Hydraulic Engineering

Permanent URI for this collectionhttps://etd.hu.edu.et/handle/123456789/69

Browse

Start date: 2020Subject: search.filters.subject.HEC-RAS

Search Results

Now showing 1 - 5 of 5
  • No Thumbnail Available
    Item
    FLOOD RISK MAPPING USING HEC-RAS MODEL: CASE STUDY ON WAJA WATERSHED IN RIFT VALLEY BASIN CENTRAL ETHIOPIA REGION, ETHIOPIA
    (Hawassa University, 2024-04-22) ATEREFE TAMIRAT DEBOCH
    Flood is among the most devastating natural disasters worldwide, significantly affecting human lives and property. The current study conducted on the Waja River floodplain aimed to model and maps the flood inundation, flood hazard, flood vulnerability, and flood risk associated with flooding in the area. To achieve this objective, various data sources were utilized, including meteorological, hydrologic, and topographic data collected from different organizations. The study employed several tools and materials, including the HEC HMS and HEC-RAS models, GIS software, GPS devices, and metering tape. The HEC HMS model was used to analyze flood hazard and risk by developing inflow design floods for different return periods. The model was calibrated and validated using actual stream flow data. During model calibration the NSE value was 0.75, Percent Bias (PBIAS) was 2.02, coefficient of determination (R2 ) was 0.78, and Relative Mean Square Error (RMSE) was 2.03. During the validation period, the model achieved an R2 of 0.77, NSE of 0.76, PBIAS of 1.64, and RMSE of 1.3. After calibration and validation, the annual maximum precipitation from rainfall data was extracted to develop frequency storms for different return periods. These storms were then used as input for the HEC HMS model to generate flood hydrographs. The HEC-RAS model, combined with the flood hydrographs, was used to produce flood inundation maps, which were visualized in ARC-GIS software for detailed analysis. The results of the study indicated that for return periods of 10, 25, 50, and 100 years, the areas inundated by floods were 3030 ha, 3364 ha, 3520 ha, and 3683 ha, respectively. Additionally, the maximum flood depths were found to be 6.3m, 9.2m, 12.6m, and 14.45m for the respective return periods. The maximum flood velocities were 3.8 m/s, 4.7 m/s, 5.5 m/s, and 6.8 m/s for the same return periods. Flood hazard maps were derived from the depth, velocity, and duration of floodwaters, revealing that 35% of the flooded area was categorized as having very high and high hazard, while approximately 65% was classified as medium and low hazard. The flood vulnerability map classified approximately 17% of the flooded area as having high and very high vulnerability. About 18% of the flooded area fell into the moderate vulnerability class. The majority of the flooded area, approximately 65%, had low and very low vulnerability. By combining the flood hazard and vulnerability information, the study developed a flood risk map. The results showed that 24% of the area fell into the high and very high-risk categories
  • No Thumbnail Available
    Item
    FLOOD INUNDATION MODELING AND RISK MAPPING OF BIG AKAKI RIVER, ADDIS ABABA, ETHIOPIA
    (Hawassa University, 2023-03-06) GIZACHEW MUSIE ALENBO
    The occurrence of floods as natural disasters has severe consequences worldwide, including loss of life, the spread of diseases, property damage, economic hardships, and social and psychological impacts on affected individuals. This study focused on modeling and analyzing the flood inundation and associated risks of the Akaki River, located in Addis Ababa, the capital city of Ethiopia. The primary objective of this study was to create models and maps that depict the extent of flood inundation and the risks associated with flooding events. To accomplish this, both primary field data and secondary data from various sources was collected. The materials utilized in this study included the HEC-RAS model, GIS software, GPS, and metering tape. The study involved conducting a hydrologic flood frequency analysis for different return periods, which served as input for flood inundation modeling and risk analysis. The HEC-RAS model was employed to develop flood inundation, flood hazard, flood vulnerability, and flood risk maps, which were subsequently mapped using ARC-GIS software. The results of the study revealed that the areas affected by floods varied depending on the return period. For return periods of 10, 25, 50, 100, and 200 years, the areas inundated by floods were measured to be 7.58 km², 9.79 km², 11.2 km², 12.45 km², and 13.83 km², respectively. The study also determined the maximum flood depths and velocities for each return period, with values ranging from 10.21 to 15.02 meters and 3.12 to 5.26 meters per second, respectively. Based on the flood hazard map for the 200-year return period, it was identified that approximately 13.7% of the total flooded area was categorized as an extreme hazard, rendering it unsafe for all individuals, vehicles, and structures vulnerable to flooding. Additionally, 17.6%, 16.7%, 18.9%, and 33.1% of the total area fell under the categories of very high, high, medium, and low hazards, respectively. The flood vulnerability map highlighted five levels of vulnerability, ranging from very low to very high. The very high and high vulnerability classes covered 9.59% (1.21 km²) and 15.54% (1.96 km²) of the flooded area, respectively. Furthermore, the flood risk was classified into five levels, revealing that 3.6%, 12.6%, 18.5%, 19.8%, and 45.5% of the flooded area were associated with very high, high, moderate, low, and very low risks, respectively. Considering the high risk and danger posed, particularly to residents residing in the flood buffer zone, a proposed solution to protect the area from flood hazards involved the construction of a 5.83 km levee embankment along the settlements on the left side of the river, specifically in areas with high population density. Finally, the performance of the HEC-RAS model was evaluated using model evaluation statistics, resulting in a coefficient of determination (R2) value of 0.94 for the water surface elevation, indicating a strong correlation between observed and simulated data. This study provides valuable insights into the flood dynamics, risks, and vulnerabilities associated with the Big Akaki River in Addis Ababa. The findings can inform decision-making processes aimed at mitigating the impacts of floods, protecting vulnerable populations, and enhancing overall flood management strategies in the area
  • No Thumbnail Available
    Item
    FLOOD HAZARD MODELING AND RISK MAPPING: CASE STUDY ON LOWER WEITO RIVER RIFT VALLEY BASIN SNNPR, ETHIOPIA
    (Hawassa University, 2025-08-12) GELMA BORU
    This study focuses on the modeling and mapping of flood inundation and associated risks in the Lower Weito River, a tributary of Lake Abaya by means of coupled hydrological and hydraulic models with different return periods. Meteorological, hydrologic, and topographic data were collected from various sources. Rainfall data from 1990 to 2015 were collected from the National Meteorological Agency and the stream flow data from 1990 to 2007 were collected from the Ministry of Water and Energy. DEM 12 * 12m resolution was downloaded from Alaska satellite facility, soil data was taken from FAO and LULC data were collected from the Ministry of Water and Energy. These data were integrated using modeling tools such as HEC-HMS and HEC-RAS, along with GIS software. To examine the accuracy of the HEC-HMS model, calibration and validation is performed using observed stream flow data. The results showed a strong relationship between simulated and observed data, with R2 and NSE values of 0.82 and 0.77, for calibration periods and 0.78 and 0.75 for validation period respectively which indicating a very good agreement between observed and simulated flow . The calibrated and validated model was then used to develop flood hydrographs for different return periods based on frequency storm analysis. The result of flood frequency analysis showed minimum peak flow of 77.9m 3 /s for a 2-year return period with 24-hour storm duration and, the maximum peak flow 606.2 m3 /s occurs with a 100-year frequency storm for the same duration. The HEC-RAS model was used to generate flood inundation maps, which revealed the extent of flooded areas and the maximum flood depths and velocities for various return periods. The results indicated that the areas inundated by floods ranged from 1711.2 hectares for a 10-year return period to 2763.3 hectares for a 100-year return period. The maximum flood depths varied from 5.2 meters for a 10-year return period to 7.5 meters for a 100-year return period. The maximum flood velocities ranged from 3.15 meters per second for a 10-year return period to 7.01 meters per second for a 100-year return period. Flood hazard maps were derived by considering the depth, velocity, and duration of floodwaters. The results showed that about 0.01% of the total flooded area was under extreme hazard, 14% under very high hazard, 29% under high hazard, 35% under medium hazard, and 21% under low hazard. The flood vulnerability map classified the flooded areas into five vulnerability classes. Approximately 44% of the flooded area was classified as high and very high vulnerability, 19% as moderate vulnerability, and 37% as low or very low vulnerability. The flood risk map was developed by combining the flood hazard and vulnerability information. The results showed that 16% of the area was classified as very high to high risk, 46% as medium risk, and 38% from low to very low risk.
  • No Thumbnail Available
    Item
    EVALUATION OF THE HYDRAULIC PERFORMANCE OF THE GEDEBA CULVERT ON THE HALABA SHASHEMENE ROAD
    (Hawassa University, 2024-10-07) TEMESGEN AYANO ABISO
    The increasing severity of climate change is causing a global rise in extreme weather events, characterized by intensified rainfall and flooding. These changes create significant challenges for drainage systems. Inadequate drainage infrastructure can lead to severe consequences, including erosion, property damage, and disruptions to transportation and essential services. The main objective of this study was to evaluate the hydraulic performance of Gedeba culvert using hydrological and hydraulic modeling analysis. To carry out the study, primary data was collected from field surveys, and secondary data was gathered from various organizations. The models and materials used in the study were HEC-HMS, HEC-RAS, GIS, and GPS. Continuous hydrologic simulation was initially done using HEC HMS model to calibrate and validate the model. The calibration and validation result indicated that there was strong relationship between simulated and observed stream flow data. Hence, based on these statistical error test criteria HEC-HMS model performance of the model is classified as very good. After model was calibrated and validated using actual observed flow data, frequency storm was generated using the annual maximum precipitation available from rainfall data and it is used as an input for HEC-HMS model to conduct event based simulation for developing flood hydrograph for different return periods. The result of event based simulation shows that, the maximum flood hydrograph for 2, 5, 10, 25, and 50 years were 87.1, 117.8, 135.4, 155, and 179.8m3 /s respectively. To analyze the hydraulic performance of the culvert, the HEC-RAS model was used to develop water surface and velocity profiles. The analysis indicated that, for different flood frequency, the water level exceeded the culvert crest, resulting in area, with overtopping and subsequent flooding of the main road connecting Halaba to Shashamene. This overtopping not only posed a risk to the road infrastructure but also led to erosion of the downstream area and collapse of some parts of the road. Furthermore, the analysis revealed that the velocity of the floodwaters passing over the culvert crest was significantly high, possessing erosive characteristics that worsened erosion downstream. The downstream area suffered substantial damage, with some sections of the road collapsing due to the intense flow and erosion. This underperformance of the culvert highlights critical infrastructure vulnerability, necessitating urgent attention and action. To reduce the problems of flooding, Mitigation measures, such as installing erosion control structures (e.g., riprap, check dams) and implementing vegetative buffers, can help stabilize the terrain and reduce the risk of erosion. To alleviate these problems, different type of culverts were selected for analysis to redesign the existing culvert which accommodates the floods. The analysis of various culvert types reveals significant limitations in their capacity to manage floodwaters, with existing designs inadequate for anticipated flood flows, raising risks of flooding and property damage. Modifications like widening river cross sections and using larger culverts are vital for flood management, Box culverts present an exciting option due to their moderate complexity in construction, which requires careful placement and alignment but is generally straightforward. They are designed to support heavy loads and withstand environmental stresses, making them highly durable
  • No Thumbnail Available
    Item
    DAM BREACH ANALYSIS AND DOWNSTREAM FLOOD MAPPING USING HEC-RAS AND HEC-FIA (A CASE STUDY OF GERHU-SIRNAY DAM)
    (Hawassa University, 2020-07-03) KEHASE NEWAY GEBRETSADKAN
    Dam breach analysis is a science that quantifies the hazard sourced from dam failures. On downstream of Gerhu-sirnay dam there are developments including water treatment plant and multi owner seasonal agricultural areas. The objective of this study was to estimate breach outflow hydrograph to the downstream reach for overtopping and piping scenarios henceforward to assess flood damage for the worst scenario. The quality of rainfall data was tested for outlier, adequacy, homogeneity using Pettitt (1979) test and consistency tests. The probable maximum precipitation calculated by Hershfield (1965) method was 129.7 mm. The inflow hydrograph was obtained by using soil conservation service (SCS) method and its probable maximum flood (PMF) reaches 329.1 m 3 /s. The breach parameters for both scenarios were early calculated by the four regression equations integrated with Hydrologic Engineering Center River Analysis System (HEC-RAS) breach calculator tab. Due to comparison in both scenarios, the final breach parameters were taken from Von Thun and Gillette (1990). For overtopping the resulting parameters were 54 m breach bottom width, 85.75 m breach top width, 0.5 side slope (H: V) and 0.73 hrs breach formation time whereas in case of piping these parameters were 32 m, 57.75 m, 0.5 and 0.53 hrs respectively. Then HEC-RAS version 5.0.3 has used to model the dam breach analysis with two dimensional unsteady flow conditions of inflow hydrograph as upstream boundary condition and normal depth as downstream boundary condition. The peak breach outflow for both scenarios were 2,239.7 and 1,282.68 m 3 /s respectively as overtopping was the worst scenario. From the prepared inundation maps by GIS for about 521.1 ha area was inundated under the worst scenario with a maximum depth 24.07 m and duration of 1.0 hrs. By using Hydrologic Engineering Center Flood Impact Analysis (HEC-FIA) version 2.2, the flood damage was estimated in terms of direct economic damage and life loss. The total ex-ant direct economic damage result shows 63,650,493.3 Birr. From the report of LIFE-Sim dynamic model integrated with HEC-FIA, about four persons could be lost their life. To minimize the quantified damage, well operation of emergency action plan would be an important tool. The water treatment plant of Gerhu-sirnay town must be displaced from its current place to at least 0.073 km apart from both sides of the river banks until to do this the stakeholders of the plant must be under the age of 65 years to have an efficient warning mobilization