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Subject: search.filters.subject.Sediment yield

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    ESTIMATION OF SEDIMENT YIELD AND EFFECTIVENESS OF LEVEL STONE BUNDS TO REDUCE SEDIMENT LOSS: IN GUMARA-MAKSEGNIT WATERSHED, NILE BASIN, ETHIOPIA
    (Hawassa University, 2018-10-21) ATIKILT ABERA ALEMAYEHU
    The study was conducted in Gumara-Maksegnit watershed and it’s sub-catchments to estimate event-based sediment yield and to evaluate the effectiveness of level stone bunds based on sediment loss reduction. Modified Universal Soil Loss Equation (MUSLE) was used for estimation of sediment yield. The model input parameters were collected from different sources and these are discretized and preprocessed with the help of various suitable software and tools. Finally, all six model factors were combined together using the raster calculator in map algebra to estimate the sediment yields of the study watersheds. The event-based mean observed and model estimated sediment yields were (0.5581, 0.4031 ton ha-1 ) for Gumara-Maksegnit watershed, (0.5125, 0.4194 ton ha-1 ) for treated sub-catchment and (1.0694, 1.0150 ton ha-1 ) for untreated sub-catchments respectively. The sediment losses between treated and untreated sub-catchments were highly significantly different when the sediment loss reduced by 58.8% as a result of level stone bund interventions. However, the observed and estimated sediment losses are not significantly different within a watershed. Hence, the model was well performed to estimate sediment yield in the study area with R2 (0.62, 0.72 and 0.7) and NSE (0.53, 0.71 and 0.34) for treated, untreated and Gumara-Maksegnit watershed respectively. Hence, the result showed that the Modified Universal Soil Loss Equation (MUSLE) model was well suited for reliable applications of sediment yield estimation in the study area as well as similar agroecologies
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    HYDRO-SEDIMENT RESPONSES TO MANAGEMENT OPTIONS UNDER CURRENT AND FUTURE CLIMATE CHANGE SCENARIOS IN MAYBAR SUB WATERSHED, SOUTH WOLLO ZONE, ETHIOPIA
    (Hawassa University, 2022-10-22) MULUKEN LEBAY EGIGU
    Climate change coupled with inappropriate land use management is a serious environmental challenge in the highland part of Ethiopia. The aim of this study was to investigate hydro-sediment responses to management options under current and future climate change scenarios in Maybar watershed, Northern Ethiopia. We employed soil and water assessment tool (SWAT) for hydrologic modeling and CORDEX-climate data under RCP 4.5 and RCP 8.5 emission scenarios was used for climate projections. Soil map was prepared by digitizing soil characterization map of the watershed generated by Weigel in 1986. DEM data with 2m spatial resolution was obtained from water and land resource center and land use classification was done through digitization of google earth images. Better agreement between calibrated SWAT simulation and observed variables was achieved. Delta change bias correction method was empolyed to improve the climate simulation in reproducing the observed climate variables. We found a considerable increase in annual precipitation by 18.71% and 22.33% for RCP 4.5 and RCP 8.5, respectively compared with the current climate conditions. Climate change induced hydro-sediment results were observed to be consistent with predicted precipitation. Under the current climatatic conditions, average sediment yield at the subbasin scale varies from negligible (under terrace complementation) to approximately more than 50 t ha-1 yr-1 with a basin average of 32 t ha-1 yr-1 (under no-terrace conditions). The implementation of management alternatives gets the dry seasons hydrological behavior of the catchment improved and climate change induced sediment yield reduction. Generally, the information could possibly support decision makers and planners to implement best-fitted management options and thereby reduce current and expected aggressive sediment loss situations.
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    APPLICATION OF THE MODIFIED UNIVERSAL SOIL LOSS EQUATION (MUSLE) IN THE PREDICTION OF SEDIMENT YIELD IN AGEWMARIAM EXPERIMENTAL WATERSHED; TEKEZE RIVER BASIN, NORTHERN ETHIOPIA
    (Hawassa University, 2022-10-20) YONAS REDA SHAREW
    The severe effect of soil and water resource degradation in Ethiopia is putting pressure to take soil and water erosion control measures. To support the planning, management, and appropriate use of the soil and water resources the Modified Universal Soil Loss Equation (MUSLE) was used to model eventual sediment loss in Agewmariam experimental watershed. The model uses different methods for the estimation of the runoff energy, soil erodibility, slope length & steepness, cover management, and support practice factors input parameter values; so that calibration, evaluation, and validation of parameter values become mandatory. The model input parameters were collected from a combined process of field observation, laboratory analysis, Google Earth Pro, and GIS processing while cover management and support practice are adopted from literature. Analysis of input parameters was done with the help of ArcGIS and MS-EXCEL. The input parameter maps were overlaid to assign a value and the combined effect of the parameters for the suspended sediment yield was calculated on a raster calculator. The runoff energy factor is the most sensitive parameter followed by the slope length and steepness factor. For the calibration period, the event-based mean observed and estimated suspended sediment yields were 0.2 and 0.23 ton/ha respectively with a little overestimation; while for the validation period, is 0.7 and 0.53 ton/ha with great underestimation. The model evaluation shows a 0.85 coefficient of determination, a 0.85 coefficient of efficiency, and an index of agreement value of 0.96 for the calibration period which can be considered a good model performance, whereas a 0.84 coefficient of determination, 0.65 coefficient of efficiency, and an index of agreement value of 0.83 for the validation period. The result revealed the use of the MUSLE model in its original form without calibration is not proper. The evaluation result shows the model with the appropriate calibration is a good estimator of sediment yield so that it can be used for spatial prioritization of soil and water conservation need within the watershed or extrapolated to the neighboring similar watersheds
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    COMPARISON OF SWAT AND WEPP FOR MODELING ANNUAL RUNOFF AND SEDIMENT YIELD AND QUANTIFCATION OF NUTRENT LOSS IN AGEWU MARIYAM WATERSHED, NORTHERN ETHIOPIA
    (Hawassa University, 2022-10-22) YALELET ABIE WORKU
    Unevenly heavy rainstorms during the rainy season create runoff and soil erosion which affects soil fertility and production, especially in northern Ethiopia. In this study soil and water assessment tool (SWAT) and geographic water erosion prediction project (GeoWEPP) were applied to compare estimation of annual runoff and sediment yield and quantification of nutrient loss in Agewu-Maryam watersheds eastern Amhara, region, Ethiopia. To run both models, need spatial and temporal data distribution is required as an input. The soil textures and other selected soil properties were determined in the field and the laboratory and a soil map were derived from the digital soil map of the world. A land-use map was prepared based on manually digitizing from Google earth image. A Digital Elevation Model of the watershed was used for delineating the watershed and preparing a slope map. ArcGIS 10.4 was used for both models for basic interface for further analysis. During each runoff event, runoff samples were collected and the sediment concentrations were analyzed in the laboratory. The simulation result of long-term (24-year) average means annual runoff and sediment yield from WEPP and SWAT models were estimated. The results were performed well as indicated by R 2 0.86 and 0.91 and with NSE 0.54 and 0.71 for monthly runoff were satisfactory for SWAT and WEPP models compared with observed value respectively The estimated average mean annual runoff and sediment yield at the outlet of the watershed was 65.54mm and 146.14mm and 43t/ha/yr and 41.7t/ha/yr respectively for WEPP and SWAT models. The t statics result shows that there is no statistically significant difference with p-value (0.97 for runoff and 0.98 for sediment) between the two models' simulation results. Some of the Sub watershed were identified and prioritized as more susceptible to soil erosion and give more attention first to this area for reducing runoff and soil erosion. The total nutrients loss within the suspended sediment were 33.74kg/ha/yr N,6.79kg/ha/yr P, 642.5 OM kg/ha/yr, and 1.52 K for the watershed. Hence SWAT and WEPP models were well suited for the estimation of annual runoff and sediment yield. The sediment yield simulated from both models was high which was alarming and far beyond the soil loss tolerable rate. Therefore, the result of the model could be used as a decision-making tool
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    ASSESSING THE EFFECT OF LAND USE LAND COVER CHANGE ON STREAM FLOW AND SEDIMENT YIELD: THE CASE OF ROBIGUMERO WATERSHED, UPPER BLUE NILE BASIN, ETHIOPIA
    (Hawassa University, 2024-07-26) KASAHUN TADESSE MARE
    Land use and land cover change significantly affected global water yield and sediment yield. The population within the Robigumero watershed experiences periodic increases that are attributable to changes in land use and land cover patterns occurring over both a spatial and temporal scale. Therefore, this study mainly focused on assessing LULC change and analyzing its impact on stream flow and sediment yield in the Robigumero watershed. For this study, spatial and hydro-meteorological data were used as model input. ERDAS Image 2015 was used to assess land cover classification and accuracy. SWAT model was used to simulate stream flow and sediment yield in monthly time steps. The model predicted stream flow with R2 values of 0.89 and 0.77, NSE values of 0.87 and 0.76, and PBIAS values of -2.3 and -5.1 during calibration and validation periods, respectively. Similarly, the model predicted sediment yield with R2 values of 0.80 and 0.75, NSE values of 0.80 and 0.74, and PBIAS values of -7.1 and 0..9 during the calibration and validation periods, respectively. During the study period from 1994 to 2021, the Robigumero watershed experienced substantial LULC change, with agricultural land and built-up area increasing by 18.6% and 160.8%, respectively, while forest, grassland, and shrubland cover decreased by 12.7%, 10.4%, and 40%, respectively. The calibrated model predicted results showed that on the watershed outlet point, mean annual stream flow increased by 4.64 m3 /s, and mean monthly stream flow increased by 0.86 m3 /s during the wet season and decreased by 0.14 m3 /s during the dry season from 1994 to 2021. Similarly, annual sediment yield increased by 5.5 t ha- 1 .yr-1 , with seasonal yields increasing by 4.84 t ha-1 .yr-1 during the wet season and 0.49 t ha- 1 .yr-1 during the dry season. Spatially, nine subbasins (43.3%) of the catchment revealed sediment yield-critical areas; from these, 24.02 t ha-1 yr-1 of sediment was generated. Implementing terracing, filter strips, and contouring in the critical subbasins demonstrated sediment yield reductions of 71.1%, 46.3%, and 51.9%, respectively. The findings of this study indicate that annual and wet season stream flow and sediment yield increased, while dry season stream flow was reduced. The change in stream flow and sediment yield is a direct result of the significant change in land use and land cover in the watershed. This suggests soil and water resource development in the catchment needs urgent regulation by the LULC and should be given priority to sediment reduction measures
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    ESTIMATION OF RUNOFF AND SEDIMENT YIELD USING SWAT MODEL: THE CASE OF KATAR WATERSHED, RIFT VALLEYLAKE BASIN OF ETHIOPIA
    (Hawassa University, 2019-07-27) Dulo Husen
    Estimating of runoff and sediment yield at watershed level is important for better understanding of hydrologic processes and identifying appropriate measures to combat erosion. In this study, Soil and Water Assessment Tool (SWAT) was used to calibrate and validate a hydrologic component on Katar river discharges at Habura gauging station and predict the stream flow of Katar watershed. The objective of the study was estimating the runoff and sediment yield for the Katar watershed using SWAT model. Sensitivity analysis, model calibration and validation were also performed to assess the model performance. From the result of Global sensitivity analysis, twelve(12) highly sensitive parameters were identified, and coefficient of determination (R2 ), Nash-Sutcliffe (ENS) and percent bias (PBIAS) were used as objective function to evaluate model calibration and validation on the monthly basis, and it could simulate runoff to a good level of accuracy. The results obtained were satisfactory for the gauging station (R2 = 0.80, ENS = 0.6 and PBIAS=0) for calibration and (R2 = 0.6, ENS = 0.55 and PBIAS=1.2) validation period. The simulated runoff and sediment yield of Katar watershed was quantified and also the utmost erodible part of the watershed was identified and prioritized. Among all sub-watersheds, nine (9) sub watersheds were more vulnerable to soil loss and potentially prone to erosion risk, which was out of range of tolerable soil loss rate (18 tha-1 yr-1 ). Large area of watershed covered by Haplic Luvisols(high clay content) and agriculture is the dominant activities in area. The simulated mean of sediment yield and runoff loss from watershed for 26 years were 11 tha-1 yr-1 and 12.3 m 3 s -1 respectively. The result of the study could help stakeholders to plan and implement appropriate watershed management strategies based prioritizations of severity of erosion. In conclusion, the SWAT model could be effectively used to predict runoff and sediment yield and result of the study could help different stakeholders to plan and implement appropriate interventions strategies in the Katar watershed.