Your search found 6 records
1 White, E. D.; Easton, Z. M.; Fuka, D. R.; Collick, A. S.; Adgo, E.; McCartney, Matthew; Awulachew, Seleshi Bekele; Selassie, Y. G.; Steenhuis, T. S. 2008. Adapting the soil and water assessment tool (SWAT) for the Nile Basin. In Humphreys, E.; Bayot, R. S.; van Brakel, M.; Gichuki, F.; Svendsen, M.; Wester, P.; Huber-Lee, A.; Cook, S. Douthwaite, B.; Hoanh, Chu Thai; Johnson, N.; Nguyen-Khoa, Sophie; Vidal, A.; MacIntyre, I.; MacIntyre, R. (Eds.). Fighting poverty through sustainable water use: proceedings of the CGIAR Challenge Program on Water and Food, 2nd International Forum on Water and Food, Addis Ababa, Ethiopia, 10-14 November 2008. Vol.3. Water benefits sharing for poverty alleviation and conflict management; Drivers and processes of change. Colombo, Sri Lanka: CGIAR Challenge Program on Water and Food. pp.22-26.
River basin management ; Watershed management ; Soil management ; Assessment ; Simulation models ; Water balance ; Water quality ; Stream flow ; Sedimentation ; Infiltration ; Runoff ; Climate / Ethiopia / Nile River Basin / Blue Nile River / Lake Tana Watershed / Anjeni Watershed
(Location: IWMI HQ Call no: IWMI 333.91 G000 HUM Record No: H041847)
http://cgspace.cgiar.org/bitstream/handle/10568/3708/IFWF2_proceedings_Volume%20III.pdf?sequence=1
https://vlibrary.iwmi.org/pdf/H041847.pdf
https://vlibrary.iwmi.org/pdf/H041847.pdf
(0.19 MB) (4.879MB)
2 White, E. D.; Easton, Z. M.; Fuka, D. R.; Collick, A. S.; McCartney, Matthew; Awulachew, Seleshi Bekele; Steenhuis, T. S. 2009. A water balance-based Soil and Water Assessment Tool (SWAT) for improved performance in the Ethiopian highlands. In Awulachew, Seleshi Bekele; Erkossa, Teklu; Smakhtin, Vladimir; Fernando, Ashra (Comps.). Improved water and land management in the Ethiopian highlands: its impact on downstream stakeholders dependent on the Blue Nile. Intermediate Results Dissemination Workshop held at the International Livestock Research Institute (ILRI), Addis Ababa, Ethiopia, 5-6 February 2009. Colombo, Sri Lanka: International Water Management Institute (IWMI). pp.152-158.
Hydrology ; Simulation models ; Water balance ; Soil water ; Infiltration ; Runoff ; Highlands / Africa / Ethiopia / Blue Nile River Basin / Abay Blue Nile / Gumera Basin / Laka Tana
(Location: IWMI HQ Call no: IWMI 333.9162 G100 AWU Record No: H042515)
(0.62 MB)
The Soil Water Assessment Tool (SWAT) is a watershed model widely used to predict water quantity and quality under varying land use and water use regimes. To determine the respective amounts of infiltration and surface runoff, SWAT uses the popular Curve Number (CN). While being appropriate for engineering design in temperate climates, the CN is less than ideal when used in monsoonal regions where rainfall is concentrated into distinct time periods. The CN methodology is based on the assumption that Hortonian flow is the driving force behind surface runoff production, a questionable assumption in many regions. In monsoonal climates water balance models generally capture the runoff generation processes and thus the flux water or transport of chemicals and sediments better than CN-based models. In order to use SWAT in monsoonal climates, the CN routine to predict runoff was replaced with a simple water balance routine in the code base. To compare this new water balance-based SWAT (SWAT-WB) to the original CN-based SWAT (SWAT-CN), several watersheds in the headwaters of the Abay Blue Nile in Ethiopia were modeled at a daily time step. While long term, daily data is largely nonexistent for portions of the Abay Blue Nile, data was available for one 1,270 km2 subbasin of the Lake Tana watershed, northeast of Bahir Dar, Ethiopia, which was used to initialize both versions of SWAT. Prior to any calibration of the model, daily Nash-Sutcliffe model efficiencies improved from -0.05 to 0.39 for SWAT-CN and SWAT-WB, respectively. Following calibration of SWAT-WB, daily model efficiency improved to 0.73, indicating that SWAT can accurately model saturation-excess processes without using the Curve Number technique.
3 Zegeye, A. D.; Tebebu, T. Y.; Abiy, A. Z.; Dahlke, H. E.; White, E. D.; Collick, A. S.; Kidnau, S.; Dadgari, F.; McCartney, Matthew; Steenhuis, T. S. 2009. Assessment of hydrological and landscape controls on gully formation and upland erosion near Lake Tana. In Awulachew, Seleshi Bekele; Erkossa, Teklu; Smakhtin, Vladimir; Fernando, Ashra (Comps.). Improved water and land management in the Ethiopian highlands: its impact on downstream stakeholders dependent on the Blue Nile. Intermediate Results Dissemination Workshop held at the International Livestock Research Institute (ILRI), Addis Ababa, Ethiopia, 5-6 February 2009. Colombo, Sri Lanka: International Water Management Institute (IWMI). pp.162-169.
Hydrology ; Water erosion ; Highlands ; Watersheds ; Simulation models / Africa / Ethiopia / Gilgil Abay Basin / Debre-Mewi Watershed / Lake Tana
(Location: IWMI HQ Call no: IWMI 333.9162 G100 AWU Record No: H042516)
(0.62 MB)
Gully formation and upland erosion were studied in the Debre-Mewi Watershed in the Gilgil Abay Basin south of Lake Tana. Gully erosion rates were found to be equivalent to over 500 tonnes/ha/year for the 2008 rainy season when averaged over the contributing watershed. Upland erosion rates were twentyfold less. Gully formation is accelerated when the soils are saturated with water as indicated by water table readings above bottom of the gully. Similarly, upland erosion was accelerated when the fields were close to saturation during the occurrence of a rainfall event. Height of the water table is an important parameter determining the amount of erosion and should, therefore, be included in simulation models.
4 Steenhuis, T. S.; Collick, A. S.; Easton, Z. M.; Leggesse, E. S.; Bayabil, H. K.; White, E. D.; Awulachew, Seleshi Bekele; Adgo, E.; Ahmed, A. A. 2009. Predicting discharge and sediment for the Abay (Blue Nile) with a simple model. Hydrological Processes, 23:3728-3737. [doi: https://doi.org/10.1002/hyp.7513]
Simulation models ; Forecasting ; Erosion ; Sedimentation ; Calibration ; Water balance ; Rainfall-runoff relationships ; River basins ; Climate / Ethiopia / Sudan / Egypt / Abay River / Blue Nile River
(Location: IWMI HQ Call no: e-copy only Record No: H042576)
(0.28 MB)
Models accurately representing the underlying hydrological processes and sediment dynamics in the Nile Basin are necessary for optimum use of water resources. Previous research in the Abay (Blue Nile) has indicated that direct runoff is generated either from saturated areas at the lower portions of the hillslopes or from areas of exposed bedrock. Thus, models that are based on infiltration excess processes are not appropriate. Furthermore, many of these same models are developed for temperate climates and might not be suitable for monsoonal climates with distinct dry periods in the Nile Basin. The objective of this study is to develop simple hydrology and erosion models using saturation excess runoff principles and interflow processes appropriate for a monsoonal climate and a mountainous landscape. We developed a hydrology model using a water balance approach by dividing the landscape into variable saturated areas, exposed rock and hillslopes. Water balance models have been shown to simulate river flows well at intervals of 5 days or longer when the main runoff mechanism is saturation excess. The hydrology model was developed and coupled with an erosion model using available precipitation and potential evaporation data and a minimum of calibration parameters. This model was applied to the Blue Nile. The model predicts direct runoff from saturated areas and impermeable areas (such as bedrock outcrops) and subsurface flow from the remainder of the hillslopes. The ratio of direct runoff to total flow is used to predict the sediment concentration by assuming that only the direct runoff is responsible for the sediment load in the stream. There is reasonable agreement between the model predictions and the 10-day observed discharge and sediment concentration at the gauging station on Blue Nile upstream of Rosaries Dam at the Ethiopia–Sudan border.
5 Easton, Z. M.; Fuka, D. R.; White, E. D.; Collick, A. S.; Ashagre, B. B.; McCartney, Matthew; Awulachew, Seleshi Bekele; Ahmed, A. A.; Steenhuis, T. S. 2010. A multi basin SWAT model analysis of runoff and sedimentation in the Blue Nile, Ethiopia. Hydrology and Earth System Sciences, 14(10):1827-1841. [doi: https://doi.org/10.5194/hess-14-1827-2010]
Simulation models ; Calibration ; Runoff ; Erosion ; River basins ; Sedimentation ; Watersheds / Ethiopia / Blue Nile River Basin
(Location: IWMI HQ Call no: e-copy only Record No: H043234)
http://www.hydrol-earth-syst-sci.net/14/1827/2010/hess-14-1827-2010.pdf
https://vlibrary.iwmi.org/pdf/H043234.pdf
https://vlibrary.iwmi.org/pdf/H043234.pdf
(1.82 MB)
A multi basin analysis of runoff and erosion in the Blue Nile Basin, Ethiopia was conducted to elucidate sources of runoff and sediment. Erosion is arguably the most critical problem in the Blue Nile Basin, as it limits agricultural productivity in Ethiopia, degrades benthos in the Nile, and results in sedimentation of dams in downstream countries. A modified version of the Soil and Water Assessment Tool (SWAT) model was developed to predict runoff and sediment losses from the Ethiopian Blue Nile Basin. The model simulates saturation excess runoff from the landscape using a simple daily water balance coupled to a topographic wetness index in ways that are consistent with observed runoff processes in the basin. The spatial distribution of landscape erosion is thus simulated more correctly. The model was parameterized in a nested design for flow at eight and sediment at three locations in the basin. Subbasins ranged in size from 1.3 to 174 000 km2, and interestingly, the partitioning of runoff and infiltrating flow could be predicted by topographic information. Model predictions showed reasonable accuracy (Nash Sutcliffe Efficiencies ranged from 0.53–0.92) with measured data across all sites except Kessie, where the water budget could not be closed; however, the timing of flow was well captured. Runoff losses increased with rainfall during the monsoonal season and were greatest from areas with shallow soils and large contributing areas. Analysis of model results indicate that upland landscape erosion dominated sediment delivery to the main stem of the Blue Nile in the early part of the growing season when tillage occurs and before the soil was wetted up and plant cover was established. Once plant cover was established in mid August landscape erosion was negligible and sediment export was ominated by channel processes and re-suspension of landscape sediment deposited early in the growing season. These results imply that targeting small areas of the landscape where runoff is produced can be the most effective at controlling erosion and protecting water resources. However, it is not clear what can be done to manage channel erosion, particularly in first order streams in the basin.
6 White, E. D.; Easton, Z. M.; Fuka, D. R.; Collick, A. S.; Adgo, E.; McCartney, Matthew; Awulachew, Seleshi Bekele; Selassie, Y. G.; Steenhuis, T. S. 2011. Development and application of a physically based landscape water balance in the SWAT model. Hydrological Processes, 25(6):915-925. [doi: https://doi.org/ 10.1002/hyp.7876]
Simulation models ; Hydrology ; Water balance ; Water table ; Runoff ; Stream flow ; Watersheds ; River basins / Ethiopia / USA / Blue Nile River / Gumera Watershed / New York / Catskill Mountains / Town Brook Watershed
(Location: IWMI HQ Call no: e-copy only Record No: H043240)
(0.61 MB)
Watershed scale hydrological and biogeochemical models rely on the correct spatial-temporal prediction of processes governing water and contaminant movement. The Soil and Water Assessment Tool (SWAT) model, one of the most commonly used watershed scale models, uses the popular curve number (CN) method to determine the respective amounts of infiltration and surface runoff. Although appropriate for flood forecasting in temperate climates, the CN method has been shown to be less than ideal in many situations (e.g. monsoonal climates and areas dominated by variable source area hydrology). The CN model is based on the assumption that there is a unique relationship between the average moisture content and the CN for all hydrologic response units (HRUs), and that the moisture content distribution is similar for each runoff event, which is not the case in many regions. Presented here is a physically based water balance that was coded in the SWAT model to replace the CN method of runoff generation. To compare this new water balance SWAT (SWAT-WB) to the original CN-based SWAT SWAT-CN), two watersheds were initialized; one in the headwaters of the Blue Nile in Ethiopia and one in the Catskill Mountains of New York. In the Ethiopian watershed, streamflow predictions were better using SWAT-WB than SWAT-CN [Nash–Sutcliffe efficiencies (NSE) of 0Ð79 and 0Ð67, respectively]. In the temperate Catskills, SWAT-WB and SWAT-CN predictions were approximately equivalent (NSE >0Ð70). The spatial distribution of runoff-generating areas differed greatly between the two models, with SWAT-WB reflecting the topographical controls imposed on the model. Results show that a water balance provides results equal to or better than the CN, but with a more physically based approach.
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