Hydraulic Engineering
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Item 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 HusenEstimating 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.Item QUANTIFYING SURFACE AND GROUND WATER AVAILABILITY OF THE MEKI RIVER, CENTRAL RIFT VALLEY LAKES BASIN, ETHIOPIA(Hawassa University, 2024-08-19) SALAME ABDI AHMEDQuantifying surface water (SW) and groundwater (GW) availability is crucial for effective water resource management. This study assesses SW and GW in the Meki River sub-basin, central Rift Valley, Ethiopia, by SWAT and MODFLOW models. Integrating SWAT and MODFLOW. This study analyzed hydrological dynamics and groundwater resources for a period 2000 to 2020. SWAT divided the watershed into 18 sub-basins and 86 Hydrological Response Units (HRUs), simulating over 21 years with a three-year warm-up period. The SWAT model, calibrated and validated for 2000–2013, successfully simulated hydrological processes. Model performance was robust, with R² values of 0.76 and 0.85 and NSE values of 0.61 and 0.74, following 1000 simulations during calibration and validation. Critical parameters influencing streamflow included CN2, SOL_K, and GWQMN. Using SWAT-derived GW recharge and evapotranspiration, the MODFLOW-NWT model simulated groundwater flow. Calibration with PEST ensured accuracy, achieving a strong correlation (R² = 0.9922) between observed and simulated groundwater levels across 62 piezometers. Error metrics (RMSE = 9.46 m, MAE = 7.22 m) confirmed model accuracy. Spatial analyses showed heterogeneous groundwater flow influenced by local conditions and SW interactions. River-aquifer interactions revealed significant groundwater discharge to rivers, with daily discharge (91,198.128 m³/day) exceeding recharge (24,866.406 m³/day). The steady-state model showed balanced inflows and outflows, with recharge and river discharge being major inputs. This calibrated model offers a solid framework for managing groundwater resources in the Meki River sub-basin, supporting sustainable water management and planning. Groundwater flow primarily moved from the western escarpment towards the Tora-Koshe-Dugda ridge, influenced by varying hydraulic conductivity. The steady-state model balanced inflows and outflows (40.947 Mm³/year), with recharge (23.5 Mm³/year) and river contributions (9.1 Mm³/year) as key inputs. Evapotranspiration, river discharge, and extraction also played significant rolesItem ASSESSMENT OF CLIMATE CHANGE IMPACT ON STREAM FLOW OF GIDABO SUBBASIN, RIFT VALLEY BASIN, ETHIOPI(Hawassa University, 2022-08-10) YIDIDYA TSEGAYE ALEMUClimate changes alter regional hydrologic conditions and result in a variety of impacts on water resource systems. Such hydrologic changes will affect almost every aspect of human well-being. The goal of this thesis is to assess the impact of climate change on the hydrology of Gidabo subbasin located in the Rift Valley basin of Ethiopia. The RCP scenarios of types 2.6, 4.5, and 8.5 were used for the climate projection from the CORDEX Africa domain from CMIP5. The RCM of RCA4 was used to generate future possible local meteorological variables in the study area. These data were used as input to the Soil and Water Assessment Tool (SWAT) model to simulate the corresponding future streamflow Variability in the Gidabo subbasin. SWAT-CUP, a program for calibration and uncertainty was utilized for uncertainty analysis. The three projected time periods for this study were the 2040s, 2060s, and 2090s. The time series generated by RCM of RCA4 driven by MIROC5 indicate a significant increasing trend in maximum and minimum temperature values and a decreasing trend in precipitation for all RCP emission scenarios in Measso station for all time periods. The hydrologic impact analysis made with the downscaled temperature and precipitation time series indicates variation in an increasing and decreasing trend for the three RCP scenarios at different periods respectively. The model output shows that there may be a mean annual, seasonal, and mean monthly decrease in stream flow volume for all RCP scenarios in the Projected time periods in the future. It also shows most of the projections are within the uncertainty bandwidth of 95PPUItem LAND USE LAND COVER DYNAMICS AND CLIMATE CHANGE IMPACT ON THE HYDROLOGY OF RIBB RIVER CATCHMENT, UPPER BLUE NILE BASIN, ETHIOPIA(Hawassa University, 2020-10-06) SAMSON iHAILEThis iinvestigation iexpects ito iassess ithe ieffects iof iclimate iand iland-use ichange ion ithe ihydrology iof iRibb iwatersheds iusing ithe iSoil iand iWater iAssessment iTool i(SWAT). iRibb iwatershed iis ilocated iin ithe inorthwestern iEthiopia iRiver ibasin iwhich iextends ifrom i10.00ºN ito i11.00ºN ilatitude iand ifrom i35.00ºE ito i38.00ºE ilongitude. iThe iexamination idissected ithe ihydrologic ieffects iof iclimate iand iland-use ichanges iin itwo idifferent iways. iThe imain iperspective icomprises iof idescribing ihydrological ichanges itwo iverifiable iland iuse imaps i(Land iSat_8 i2001, i2017) iwere iutilized ito ispeak ito iland-use ichange ion ithe iwatershed, iand ihistorical iclimate idatasets i(1988-2017) iwas iutilized ito imake iSWAT imodels ifor iRibb iwatershed. iLand-use ichange irecognition iwas ifinished iusing iremote idetecting iprocedures iand ithe imaps iwere iprepared iusing iERDAS iImagine i14 iand iArc iGIS i10.3 isoftware. iClimate iand iLand iuse iis itwo iprimary ifactors istraightforwardly iimpacting ithe ihydrological iprocedures iof ithe iwatershed. iRCP i4.5 iand iRCP i8.5 iscenario iwere iused ito iproject ithe ifuture iclimate iof ithe i2050s, iand i2080's. iThe ianalysis iwas iperformed iin itwo ifuture iprojection, i2050 iand i2080 iconsidering ithe ireference ibaseline iperiod i1988-2017 iwith iboth iRCPs. iMaximum itemperature ichanges ifor iRCP i4.5 iraised iby i0.17°C ito i0.9°C iand i0.2°C ito i1.1°C, iand ifor iRCP8.5 i0.2°C ito i1.06°C iand i1.04°C ito i1.73°C iMean imonthly imaximum itemperature ichange ifor ithe i2050s iand i2080s. iand iMinimum itemperature ichanges ifor iRCP i4.5 iand iincrease iby i0.03°C ito i0.8°C iand i0.2°C ito i0.95°C iand ifor iRCP i8.5 i0.25°C ito i0.84°C iand i0.31°C ito i1.65°C ifor ithe i2050s iand i2080s itime iperiods iwith ireference ito ithe ibaseline iperiods irespectively. iAnd ialso, ithe imean imonthly iprecipitation ichange ishowed iincreasing i iby i4.25mm ito i6.25mm iand66.42mm ito i78.32mm ifor iboth iRCP4.5 iand iRCP8.5 iscenarios irespectively. iCombined iimpacts iof iland iuse iand iatmosphere ichanges iindicated ithat i88.15m3/s ifor ibaseline, i40.57 im3/s imore iin ithe i2050s, iand i38.48m3/s imore iin iThe i2080s ifor istream iflow icompared ito iclimate ichange iscenario. iThe icombination iof iclimate iand iland-use ichanges iwould ilead ito ia idecrease iin istream iflow i(73.55% ito i29% iin ithe i2050s iand i64.98% ito i14.67% iin ithe i2080s). iSWAT ioutput ito ibaseline irun i(1987-2017). iClimate iand ithe iland iuse iland/cover ichange iand iits imain iimpetus ion iRibb iwatershed iutilizing iLANDSAT_8 iimage ito icreate itwo ithe ihydrological imodel ioutcome ishows ithat ithe istream iwas itouchy ito iland icover ichange iby ilessening ibase istream iand iincrement itop istream ithis iis ibecause iof iincrement iagrarian iland iand ideforestation.Item EVALUATION OF THE IMPACTS OF CLIMATE CHANGE ON SEDIMENT YIELD FROM THE KATAR WATERSHED, CENTRAL RIFT-VALLEY BASIN, ETHIOPIA(Hawassa University, 2021-12-10) GELILA SAMUELClimate change is one of the issues that, the world facing today including Ethiopia and it is anticipated that climate change will impact sediment yield in watersheds. The purpose of this study was to investigate the impacts of climate change on sediment yield from the Katar watershed in the Eastern Lake Ziway Basin, Ethiopia. Here, used the coordinated regional climate downscaling experiment (CORDEX)-Africa data outputs of Hadley Global Environment Model 2-Earth System (HadGEM2-ES) under representative concentration pathway (RCP) scenarios (RCP4.5). The analysis was performed in two future projection of 2030’s and 2060’s under the reference of baseline period of 1987-2017 with their RCP correction. After assessment of missing, quality and consistency of data; bias, the coefficient of variation and correlation were used to evaluate the systematic error of precipitation amount, the degree of precipitation variability and bias-corrected before serving as input to the impact analysis A Soil and Water Assessment Tool (SWAT) model was constructed to simulate the hydrological and the sedimentological responses to climate change. The model performance was calibrated and validated using the coefficient of determination (R2 ) and Nash–Sutcliffe efficiency (NSE). The results of the calibration and the validation of the sediment yield R2 and NSE were 0.65 and 0.61, and 0.66 and 0.65, respectively. Climate change output from this research shows that the watershed will get warmer in the future. Both minimum and maximum temperature of the catchment have an increasing trend by 1.04 0C for 2030’s and 2.04 0C for 2060’s for minimum temperature and 0.90 0C for 2030’s and 1.56 0C for 2060’s for maximum temperature. Also, average annual rainfall shows increase by 4.8% for 2030’s and 1.6 % for 2060’s. The results of downscaled precipitation and temperature increased in both future period under RCP4.5 scenario. These climate variable increments were expected to result in intensifications in the mean annual sediment yield of 41.1% and 8.9% for RCP4.5 by the 2030s and the 2060s, respectively. The average annual sediment yield were 398 ton/km2 and 307 ton/km2 for the 2030’s and 2060’s, respectively. From this study, the results show that the sediment yield of the watershed is likely to increase under climate change scenarios. This will help water resources managers make informed decisions regarding the planning, management, and mitigation of the river basins.