Hydraulic Engineering

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Start date: 2020Subject: search.filters.subject.SWAT model

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    IMPACTS OF LAND USE LAND COVER CHANGE ON RESERVOIR SEDIMENTATION (THE CASE OF RIBB DAM, IN LAKE TANA SUB BASIN, ETHIOPIA)
    (Hawassa University, 2020-10-21) MEBRATU ESUBALEW ENGIDA
    Land use land cover (LULC) change is the challenge and continuous drivers of environmental change. Understanding the rate and process of change is, therefore, basic for managing the water resources and the environment at large. This study was intended to analyze the LULC changes impacts on sediment load from 2000 to 2018 periods, and select critical (hot spot area) sub basins and recommend best management practice for Ribb watershed of Lake Tana sub basin, Ethiopia. Both climate and hydrometric (flow and sediment) data were collected and analyzed over the period 1990 to 2018. Two time satellite imageries of the Land sat product (2000 and 2018) were used for land use change detection. The hybrid classification technique for extracting thematic information from satellite images were employed by using ERDAS model for classification of LULC. The Soil and Water Assessment Tool (SWAT) model was calibrated and validated to estimate sediment load of the watershed during the period 1992 to 2001 and 2002 to 2007 respectively. To manage the sediment load best management practices (BMP) as a scenario (filter strip, grassed water way and contouring) were implemented on 2018 LU map. The land use change detection result indicate that cultivated land has expanded from 66.87% in 2000 to 75.53% in 2018. Between 2000 and 2018 periods, it was increased by 8.66 %. The rate of increment during 2000–2018 periods were 608.915 ha/year. Similarly, settlement area had also increased by 2.09% from 2000–2018 periods. Similarly, shrub land and bare land also decreased at a rate of 412.868 and 227.651 ha/year, respectively, between 2000 and 2018 periods. Also the water body decreased at a rate of 1.593 ha/year between 2000 and 2018. The SWAT model result depict that the model give reasonable fit of sediment flux with observation during calibration and validation as evaluated with ENS ( 0.63 ) , R2 ( 0.67) and percent bias (17%) during calibration and ENS ( 0.58) , R2 ( 0.71) and percent bias of (12%) during validation period. Moreover, the severity of soil loss rate was increased with the average of 26.89 ton/ha/year from 2000 to 2018 LULC, which indicates that the management practice, was weak within the watershed. The BMP scenarios depict that filter strip was significant amount of LULC conversions practice and soil loss rate had occurred in the watershed from 2000 to 2018 periods, and expected to continue in the future. Thus, appropriate conservation and management practice are very much crucial to safe guard the life of the reservoir
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    ASSESSMENT OF LAND USE / LAND COVER CHANGE IMPACT ON STREAM FLOW USING SWAT MODEL, THE CASE OF KULFO RIVER CATCHMENT, RIFT VALLEY BASIN, ETHIOPIA
    (Hawassa University, 2024-01-06) OBSE FUFA ARFASA
    In order to conserve land and water resources and ensure its long-term sustainability, land use land cover change dynamics and its impact on the water resources of watersheds have emerged as key issues in hydrology. The main objective of this study was to investigate impact of land use land cover change on stream flow of Kulfo River. ERDAS IMAGINE-2015 using the maximum likelihood algorithm of supervised classification was used to evaluate changes in land use and land cover of study area. Land sat-5 images of year 2000 and 2010 as well as land sat-8 images of year 2022 obtained from USGS with spatial resolution of 30m were used for land use land cover classification. Accuracy of model to classify land features accurately and precisely was evaluated by making comparison matrix between classified classes with those collected by GPS and from Google earth. Kappa coefficient from comparison matrix has been used to evaluate performance of model and it has been determined over 80% for all classification periods verifying the accuracy of classification. From comparison observed from each periods of land use land cover maps, there are some significant changes on land use and land cover features of study area. Over the past study years, the watershed has undergone significant changes, including the expansion of agricultural land and towns at the expense of the reduction of grassland, forest, and shrub area. Those LULC maps of different periods were varied as SWAT inputs while maintaining the remaining inputs the same in order to evaluate its impact on stream flow using SWAT model. The sensitivity analysis, calibration and validation was conducted using Sequential Uncertainty Fitting (SUFI-2) within SWAT-CUP. The calibration results showed very good match of simulation with observation with Nash-Sutcliff efficiency (NSE) of 0.81, coefficient of determination (R2 ) of 0.83, root mean square error (RMSE) of 0.12 and percent of bias (PBIAS) of -0.1.Perspective objective functions during validation have been determined as 0.84,0.86,0.01 and 0.03 respectively. Well calibrated stream flow for different periods has been compared to evaluate impact of LULC changes on stream flow. It has been pointed out that some increases in agricultural land and urbanization promoted runoff formation by reducing water infiltration into deep soil, result in an increase in surface runoff and a decrease in ground water flow. It is also revealed by the study that increased surface due to land use land cover change is more significant during wet seasons than that of dry seasons. The study's methodology and findings will be pertinent to environmental policy makers and other relevant bodies which will involve in the development, occupancy, and management of resources related to water and land
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    ANALYSIS AND CHARACTERIZATION OF HYDROLOGICAL DROUGHT UNDER CLIMATE CHANGE IN HAMASSA WATERSHED, RIFT VALLEY BASIN
    (Hawassa University, 2024-07-20) REDIAT LEGESE SIME
    Hydrological drought occurs when there is an extended period of significantly reduced water availability, leading to depleted water sources and severe impacts on ecosystem and communities. Water scarcity caused by prolonged periods of reduced rainfall due to climate change can lead to the natural disaster of drought. However, little has been done so far on hydrological drought under climate change in Hamassa watershed. This study aimed to analyze and characterize hydrological drought under climate change in the Hamassa watershed, Rift Valley Basin, Ethiopia. Hydrological data (1992-2015), meteorological data (1992-2022), future climate data 2030-2090), spatial data, DEM, land use land cover, and soil were collected. CMhyd software package was used for bias correction of the climate data. The hydrological model soil and water assessment tool (SWAT) was used for hydrological analysis. The simulation result was calibrated and validated using the SWAT calibration uncertainty procedure (SWAT-CUP). Standard precipitation index (SPI) and stream flow drought index (SDI) are used to decide drought conditions in a watershed and to identify drought-prone areas in the watershed. Temperature projections for both the near and long term indicate an increase compared to the current period under both RCP2.6 and RCP8.5 scenarios. Meanwhile, precipitation projections suggest a decrease for the periods 2040-2060 and 2061-2072 under both RCP2.6 and RCP8.5 scenarios. The standard precipitation index (SPI) and stream flow drought index (SDI) results showed that the watershed experiences mild (-0.5- -0.999), moderate (-1- -1.49), severe (-1.5- -1.99), and extreme (≤ - 2) drought events. Droughts are projected to occur in the periods 2040-2060 and 2061-2072 under both RCP2.6 and RCP8.5 scenarios. Sub-watersheds 7, 8, 9, 10, and 11 showed high vulnerability to severe and extreme drought. Drought-mitigating structures are needed to mitigate drought in the watershed
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    IMPACTS OF LAND USE LAND COVER CHANGE ON RESERVOIR SEDIMENTATION (THE CASE OF RIBB DAM, IN LAKE TANA SUB-BASIN, ETHIOPIA)
    (Hawassa University, 2020-10-06) MEBRATU ESUBALEW ENGIDA
    Land use land cover (LULC) change is the challenge and continuous drivers of environmental change. Understanding the rate and process of change is, therefore, basic for managing the water resources and the environment at large. This study was intended to analyze the LULC changes impacts on sediment load from 2000 to 2018 periods, and select critical (hot spot area) sub basins and recommend best management practice for Ribb watershed of Lake Tana sub basin, Ethiopia. Both climate and hydrometric (flow and sediment) data were collected and analyzed over the period 1990 to 2018. Two time satellite imageries of the Land sat product (2000 and 2018) were used for land use change detection. The hybrid classification technique for extracting thematic information from satellite images were employed by using ERDAS model for classification of LULC. The Soil and Water Assessment Tool (SWAT) model was calibrated and validated to estimate sediment load of the watershed during the period 1992 to 2001 and 2002 to 2007 respectively. To manage the sediment load best management practices (BMP) as a scenario (filter strip, grassed water way and contouring) were implemented on 2018 LU map. The land use change detection result indicate that cultivated land has expanded from 66.87% in 2000 to 75.53% in 2018. Between 2000 and 2018 periods, it was increased by 8.66 %. The rate of increment during 2000–2018 periods were 608.915 ha/year. Similarly, settlement area had also increased by 2.09% from 2000–2018 periods. Similarly, shrub land and bare land also decreased at a rate of 412.868 and 227.651 ha/year, respectively, between 2000 and 2018 periods. Also the water body decreased at a rate of 1.593 ha/year between 2000 and 2018. The SWAT model result depict that the model give reasonable fit of sediment flux with observation during calibration and validation as evaluated with ENS ( 0.63 ) , R2 ( 0.67) and percent bias (17%) during calibration and ENS ( 0.58) , R2 ( 0.71) and percent bias of (12%) during validation period. Moreover, the severity of soil loss rate was increased with the average of 26.89 ton/ha/year from 2000 to 2018 LULC, which indicates that the management practice, was weak within the watershed. The BMP scenarios depict that filter strip was significant amount of LULC conversions practice and soil loss rate had occurred in the watershed from 2000 to 2018 periods, and expected to continue in the future. Thus, appropriate conservation and management practice are very much crucial to safe guard the life of the reservoir