Your search found 7 records
1 Ebrahim, Girma Yimer; Jonoski, A.; Al-Maktoumi, A.; Ahmed, M.; Mynett, A. 2016. Simulation-optimization approach for evaluating the feasibility of managed aquifer recharge in the Samail Lower Catchment, Oman. Journal of Water Resources Planning and Management, 142(2):1-16. [doi: https://doi.org/10.1061/(ASCE)WR.1943-5452.0000588]
Aquifers ; Groundwater recharge ; Groundwater management ; Water levels ; Water budget ; Water supply ; Catchment areas ; Dams ; Mathematical models ; Simulation models ; Algorithms ; Sensitivity analysis ; Hydraulic conductivity ; Calibration ; Salt water intrusion / Oman / Samail Lower Catchment
(Location: IWMI HQ Call no: e-copy only Record No: H047227)
(16.33 MB)
This article presents a simulation-optimization approach for evaluating the feasibility of managed aquifer recharge (MAR) in the Samail Lower Catchment, Oman. The objective is to provide a maximum recharge and extraction rate through MAR in an annual cycle of two successive injection and recovery periods, while meeting operational and system constraints such as water level, gradient, and travel time. Three groundwater management problems were solved by coupling a simulation model with successive linear programming (SLP) and the nondominated sorting genetic algorithm (NSGA-II) multiobjective genetic algorithm. Sensitivity analysis was also completed to examine the overall response of the simulation-optimization results to changes in hydraulic conductivities and maximum injection rates. Results using the SLP algorithm showed that the total volume of injected water for 4 months of injection without recovery is as high as 8 × 106 m3, and the total recovered volume of water for 4months injection and 8 months recovery is approximately 5.3 × 106 m3, giving a total recovery efficiency of approximately 66%. For the same setup the NSGA-II algorithm derived the entire nondominated front of solutions for two conflicting objectives: maximizing recovery rate and maximizing minimum groundwater head close to the sea (for preventing seawater intrusion). This algorithm includes travel time constraints directly in the optimization process. In conclusion, the proposed approach provides a cost-effective means to evaluate MAR in a coastal aquifer.
2 Ebrahim, Girma Yimer; Villholth, Karen Grothe. 2015. Assessment of groundwater availability from recession flows and instream flow requirements of rivers in South Africa. Gezina, Pretoria, South Africa: Water Research Commission. 60p. (Water Research Commission Report KV 339/15)
Groundwater recharge ; Groundwater extraction ; Water storage ; Water availability ; Water allocation ; Water requirements ; Stream flow ; Flow discharge ; Rivers ; Catchment areas ; Drainage ; Environmental flows ; Rain ; Multiple use ; Ecological factors ; Aquifers / South Africa
(Location: IWMI HQ Call no: e-copy only Record No: H047542)
(4.38 MB)
Groundwater is an important resource for multiple uses in South Africa. However, setting limits to its sustainable abstraction while assuring basic human needs is a must. Due to prevalent data scarcity related to groundwater replenishment, which is the traditional basis for estimating groundwater availability, the present report presents a novel method for determining allocatable groundwater in quaternary catchment through information on streamflows. Using established methodologies for assessing baseflows, recession flows, and instream ecological flow requirements, the methodology develops a combined stepwise methodology to determine annual groundwater storage volumes in the catchments using linear reservoir theory, essentially linking low flows proportionally to upstream groundwater storages. The approach was trialled for twenty-one perennial and relatively undisturbed quaternary catchments with long-term and good streamflow records. Using the Desktop Reserve Model to estimate instream ecological flow requirements of the streams and equating these with ecological groundwater reserve, excess baseflows were converted into groundwater storages on an annual basis. Results show that groundwater development potential exists in nineteen of the catchments, with upper limits to allocatable groundwater volumes ranging from 0.01 to 1.58 MCM/yr over the catchments. With a secured availability of these volumes 75% of the years, variability between years is assumed to be manageable. A significant (R2 = 0.86) correlation between baseflow index and the drainage time scale for the catchments underscored the physical basis of the methodology and also enables the reduction of the procedure by one step, omitting recession flow analysis. The method serves as an important complementary tool for the assessment of the groundwater part of the Reserve and the groundwater directed measures.
3 Cuthbert, M. O.; Taylor, R. G.; Favreau, G.; Todd, M. C.; Shamsudduha, M.; Villholth, Karen G.; MacDonald, A. M.; Scanlon, B. R.; Kotchoni, D. O. V.; Vouillamoz, J.-M.; Lawson, F. M. A.; Adjomayi, P. A.; Kashaigili, J.; Seddon, D.; Sorensen, J. P. R.; Ebrahim, Girma Yimer; Owor, M.; Nyenje, P. M.; Nazoumou, Y.; Goni, I.; Ousmane, B. I.; Sibanda, T.; Ascott, M. J.; Macdonald, D. M. J.; Agyekum, W.; Koussoube, Y.; Wanke, H.; Kim, H.; Wada, Y.; Lo, M.-H.; Oki, T.; Kukuric, N. 2019. Observed controls on resilience of groundwater to climate variability in sub-Saharan Africa. Nature, 572(7768):230-234. [doi: https://doi.org/10.1038/s41586-019-1441-7]
Groundwater recharge ; Climate change ; Resilience ; Groundwater table ; Observation ; Precipitation ; Hydrology ; Hydrography ; Models ; Arid zones ; Rain / Africa South of Sahara / Benin / Uganda / United Republic of Tanzania / Zimbabwe / South Africa / Namibia / Niger / Ghana / Burkina Faso
(Location: IWMI HQ Call no: e-copy only Record No: H049316)
https://www.nature.com/articles/s41586-019-1441-7.epdf?author_access_token=UgizrPwmrGzlbL33bjbvQdRgN0jAjWel9jnR3ZoTv0M3C122Ih9FQbr0PbeOlDAX9EZlbSwXsaUcJ-Vq-8EelgPfWJQTdVE-2_3g7yypNR4C-qTOMe7Ux1weufjBdaT9SyaKgJjfKYgJ2fqsjIRLng%3D%3D
https://vlibrary.iwmi.org/pdf/H049316.pdf
https://vlibrary.iwmi.org/pdf/H049316.pdf
(7.21 MB)
Groundwater in sub-Saharan Africa supports livelihoods and poverty alleviation1,2 , maintains vital ecosystems, and strongly influences terrestrial water and energy budgets3 . Yet the hydrological processes that govern groundwater recharge and sustainability—and their sensitivity to climatic variability—are poorly constrained4,5 . Given the absence of firm observational constraints, it remains to be seen whether model-based projections of decreased water resources in dry parts of the region4 are justified. Here we show, through analysis of multidecadal groundwater hydrographs across sub-Saharan Africa, that levels of aridity dictate the predominant recharge processes, whereas local hydrogeology influences the type and sensitivity of precipitation–recharge relationships. Recharge in some humid locations varies by as little as five per cent (by coefficient of variation) across a wide range of annual precipitation values. Other regions, by contrast, show roughly linear precipitation–recharge relationships, with precipitation thresholds (of roughly ten millimetres or less per day) governing the initiation of recharge. These thresholds tend to rise as aridity increases, and recharge in drylands is more episodic and increasingly dominated by focused recharge through losses from ephemeral overland flows. Extreme annual recharge is commonly associated with intense rainfall and flooding events, themselves often driven by large-scale climate controls. Intense precipitation, even during years of lower overall precipitation, produces some of the largest years of recharge in some dry subtropical locations. Our results therefore challenge the ‘high certainty’ consensus regarding decreasing water resources4 in such regions of sub-Saharan Africa. The potential resilience of groundwater to climate variability in many areas that is revealed by these precipitation–recharge relationships is essential for informing reliable predictions of climate-change impacts and adaptation strategies.
4 Nhamo, Luxon; Ebrahim, Girma Yimer; Mabhaudhi, T.; Mpandeli, S.; Magombeyi, Manuel; Chitakira, M.; Magidi, J.; Sibanda, M. 2020. An assessment of groundwater use in irrigated agriculture using multi-spectral remote sensing. Physics and Chemistry of the Earth, 115:102810. [doi: https://doi.org/10.1016/j.pce.2019.102810]
Groundwater assessment ; Crop water use ; Irrigated farming ; Remote sensing ; Climate change ; Resilience ; Water management ; Water productivity ; Evapotranspiration ; Estimation ; Irrigated land ; Satellite imagery ; Dry season / South Africa / Limpopo / Venda-Gazankulu
(Location: IWMI HQ Call no: e-copy only Record No: H049420)
(2.23 MB)
Declining water resources in dry regions requires sustainable groundwater management as trends indicate increasing groundwater use, but without accountability. The sustainability of groundwater is uncertain, as little is known about its extent and availability, a challenge that requires a quantitative assessment of its current use. This study assessed groundwater use for irrigated agriculture in the Venda-Gazankulu area of Limpopo Province in South Africa using crop evapotranspiration and irrigated crop area derived from the normalised difference vegetation index (NDVI). Evapotranspiration data was derived from the Water Productivity through Open access of Remotely sensed Actual Evapotranspiration and Interception (WaPOR) dataset (250 m resolution), and irrigated areas were characterised using dry season NDVI data derived from Landsat 8. Field surveys were conducted for four years to assess accuracy and for post-classification correction. Daily ET for the dry season (May to September) was developed from the actual ET for the irrigated areas. The irrigated areas were overlaid on the ET map to calculate ET for only irrigated land parcels. Groundwater use during the 2015 dry period was 3627.49 billion m3 and the irrigated area during the same period was 26% of cultivated land. About 82 435 ha of cultivated area was irrigated using 44 million m3 /ha of water, compared to 186.93 million m3 /ha on a rainfed area of 237 847 ha. Groundwater management is essential for enhancing resilience in arid regions in the advent of water scarcity.
5 Taye, Meron Teferi; Ebrahim, Girma Yimer; Nigussie, Likimyelesh; Hagos, Fitsum; Uhlenbrook, Stefan; Schmitter, Petra. 2022. Integrated water availability modelling to assess sustainable agricultural intensification options in the Meki Catchment, Central Rift Valley, Ethiopia. Hydrological Sciences Journal, 67(15):2271-2293. [doi: https://doi.org/10.1080/02626667.2022.2138403]
Water availability ; Modelling ; Sustainable intensification ; Sustainable agriculture ; Catchment areas ; Surface water ; Groundwater ; Water budget ; Water balance ; Climate change ; Rain ; Temperature ; Forecasting ; Land use ; Shallow water ; Wells ; Crop water use ; Water requirements ; Water yield ; Small-scale irrigation ; Communities / Ethiopia / Central Rift Valley / Meki Catchment
(Location: IWMI HQ Call no: e-copy only Record No: H051557)
https://www.tandfonline.com/doi/pdf/10.1080/02626667.2022.2138403?needAccess=true
https://vlibrary.iwmi.org/pdf/H051557.pdf
https://vlibrary.iwmi.org/pdf/H051557.pdf
(16.50 MB) (16.5 MB)
The Meki catchment in the Central Rift Valley basin of Ethiopia is currently experiencing irrigation expansion and water scarcity challenges. The objective of this study is to understand the basin’s current and future water availability for agricultural intensification. This was done by simulating scenarios through an integrated SWAT-MODFLOW model to assess the water balance. The scenarios were co-developed with communities who expressed their aspirations for agricultural intensification in conjunction with projected climate change. The results show that with the present land use and climate, the catchment is already water stressed and communities cannot meet their irrigation water demand, particularly in the first irrigation season (October–January). However, in the second irrigation season (February–May) water resource availability is better and increasing irrigated area by 50% from the present extent is possible. With a climate change scenario that favours more rainfall and shallow groundwater use, agricultural intensification is feasible to some extent.
6 Assefa, T. T.; Taye, Meron Teferi; Ebrahim, Girma Yimer; Lautze, Jonathan; Seid, Abdulkarim Hussein. 2023. Water storages in Tana-Beles Sub-basin of Ethiopia: what do we know, and where should we go? SN Applied Sciences, 5:275. [doi: https://doi.org/10.1007/s42452-023-05499-1]
Water storage ; Water quality ; Energy ; Food security ; Ecosystems ; Nexus approaches ; Biodiversity ; Wetlands ; Reservoirs ; Groundwater ; Ponds ; Agricultural development ; Land degradation ; Sedimentation ; Climate change ; Population growth ; Economic growth ; Systematic reviews / Ethiopia / Tana-Beles Sub-Basin / Lake Tana
(Location: IWMI HQ Call no: e-copy only Record No: H052315)
https://link.springer.com/content/pdf/10.1007/s42452-023-05499-1.pdf?pdf=button
https://vlibrary.iwmi.org/pdf/H052315.pdf
https://vlibrary.iwmi.org/pdf/H052315.pdf
(2.28 MB) (2.28 MB)
The Tana-Beles sub-basin, a strategic economic growth corridor in Ethiopia, relies on water storage to provide a suite of key services to agriculture, drinking water supply, energy, and ecosystems. While there are a range of storage options (e.g., from large dams to subsurface aquifers) that can be utilized to provide these services, a systematic stock-take of literature on water storage in the Tana-Beles has not been undertaken. This knowledge gap constrains the identification of the relative contribution of different storage types in the Tana-Beles. Accordingly, in this study, we conducted a systematic review of literature on the surface and sub-surface storages to examine key issues of the different storage types and their linkages in the Tana-Beles sub-basin. Peer-reviewed and grey publications from various databases were considered for the systematic review. The results indicate that literature in the Tana-Beles sub-basin is more focused on natural storage like wetlands and Lake Tana than built storage types like human-made reservoirs. Overall, the analysis revealed three key points. First, storage volume and water quality in those storages are declining. Second, the causal factors for storage loss and water quality deterioration are agricultural expansion, land degradation, sedimentation, and increasing water withdrawals. Third, the storage gap will increase because of climate change, population, and economic growth while current management options are fragmented. Therefore, the need for more integrated nexus approaches is paramount to optimize storage resources in water, food, energy, and ecosystems in light of population-driven growth in demand and the ongoing global climate crisis.
7 Mukuyu, P.; Nyambe, N.; Magombeyi, Manuel Simba; Ebrahim, Girma Yimer. 2024. Polycentric groundwater governance: insights from the Kavango-Zambezi Transfrontier Conservation Area. International Journal of the Commons, 18(1):322-336. [doi: https://doi.org/10.5334/ijc.1336]
Groundwater ; Water governance ; Transboundary waters ; Freshwater ; Biodiversity conservation ; Aquifers / Southern Africa / Zambia / Angola / Kavango-Zambezi Transfrontier Conservation Area
(Location: IWMI HQ Call no: e-copy only Record No: H052705)
https://storage.googleapis.com/jnl-up-j-ijc-files/journals/1/articles/1336/661d0f6761216.pdf
https://vlibrary.iwmi.org/pdf/H052705.pdf
https://vlibrary.iwmi.org/pdf/H052705.pdf
(1.25 MB) (1.25 MB)
This paper analyses groundwater governance within a transfrontier conservation landscape. Given the current heightened interest in groundwater development, it is imperative that more thought be given to how groundwater resources can best be managed in different contexts for multiple uses and users. Transfrontier conservation areas are areas of vast biological diversity whose functioning and ecosystem integrity depends on the availability of water to sustain ecosystems and subsequently derive economic benefit. Further, climate vulnerable rural communities depend on and form an important part of this landscape. The work highlighted in this paper is based on a study conducted in parts of the Kavango-Zambezi Transfrontier Conservation Area (TFCA), the largest TFCA in the world. Climate induced challenges such as droughts and general poor land use planning have resulted in threats to long term sustainability of freshwater ecosystems and increased incidences of human-wildlife conflicts over limited water resources. Effective groundwater governance can potentially provide pathways for alleviating these challenges.
Building on the theoretical fundamentals of polycentric governance, this paper analyses the case of the KAZA TFCA in which multiple levels of governance exist. The paper discusses how to achieve coordination and accountability within a shared landscape to foster sustainable use and management of groundwater. Groundwater within a TFCA context has the potential to alleviate human-wildlife conflict over freshwater, support groundwater dependant ecosystems and sustain smallholder agriculture for the rural communities. Understanding this role of groundwater adds to the framing of freshwater governance and conservation efforts within a TFCA and the identification and development of platforms for the integrated management of groundwater. Bringing together freshwater and conservation institutions in a multi-country context towards integrated water resource management is an initial and novel attempt which forms the foundation for achieving optimal governance approaches in the commons.
Building on the theoretical fundamentals of polycentric governance, this paper analyses the case of the KAZA TFCA in which multiple levels of governance exist. The paper discusses how to achieve coordination and accountability within a shared landscape to foster sustainable use and management of groundwater. Groundwater within a TFCA context has the potential to alleviate human-wildlife conflict over freshwater, support groundwater dependant ecosystems and sustain smallholder agriculture for the rural communities. Understanding this role of groundwater adds to the framing of freshwater governance and conservation efforts within a TFCA and the identification and development of platforms for the integrated management of groundwater. Bringing together freshwater and conservation institutions in a multi-country context towards integrated water resource management is an initial and novel attempt which forms the foundation for achieving optimal governance approaches in the commons.
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