Analyzing the variability of sediment yield: A case study from paired watersheds in the Upper Blue Nile basin, Ethiopia

Ebabu, Kindiye; Tsunekawa, Atsushi; Haregeweyn, Nigussie; Adgo, Enyew; Meshesha, Derege Tsegaye; Aklog, Dagnachew; Masunaga, Tsugiyuki; Tsubo, Mitsuru; Sultan, Dagnenet; Fenta, Ayele Almaw; Yibeltal, Mesenbet

doi:10.1016/j.geomorph.2017.12.020

Cited by 58 publications

(47 citation statements)

References 41 publications

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“…Like the rainfall pattern in LTB, this severe rate of sediment delivery to main rivers also follows an increasing trend from north to south in clockwise direction, that is, SY in subbasins located in Megech catchment (57 Mg ha −1 yr −1 ) is lower than subbasins located in north‐east (65 Mg ha −1 yr −1 ), Gumara (73 Mg ha −1 yr −1 ), and Gilgel Abay (80 Mg ha −1 yr −1 ) catchments. This estimated SY in this study is within the range reported data that were observed in and around LTB (Ayele et al, ; Ebabu et al, ; Lemma et al, ; Melaku et al, ; Subhatu et al, ). In contrasts, relatively lower sediment is produced in the low‐lying floodplains of the basin.…”

Section: Discussionsupporting

confidence: 91%

“…A total of 3,855 suspended sediment concentration (SSC) and its corresponding streamflow data were measured in the monitoring stations in Megech, Gumara, Gelda, and Gilgel Abay rivers (2012–2016). The average SSC is 3.51 ± 6.25 g L −1 that ranges from 2.50 (±4.95) in Gelda to 4.43 (±9.63) g L −1 in Megech, which is quite within the range of values reported by Lemma et al () and Ebabu et al () in LTB. The SSC in Megech River is a bit higher than the natural condition due to intensive river bank excavation for dam construction.…”

Section: Discussionsupporting

confidence: 85%

“…Selection of land management scenarios and their parametric values is site specific and should reflect the study area reality (Abdelwahab et al, ). Therefore, five scenarios were selected and simulated based on documented local research experiences and recently introduced practices in the Ethiopian Highlands (e.g., Addis et al, ; Ebabu et al, ; Hurni, ; Melaku et al, ; Nigussie et al, ; Sultan et al, ). The scenarios encompass land use changing (reforestation of hilly cropland areas as Scenario R), physical (stone/soil bunds as Scenario S) and biological (grass contour strips as Scenario G) conservation practices, and agronomic measures ( Acacia decurrens ‐based crop rotation as Scenario A and zero free grazing as Scenario Z).…”

Section: Methodsmentioning

confidence: 99%

“…The basin is also characterized by severe land degradation driven by the combination of erosive rains, steep topography, deforestation, and land mismanagement that leads to high sediment loads FIGURE 1 Location of Lake Tana Basin, weather stations, and streamflow gauges [Colour figure can be viewed at wileyonlinelibrary.com] (SLs) and wetland losses Nyssen et al, 2004;Setegn et al, 2009). Recent studies also revealed that average observed SY in LTB ranges from 18 to 155 Mg ha −1 yr −1 , where the eastern and southern areas of the basin deliver more sediment (e.g., Ebabu et al, 2018;Lemma et al, 2018).…”

Section: Lake Tana Basinmentioning

confidence: 99%

“…Selection of land management scenarios and their parametric values is site specific and should reflect the study area reality (Abdelwahab et al, 2014). Therefore, five scenarios were selected and simulated based on documented local research experiences and recently introduced practices in the Ethiopian Highlands (e.g., Addis et al, 2016;Ebabu et al, 2018;Hurni, 1985;Melaku et al, 2018;Nigussie et al, 2017;Sultan et al, 2017). The scenarios Ethiopia (Hurni et al, 2016;National Planning Commission, 2015).…”

Section: Scenarios For Alternative Catchment Managementmentioning

confidence: 99%

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Identifying erosion hotspots in Lake Tana Basin from a multisite Soil and Water Assessment Tool validation: Opportunity for land managers

et al. 2019

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Extensive catchment degradation throughout the Ethiopian Highlands induced by long‐term intensified land use, erosion‐prone topography, and climate causes substantial soil erosion that limits agricultural productivity and results in lake sedimentation. However, before taking soil conservation measures, management of the soil loss problem essentially needs catchment‐level modelling to estimate the geographic distribution of erosion hotspots. With the increasing availability of sediment and spatial data and development of physically based models, this study aims multisite calibration of Soil and Water Assessment Tool (SWAT) to map erosion hotspot areas and to assess the effect of well‐known land management alternatives in sediment reduction in the Lake Tana Basin. The SWAT simulations indicated that the goodness of fit between predicted and observed data was satisfactory for all gauge stations except for one, and the model performance was within acceptable evaluation ratings. Simulated average sediment yield (SY) for the period 2001–2016 at subbasin level varies from negligible to about 169 Mg ha−1 yr−1 (basin average 32 Mg ha−1 yr−1). High potential SY (>50 Mg ha−1 yr−1) was simulated for 23% of the subbasins in Megech, upper Rib, upper Gumara, and Gilgel Abay catchments due to steep slope topography, aggressive rainfall, croplands dominance, and low rock fragment cover. The differences in level of erosion risk among subbasins help to prioritize and target specific areas of the basin that need urgent soil conservation activities. Scenario analysis also showed that implementing stone bunds, Acacia decurrens‐based crop rotation, reforestation, and grass contour strips reduces the existing SY by 51–61% at basin level. The potential sediment production could reach tolerable levels by implementing stone bunds, tree‐based crop rotation, reforestation in steep slope areas, and grass contour strips on gentle slopes. Overall, the multisite calibration of SWAT model using the measured run‐off and sediment data produces reasonable results that may support decision makers and planners to implement relevant land management measures and thereby reduce the alarming problems of soil loss in the basin and sedimentation of Lake Tana.

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Section: Discussionsupporting

confidence: 91%

Section: Discussionsupporting

confidence: 85%

Section: Methodsmentioning

confidence: 99%

Section: Lake Tana Basinmentioning

confidence: 99%

Section: Scenarios For Alternative Catchment Managementmentioning

confidence: 99%

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Identifying erosion hotspots in Lake Tana Basin from a multisite Soil and Water Assessment Tool validation: Opportunity for land managers

et al. 2019

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Effect of subsurface water level on gully headcut retreat in tropical highlands of Ethiopia

Yibeltal

Tsunekawa

Haregeweyn

et al. 2021

Earth Surf Processes Landf

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Gully erosion is a major cause of soil loss and severe land degradation in sub-humid Ethiopia. The objective of this study was to investigate the role and the effect of subsurface water level change on gully headcut retreat, gully formation and expansion in high rainfall tropical regions in the Ethiopian highlands. During the rainy seasons of 2017-2019, the expansion rate of 16 fixed gullies was measured and subsurface water levels were measured by piezometers installed near gully heads.During the study period, headcut retreats ranged from 0.70 to 2.35 m, with a mean value of 1.49 ± 0.56 m year −1 , and average depth of the surface water level varied between 1.12 and 2.82 m, with a mean value of 2.62 m. Gully cross-section areas ranged from 2.90 to 20.90 m 2 , with an average of 9.31 ± 4.80 m 2 . Volumetric retreat of gully headcuts ranged from 4.49 to 40.55 m 3 and averaged 13.34 ± 9.10 m 3 . Soil loss from individual gullies ranged from 5.79 to 52.31 t year −1 and averaged 17.21 ± 11.74 t year −1 . The headcut retreat rate and sediment yield were closely related over the three study seasons. Elevated subsurface water levels facilitated the slumping of gully banks and heads, causing high sediment yield.When the soil was saturated, bank collapse and headcut retreat were favoured by the combination of elevated subsurface water and high rainfall. This study indicates that area exclosures are effective in controlling subsurface water level, thus reducing gully headcut retreat and associated soil loss.

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Predicting the sediment transport capacity from flow condition and particle size in the presence of vegetation cover

et al. 2020

Land Degrad Dev

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The sediment transport capacity plays a pivotal role in erosion research, and is usually predicted using hydraulic variables. The transport capacity and hydraulic variables are affected by vegetation cover. Our understanding of the effect of vegetation cover, including the size, density, and arrangement of vegetation stems, on the relationship between the sediment transport capacity and hydraulic variables were rather limited. The objectives of this study were to investigate the effect vegetation stem cover on the relationship between hydraulic variables and the sediment transport capacity and to derive an equation for predicting the sediment transport capacity in the presence of vegetation cover. Five data sets from 288 flume experiments with a wide range of discharge (0.25–2 × 10−3 m3 s−1), slope (8.8–42.3%), median sediment diameter (0.11–1.16 × 10−3 m), stem cover (0–30%), stem diameter (2–36 mm), and stem arrangement (bead, tessellation, zigzag, random, and banding) were compiled for this study. Extensive regression analysis has shown that the sediment transport capacity could be expressed as a power function of flow velocity, shear stress, stream power, or unit stream power. Predictors of the sediment transport capacity were ranked from the unit stream power as the strongest, followed by the stream power, flow velocity, and the shear stress. Vegetation stem cover had no apparent and direct effect on the relationship between hydraulic variables and the sediment transport capacity so long as the unit stream power or stream power was used as its predictor. Vegetation cover became a significant factor only when the shear stress was used to predict the sediment transport capacity. Finally, a new equation involving the slope gradient, flow velocity, and median sediment diameter in a nondimensional form was shown to be a superior predictor of the sediment transport capacity with the Nash–Sutcliffe coefficient of efficiency of 0.92. The product of slope and flow velocity, that is, the unit stream power, captures the effect of vegetation stem cover and surface roughness and was shown to be an effective predictor of the transport capacity in the presence of vegetation cover.

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Analyzing the variability of sediment yield: A case study from paired watersheds in the Upper Blue Nile basin, Ethiopia

Cited by 58 publications

References 41 publications

Identifying erosion hotspots in Lake Tana Basin from a multisite Soil and Water Assessment Tool validation: Opportunity for land managers

Identifying erosion hotspots in Lake Tana Basin from a multisite Soil and Water Assessment Tool validation: Opportunity for land managers

Effect of subsurface water level on gully headcut retreat in tropical highlands of Ethiopia

Predicting the sediment transport capacity from flow condition and particle size in the presence of vegetation cover

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