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    STREAM FLOW AND SEDIMENT YIELD MODELING: THE CASE OF ROBI JIDA WATERSHED, UPPER BLUE NILE BASIN, ETHIOPIA
    (Hawassa University, 2024-12-24) BELSTI DEGU NURIE
    Soil erosion, streamflow, and sediment studies are crucial for supporting the agricultural sector through watershed planning and management practices. This study aimed to model stream flow and sediment yield in the Robi Jida watershed in the Upper Blue Nile Basin, Ethiopia, and identify best management scenarios with the records of suspended sediment concentration. The historical records of the meteorological, hydrological, and suspended sediment concentration data were used for the hydrological modeling. Sediment yield data was generated from the discharge-sediment rating curve equation using the suspended sediment concentration data. Spatially, 30*30 m DEM, 90*90m soil, and 30*30m resolution land use/land cover data were used as input for the hydrological model. In this study, the Soil and Water Assessment Tool (SWAT) model was used to model streamflow and sediment yield. The model performance in simulating streamflow and sediment yield was evaluated through sensitivity analysis, calibration, and validation processes. Period from 1994 to 2010 was used for calibration and 2011 to 2018 was used for validation. During calibration the model performance statics R2 , NSE, and PBIAS were obtained (0.80, 0.70), (0.80, 0.70), and (-4.8, 1.1) for stream flow and sediment yield respectively, and similarly for model validation R 2 , NSE, PBIAS as obtained (0.77, 0.72), (0.77, 0.71), (-4.7, -5.7) respectively. Therefore, the result indicated that the SWAT model performed well and the estimated average annual sediment yield of the Robi Jida watershed was 6.42 tons/ha/year. Based on the average annual simulated sediment yield, identified 9 sub-watersheds are critical whose annual sediment yield limit ranges above the tolerable limit were identified and prioritized for effective watershed management. Therefore applying and evaluating the different management scenarios, filter stripe 1m and 5m, vegetative contour strip, soil/stone bund, terracing, and contouring resulted in a 19.15%, 35.01%, 47.13%, 57.09%, 73.37%, and 52.81% decrease in the average annual sediment yield, respectively. Therefore, soil/stone bund and terracing scenarios demonstrated the highest potential for reducing sediment yield and showed promising results as effective best management practices in the Robi Jida watershed.
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    IMPACT OF LAND USE LAND COVER CHANGE ON HYDROLOGIC RESPONSE: THE CASE OF DEME CATCHMENT, OMO-GIBE RIVER BASIN, ETHIOPIA
    (Hawassa University, 2021-10-24) MULUKEN ISRAEL BIRRU
    Hydrologic modeling was conducted for each LULC map in three time periods (1999, 2010, 2018) in the Deme catchment using the SWAT model. Changes in streamflow and its components between three simulations by using the LULC map of 1999, 2010, and 2018 were related to the changes of LULC to quantify the impact of LULCC. The data used for analyses were streamflow of Deme catchment, satellite imageries of 1999,2010, and 2018, Digital elevation model, and meteorological data. LULC classification was carried out by using ERDAS imagine2014. Five types of LULC were identified in the Deme watersheds such as agricultural land, grassland, bushland, built-up area, and forest. The LULCC analysis depicted that there was an expansion of agricultural land and the built-up area in the catchment. Agricultural land was increased by 29.96% and 36.78% from 1999-2010 and 2010 -2018 respectively. The built-up area was also increased by 80.41% and 148.47% during the first and the second period respectively. The other LULC classes showed a continuous decrement in all periods. The performance evaluation result depicted that the SWAT model can be used for the analysis of the impact of LULCC on streamflow of the Deme catchment. During calibration, the value for NSE, R2, and PBIAS was 0.80, 0.75, and -1.2 respectively. During validation, the value for NSE, R2, and PBIAS was 0.74, 0.70, and -7.3 respectively. The LULCC had impacted the magnitude of streamflow and its components. During the driest season, mean monthly streamflow has decreased by 16.71% and 37.81% during the first and second periods respectively. But in contrast during the wettest month, the mean monthly streamflow has increased by 12.79% and 25.16% during the first and second period respectively. The contribution of mean annual surface runoff increased by 11.63mm and 15.94mm from 1999- 2010 and 2010 to 2018 respectively. While lateral flow decreased by 6.47mm and 9.96mm in both periods. Similarly, shallow groundwater recharge decreased by 3.77mm and4.67mm during the first and second periods. The decrease in lateral flow and shallow groundwater recharge and increase in surface runoff was related to the expansion of agricultural land, and built-up area, as well as decrement of forest, bushland and grass land. Therefore, Deme watershed requires the application of appropriate watershed management options to minimize the undesirable impacts on water and land resources.
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    PHYSICAL IRRIGATION POTENTIAL ASSESSMENT FOR SURFACE IRRICATION: A CASE STUDY IN CHEMOGA WATERSHED, UPPER BLUE NILE BASIN, ETHIOPIA
    (Hawassa University, 2020-10-11) KASSANESH MELKAM MENGISTE
    Assessment of available land and water resources for irrigation is essential for planning their use, to utilize limited resources efficiently and for the sustainable production of crops and food security of the ever increasing people in developing countries like Ethiopia. The study was mainly focused on assessing the available land and water resources potential for surface irrigation of Chemoga Watershed. This was done by using Geographic Information System (GIS)-based Multi Criteria Evaluation (MCE) tools, a hydrological Soil and Water Assessment Tool (SWAT) model, and a Crop Water and Irrigation Requirements Program of FAO (CROPWAT) model. GIS was used to map the land suitable for surface irrigation based on slope, soil, land use /land cover, and river proximity. SWAT model was used to estimate the water availability, and CROPWAT model calculate the reference crop evapotranspiration, effective rainfall, net and gross irrigation water requirement of crops. Potentially suitable land for surface irrigation development was evaluated by selecting six crops (barley, wheat, bean, maize, onion, and potato). The result of the overall weighted analysis for these factors gave about 25462.08 ha (71.4 %) of the Watershed land considered as high to moderately suitable whereas 10427.53 ha (28.6 %) were not suitable for surface irrigation. The SWAT model was calibrated and validated from the available hydro metrological and spatial data. Model performance result showed in between the observed and simulated stream flow with coefficient of determination (R2) and Nash-Sutcliffe efficiency (ENS) values 0.86 and 0.7 for calibration, and 0.74 and 0.63 for validation, respectively and indicated a good performance of the model in simulating the hydrology. The annual average simulated stream flow was evaluated and 36.2 m 3 /s. The water demand required by the selected crops was 228.18m3 /s/ha. From the total available suitable land, only 12376.03 ha can be irrigating with the available water
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    HYDROLOGICAL RESPONSES TO CURRENT AND PROJECTED LAND-USE/LAND COVER CHANGES OF THE WELMEL RIVER WATERSHED, GENALE DAWA BASIN, ETHIOPIA
    (Hawassa University, 2021-03-27) SOLOMON ESHETE AYALEW
    Land use/land cover change is one of the important concerns in many regions of the world. It is recognized that dramatic LULC change can significantly impact regional climate, ecosystem stability, water balance, stream silt up, socioeconomic practices, and biodiversity. The main objective of this study was to assess the hydrological responses to historical and future Land Use/Land Cover Change at basin and sub-basin levels of the Welmel River watershed, which is located in the Genale-Dawa Basin South Eastern Ethiopia using hydrological SWAT model. The study analyses the historical LULC change between the years 1990, 2005 and 2020 and the future year of 2035 and 2050. The hydrological responses to LULC changes in the Watershed were analyzed using the historical and future LULC maps. Images were processed using ERDAS Imagine 2014 and CA-Markov chain model was used for the prediction of the LULC map of 2035 and 2050. Discharge data from 1990 to 2006 and 2007 to 2014 were used for calibration and validation respectively with three years of warm-up period and climate data from 1990 to 2020 time period. The main finding of this study revealed that the coverage of agriculture/settlement increased by a rate of change of 6.85km2 /year, while forestland was declined by the rate of change of 9.16km2 /year over the last 31 years between 1990 and 2020. In the coming 31 years (by 2050), if the current trend of LULC change continues, agriculture/settlement land is expected to increase by the rate of change of 6.73km2 /year, while forestland is expected to diminish by a rate of change of 8.78km2 /year. As a result of LULC change, surface runoff has increased by 25.32% while lateral flow, groundwater flow, water yield, evapotranspiration and percolation declined by 19.91%, 17.17%, 2.38%, 0.36% and 17.17% respectively between 1990 and 2020. If the current rates of LULC change continue, surface runoff is expected to increase by a relative change of 18.47% while lateral flow, groundwater flow, water yield, evapotranspiration and percolation are expected to decline by 26.84%, 17.51%, 2.09%, 1.91% and 17.47% respectively by 2050. Average annually, surface runoff in all 29 sub-basins has increased by 39.90mm and groundwater flow decreased by 34.57mm. The average annual stream flow increased with a relative change of 6.18% from 1990 to 2020 and is expected to increase by 12.69% by 2050. The average wet annual flow from 1990 to 2020 increased by 10.21%, while the average dry annual flow decreased by 6.34%. The average wet and dry annual stream flow is expected to increase and decline by 19.67 % and 6.86% respectively in 2050. Therefore, the Woredas in and around the Welmel River Watershed and the Bale Mountains National Park should integrate to design and implement a proper strategy for protecting and managing the existing forest and woodlands in addition to rehabilitating the degraded areas to maintain the hydrological balance of the watershed.
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    ASSESSMENT OF WATER BALANCES USING SWAT MODEL AND AGRICULTURAL WATER DEMAND ANALYSIS OF GIDABO RIVER CATCHMENT, RIFT VALLEY BASIN, ETHIOPIA
    (Hawassa University, 2020-07-18) CHALA TADESSE
    To use water resources sustainably, it is important to understand the quantity of water resource spatially and temporally. The work presented here attempts to model water balance of one of Gidabo sub-watershed of Ethiopian Rift Valley Basin using the Soil and Water Assessment Tool (SWAT. Statistical model performance measures, the coefficient of determination (R2 ) and Nash-Sutcliffe Efficiency (NSE) were used to evaluate the correlation between the observed and simulated monthly stream flow. The result shows an acceptable performance of SWAT model in simulating the watershed hydrology as evidenced by the NSE value of 0.79 and R2 value of 0.80 at calibration (using data from1990-2009) and NSE = 0.71 and R2 =0.82 at validation (using data from2010- 2014). In terms of water balance components, the long-term annual precipitation is found to be in the magnitude of 1435.58 mm; whereas the surface runoff; total water yield; and actual evapotranspiration, are estimated as 62.20; 1189.73, and 228.40 mm respectively. In order to link the water balance estimation with the local agricultural water demand, wheat and potato are selected for they are common crops for irrigation in the watershed. While taking the month of March, which is the month of maximum agricultural water demand (11.6 m 3 /s), the watershed is found to be water-surplus as indicated by the water availability of the critical month (12.22 m3 /s) to be higher than the demand. This research implies that the use of models in supporting decisions related to water resources development and management is paramount important to understand how the system functions
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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