EVALUATION OF THE HYDRAULIC PERFORMANCE OF THE GEDEBA CULVERT ON THE HALABA SHASHEMENE ROAD

Abstract

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