Water Resource

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    PERFORMANCE EVALUATION OF STORMWATER DRAINAGE SYSTEM OF BEDELE TOWN
    (Hawassa University, 2020-10-24) YEROSAN KEBEDE AYANA
    Various factors can degrade the drainage system and reduces its performance. As the role of drainage infrastructure is very high in preventing urban floods, their performance should be monitored and quantified. This study aimed to assess the performance of stormwater drainage systems in Bedele Town. Primary and secondary data were used in this study. The catchment that contributes runoff was delineated using ArcGIS 10.4 software. The Stormwater Management Model (SWMM 5.1) was used to simulate the peak flow rate and water level in the drainage canals by considering the current land use. The intensity duration frequency (IDF) curve was developed by using the Log-Pearson Type III. The peak runoff for 10-year and 25-year return periods was estimated by using the Rational Method. The condition of the existing drainage system was assessed and poor solid waste management, lack of well-connected drainage lines, poor liquid waste disposal, and the existence of fully uncovered areas in the town with drainage structures were identified to be the drainage problem of the Town. From the total area of Bedele Town, 41.1% is uncovered with the drainage systems. The total peak runoff generated from this study area is 15.59 m3/s and the average velocity was 2.5m/s for a 10-year return period. The result from the Rational method as well as SWMM 5.1 shows there is an overflow problem in this study due to the presence of drainage canals with insufficient capacity to carry the runoff generated from this catchment. For a sustainable drainage system, the appropriate use of hydrological analysis, hydraulic design, and stream morphological study should be implemented before carrying out the construction of drainage structures for they were not considered during the construction of the drainage system of the Town. Regular maintenance and frequent clearance of drainage lines, proper integration between roads and drainage structures, provision of additional drainage canals, and improved stormwater management were recommended to solve the stormwater drainage problem of the Tow
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    MODELLING URBAN STORM WATER FLOODING IN HOSSANA TOWN: THE CASE OF ADDIS SUBCITY
    (Hawassa University, 2019-12-17) ABERA MECHA SEWORE
    Urban flooding is a condition where storm water cannot enter a storm drain or it is beyond the capacity of the urban drainage system. Such urban flooding is mainly caused by inefficient urban drainage systems, and it cause damage to public and private buildings and disrupts public life. Therefore, modeling urban floods were very essential to mitigate flooding related problems. The main objective of this research was modeling urban storm water flooding in Hossana town specifically in Addis sub-city. There were many tools for urban storm flood modeling, but out of limited free tools, Storm water management model (SWMM) has a good record of applicability in many locations elsewhere. Various rainfall and spatial data were collected to model urban floods. Daily maximum rainfall data from Hossana station for 28 years (1990-2017) was used to identify parent probability distribution and enabled to develop the Intensity duration frequency curve (IDF) for study area. SWMM was implemented to simulate the flood depth in the drainage channels and Arc GIS is used to delineate the extent of the flood contributing area. The hydrology and hydraulic routing of the watershed was estimated using the SWMM at the total of 1-hour time of concentration daily time series data of different year return periods. The inputs of the models (nodes, conduits and sub- catchment area property) were assigned with the help of Auto-CAD, Arc-GIS 10, Google earth pro, and field survey. The result obtained from the model showed that (39%), (41%) drainage manholes encountered flooding for 10 and 25 years return periods respectively. Hence, approximately (40%) of the drainage system of the city previously designed was inadequate to discharge the system runoff to final point. Discharge of the catchment was also determined by using Soil conservation service (SCS) curve method and rational method that was used to relate and check the SWMM model output value. In general, the results of this study will be useful for further design and planning of the sub cities in the Hossana town. Moreover, further research on urban flooding which accounts two-dimensional flow is recommended to account the flood extent and risks associated with it.
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    HYDRAULIC PERFORMANCE EVALUATION OF URBAN DRAINAGE SYSTEM AND PROPOSED MITIGATION MEASURES: A CASE STUDY AT KOFE KEBELE IN DILLA TOWN
    (Hawassa University, 2023-10-23)
    This thesis aims to provide a comprehensive evaluation of the hydraulic performance of an urban drainage system and propose effective mitigation measures to address the negative impact of flooding in Kofe Kebele of Dilla town using the Stormwater Management Model (SWMM) 5.1. The study area covers 180 hectares of land; it has three outlets, the catchment is classified into 34 sub-catchments, and the drainage system has 144 junction nodes and 191 conduit links. Flow routing was computed using kinematic waves and Green-Ampt was used for the infiltration model. Rainfall data for Dilla were obtained from the National Meteorological Agency and twenty-five years of data were used (1997–2021). The normal ratio method was used to fill in missing data. A double mass curve was used to check consistency, outlier identification was performed to check for higher and lower outliers, and rainfall frequency analysis and frequency distribution fitting were performed to evaluate the goodness of fit. A goodness-of-fit test was performed, and it was found that Gumbel, or GEV (I), has a good fitness value, and IDF curves were developed based on the ERA standard. A 25-year return period was used as the design storm. The United States Environmental Protection Agency’s Storm Water Management Model (EPA SWMM 5.1) and the Geographic Information Systems (ArcGIS) tool were used to model and analyze stormwater characteristics. recorded water levels and velocities were used to calibrate and validate the EPA SWMM 5.1 model. Three conduits were selected for calibration and validation. The results obtained for the calibration of the performance indicator of the Nash-Sutcliffe efficiency (NSE) for each conduit (C78, C97, and C184) were 0.87, 0.91, and 0.85, respectively, and for the coefficient of determination (R2 ) were 0.75, 0.84, and 0.77, respectively. The other indicator considered was the relative error, where the errors were 8.3%, 4%, and 7%. Referring to the validation, the performance of the model for Nash Sutcliffe efficiency (NSE) for the aforementioned conduits was 0.91, 0.88, and 0.88, respectively; it was 0.88, 0.99, and 0.78 for the coefficient of determination (R2 ), with a relative error of 3.7%. These results show that the model has a good performance and can perform the analysis for the study area. Low-impact development (LID) techniques were investigated based on land use and land cover conditions to sustainably solve the flooding problem. From various LID alternatives, three LID techniques were chosen based on site conditions: bioretention cells, infiltration trenches, and rain barrels. The simulation results indicated that the combination of bioretention cells, infiltration trenches, and rain barrels had a better capacity to minimize runoff. This study suggests using low-impact development (LID) to address flooding issues in a sustainable manner.
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    HYDROLOGICAL AND HYDRAULIC PERFORMANCE EVALUATION OF STORMWATER DRAINAGE SYSTEMS, OF AWASHO-ALELU KEBELE (01 AND 10) SHASHEMENE TOWN, ETHIOPIA
    (Hawassa University, 2021-04-12) USMAN TUSA WAKO
    Shashemene town is one of the fastest-growing towns to urbanization and increases the amount of runoff generated from the urban catchment. This study intended to hydrological and hydraulic performance evaluation of stormwater drainage systems, of Awasho-Alelu kebele (01 and 10). Due to urbanization, lack of proper design and management, the transport infrastructure and drainage systems are caused by flooding. Data used for this study were meteorological (rainfall) data, drainage systems dimensions, digital elevation model (DEM). Determining the peak discharge by the rational method using land-use, rainfall intensity and the catchment area of internal all sub-catchments and also the upstream catchment inflow by SCS (CN). These results show, that 78.9% of the drainage systems are not adequate to carry the design flood based on intensity with a return period of 10 years. The other problems lack well-connected and sufficient drainage lines, solid wastes were directly disposed into the storm drainage system and insufficient slope provides which results in decreasing the efficiency of the system. Most drainage systems perform severely degraded are at Farma academy school 54.3%, at new bus station 44.181%, at Malka Oda Hospital 61.6%, at Alelu market 46.5% and Alelu primary School 56.2% were severely degraded
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    EVALUATION OF URBAN DRAINAGE SYSTEM BY SWMM: A CASE STUDY AT ALABA KULITO TOWN, SNNPRS, ETHIOPIA
    (Hawassa University, 2020-03-22) ASMACHEW ABERA BEMANJO
    The general objective of the study was Evaluation of Urban Drainage System of Alaba Kulito Town by Storm Water Mmanagement Model (SWMM). The study employed the collection of primary data like measuring the existing drainage size of the flood-prone region and asking stakeholders and secondary data which was obtained from National Meteorology Agency (NMA) of Ethiopian (33 years meteorological data), Ethiopian Map Agency (topographic map and soil map data), Ministry of Water, Irrigation and Energy (soil data) and Alaba Town Municipality (historical data of flood and organizational structure of city administration). 3.7% of Missed RF data of Alaba Kulito station was filled by Normal Ratio Method (NRM). The Generalized Pareto Distribution (GPD) method which was followed by Peak Over Threshold (POT) extreme value determination method was used to predict the probability of flood occurrence due to the best fit and approach of study. For analysis of hydrology and hydraulics done by the Soil Conservation Service Curve Number (SCS-CN)/rational method and Stormwater Management Model (SWMM). It has been found that Alaba-Kulito town is geographically nearly plain which was between class 1 and class 4 slope classification and located in foothill which contributes much amount of runoff to the town and some of the drainage lines are incapable to convey runoff generated from rural catchment. In addition to this, limited landscape based mitigation strategies in the study area with insufficiency of drainage canals, limited collector and feeder drainage lines, lack of awareness of community while disposing of household wastes together have worsened the impacts of flooding. The overall result of the study is terminated by distinguishing and pointing both structural methods: diverting the upper catchment(which shares more than 64% runoff load ), providing collector and feeder drainage lines through the flood-prone section of town and constructing a lined canal at the common outlet to Bilate river which is about 1.5km from ST.Gabriel church ; and non-structural managing systems depending on the degree of the flood. The peak runoff load of each junction and nodes are obtained by summing up the runoff magnitude of all upper contributing catchments and accordingly the outlet point received about 49.45m 3 /s and 29.1m 3 /s without divertion work and if diversion work was provided for 10 years return period respectively. The coefficient of correlation between simulated and estimated peak discharge becomes greater than 0.99.