Hydraulic Engineering

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    Estimation of Sediment Yield Using SWAT Model and Reduction Methods (A Case Study of the Middle Awash Multipurpose Dam, Awash River Basin, Ethiopia)
    (Addis Ababa University, 2024-02) Saba Kidane; Daneal Fikresillassie (PhD)
    Sedimentation has been one of the critical challenges to create and sustain development opportunities for the poor families in Awash River Basin. Therefore, evaluating and understanding watershed sediment yield is vital to manage sediment related problems. Thus, this study used Middle Awash Multi-Purpose Dam (MAMD) catchment area to estimate sediment yield, to hotspot the most erodible sub-catchment area and assess the appropriate mitigation measurements to reduce the sediment load from the catchment. For the simulation of runoff and sediment yield from the MAMD watershed, the Soil and Water Assessment Tool (SWAT) model was applied. The total watershed has an area of 21,103.16 Km2 and located in Afar Regional State and Oromiya Regional State, Awash River Basin, Ethiopia. The SWAT model is calibrated and validated using SWAT-CUP with uncertainty analysis SUFI-2 (Sequential Uncertainty Fitting) procedure using measured monthly flow and sediment data from Awash and Metehara Gauge Stations. Using a data from 1993 to 2006 for calibration and 2007 to 2013 for validation, both results showed a good match between the measured and simulated flow and sediment. Flow calibration gives a coefficient of determination (R2) and Nash-Stucliffe simulation coefficient (NS) of 0.67 and 0.62 respectively. Flow validation gives R2 and NS of 0.65 and 0.63 respectively. Sediment calibration gives R2 and NS of 0.67 and 0.62 respectively. Sediment validation also gives R2 and NS of 0.69 and 0.69 respectively. Thus, the model performed well in simulating the flow and sediment for the study area. The estimated sediment result shows that the average annual sediment load at the outlet of the watershed was 40.32 ton/year. In this study, sub-basin 14 sub-basins were found to be a sediment prone areas having an annual sediment load that varies from 10.01 to 169.94ton/ha/year. Also, the model was applied to examine the Best Practice Management (BMP) scenario under the change of 25%, 35% and 50% Agricultural land use type to forest land, and other recommended scenarios to reduce the production of sediment. The investigation showed that the conversion of 25%, 35% and 50% of Agricultural land to forest land can reduce the total sediment yield by 26.59%, 34.15% and 45.76%, respectively. The implementation of Filter Strips, Grassed Waterways, Terracing, and Contouring can reduce the mean annual sediment yield at the outlet by 67.19%, 81.80%, 84.30% and 59.25%, respectively. The application of Terracing has high sediment reduction potential than other best management practices.
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    Hydro-Economic Modelling of Multi-Objective Cascade Reservoir Operations under Seasonal Streamflow Variability
    (Addis Ababa University, 2023-10) Bahru Mekuria; Asie Kemal (PhD); Getachew Tegegne (PhD); Assefa M. Melesse (Prof.)
    Effective river basin management is challenging due to competing demands and environmental constraints. Understanding current reservoir operations is critical for developing alternative policies. This study applies a reservoir operation simulation-optimization technique to identify the best policies by utilizing economical approaches that balance competing objectives and system uncertainty. It may not accurately reflect a hydrologic model's genuine simulation capability to evaluate its performance just in terms of a formal simulation method. Hence, this study examined the effect of subbasin spatial scale on the hydrological model prediction uncertainty for different flow quantiles within the Omo Gibe River basin's sub-basins: Abelti, Wabi, and Gecha watersheds, from 1989 to 2020. The study found that the SWAT model accurately reproduced the observed hydrograph with over 85% accuracy for the Abelti watershed, over 82% accuracy for the Wabi watershed, and over 73% accuracy for the Gecha watershed. The subbasin spatial scale impacted the reproduction of flow quantiles, and the best scales for peak and low flows were found to be 79-98% and 29-42%, respectively. The study highlights the importance of investigating proper subbasin spatial scales for sustainable management of floods and drought. Furthermore, it suggests an improvement over the existing method of evaluating hydrological models and emphasizes the need to account for hydrologic model uncertainty for a good assessment. This study also addresses the challenge of estimating water resources in ungauged catchments, such as the Omo-Gibe River basin in Ethiopia, which is ungauged in about 70% of its area. The Reliability-weighted (RB) approach, a new method that combines three commonly used parameter transfer techniques (Global mean, Physical similarity, and Spatial proximity), was introduced to predict runoff in regions with unreliable data. The weights are computed using the donor catchment's hydrological model's reliability value during the calibration and validation periods. The RB method outperformed all three regionalization approaches by about 30% for the test catchments, and the proposed strategy's regionalization performance had a metric Nash-Sutcliffe efficiency greater than 0.50 approximately 85% of the time. The study shows that the RB approach is a useful tool for assessing available water resources in ungauged catchments.The Omo Gibe cascade reservoir operations problem was examined and solved using a cutting-edge evolutionary optimization method (Borg MOEA). The Omo Gibe River Basin system faces competing sectoral needs for hydropower generation, flood management, public and private irrigation, flood recession farming, and environmental flows. The results of the model showed reliable and robust optimal solutions, enabling the evaluation of the tradeoffs between revenue generation, minimum environmental flow provision, and reservoir storage conditions. Under the existing scenario, the hydropower can produce up to 4.6 billion ETB, while the irrigation revenue is 720 million, which is expected to increase faster than hydropower revenue in the near-future scenario, up to 9 billion, whereas hydropower revenue will produce 10 billion, creating more competition, higher water usage, and necessitate better resource management. In addition, the renovated Gibe III Power Station's hydropower production can increase by approximately 65% in 2019 compared to the actual hydropower production. The evolutionary algorithm models used for reservoir operations are outstanding. Employing these advanced optimization models with more data can lead to a better understanding and improved reservoir operations.
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    Flood Hazard Mapping and Propose Mitigation Measure: a case of Wera District, in Halaba Zone, Ethiopia
    (2024-02) Martha Ersumo; Dereje Hailu (PhD)
    For flood prone areas, identifying flood generating factors, mapping flood hazardous zones and propose flood eliminating methods can increase the knowledge, awareness and individual initiatives to prevent themselves and their properties from flood effects by using appropriate flood mitigation measures before and during flood events. Developing Flood Hazard Maps for flood prone area can be developed by integrating geo-spatial information on flood conditioning factors. Based on the AHP and GIS techniques, Flood Hazard Map for Wera District was develop by using Soil data, Lu/Lc data, Drainage Density, Slope, Rainfall and Topographic data of the Catchment. This study aims to map flood hazardous area and propose mitigation measures, for Wera Woreda in Bilate River sub-basin by using GIS, HEC-HMS, AHP, HEC-RAS and HEC – GeoRas software. Depending on the L-momentum Ratio diagram of the three distribution methods, Gumbel Distribution was used for this study to compute peak discharge. Thus, the final peak Discharges for 2,5,10, 25, 50 and 100 years was estimated 119.44, 189.18, 235.36, 293.70, 336.71 and 379.94m3/s respectively. HEC-Geo RAS Software was used to develop river geometry such as: the river centerline, river bank, flow path and cut cross-section for Bilate River. HEC-RAS, hydraulic analysis includes the computation of the water surface profiles. Based on the degree to flooding, the importance of selected factors was ranked to five flood hazard category, namely very low, low, moderate, high and very high flooding. The weight coefficients were determined for each parameter by Analytical Hierarch Process (AHP) and overlay of ranked spatial information result the final flood hazard map of study areas. The flood hazard maps indicate that 60, 91, 93, 58, and 12.5km2 corresponds with very high, high, moderate, low and very low hazard areas respectively for Wera Woreda. For this thesis work, I was try to compare construction of levee along the channel and channel modification as alternatives for remedial measures to protect the flood from study area. From two alternatives, construction of levee along the river was the best alternative for study area.
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    Dam Hazard Classification using ENTRO Guideline in the case of Fato Dam, Ethiopia
    (Addis Ababa University, 2023-07) Firaol Chalchisa; Netsanet Nigatu (PhD)
    The phenomenon of spontaneous breaches of dams and consequent flooding that have occurred throughout history have made it necessary to design dam safety plans and hazard management measures. In this case, the preliminary job was analyzing the dam breach before the event and ranking these dams based on risk. The pre-event analysis of a dam breach scenario for the Fato dam was the focus of this thesis. A deterministic approach is applied to model the dam breach. The extent of the resulting flood inundation is mapped and overtopping, and piping failure scenarios are evaluated. The upstream boundary condition comprises a 2.3*PMF inflow hydrograph and a base inflow hydrograph, and the downstream boundary condition is made up of a riverbed slope assuming the bed slope and energy grade line slope are equal to HAEC. The main reason why the PMF flood to overtop to dam needed is large is that a large freeboard is provided for the Fato dam about 3 meters here between the spillway crest and the dam crest. Seven 2D simulations were run, five of which are for various overtopping failures and two of which are for piping failure modes. HEC-RAS Version 6.3.1 hydraulic modeling software is used. Furthermore, seven deterministic non-physical empirical are assessed and compared. The five deterministic non-physical empirical methods have resulted in peak flow values between 32,940.26m3/s and 22,404.28m3/s for overtopping and two of them were 20,224.88m3/s and 11,799.72m3/s for piping modes of failure, respectively. Of the failures, overtopping failure generates the biggest peak discharge, which is 32,940.26 m3/sec using Von Thun & Gillete Equation. Not only the peak discharge results from this equation but also the flood reach to Guder Town is short for it, which is 1.35Hrs. Guder town is the focus of the study since most of the population at risk was situated in this town. Based on this flood inundation map the possible people at risk (PAR) were found to be 9,425 people. And based on the DSO-99-06 manual the Loss of life is found to be 4,713. The study found the dam breach and its corresponding flooding to be catastrophic in Loss of Life therefore its categorized as a very high-hazard dam based on ENTRO guidelines. The author also checks for the level of reduction if EAP is introduced, and the Loss of life is found to be only 10 people. Therefore, the study highlighted the provision of EAP to this dam will reduce the possible loss of life in case the dam fails. Taking this dam as a case study recommended the need for a national-level regulatory framework for different levels of dam life (Design, Construction, Filling, Operation, and Decommissioning).
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    Flow Estimation in Zarima May Day Dam watershed using SWAT Model
    (Addis Ababa University, 2023-03) Haftom Teklay; Yilma Seleshi (Prof.)
    Estimation of flow on the hydrological regime of river basins is one of the most concerns in the river sub basin of zarima. With plethora of tools available in the literature choosing of an appropriate tool that can quantify and analyze the impact of flow on the hydrological regime in a systematic and planned manner is important. Soil and Water Assessment Tool (SWAT) integrated with Geographic Information System (GIS) based interfaces and its easy linkage to sensitivity, calibration and uncertainty analysis tools made its applicability more simple and has great potential in simulation of the past, present and future scenarios. A number of standards were used to appraise the model set-up, model performances, physical representation of the model parameters, and the accuracy of the hydrological model balance to assess the models that are defined in journal papers. On the basis of performance indicators, the mainstream of the SWAT models were categorized as providing satisfactory to very good. This review debates on the application of SWAT in analyzing land use land cover and run of estimation for the case study of Zarima May Day dam watershed. The Application of SWAT and land use land cover change in simulation models for Zarima May Day dam watershed is to improve accuracy, reduces costs, and allows the simulation of a wide variety of conservation practices at watershed scale. It is also observed that different researchers and/or model versions bring about in different outcomes while a comparison of SWAT model applications on similar case study was applied. This review determines the interactive role of SWAT and GIS technologies in improving integrated watershed management in Runoff Estimation and land use land cover for the topic of the study area.
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    am Breach Modelling and Flood mapping, a Case Study of Ribb Dam
    (Addis Ababa University, 2021-01) Fasika, Worku; Daneal, Fikreselassie (PhD0
    The spontaneous dam breach phenomenon and the resultant flooding that happened in the world history leads to the requirement of establishing a dam safety plans and hazard management strategies. In this regard, the dam breach pre-event analysis will be the prerequisite work. This thesis addressed a pre-event analysis of a dam breach scenario for Ribb dam located in Amhara regional state, Ethiopia. Deterministic and probabilistic approach for the modelling of the dam breach is used. Overtopping and piping failure modes are assessed and the resulting flood inundation is mapped. A 1.5 PMF inflow hydrograph and a base inflow hydrograph are used as upstream boundary condition, while Lake Tana makes the downstream boundary condition. Fourteen 2D simulations are carried out and of which ten are for different breach parameters, two are for uncertainty analysis on breach parameters, and two are sensitivity analysis on Manning’s roughness coefficient ‘n’. HEC-RAS Ver 5.0.7 hydraulic model is employed, and McBreach is used for probabilistic dam breach modelling. In this study, five deterministic non-physical empirical methods and probabilistic breach modelling are assessed and compared. The five deterministic non-physical empirical methods have resulted in peak flow values between 67,570m 3 /s and 113,153m 3 /s for overtopping and between 22,269m 3 /s and 40,926m 3 /s for piping modes of failure respectively. For both modes of failure, MacDonald and langridge-Monopolis and Frohelich (1995a) produced the lowest and highest peak discharge respectively. The 1% and 90% exceedance probability peak discharge for overtopping failure mode is 104,379m 3 /s and 77,521m 3 /s respectively. The Manning roughness coefficient ‘n’ sensitivity analysis showed a 0.11 to 39.9 percentage increase in flood depth and 2.20 to 20.67 percentage decrease in velocity for an increase of the Manning roughness coefficient by 30%. In addition, the Manning roughness coefficient ‘n’ sensitivity analysis showed a 0.00 to 15.32 percentage decrease in flood depth and 10.81 to 28.09 percentage increase in velocity for a decrease of the Manning roughness coefficient by 30%. The study highlighted the dam breach and its corresponding flooding could be potentially catastrophic and high priority should be given to monitoring and surveillance of the dam.
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    Flood Change Detection, Attribution and Management Implication in Data-Scarce Watersheds: A Case of Wabi Shebele River Basin, Ethiopia
    (Addis Ababa University, 2022-03) Fraol, Abebe; Belete, Berhanu (PhD); Semu, Ayalew (PhD)
    Trends and variability of hydroclimatic extremes have received excessive attention in many hydrological modeling studies. However, many scientists are still uncertain to attribute the proportion of hydrologic variability is driven by climate change/variability and anthropogenic factors, particularly in tropical catchments. Wabi Shebele River Basin in Ethiopia experiences flooding with limited availability of the type data is used as a case study to investigate changes in flood discharges and potential driving factors affecting hydrologic response changes and management implication of understanding flood variabilities. Both statistical non-parametric tests and SWAT hydrologic model are used in flood change detection and attribution process. Among the discharge-based flood indicators, annual maximum series (AMS) and peak over threshold (POT) are used to analysis flood time series. Overview of flood discharge analysis indicates the increasing tendency of flood events throughout the basin since 2000. The seasonality analysis reveals cycles of significant extreme high river flows at five to ten-year intervals in the river basin. Precipitation extremes show an increasing trend in the western and eastern upper basin and a decreasing trend in the middle between 1980-2018. The assessment upon driving forces of floods: rainfall, drainage area, elevation, slope, sand soil, forest, and agricultural land coverage identified as the most influential variables in flood formation of the basin. The correlation analysis between extreme streamflow with precipitation and global climate indices reveals a moderate to high correlation value. The semi-distributed hydrological model (i.e., SWAT) conducted to disentangle the impact of climate change and LULC change on flood hazard showed that precipitation and agricultural land coverage led to increment in flood indices. In the middle and upper parts of the Wabi Shebele basin, streamflow increases with increases in agricultural land, and forest coverage decrease. The simulation of hydrologic response to climate change in the future (i.e., 2041-2060 and 2081-2100) showed that the river basin is likely to experience an increase in flood hazard with an increase in precipitation in the future as temperatures increase less than 2oC. Finally, the study on the implication of flood variability revealed that socio-economic damages follow a similar trend tendency to flood variabilities in the river basin. In such cases, development-based climate adaptation mechanisms and flood risk management strategies need to placed. In transboundary river basins like Wabi Shebele, floods have transboundary consequences which need cooperation between riparian countries for Integrated Flood Management (IMF).
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    Estimation of Sediment Yield under the Impact of Climate Change (Case of Mille River Watershed, Lower Awash Sub-Basin, Ethiopia)
    (Addis Ababa University, 2022-03) Samuel, Tadesse; Bayou, Chane (PhD)
    Climate change impact and its variability on stream flows and sediment yield are now becoming one of the significant challenges. Hence evaluation of the impact and the trends of the climate change on hydrological process is very important at watershed level. The aim of this study was to assess the impact of climate change on the sediment yield of Mille river watershed at the lower Awash sub-basin using both climate and SWAT hydrological model. The climate model variables (precipitation and temperature) were obtained from Coordinated Regional Downscaling Experiment (CORDEX) of RACMO22 RCM climate model under HadGEM2-ES GCM and CCLM4 regional Climate model under ICHEC-ES global climate model with representative concentration pathway (RCP4.5) and (RCP8.5) scenarios. Bias correction was applied to climate variables and average value of the two RCM models arranged before future climate data’s transferred to hydrological model (SWAT) to simulate discharge and sediment for future time period. For model performance evaluation; Coefficient of determination (R2) and Nash Sutcliffe Efficiency (NSE) were used during calibration (1989-1997) and validated (1998-2002) period. The result of calibration and validation flow (R2 and NSE) are 0.68, 0.54 and 0.7, 0.6 respectively. Calibration and validation of sediment also provided a result of 0.81, 0.81 during calibration and 0.8, 0.79 during validation for R2, NSE respectively. Stream flow was simulated for two consecutive thirty years periods of (2031–2060) and (2061-2090) for both scenarios and compared with the base period (1986–2015) to investigate impact of climate change on hydrological process. The result obtained shows that overall mean annual precipitation projected to increase by 3.86% in 2050s and 7.82% during 2070s under RCP 4.5. For RCP 8.5 climate scenario precipitation increase by 4.61% during 2050s and 10.57% during 2070s. The hydrological response of a catchment also show an increment for the increasing precipitation amount such as sediment yield increase by 5.85% and 10.11% during 2050s and 2070s respectively under RCP 4.5 and 8.99% and 14.25% of increment occur in 2050s and 2070s respectively for RCP 8.5 climate scenario. Temperature maximum also shows an increment with a magnitude of 0.11oc and 0.09oc under RCP 4.5 of the 2050s and 2070s on the other hand 0.2oc and 0.15oc increment was observed with in the same period of RCP 8.5. Temperature minimum will be increase for the future over the Mille watershed by 0.09oc and 0.15oc Under RCP 4.5 and by 0.13oc and 0.18oc under RCP 8.5 for the same time horizons of 2050s and 2070s.Overall there will be a variations of precipitation, temperature and sediment yield month to month and season to season. Therefore, it is important to consider this variation of sediment yield and climatic variable to draw appropriate guidelines for planning and management of different water resources project.
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    Evaluation of Ring Road Drainage Structure (Case Study Megenagna to Bole Road)
    (Addis Ababa University, 2021-11) Yisake, Desalegn; Daniel, Fikresilassie (PhD)
    The Purpose of the study is to assess the Performance of Drainage Structures of the Ring Road from Megenagna to Bole Round About and gives a mitigation measures regarding the drainages structure along the Road. An exploratory method of research has been used in the study. The study uses both primary and secondary instruments of data collection. The primary data collection instruments are observation, measuring the geometry (width and height) of existing cross drainage structures on the site, photographs that show the existing drainage structure conditions. The secondary data sources are Rainfall data, soil type, land use, geological map, and DEM data and QGIS 3.16 (open-source software) uses for watershed delineation of the catchment and extraction of other important geometric characteristics (i.e length of longest flow path, slope, elevation of the river and area of the catchment). Hydrological analyses have been carried out by using Soil Conservation Service (SCS) curve number Method and Rational method, the hydraulic analysis computed using the HEC RAS (open-source software) that to determine water surface elevations at all locations of interest for either a given set of flow data (steady flow simulation). The next step is to check the adequacy of the existing drainage system that suite the site conditions for the computed discharge, thus based on the hydraulics result, the major river exist around imperial not functioned well for the 100-return period, so shall be replaced with the new Bridge as span of 15m and 3.5m, which will accommodate the incoming 100-year discharge. The minor river exists between Ayat hospital and Imperial Round about, it is not having a significant flow and Can be retain as it is, only required maintenance and clearing of the channel. Regarding to the storm drainage all the inlets are not functioned properly due to complete damage of inlets and blockages of by rubbish/dribs. Therefore, this study recommends to maintain all the damaged inlets and clear the drainage system that has been blocked by rubbish/ dribs.
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    Evaluation of Hydraulic Parametersi n Case of Akaki Wells on WF02-PW16 aND WF02-PW17 Wells
    (Addis Ababa University, 2021-10) Solomon, Lake; Daniel, Fikresilassie (PhD)
    The term groundwater is usually reserved for the subsurface water that occurs beneath the water table in soils and geologic formations that are fully saturated. In recent decades it has become apparent in many countries of the world that groundwater is one of the most important natural resources. So far, in Ethiopia, groundwater is mainly utilized for the water supply purposes. It takes care at present of 70% of rural water supply and plays a major role in several of the largest cities (Addis Ababa, Dire Dawa, Mekelle, Bishoftu, and Harari) and a number of medium-sized towns. As capital of Ethiopian, Addis Ababa has seen greater expansions and urbanization than other major city in the country. The primary objective of this project is evaluation of pumping test data to determine the hydraulic parameter of the Akaki phase IIIA bore holes in case of WF02-PW16 and WF02-PW17 by using Theis curve matching method, Cooper Jacob and recovery method on excel sheet and aquifer test software. Akaki well phase IIIA on WF02-16, WF02-17 Wells is located between 8°45' 20" to 9°13' 17" N latitude and 38°34' 3" to 39°4'10" E longitude in Oromiya Regional State, Akaki Kality Sub city south of Addis Ababa about 20 km from the city center. Akaki well field is one of the water supply projects implemented to alleviate the prevailing unsatisfactory water supply situation at the capital city, which is an important service for one of the most water deficit areas of the city-western & central Addis Ababa. The transmissivity values obtained in this project has great variation from the study of WWDSE which accounts for 5 to 100%. These two wells analyses results have overestimated. The overestimated Transmissivity envisions good aquifer with better yield than the capacity of the aquifer.
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    Spillway Design Discharge Estimation: Its Limitation and Proposed Solution (Case Study Kesem Dam)
    (Addis Ababa University, 2021-12) Eden, Destahun; Mebruk, Mohammed (PhD)
    Spillway design discharge and stage are determined by the routing method chosen, and they are crucial in determining the dam crest level. Because a dam is such a large structure, its height has a substantial impact on its cost estimation, the necessity of optimum spillway capacity and design discharge estimation need worth consideration. The commonly used Modified Pul's routing method, which is widely accepted as a standard method, presupposes that there is a horizontal water surface level above the FRL which controls by the downstream structure. However, upstream boundaries such as the inlet cross sectional geometry, river bed slope, and surface roughness regulate the flow, therefore upstream control prevails at the entrance, and downstream structure controls the water surface level at the exit. As a result, there is a variation in elevation between the upstream and downstream edges, resulting in a sloped reservoir water surface. When we substitute the horizontal water surface of the usual Modified Pul's Technique assumption with this sloped water surface, the reservoir adds an extra storage that the common method does not account for, and this extra storage reduces the out-flow discharge. This research modify the common Modified Pul’s Method which tries to handle and consider this extra storage which ignored in the common method using a MATLAB computer program by taking Kesem Dam as a case study and develop a standalone application. The result shows that there is a reduction in the out-flow discharge and design head through the new modified method.
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    Ground Water- Surface Water Interaction and Impact Assessment, In the Case 0f Western Ziway-Meki River Catchment
    (Addis Ababa University, 2021-07) Solomon, Kassa; Asie, Kemal (PhD)
    As the combined pumping rate of the water supply and irrigation of the towns and rural areas ,were the cause of the depletion of groundwater resources in the groundwater basin and the drying up of stream water. The goal of this research was to enhance the current understanding of the interaction of surface water-ground water and impact assessment using a numerical model. Initially, to measure the natural recharge of the aquifer and to model streamflow, the surface water hydrology of the sub basin was researched using the HEC-HMS (SMA)model. The ground flow mechanism was analyzed by using 3D numerical groundwater flow model (Processing Modflow Pro (Version The required model inputs were obtained from the results of field observation, secondary data and previous work carried out in the area. As calibration parameters, horizontal hydraulic conductivity from 0.1 m/day to 15 m/day and ground water recharge 64.6 mm/year, which constitute the main groundwater model parameters, were considered. The HEC-HMS(SMA) model was used to measure the recharge rate for the sub-basin in order to achieve a recharge. Model calibration was subsequently carried out using the process of trial-and-error calibration using groundwater contours formed from heads collected at 56 observation points. Therefore, the average RMSE for simulated hydraulic heads was approximately 20.65m. The calibrated model is used to assess the groundwater-surface water interactions, and groundwater system activity under various potential use scenarios. Simulated water levels in the model were more sensitive to decreases in recharge values and sensitive to decreases in hydraulic conductivity values. However, relative to recharge and hydraulic conductivity, the model is not as sensitive to decreases or increases in pumpage. According to the simulation, groundwater flows from the western escarpment to the east eventually join Lake Ziway. Lakes and rivers are significant sources of aquifer recharge. Increased pumping rate results substantial regional groundwater level decline, which leads to the drying of springs and shallow hand dug wells, according to simulations conducted under various potential future use scenarios. Finally, the model's water budget results showed that groundwater recharge comprised 81.48%, through river leakage 3.28 % and constant head was 15.24% of the total water input for the entire study region. Because of this, it can be noted that the surface water impacts to the water budget of the sub-basin.
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    Surface Water Resource Allocation for Abaya-Chamo Sub-Basin Using Weap Model, Southern Ethiopian Rift Valley
    (Addis Ababa University, 2021-09) Eyerus, Nigussie; Fiseha, Behulu (PhD)
    The development of water resource projects, population growth, and increase in irrigation areas has a higher effect on excessive usage of water resources and causes exploitation of the existing river systems and ecosystem of the natural environment. Therefore, water allocation study is essential to maintain the ecosystem and to balance the water demand with the supply in the catchment. In the present study, the allocation of surface water resource carried out in Bilate watershed, in Abaya-Chamo sub-basin of Ethiopian Rift Valley Lake Basin. The necessary data used to define the hydrology of study area are: DEM, LULC and soil data, climatic and stream flow data. The main aim of this study is, quantifying the available surface water of the Bilate watershed and allocation to the required demand sites of different activities. There are 25 demand nodes used to estimate water requirements in the study area. This demand sites are domestic demand for urban and rural towns, livestock water demand and irrigation water demand. In addition, to quantify the water available in the catchment, soil moisture method is used for catchment simulation. Three scenarios were developed to evaluate the effect of population growth and irrigation area expansion on future water demand. The result of the study showed no unmet demand of water requirement in the reference scenario from the years 1987 to 2020 for all cumulative demands with annual water demand of 88 MCM. Under future population growth scenario (2020–2035), the total water requirement demand for domestic , industrial, livestock and irrigation water demand is 121MCM, 39MCM and 27 MCM with 8% unmet demand of total water requirement. For the irrigation expansion scenario II, for mean monthly irrigation water demand of 26.37 MCM, 0.4 MCM of the total monthly irrigation demand is unmet in the analysis. Scenario III (combination scenario) both population growth and irrigation expansion are considered and analyzed. Based on the simulation results from the total demand of 188MCM, the total unmet demand is found to be 9 MCM. Finally, the environmental flow requirement coverage of WEAP out put shows some unmet instream flow requirement in October and November. Therefore, it can be concluded that the occurrence of maximum water shortage in catchment will not happened up to 2035 and also the future water resources development in Bilate sub-basin need to be carefully designed to optimize the balance between demand and supply. More importantly, basin level planning and catchment protection shall be taken as integral component of water resources development.
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    Operation Modeling For Zarima May Day Dam Reservoir
    (Addis Ababa University, 2021-08) Biruk, Woldetsadik; Yilma, Sileshi (Prof.)
    The Ethiopian government is involved in the development of massive irrigation projects for sugar production in different parts of the country. One of these schemes is the Wolkayite sugar development project, located in the western zone of the Tigray region. It is planned to utilize the runoff of the Zarema River, which is a major tributary of the Tekeze river basin. To achieve this objective, a dam has been built across river Zarema, which would enable irrigation of more than 40,000 ha of land. The Sugar cane which is estimated to be cultivated around 40,000 ha of land is to be utilized as raw material for Welkit sugar factory which has a capacity of 24,000 TCD. The objective of the study is to develop operation modeling for the Zarema May Day Dam reservoir. The input data consider for the model are daily inflow, monthly irrigation, and monthly reservoir surface evaporation, and Zarema May Day Dam physical data. The reservoir operation modeling was done using Zarema river inflow source options. The high Simien mountain range ensures relatively high runoff in the river Zarema at the dam sit. The annual average runoff is around 1300Mm3. The seasonal flow regime is characterized by an important average monthly flow, particularly in July (169 m3/s) and August (225 m3/s), whereas the period from October to May exhibits a monthly average lower than the annual mean. The reservoir operation modeling has been developed using two cases of inflow and three different scenarios, which has the same operation zone but differ irrigation area in Ha. And also reservoir operation guide curve and each year reservoir pool level were established.
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    Water Resource Developments and Flow Alteration in Didessa River Basin
    (Addis Ababa University, 2021-10) Uchulu, Kebede; Fiseha, Behulu (PhD)
    Water demand increases due to population growth and the associated economic growth and irrigation factors for food production. Water becomes scarce as the amount of demand exceeds the available supply. Didessa River is the largest tributary of the Abbay river basin in terms of discharge capacity per unit area and still susceptible to supply-demand misbalance issues. The study's main objective was to assess the impact of water resource development and flow alteration in the Didessa river basin. The Water Evaluation And Planning (WEAP21) tool was used to simulate the catchments and integrate supply sources and demand sites. The hydrological model performances manually for calibrated (1990-2008) and Validated (2009-2017) of NSE and R2 are 0.89 and 0.68, and 0 9 and 0.73 respectively. The crops water requirement and degree of hydrologic alteration respectively CROPWAT 8.0 and Indicator of Hydrologic Alteration (IHA) programs were used to estimates. Two different scenario development were built. The first scenario is based on increasing population growth rate divided into Reference (1990-2017), small population growth rate (2018-2035), and higher population growth rate (2036-2050). The results indicated the unmet water demand, 0.74, 297. 87, and 784.46 in a million-meter cube. The second scenario was developed based on the expansion of irrigation activity, reference, short-term plan, and long-term plan remained the results indicate that the unmet water demand values: 0.195, 0.55, and 7.5-billion-meter cube in respectively. The results of the first and second scenarios specify that the population growth rate and irrigation activities increased the unmet water demand also increased. It was shown that the degree of flow alteration was low in most months, and the Didessa near Dembi gauge station has high susceptibility to flow alteration than Didessa near Arjo gauge station. It was found that when the environmental flow has taken 20 up to 50 percent mean annual runoff, the unmet demand was reduced accordingly. Finally, it can be concluded that any future water development shall take into account all possible scenarios that can address environmental alteration and extra water requirements.
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    Assessment of Reservoir Sedimentation using Remotely Sensed and Ground Observation Data (The Case of Legedadi Reservoir, Ethiopia)
    (Addis Ababa University, 2021-07) Almaz, Girma; Fiseha, Behulu(PhD)
    Reservoir sedimentation is one of the issues that need to be addressed in water resources management. Sediment deposition in reservoirs for water system, hydroelectric power control, and urban water supply, reduces their capacity, service life, water quality and requires expensive operations for removal and treatment. Lack of normal and less cumbersome methods for assessment of sedimentation ranges and available potential poses undertaking for the sustainable administration of reservoirs. The conventional methods for quantification of sediment such as inflow- outflow and hydrographic survey methods are clumsy, expensive and time consuming. Hence, there is a need for simple methods, which requires less time and economical. The remote sensing is incredibly useful, economical and reliable tool for conducting such surveys and monitoring sedimentation in reservoir. This study examines to assess Legedadi reservoir sedimentation by using remotely sensed data. Satellite imageries have been employed for the water spread area, which was used for calculating sedimentation rate. This research put together the geographical information system (GIS), Envi software, and DEM to assess the reservoir sedimentation by using remote sensing data. The result indicated that the current 2019/20 capacity of the Legedadi reservoir estimated using remote sensing techniques becomes 34.87Mm3 at an elevation of 2465.13m a.m.s.l and the original capacity (using hydrographic survey) was 40.8 Mm3 at the same level, the loss in reservoir gross capacity due to sediment deposition for the period of 41 years of reservoir since 1979 to 2020 was determined to be 5.93 Mm3 which convert to 14.53 % gross capacity loss or showing annual storage loss due to sedimentation deposition is found to be 0.35% loss between elevation 2465.13 and 2457.46 m a.m.s.l. Accordingly, the annual rate of sedimentation using remote sensing was found to be 0.145Mm3/year. Those values are found to be in close correspondence with results obtained from the hydrographic survey. LULC change and domination of cultivated land indicate a significant impact on reservoir sedimentation.
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    Estimation of Reservoir Sediment by using Satellite Remote Sensing for Legedadi Dam Reservoir
    (Addis Ababa University, 2021-04) Eyob, Biresaw; Bayou, Chane (PhD)
    Reservoir sedimentation is the gradual accumulation of inward sediments from upstream catchment that has driven the decrease in useful storage volume of the reservoir. Enumerating the reservoir sedimentation amount is vital for improved water resources management. The conventional methods to estimate sediment deposition in a reservoir, such as hydrographic surveys and the inflow-outflow approaches, are bulky, costly, and time-consuming. Further, forecasting of sediment deposition outlines using empirical and numerical methods needs a large quantity of input data and the outcomes are still not inspiring. It is necessary to develop a precise approaches, which need less time and cost-effective. Because of sediment deposition, the water-spread area of a reservoir at different levels keeps on decreasing. The Satellite Remote Sensing (SRS) method for estimation of reservoir sediment uses the fact, that the water spread area of reservoir at different elevations keeps on decreasing due to the sediment accumulation takes the area of the water. The remote Sensing technique gives us directly the water spread area of the reservoir at a particular elevation on the date of pass of the satellite. This helps us to determine sedimentation over a specified time. By using remote sensing data in combination with a geographic information system and Envi 5.3 software the chronological variation in the water-spread area can be investigated to assess the sediment deposition in a reservoir. The revised capacity of the reservoir for available satellite image and at fluctuation levels was computed using the Simpsons 1/3 Rule formula. In this paper, a remote sensing method has been tried to estimate sedimentation in Legedadi Dam Reservoir, the reservoir placed on the upper part of Awash Basin, the outflow is joining Akaki river. Multi-date remote sensing data level 1 Landsat 8 and 7 gives the information on the water spread area of the reservoir, which will be used for calculating the sedimentation amount. The current (2018/19 GC) live storage capacity of Legedadi reservoir estimated using remote sensing approach is 36.087 Mm3 at an elevation of 2465.16 m.a,m,s,l. According to 1979Gc study result the capacity was 41.610 Mm3 at the same level. The loss in reservoir capacity due to sediment deposition for a period of 39 years since the 1979 hydrographic survey to 2018/19 Gc is determined by deducting the 1979 and 2018/19 GC value it gives 5.523 Mm3 which is 13.27 % capacity loss between 2465.16 and 2460.98 m.a,m,s,l. At the live storage zone, Therefore, the result shows that there is a need to give a serious attention for reservoir sedimentation. To protect the reservoir from sedimentation problem we need to protect the upstream and downstream catchment by means of integrated environmental protection.
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    Flood Risk Analysis (Case Study of Upper Awash River from Wonji to Awash Malkessa)
    (Addis Ababa University, 2021-09) Dawit, Mokonen; Daneal, Fikresilassie
    Flood is probably the greatest devastating, wide spread and frequently natural hazard of the world wide that producing several socioeconomic and environmental consequences within the affected floodplain. In Ethiopia, Awash River basin is one of the areas affecting by flood plain problem and among Awash River basin, wonji to awash melkessa is one the most frequently severed area by floodplain along Awash River, for those flood risk analysis is so important. The main objective of this study was flood inundation mapping and quantifies the risk of flood on the area by using hydrological model HEC-HMS for peak flood forecasting for different return period and GIS extension HEC-GeoRAS integration with hydraulic model HEC-RAS for flood inundation mapping. For hydrological model (HEC-HMS) daily rainfall and stream flow data of 16 years from (1998-2013 G.C) was used. Among the data used eight years for calibration and five years for validation of HEC-HMS model at wonji Gauged station. HEC-RAS model was calibrated and validated using satellite imaginary Landsat-7 flood event and observed flood event of September, 06/2000 and September, 22/2007 G.C respectively. The missing values were filled by using normal ration method for daily precipitation data. Consistent data was checked by double mass curve method. The initial and constant loss method was selected for loss method and for transform method Clark unit hydrography was applied. The estimated peak flood by hydrological model (HEC-HMS) was 147.2m3/s, 161.9m3/s, 329.4m3/s, 409.5m3/s and 506.8m3/s for 5year, 10year, 25years, 50years and 100year return period correspondingly. The flood inundated area corresponding to peak flood were 1052.7 hectare, 1086.9 hectare, 1429.5 hectare, 1559.1 hectare and 1694.1 hectare respectively. The total crop losses were calculated for flood inundated area, for 5 years and 100 year return period of crop loss were 75501.6 quintal and 121503 quintal correspondingly. Thus finding of the study may help in planning and management of flood plain area to mitigate probable disaster through technical approach.
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    Assessment of Sediment Inflow in Dire Dam Reservoir and Sediment Reduction method using SWAT Model, Dire Catchment, Ethiopia
    (Addis Ababa University, 2021-08) Yared, Tadesse; Bayou, Chane (PhD)
    Soil erosion or sedimentation is a major problem of reservoir operation in Ethiopia. Deforestation, overgrazing and poor land management practice are some which accelerate the rate of erosion. The topography of Ethiopia in general is full of ups and downs and local farmers commonly cultivate on the hilly sides causing easy topsoil wash away. Hence, this study has tried to determine the sediment yield at the dire dam reservoir, identify the high sediment source sub basin and check the applicability of SWAT model on the dire dam watershed. To go through this objective, SWAT model was applied with methodology of collecting hydro metrological data, sediment data, topographic, land use and soil map data by overlaying mechanism, the SWAT model run. Simulation was carried out using metrological and spatial data by dividing the watershed in to 9 sub basins with 103 hydrological response unit (HRUs) at outlet of dire watershed. Based on the availability of data the model calibration period (1988-1999) and validation period (2000-2006) were performed for monthly flow and sediment data using Sequential Uncertainty Fitting (SUFI-2) with in SWAT calibration uncertainty program (SWAT-CUP). The model was found applicable in this watershed with the performance evaluation statistics (Nash-Sutcliffe model efficiency (ENS), coefficient of determination (R2)) in the acceptable range, (R2in the range of 0.74 to 0.78, ENS in the range of 0.73 to 0.77). From the model simulation output, sub basin 1, 2, and 6 were found the top three severely eroded sub basin with average annual sediment yield of 19.01 t/ha,34.26t/ha and 27.31t/ha respectively. While sub basin 7 and 9 were found the least sediment source sub basin with annual average sediment yield of 8.06t/ha and 7.22t/ha respectively. Generally, the annual averaged sediment inflow in to dire dam reservoir was 1850 t/km2/yr. Three watershed management scenarios were simulated to compare their effectiveness of sediment yield reduction from the existing baseline condition. The result shows that the mean annual sediment yield at the outlet can be reduced by 34.14% by applying filter strips, 57.12% by applying grassed waterway, and 70.06% by applying terracing. To generalize, applying terracing is relatively effective to reduce the mean annual sediment yield for the proposed dam.
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    Runoff and Sediment Yield Modeling in Laga Dadi Reservoir and its Watersheds
    (Addis Ababa University, 2021-07) Tesfaye, Girma; Bayou, Chane (PhD)
    Reservoir sedimentation is a serious moment of surface runoff and soil erosion with large environmental and economic implications. Deposition of sediment in reservoirs reduces the storage capacity of the reservoirs and affects the operation and stability of the dams. The main objective of this study is to assess runoff & sediment yield at Laga Dadi reservoir and its catchment and identify hotspot areas of the watershed in runoff & sediment yield. The outlined objective is attained by a physical based hydrological model Soil and Water Assessment Tool (SWAT). Daily runoff and sediment data from 1994-2009 were used in this study. Data from 1994-2003 were used for calibration and 2004-2009 for validation. Following the successful calibration and validation of the model on the study area, runoff and sediment yield have been estimated. The annual runoff volume generated on the watershed was estimated to be 654.5 mm as it is known that SWAT Generate Runoff in mm. The total simulated mean annual Sediment yield loading from Laga Dadi watershed simulated is 6.73 ton/ha/yr. The total mean annual sediment yield that is drawn from Laga Dadi watershed predicted by SWAT model is found to be 138146.71 tons. The model prediction verified that about 17% of the watershed around the dam site has erosion potential area contributing very high sediment yield exceeding the tolerance limit. Hence, the researcher recommends conservation and environmental protection in upper catchments, tributary rivers site and on the spot, area shall be done continuously.