Evaluation of scour at Kyabikere suspension footbridge abutments connecting Kitholhu and Karambi sub counties.

Abstract

The Kasese region and its sub-catchments has over time been associated with flooding as a result of high-intensity rainfall often causing stormwater runoff that exceeds the capacity of the current drainage system of the flowing rivers. The researchers aimed to assess the scour at the Kyabikere suspension footbridge abutments in relation to the seasonal flooding of the Lhubiriha River in Kitholhu and Karambi sub-counties within the Kasese District. They specifically focused on understanding the impact of the river's seasonal flooding on scouring at the abutments. To accomplish this, the researchers utilized the Hydrological Engineering Centre River Analysis System (HECRAS) software, which enabled them to evaluate and quantify the extent of scouring. The analysis encompassed both the abutment positioned adjacent to the river channel and the abutment located 8m away from it. By employing maximum daily flow data for a 100-year return period, the assessment provided valuable insights into the behavior of scouring at the site. Using (HEC-RAS) software, a hydrological model was developed to estimate both the abutment scour and the contraction scour. Using input data from the Particle Size Distribution (PSD), the daily rainfall intensities, and the existing dimensions of the abutment. The investigation revealed that the total scour on the abutment measured 7.04m, with a diameterto- scouring ratio of 0.303, categorizing it as narrow scour due to being less than 0.7. This suggests that the scouring depth primarily depended on the abutment size. When examining the failure mechanism of the abutment foundation, it became evident that limiting surface factors like erosion, silt accumulation in the river, and the growth of vegetation around the abutment foundations can effectively reduce abutment failures. Furthermore, the sand was classified as well graded (SW) with 50% of the sample retained on sieve number 4 and a coefficient of conformity (Cc) less than 3, and a coefficient of uniformity (Cu) greater than 4. The recommendations made by the researcher included; Firstly, it was suggested that visible damages on the abutment and decking, such as surface cracks, should be repaired using suitable methods, materials, and techniques. This will help prolong the lifespan of the bridge. Secondly, xi research should be conducted to examine the relationship between the foundation aspects of the abutment and its scouring depth.