Calibration of Channel Roughness for Lower Mahi River, Using HEC-RAS

Abstract

Channel roughness is the most sensitive parameter in development of hydraulic model for flood forecasting
and flood plain mapping. Hence, in present study it is attempted to calibrate the channel roughness coefficient
(manning’s ‘n’ value) along the river Mahi, Gujarat through simulation of flood using HEC-RAS. The requirement of
multiple channel roughness coefficient manning’s ‘n’ values along the river has been spelled out through simulation of
floods, using HEC-RAS, for year 2001 and 2003 , supported with the photographs of river reaches collected during the
field visit of the lower Mahi river. The calibrated model, in terms of channel roughness, has been used to simulate the
flood for year 2005 and 2011 in the river. The performance of the calibrated HEC-RAS based model has been accessed
by capturing the flood peaks of observed and simulated floods; and computation of Root Mean Squared Error (RMSE) for
the intermediated gauging stations on the lower Mahi River