scholarly journals Modeling Impact of Land Use Dynamics on Hydrology and Sedimentation of Megech Dam Watershed, Ethiopia

2020 ◽  
Vol 2020 ◽  
pp. 1-20
Author(s):  
Abebe Tarko Assfaw
Keyword(s):  
Land Use ◽  
Sediment Yield ◽  
Surface Runoff ◽  
Hydrological Modeling ◽  
Plantation Forest ◽  
Dam Reservoir ◽  
Land Use Dynamics ◽  
The Mean ◽  
The Government ◽  
Runoff And Sediment Yield

Land use/land cover dynamics change the hydrology and sediment yield of the watershed. This research on how land use dynamics alters catchment hydrology and reservoir sedimentation aids the government to implement appropriate response strategies to minimize undesirable future impacts on the upper Megech dam reservoir. For this study, the impacts were quantified and analyzed through hydrological modeling (SWAT). The overall analysis was performed by using 1998 historical and 2016 recent land use satellite images. The analysis has shown that the cultivated land has increased from 60.69% to 67.17% and urban land from 2.3% to 3.36% between 1998 and 2016. Whereas the grassland area has decreased from 11.42% to 5.33%, plantation forest from 1.84% to 0.9%, and bareland from 3.58% to 2.56%. A comparison of the simulated outputs of the model shows that the mean annual surface runoff for 1998 land use was 251.3 mm and had changed to 316.7 mm in 2016 land use. The mean annual streamflow changed from 150.3 m3/sec to 165.6 m3/sec for 1998 and 2016 land uses, respectively. Similarly, 10.23 t/ha mean annual sediment load gets into Megech dam reservoir in 1998 LULC and was changed to 13.61 t/ha in 2016 LULC. This shows that streamflow, surface runoff, and sediment yield increases by 10.2%, 26.03%, and 33.3% in 2016 land use as compared with 1998 land use. Finally, the most dynamic subbasins that have a significant impact on streamflow and sediment yield were identified. Based on this, subbasins 13, 17, 19, 20, 23, 24, and 25 were found to be the most dynamic and change sensitive subbasins that have a significant contribution to the increment of runoff and sediment yield in Megech dam watershed.

scholarly journals Modeling runoff response to land-use changes using the SWAT model in the Mundaú watershed, Brazil

2020 ◽  
Vol 5 (2) ◽  
pp. 194-206
Author(s):  
Carolyne Wanessa Lins de Andrade Farias ◽  
Suzana Maria Gico Lima Montenegro ◽  
Abelardo Antônio de Assunção Montenegro ◽  
José Romualdo de Sousa Lima ◽  
Raghavan Srinivasan ◽  
...  
Keyword(s):  
Land Use ◽  
Land Use Change ◽  
Sediment Yield ◽  
Surface Runoff ◽  
Assessment Tool ◽  
Swat Model ◽  
Land Use Changes ◽  
Water Yield ◽  
Grazing Land ◽  
Runoff And Sediment Yield

Land-use change has a significant influence on runoff process of any watershed, and the deepening of this theme is essential to assist decision making, within the scope of water resources management. The study was conducted for Mundaú River Basin (MRB) using the Soil and Water Assessment Tool (SWAT) model. The study aims to assess the issue of land-use change and its effect on evapotranspiration, surface runoff, and sediment yield. Input data like land use, topography, weather, and soil data features are required to undertake watershed simulation. Two scenarios of land use were analyzed over 30 years, which were: a regeneration scenario (referring to use in the year 1987) and another scene of degradation (relating to use in the year 2017). Land use maps for 1987 and 2017 were acquired from satellite images. Overall, during the last three decades, 76.4% of forest was lost in the MRB. The grazing land increased in 2017 at a few more than double the area that existed in 1987. Changes in land use, over the years, resulted in an increase of about 37% in the water yield of MRB. Changes have led to increased processes such as surface runoff and sediment yield and in the decrease of evapotranspiration. The spatial and temporal distribution of land use controls the water balance and sediment production in the MRB.

scholarly journals Event-based runoff and sediment yield dynamics and controls in the sub-humid headwaters of the Blue Nile, Ethiopia

2021 ◽  
Author(s):  
Habtamu Assaye Deffersha ◽  
Jan Nyssen ◽  
Jean Poesen ◽  
Hanibal Lemma ◽  
Derege Meshesha ◽  
...  
Keyword(s):  
Land Use ◽  
Land Management ◽  
Sediment Yield ◽  
Management Practices ◽  
Sediment Concentration ◽  
Rock Fragment ◽  
Grazing Land ◽  
The Mean ◽  
The Impact ◽  
Runoff And Sediment Yield

Land degradation due to soil erosion presents a challenge for sustainable development. We investigated the impact of land use type and land management practices on runoff and sediment yield dynamics in the northwestern highlands of Ethiopia. The study area included 14 zero-order catchments with a surface area ranging from 324 m2 to 1715 m2. V-notch weirs produced from plastic jars were introduced as measuring alternatives that met local constraints. Runoff depth at the weir was registered at 5-min intervals during two rainy seasons in 2018 and 2019. Rainfall was measured using tipping-bucket rain gauges. Runoff samples were collected in 1-L bottles and suspended sediment concentration (SSC) was determined. The mean event runoff coefficient ranged from 3% for forests to 56% for badlands. Similarly, the mean annual sediment yield (SY) was lowest for forests (0.8 Mg ha-1 yr-1) and highest for badlands (43.4 Mg ha-1 yr-1), with significant differences among land use types (14.8 Mg ha-1 yr-1 in cropland, 5.7 Mg ha-1 yr-1 in grazing land, and 2.9 Mg ha-1 yr-1 in plantations). Soil organic matter (SOM) reduced runoff and SY, necessitating the consideration of agronomic and land management practices that enhance SOM. Annual SY decreased exponentially with the rock fragment cover (RFC). In fields where RFC was less than 20%, collecting rock fragments for installing stone bunds resulted in a net increase in SY. Rehabilitating badlands and enhancing SOM content in croplands can substantially reduce catchment SY and, hence considerably contribute to the sustainability of this type of environment.

scholarly journals Impact of Land Use and Land Cover Changes on Surface Runoff and Sediment Yield in the Little Ruaha River Catchment

2021 ◽  
Vol 11 (03) ◽  
pp. 54-74
Author(s):  
Nyemo A. Chilagane ◽  
Japhet J. Kashaigili ◽  
Edmund Mutayoba ◽  
Paul Lyimo ◽  
Pantaleo Munishi ◽  
...  
Keyword(s):  
Land Use ◽  
Land Cover ◽  
Sediment Yield ◽  
Surface Runoff ◽  
Land Cover Changes ◽  
River Catchment ◽  
Runoff And Sediment Yield

scholarly journals Calibration, Validation and Performance Evaluation of Swat Model for Sediment Yield Modelling in Megech Reservoir Catchment, Ethiopia

2019 ◽  
Vol 12 (3-4) ◽  
pp. 21-31
Author(s):  
Abebe Tarko Assfaw
Keyword(s):  
Soil Erosion ◽  
Sediment Yield ◽  
Local Governments ◽  
Hydrological Modeling ◽  
Swat Model ◽  
Management Strategies ◽  
Model Performance ◽  
Performance Standard ◽  
Agricultural Practice ◽  
The Mean

Abstract Intensive agricultural practice in Ethiopian highlands results in increasing rates of soil erosion and reservoir sedimentation. The estimation of sediment yield and prediction of the spatial distribution of soil erosion on the upper Megech reservoir catchment enables the local governments and policymakers to maximize the design span life of the Megech reservoir through implementing appropriate soil conservation practices. For this study, the sediment yield was estimated and analyzed through hydrological modeling (SWAT). The simulated outputs of the model show that the mean annual surface runoff was 282 mm and the mean annual streamflow was 153 m3/s. Similarly, 12.33 t/ha mean annual total sediment load gets into the Megech reservoir. The model performance standard used to evaluate the model result indicates that the model was superior in performing the trend of runoff and sediment yield in both calibration and validation periods. Finally, the most erosion vulnerable sub-basins that could have a significant impact on the sediment yield of the reservoir were identified. Based on this, sub-basin 7, 25, 27, 18 and 29 were found to be the most erosion sensitive areas that could have a significant contribution to the increment of sediment yield in the Megech reservoir. Considering the land use, soil type, slope, and relief of erosion vulnerable sub-basins cut off drains, fallow land, contour ploughing, Fanya juu terraces, soil bunds combined with trenches and trees could be the possible management strategies to reduce the sediment yield in the catchment.

Spatio-temporal analysis of soil erosion in Tokoro river watershed in eastern Hokkaido, Japan

2021 ◽  
Author(s):  
Kunihito Mihara ◽  
Kanta Kuramochi ◽  
Ryusuke Hatano
Keyword(s):  
Land Use ◽  
Soil Erosion ◽  
Sediment Yield ◽  
Surface Runoff ◽  
Stream Flow ◽  
Erosion Rate ◽  
Sediment Load ◽  
Agricultural Lands ◽  
Sediment Movement ◽  
Water And Sediment

<p>Introduction</p><p>Accelerated erosion by human activities leads to degradation of soil ecosystem services and aquatic environment. It is unavoidable issue in Japan because it holds many sloped agricultural lands. Tokoro river watershed, TRW, in eastern Hokkaido, Japan has unique climate characterized with the least precipitation in Japan and cold winter with little snow which induces soil freezing. Frozen subsoil forms impermeable layers to increase surface runoff in early spring. The objectives of this study were i) to understand the spatial and seasonal variation of water and sediment movement in TRW using Soil and Water Assessment Tool, SWAT which is a process-based hydrological model and ii) to evaluate the impact of agricultural activities, topography of agricultural lands, and runoff characteristics on soil erosion through identification of highly erosive areas and seasons based on the simulation output.</p><p>Materials and methods</p><p>Water and sediment movement in TRW was simulated from 2011/1/1 to 2015/12/31. SWAT calculates water and sediment movement processes using spatial and temporal information of topography, land use, soil, weather, and land management in watershed. TRW was delineated into 17 subbasins based on topographic information and further divided into 764 HRUs which had homogenous combination of slope class, soil type, and land use in each subbasin. On-land processes were calculated in each HRU. After water and sediment yield from HRUs were summed in each subbasin, stream routing processes were calculated. Model parameters were calibrated so that the estimated stream flow and sediment load at the outlet would fit the measurements. From the simulation by the calibrated model, outputs were extracted as follows: 1) Contribution to the gross sediment yield and erosion rate of each land use; 2) Erosion rate of each subbasin; 3) Erosion rate of whole watershed on each month; and 4) Surface runoff and percentage of surface runoff in water yield in each month.</p><p>Results and Discussions</p><p>Calibrated SWAT reproduced well the fluctuation of stream flow and sediment load at the outlet of TRW. Although the model underestimated sediment load during large flood events with the average estimation error of -16.1±5.4% on peak-discharge months, it showed satisfactory performance with coefficient of determination: R<sup>2</sup>=0.88, Nash-Sutcliffe efficiency coefficient: Ens=0.86, and percentage of bias: PBIAS=0.34% for monthly sediment load estimation. Agricultural lands which covered 17.6% of the watershed were considered as the primary sediment sources contributing to 68.5% of estimated gross sediment yield of the watershed. Spatial variation of estimated erosion rate showed high sediment yield in the middle- and down-stream area of TRW where agricultural activities were intensive, and higher sediment yield particularly in the area where more agricultural lands had steep slopes (more than 51 t km<sup>-2</sup> yr<sup>-1</sup>). Monthly erosion rate estimation indicated that the most severe erosion occurred on March and April (6.9±1.4 and 7.3±1.9 t km<sup>-2</sup> mon<sup>-1</sup> respectively). On March, average percentage of surface runoff was estimated as 90.5±6.5%. Therefore, surface runoff in early snowmelt season when the frozen subsoil prevented infiltration was considered as an important driver of soil erosion.</p>

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