Hydrogeological framework and occurrence of groundwater in the Ethiopian aquifers

Ayenew, Tenalem; Demlie, Molla; Wohnlich, Stefan

doi:10.1016/j.jafrearsci.2008.06.006

Cited by 132 publications

(85 citation statements)

References 16 publications

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“…Groundwater chemistry depends on a number of factors such as general geology, degree of chemical weathering of the various rock types, quality of recharge water, and inputs from sources other than waterrock interaction. Such factors and their interactions result in a complex groundwater quality (Domenico and Schwartz 1990;Edmunds et al 2003;Risacher et al 2003;Guler and Thyne 2004;Vengosh et al 2005;Boughriba et al 2006;Ayenew et al 2008;Giridharan et al 2008;Han et al 2009;Trabelsi et al 2009Trabelsi et al , 2011. In Tunisia and other similar parts worldwide, common studies have been carried out to assess the geochemical characteristics of groundwater (Subba Rao et al 1998;Graniel et al 1999;Umar and Sami Ahmad 2000;Guler et al 2002;Guler and Thyne 2004;Elango et al 2003;Krishnakumar 2004;Jeevanandam et al 2006;Ravikumar et al 2009Ravikumar et al , 2010Aghazadeh and Mogaddam 2011;Hamzaoui-Azaza et al 2011, 2012.…”

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confidence: 99%

Suitability assessment of deep groundwater for drinking and irrigation use in the Djeffara aquifers (Northern Gabes, south-eastern Tunisia)

et al. 2013

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The multilayered Djeffara aquifer system, south-eastern Tunisia, has been intensively used as a primary source to meet the growing needs of the various sectors (drinking, agricultural and industrial purposes). The analysis of groundwater chemical characteristics provides much important information useful in water resources management. Detailed knowledge of the geochemical evolution of groundwater and assessing the water quality status for special use are the main objective of any water monitoring study. An attempt has been made for the first time in this region to characterize aquifer behavior and appreciate the quality and/or the suitability of groundwater for drinking and irrigation purposes. In order to attend this objective, a total of 54 groundwater samples were collected and analyzed during January 2008 for the major cations (sodium, calcium, magnesium and potassium), anions (chloride, sulfate, bicarbonate), trace elements (boron, strontium and fluoride), and physicochemical parameters (temperature, pH, total dissolved salts and electrical conductivity). The evolution of chemical composition of groundwater from recharge areas to discharge areas is characterized by increasing sodium, chloride and sulfate contents as a result of leaching of evaporite rock. In this study, three distinct chemical trends in groundwater were identified. The major reactions responsible for the chemical evolution of groundwater in the investigated area fall into three categories: (1) calcite precipitation, (2) gypsum and halite dissolution, and (3) ion exchange. Based on the physicochemical analyses, irrigation quality parameters such as sodium absorption ratio (SAR), percentage of sodium, residual sodium carbonate, residual sodium bicarbonate, and permeability index (PI) were calculated. In addition, groundwater quality maps were elabortaed using the geographic information system to delineate spatial variation in physico-chemical characteristics of the groundwater samples. The integration of various dataset indicates that the groundwater of the Djeffara aquifers of the northern Gabes is generally very hard, brackish and high to very high saline and alkaline in nature. The water suitability for drinking and irrigation purposes was evaluated by comparing the values of different water quality parameters with World Health Organization (WHO) guideline values for drinking water. Piper trilinear diagram was constructed to identify groundwater groups where the relative major anionic and cationic concentrations are expressed in percentage of the milliequivalent per liter (meq/l), and it was demonstrated that the majority of the samples belongs to SO 4 -Cl-Ca-Na, Cl-SO 4 -Na-Ca and Na-Cl hydrochemical facies. As a whole, all the analyzed waters from this groundwater have revealed that this water is unsuitable for drinking purposes when comparing to the drinking water standards. Salinity, high electric conductivity, sodium adsorption ratio and sodium percentages indicate that most of the groundwater samples are inappropriate for ir...

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confidence: 99%

Suitability assessment of deep groundwater for drinking and irrigation use in the Djeffara aquifers (Northern Gabes, south-eastern Tunisia)

et al. 2013

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“…As hypothesized by Kebede et al (2005) and supported by Ayenew et al (2008), the groundwater could be in a perched form with high water table and flux around streams. However, such qualitative understanding is not quantified and elaborated regarding its implication on groundwater use.…”

Section: Three-dimensional Flow Analysismentioning

confidence: 76%

“…Ayenew et al (2008) and EIGS (1993) indicated two broad classifications of aquifers related to the Lake Tana basin: one at the low lying floodplain as moderately permeable intergranular aquifers, while the rest at parts of the sub-basins as medium productive aquifers with dominance of fractures. The study indicated permeability ranging predominantly from 150-250 mm/year.…”

Section: Geological and Hydrogeological Settingmentioning

confidence: 99%

Numerical modeling of the groundwater flow system of the Gumera sub‐basin in Lake Tana basin, Ethiopia

Chebud

Melesse

2009

Hydrological Processes

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Abstract:The groundwater flow contribution into Lake Tana was simulated using Gumera River sub-basin as a case study. Draining into Lake Tana, the Gumera sub-basin boundary was delineated from a 90-m Shuttle Radar Terrain Mapping (SRTM) digital elevation model (DEM) using ArcHydro tools. The sub-basin boundary served as the divide line of the groundwater flow while stream networks were used as internal drainage lines. Input parameters such as transmissivity and hydraulic conductivity were obtained from past studies and experts' knowledge. Based on the geological information of the sub-basin, unconfined subsurface flow condition was considered and simulated using MODular 3D finite difference ground-water FLOW model (MODFLOW). Analytical solutions were also used for comparison purposes. The result indicates that head contours are aligned to the streams showing their relationship as a subdued form of the surface water flow, which are dictated by the morphology of the basin. This suggested the need to account groundwater contribution of the sub-basins to Lake Tana as baseflow, and to estimate groundwater inflow from the floodplain separately. The contribution from the floodplain was estimated using a finite differences method which showed an inflow of 0Ð15 billion cubic meter (BCM) from rivers into the floodplain out of which 0Ð09 BCM is flowing out to the Lake Tana and 0Ð06 BCM stored in the aquifers of the floodplain. The stored quantity could meet irrigation demands as well as contribute to the preservation of the ecological structure and function of the area. The study suggests further research on validation of parameters through inverse modeling approaches and optimization of water allocations.

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“…The complexity of the impact of faults related to e.g. their type and orientation on the hydrogeologic system in the MER is shown by Ayenew et al (2008), Kebede et al (2008) and Furi et al (2010). In particular, based on isotopic data, Kebebe et al (2008) suggested an opposed impact of transverse faults and marginal graben on the regional groundwater flow acting as channels from the mountain region to the rift floor and barriers, respectively, in a northern part of the MER.…”

Section: Introductionmentioning

confidence: 99%

Characterizing regional groundwater flow in the Ethiopian Rift: A multimodel approach applied to Gidabo River Basin

Mechal¹,

Birk²,

Winkler³

et al. 2016

AJES

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Being located in the tectonically active Ethiopian Rift, the hydrogeology of the Gidabo River Basin is complex due to the disruption of lithologies by faults and the variability and lateral discontinuity of the aquifers. Hydrogeochemical and isotopic data suggest that the aquifers within the rift floor receive a relevant contribution of groundwater recharged in the highland. However, the incomplete knowledge about the aquifer properties, the hydraulic behavior of the faults, and the boundary conditions cause uncertainties in this conceptual hydrogeological model. To account for these uncertainties fourteen different numerical models with a stepwise increase from 7 to 40 adjustable parameters were developed, calibrated against the same hydraulic head observations, and ranked according to the Akaike information criteria (AIC and AICc) and Bayesian information criterion (BIC). Based on the information criteria five plausible models were identified, all of which were successfully verified against the river baseflow. The highest likelihood is attributed to a model with eleven adjustable parameters that does not explicitly account for the fault zones; other plausible models considering faults as semi-barriers achieve a slight improvement in model fit but have lower likelihood due to the increased number of calibration parameters. Thus, the effect of faults on groundwater flow needs further investigation, particularly at a local scale.On a regional scale, the hydraulic head distributions of the plausible models agree reasonably well with the equipotential map interpolated from well observations. The estimated transmissivity values range between 30 m 2 / day and 1350 m 2 / day and generally increase from the mountains towards the rift floor. The water budget shows that 75 % of the groundwater recharge supplies baseflow to the rivers. The remaining water infiltrates to the deeper aquifers where less than 1 % is abstracted by pumping wells and the rest flows towards Lake Abaya. Within the rift floor, the majority of inflow to the aquifers is from direct recharge; nevertheless, 35 % of the inflow is contributed by mountain block recharge (lateral groundwater flow from the escarpment and highland). The results of this study strongly advocate the idea to incorporate alternative plausible models instead of relying on single models in the practice of groundwater modeling especially in areas of complex hydrogeology and limited data availability.Die Hydrogeologie des im tektonisch aktiven Äthiopischen Graben gelegenen Gidabo-Flusseinzugsgebiets ist aufgrund der störungs bedingten Unterbrechungen der Lithologien sowie der Variabilität und lateralen Diskontinuität der Aquifere komplex. Hydro geochemische und Isotopen-Daten weisen darauf hin, dass in den Aquiferen der Grabensohle ein relevanter Beitrag von Grundwässern vorliegt, die im Hochland neugebildet werden. Die unvollständige Kenntnis der Aquifereigenschaften, der hydraulischen Wirkung der Störungen und der Randbedingungen führen jedoch zu Unsicherheiten in diesem ko...

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Hydrogeological framework and occurrence of groundwater in the Ethiopian aquifers

Cited by 132 publications

References 16 publications

Suitability assessment of deep groundwater for drinking and irrigation use in the Djeffara aquifers (Northern Gabes, south-eastern Tunisia)

Suitability assessment of deep groundwater for drinking and irrigation use in the Djeffara aquifers (Northern Gabes, south-eastern Tunisia)

Numerical modeling of the groundwater flow system of the Gumera sub‐basin in Lake Tana basin, Ethiopia

Characterizing regional groundwater flow in the Ethiopian Rift: A multimodel approach applied to Gidabo River Basin

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