Analysis and Estimation
of local scour around bridge piers using modified HEC-RAS programming tool
Dalal Biswajit and Deb Subhrajyoti
Disaster Advances; Vol. 15(10); 52-62;
doi: https://doi.org/10.25303/1510da052062; (2022)
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.
