017), although it is less common for studies to report investigation of the reasons for the range of values. Some previous studies, typically using at most three to five recharge estimation techniques, have considered the basis for differing recharge estimates in more detail, and concluded that the range of recharge estimates contains useful information to inform further understanding of the conceptual model (e.g., Coes et al 2007;King et al 2017).…”