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This work investigates the applicability of an analytical method for quick assessments of the long-term morphological effects of different dam operations on downstream river reaches with the idea to apply the method in feasibility studies to identify the least morphologic-impacting operation scenario. The Ribb River (Ethiopia) is used as a study case. The analytical method estimates the idealized, new equilibrium of the river bed profile without considering the duration of the morphological evolution. We apply the analytical method distinguishing sand-bed from gravel-bed reaches. The outcome of the analytical method is compared to that of a calibrated one-dimensional river morphology computer model. The analytical method overestimated the morphological changes compared to the one-dimensional model. By establishing the upper limits of the impact, the analytical method identifies a theoretical maximum river bed degradation near the base of the dam. If all sediment is trapped in the reservoir, the method allows distinguishing the effects of different dam operation scenarios, but only for gravel-bed river reaches. However, the method can also be applicable for sand-bed reaches if there is sediment input from the upper reaches. Further research works should be done to validate both methods if they indeed allow to detect the least impacting scenario, considering that data showing the effects of long-term dam operations on the downstream river reaches are lacking.
Chalachew A. Mulatu; Alessandra Crosato; Eddy J. Langendoen; Michael M. Moges; Michael E. McClain. Long-term effects of dam operations for water supply to irrigation on downstream river reaches. The case of the Ribb River, Ethiopia. International Journal of River Basin Management 2020, 1 -15.
AMA StyleChalachew A. Mulatu, Alessandra Crosato, Eddy J. Langendoen, Michael M. Moges, Michael E. McClain. Long-term effects of dam operations for water supply to irrigation on downstream river reaches. The case of the Ribb River, Ethiopia. International Journal of River Basin Management. 2020; ():1-15.
Chicago/Turabian StyleChalachew A. Mulatu; Alessandra Crosato; Eddy J. Langendoen; Michael M. Moges; Michael E. McClain. 2020. "Long-term effects of dam operations for water supply to irrigation on downstream river reaches. The case of the Ribb River, Ethiopia." International Journal of River Basin Management , no. : 1-15.
The sustainable development of water resources includes retaining some amount of the natural flow regime in water bodies to protect and maintain aquatic ecosystem health and the human livelihoods and wellbeing dependent upon them. Although assessment of environmental flows is now occurring globally, limited studies have been carried out in the Ethiopian highlands, especially studies to understand flow-ecological response relationships. This paper establishes a hydrological foundation of Gumara River from an ecological perspective. The data analysis followed three steps: first, determination of the current flow regime—flow indices and ecologically relevant flow regime; second, naturalization of the current flow regime—looking at how flow regime is changing; and, finally, an initial exploration of flow linkages with ecological processes. Flow data of Gumara River from 1973 to 2018 are used for the analysis. Monthly low flow occurred from December to June; the lowest being in March, with a median flow of 4.0 m3 s−1. Monthly high flow occurred from July to November; the highest being in August, with a median flow of 236 m3 s−1. 1-Day low flows decreased from 1.55 m3 s−1 in 1973 to 0.16 m3 s−1 in 2018, and 90-Day (seasonal) low flow decreased from 4.9 m3 s−1 in 1973 to 2.04 m3 s−1 in 2018. The Mann–Kendall trend test indicated that the decrease in low flow was significant for both durations at α = 0.05. A similar trend is indicated for both durations of high flow. The decrease in both low flows and high flows is attributed to the expansion of pump irrigation by 29 km2 and expansion of plantations, which resulted in an increase of NDVI from 0.25 in 2000 to 0.29 in 2019. In addition, an analysis of environmental flow components revealed that only four “large floods” appeared in the last 46 years; no “large flood” occurred after 1988. Lacking “large floods” which inundate floodplain wetlands has resulted in early disconnection of floodplain wetlands from the river and the lake; which has impacts on breeding and nursery habitat shrinkage for migratory fish species in Lake Tana. On the other hand, the extreme decrease in “low flow” components has impacts on predators, reducing their mobility and ability to access prey concentrated in smaller pools. These results serve as the hydrological foundation for continued studies in the Gumara catchment, with the eventual goal of quantifying environmental flow requirements.
Wubneh B. Abebe; Seifu A. Tilahun; Michael M. Moges; Ayalew Wondie; Minychl G. Derseh; Teshager A. Nigatu; Demesew A. Mhiret; Tammo S. Steenhuis; Marc Van Camp; Kristine Walraevens; Michael E. McClain. Hydrological Foundation as a Basis for a Holistic Environmental Flow Assessment of Tropical Highland Rivers in Ethiopia. Water 2020, 12, 547 .
AMA StyleWubneh B. Abebe, Seifu A. Tilahun, Michael M. Moges, Ayalew Wondie, Minychl G. Derseh, Teshager A. Nigatu, Demesew A. Mhiret, Tammo S. Steenhuis, Marc Van Camp, Kristine Walraevens, Michael E. McClain. Hydrological Foundation as a Basis for a Holistic Environmental Flow Assessment of Tropical Highland Rivers in Ethiopia. Water. 2020; 12 (2):547.
Chicago/Turabian StyleWubneh B. Abebe; Seifu A. Tilahun; Michael M. Moges; Ayalew Wondie; Minychl G. Derseh; Teshager A. Nigatu; Demesew A. Mhiret; Tammo S. Steenhuis; Marc Van Camp; Kristine Walraevens; Michael E. McClain. 2020. "Hydrological Foundation as a Basis for a Holistic Environmental Flow Assessment of Tropical Highland Rivers in Ethiopia." Water 12, no. 2: 547.
The spatio-temporal characteristic of rainfall in the Beles Basin of Ethiopia is poorly understood, mainly due to lack of data. With recent advances in remote sensing, satellite derived rainfall products have become alternative sources of rainfall data for such poorly gauged areas. The objectives of this study were: (i) to evaluate a multi-source rainfall product (Climate Hazards Group Infrared Precipitation with Stations: CHIRPS) for the Beles Basin using gauge measurements and (ii) to assess the spatial and temporal variability of rainfall across the basin using validated CHIRPS data for the period 1981–2017. Categorical and continuous validation statistics were used to evaluate the performance, and time-space variability of rainfall was analyzed using GIS operations and statistical methods. Results showed a slight overestimation of rainfall occurrence by CHIRPS for the lowland region and underestimation for the highland region. CHIRPS underestimated the proportion of light daily rainfall events and overestimated the proportion of high intensity daily rainfall events. CHIRPS rainfall amount estimates were better in highland regions than in lowland regions, and became more accurate as the duration of the integration time increases from days to months. The annual spatio-temporal analysis result using CHIRPS revealed: a mean annual rainfall of the basin is 1490 mm (1050–2090 mm), a 50 mm increase of mean annual rainfall per 100 m elevation rise, periodical and persistent drought occurrence every 8 to 10 years, a significant increasing trend of rainfall (~5 mm year−1), high rainfall variability observed at the lowland and drier parts of the basin and high coefficient of variation of monthly rainfall in March and April (revealing occurrence of bimodal rainfall characteristics). This study shows that the performance of CHIRPS product can vary spatially within a small basin level, and CHIRPS can help for better decision making in poorly gauged areas by giving an option to understand the space-time variability of rainfall characteristics.
Ashebir Sewale Belay; Ayele Almaw Fenta; Alemu Yenehun; Fenta Nigate; Seifu A. Tilahun; Michael Mehari Moges; Mekete Dessie; Enyew Adgo; Jan Nyssen; Margaret Chen; Ann Van Griensven; Kristine Walraevens. Evaluation and Application of Multi-Source Satellite Rainfall Product CHIRPS to Assess Spatio-Temporal Rainfall Variability on Data-Sparse Western Margins of Ethiopian Highlands. Remote Sensing 2019, 11, 2688 .
AMA StyleAshebir Sewale Belay, Ayele Almaw Fenta, Alemu Yenehun, Fenta Nigate, Seifu A. Tilahun, Michael Mehari Moges, Mekete Dessie, Enyew Adgo, Jan Nyssen, Margaret Chen, Ann Van Griensven, Kristine Walraevens. Evaluation and Application of Multi-Source Satellite Rainfall Product CHIRPS to Assess Spatio-Temporal Rainfall Variability on Data-Sparse Western Margins of Ethiopian Highlands. Remote Sensing. 2019; 11 (22):2688.
Chicago/Turabian StyleAshebir Sewale Belay; Ayele Almaw Fenta; Alemu Yenehun; Fenta Nigate; Seifu A. Tilahun; Michael Mehari Moges; Mekete Dessie; Enyew Adgo; Jan Nyssen; Margaret Chen; Ann Van Griensven; Kristine Walraevens. 2019. "Evaluation and Application of Multi-Source Satellite Rainfall Product CHIRPS to Assess Spatio-Temporal Rainfall Variability on Data-Sparse Western Margins of Ethiopian Highlands." Remote Sensing 11, no. 22: 2688.
Planning and decision making for new irrigation development projects requires the systematic assessment of irrigable land together with available water resources. The data required are usually not available in developing countries, and therefore a method was developed for quantifying surface water resources and potentially irrigable land in ungauged watersheds in the Upper Blue Nile Basin using Soil and Water Assessment Tool (SWAT) model and Multi-Criterion Decision Evaluation (MCDE). The method was tested using the Lah river basin in the Jabitenan district and then applied in the whole area, including ungauged areas. In MCDE, soil type, slope, land use, and river proximity were considered. Onion, Cabbage and Tomato were grown on the identified irrigable areas. The predicted monthly stream discharge agreed well with observed values, with Nash and Sutcliffe efficiencies of 0.87 during calibration and 0.68 for validation. The SWAT model calibrated parameters from the gauged catchment were used to simulate the discharge of the ungauged catchments. The potential irrigable land was determined in Jabitenan woreda and included the Rivers like Birr, Tikurwuha, Gunagun, Leza Lah, Geray, Arara, Debolah, Guysa, and Silala, with an area of 460 km2. By evaluating gross irrigation demand of irrigable land with available flow in rivers (both observed and simulated), the actual surface irrigation potential was 47 km2. The main limitation for surface irrigation in all districts was the available water and not the land suitable for irrigation. Therefore, the study suggests that in order to irrigate a greater portion of the irrigable land, water should be stored during the monsoon rain phase for use in the last part of the dry phase.
Getenet Nigussie; Mamaru A. Moges; Michael M. Moges; Tammo S. Steenhuis. Assessment of Suitable Land for Surface Irrigation in Ungauged Catchments: Blue Nile Basin, Ethiopia. Water 2019, 11, 1465 .
AMA StyleGetenet Nigussie, Mamaru A. Moges, Michael M. Moges, Tammo S. Steenhuis. Assessment of Suitable Land for Surface Irrigation in Ungauged Catchments: Blue Nile Basin, Ethiopia. Water. 2019; 11 (7):1465.
Chicago/Turabian StyleGetenet Nigussie; Mamaru A. Moges; Michael M. Moges; Tammo S. Steenhuis. 2019. "Assessment of Suitable Land for Surface Irrigation in Ungauged Catchments: Blue Nile Basin, Ethiopia." Water 11, no. 7: 1465.
This study was conducted to investigate technical and socio-political attributes that lead to the underperformance of two selected irrigation schemes (Shina and Bebeks) in the Lake Tana floodplains, Ethiopia. Irrigation application efficiency (AE) at nine experimental fields showed a wide range, from 20 to 80%, but was mostly between 40 and 60%. Irrigation water-use efficiency (IWUE) varied from 1.9 to 7.2 kg m−3 for onion and 0.9 to 1.2 kg m−3 for maize. The lined and earthen canal conveyance losses in Bebeks were 0.037 and 0.047 l s−1 m−1, whereas in Shina they were 0.033 and 0.044 l s−1 m−1, respectively. The overall consumed ratio (OCR) of water was 0.58 for Bebeks and varied from 0.73 to 1.2 in Shina. Both schemes are performing below the standard based on technical performance indicators. Irrigation water user associations (WUAs) were not implemented, but irrigation committees (ICs), composed of local political leaders, are managing both schemes. Canal and reservoir sedimentation from erosion of upstream catchment areas during the rainy season was the major problem.
Abebech Abera; Niko E.C. Verhoest; Seifu A. Tilahun; Tena Alamirew; Enyew Adgo; Michael M. Moges; Jan Nyssen. Performance of small-scale irrigation schemes in Lake Tana Basin of Ethiopia: technical and socio-political attributes. Physical Geography 2018, 40, 227 -251.
AMA StyleAbebech Abera, Niko E.C. Verhoest, Seifu A. Tilahun, Tena Alamirew, Enyew Adgo, Michael M. Moges, Jan Nyssen. Performance of small-scale irrigation schemes in Lake Tana Basin of Ethiopia: technical and socio-political attributes. Physical Geography. 2018; 40 (3):227-251.
Chicago/Turabian StyleAbebech Abera; Niko E.C. Verhoest; Seifu A. Tilahun; Tena Alamirew; Enyew Adgo; Michael M. Moges; Jan Nyssen. 2018. "Performance of small-scale irrigation schemes in Lake Tana Basin of Ethiopia: technical and socio-political attributes." Physical Geography 40, no. 3: 227-251.
Bathymetric and sedimentation surveys were conducted with a sonar‐based depth gauge system in two small reservoirs (Selamko and Shina) in the data‐scarce upper Blue Nile Basin, Ethiopia. Bathymetric survey data were merged within geographic information system (GIS) software to provide detailed visualization and analyses of current depths. Preimpoundment topographic information was obtained from dam owners and designers. Bathymetric differencing was used to investigate and quantify the distribution and estimate volumes of deposited sediment, long‐term average annual sediment fluxes and remaining water storage capacity. Calculated long‐term average sediment accumulation rates were used to estimate remaining lifetimes of each reservoir. Results from the depth sonar surveys and GIS analyses suggest a projected lifetime of ~7 years for Shina Reservoir, compared to a projected lifetime of ~22 years for Selamko Reservoir. It also indicated the annual average sedimentation rate for both reservoirs was greater than the global average of one per cent (1.67% for Shina Reservoir; 2.295% for Selamko Reservoir). The specific sediment yield (SSY) is relatively larger for both watersheds (2,499 and 4,333.6 t km−2 year−1 for Shina and Selamko, respectively) indicating the watersheds are degraded by any global standard. The Revised Universal Soil Loss Equation (RUSLE) model‐generated erosion magnitude was only slightly larger from the watersheds of both reservoirs, compared to the bathymetric estimates. These data and analyses also provide a baseline relevant to understanding sedimentation processes and are necessary for developing long‐term management plans for these reservoirs and their watersheds.
Michael M. Moges; Dawit Abay; Hailu Engidayehu. Investigating reservoir sedimentation and its implications to watershed sediment yield: The case of two small dams in data-scarce upper Blue Nile Basin, Ethiopia. Lakes & Reservoirs: Research & Management 2018, 23, 217 -229.
AMA StyleMichael M. Moges, Dawit Abay, Hailu Engidayehu. Investigating reservoir sedimentation and its implications to watershed sediment yield: The case of two small dams in data-scarce upper Blue Nile Basin, Ethiopia. Lakes & Reservoirs: Research & Management. 2018; 23 (3):217-229.
Chicago/Turabian StyleMichael M. Moges; Dawit Abay; Hailu Engidayehu. 2018. "Investigating reservoir sedimentation and its implications to watershed sediment yield: The case of two small dams in data-scarce upper Blue Nile Basin, Ethiopia." Lakes & Reservoirs: Research & Management 23, no. 3: 217-229.
The meandering Ribb River flows in northwest Ethiopia to Lake Tana, the source of the Blue Nile River. The river has already undergone changes due to several human interventions, such as embanking, sand mining, water extraction and lake level regulation for hydropower. At present, a dam and a weir are under construction to store and divert water for irrigation. This will strongly alter both water and sediment discharges to the downstream river reaches, causing adjustments to the morphology. Assessing the current morphodynamic trends is the first necessary step to study the future effects and find ways to mitigate them. This paper presents an analysis of the current and past river based on newly collected data, aerial photographs, SPOT and Google Earth images. The riverbed changes are derived from historical staff gauge height analysis. The effects of sediment mining and water extraction are assessed using the theory of morphodynamic equilibrium. The findings of the analysis show a reduction of sediment transport capacity in the downstream direction, which has resulted in intense sediment deposition, resulting in blockage of the Lower River reach and subsequent channel avulsion. The effects of Lake Tana level regulation on the observed processes appear to be minor.
Chalachew A. Mulatu; Alessandra Crosato; Michael M. Moges; Eddy J. Langendoen; Michael McClain. Morphodynamic Trends of the Ribb River, Ethiopia, Prior to Dam Construction. Geosciences 2018, 8, 255 .
AMA StyleChalachew A. Mulatu, Alessandra Crosato, Michael M. Moges, Eddy J. Langendoen, Michael McClain. Morphodynamic Trends of the Ribb River, Ethiopia, Prior to Dam Construction. Geosciences. 2018; 8 (7):255.
Chicago/Turabian StyleChalachew A. Mulatu; Alessandra Crosato; Michael M. Moges; Eddy J. Langendoen; Michael McClain. 2018. "Morphodynamic Trends of the Ribb River, Ethiopia, Prior to Dam Construction." Geosciences 8, no. 7: 255.
Mengiste Abate; Jan Nyssen; Tammo S. Steenhuis; Michael Mehari Moges; Seifu A. Tilahun; Temesgen Enku; Enyew Adgo. Morphological changes of Gumara River channel over 50 years, upper Blue Nile basin, Ethiopia. Journal of Hydrology 2015, 525, 152 -164.
AMA StyleMengiste Abate, Jan Nyssen, Tammo S. Steenhuis, Michael Mehari Moges, Seifu A. Tilahun, Temesgen Enku, Enyew Adgo. Morphological changes of Gumara River channel over 50 years, upper Blue Nile basin, Ethiopia. Journal of Hydrology. 2015; 525 ():152-164.
Chicago/Turabian StyleMengiste Abate; Jan Nyssen; Tammo S. Steenhuis; Michael Mehari Moges; Seifu A. Tilahun; Temesgen Enku; Enyew Adgo. 2015. "Morphological changes of Gumara River channel over 50 years, upper Blue Nile basin, Ethiopia." Journal of Hydrology 525, no. : 152-164.
Landscape response to drivers of change is more visible and noticeable in deltas and floodplains than in upstream. Here, we address the changes of Lake Tana basin by investigating the delta development of Gumara River and sediment deposition in the Fogera floodplain over a 58-year period when agricultural land expanded, agriculture intensified, and flooding of the alluvial plain became more frequent. Old maps show that delta formation before the 1950s was minimal, indicating that the sediment contributed by the rivers to the lake was small. However, during the last 58 years, the delta has expanded continuously. When considering the same lake level (2·68 m) from 1984 to 2014, the delta has expanded an average of 5 ha annually, and by considering different lake levels and corresponding delta areas, the delta increased in height an average of 3 cm annually. While the growth of the delta was approximately linear, the sediment concentration in the river doubled in the last 30 years, indicating more efficient sediment trapping in the floodplain as a result of higher lake levels, rising river beds, and farmers intervening with the course of the river near the shore. Unless effective river restoration and catchment-based treatment measures are put in place, the capacity of the rivers will further reduce and aggravate the flooding of the floodplain, causing more sediment deposition in the river channel and on the floodplain. Copyright © 2016 John Wiley & Sons, Ltd.
Mengiste Abate; Jan Nyssen; Michael Mehari Moges; Temesgen Enku; Fasikaw A. Zimale; Seifu A. Tilahun; Enyew Adgo; Tammo S. Steenhuis. Long‐Term Landscape Changes in the Lake Tana Basin as Evidenced by Delta Development and Floodplain Aggradation in Ethiopia. Land Degradation & Development 2015, 28, 1820 -1830.
AMA StyleMengiste Abate, Jan Nyssen, Michael Mehari Moges, Temesgen Enku, Fasikaw A. Zimale, Seifu A. Tilahun, Enyew Adgo, Tammo S. Steenhuis. Long‐Term Landscape Changes in the Lake Tana Basin as Evidenced by Delta Development and Floodplain Aggradation in Ethiopia. Land Degradation & Development. 2015; 28 (6):1820-1830.
Chicago/Turabian StyleMengiste Abate; Jan Nyssen; Michael Mehari Moges; Temesgen Enku; Fasikaw A. Zimale; Seifu A. Tilahun; Enyew Adgo; Tammo S. Steenhuis. 2015. "Long‐Term Landscape Changes in the Lake Tana Basin as Evidenced by Delta Development and Floodplain Aggradation in Ethiopia." Land Degradation & Development 28, no. 6: 1820-1830.