Analysis and Estimation of local scour around bridge piers using modified HEC-RAS programming tool

Abstract

The western part of Tripura in India due to its geographical location and topography, is under constant risk of rainfall-driven flash floods occurring in the Gumti River causing colossal damage to life and properties almost every year. In this view, an analysis of the scour depth around bridge piers for its safety against the scouring is necessary for mitigating such flood hazards. In this study, we have used a modified HEC-RAS programming tool (HEC-RAS version 5.0.7, March 2019) to develop a scour model for evaluating the maximum local scour depth around bridge piers. We have selected three major bridges namely Subash Sethu, Burima bridge and Machmara bridge on the river Gumti and collected various dimensions of the bridge, scour profiles, sediment properties, etc. and also daily discharge data during 1980 to 2010 from Gomati Barrage Subdivision, Udaipur. Our model is calibrated using several empirical scouring models and it was found that the calculated scour depth from the HEC-RAS software is consistent with other models such as CSU, Larras and Ahmed. The dimensionless analysis is also used to determine the correlation among scour depth (ds) and flow depth (y), Froude number (Fr), angle of attack (θ) and contraction ratio (Cr). In the present study, it is found that an increase in the angle of attack by 3˚ results in an increase in the scour depth of 12.06%, 43.75% and 22.27% for 2-span, 3-span and 4-span bridges respectively. This study also found an increase in scour depth with increasing pier diameter. Overall, the HEC-RAS modeling tool works well in predicting scour depth in all three bridges and the estimated results are in line with other empirical models.