Hydrologic and Hydraulic Analyses of Selected Reinforced Concrete Bridges in Davao de Oro using Hydrologic Engineering Center River Analysis System (HEC-RAS)


Watershed characterization is vital in hydrologic characteristics of the river basins where reinforced concrete bridges constructed. Therefore, this study conducted to determine the peak water flow in four return periods to come up essential information in bridge designing and engineering control structures. Three watersheds were chosen Compostela, New Dauis and Libay-libay for the proposed expansion of existing bridges. GIS software was used to delineate the watershed. Result showed that Compostela has the largest watershed comprising an area of 32643 hectares, total stream length of 36 kilometers and peak flow of more than 2000 m3/s. Also, New Dauis watershed have the highest slope at 21.55% and the smallest of the three watersheds but the time to peak of the water is as fast as 5.2 hours due its shape having a Gravelius index of 1.57. River analysis was accomplished using the latest version of HEC-RAS 5.0.7. The result showed that New Dauis existing bridge need to increase the bridge deck elevation at which the 25 years return period peak flow will reach its deck. The two remaining bridges are safe with the calculated flood peak flow on its current height. Bridge contraction scour of Libay-libay bridge at right overbank is the highest of the three at 7.12 meters, it’s because of the angle of attack of the water perpendicular to the right overbank. Compostela bridge right overbank have lesser contraction scour due to its constructed retaining wall. Pier scour observed at the right pier of the Libay-libay bridge and Compostela bridge. As Compostela bridge has the highest pier scour of 8.7 meters