MAPPING INUNDATION DUE TO MAXIMUM PROBABLE FLOOD USING GIS AND HEC-RAS

Abstract

A significant deficiency of most computer models used for stream floodplain analysis, is that the locations of
structures impacted by floodwaters, such as bridges, roads, and buildings, cannot be effectively compared to the
floodplain location. This research presents a straightforward approach for processing output of the HEC-RAS hydraulic
model, to enable two- and three-dimensional floodplain mapping and analysis in HEC-RAS using ArcView geographic
information system. The methodology is applied to a lower Narmada reach, located between Sardar Sarovar Dam and
proposed Garudeshwar weir. Because Garudeshwar weir has been proposed to construct at the downstream of dam
which will create tail storage for running RBPH turbine a thought year. Because of that it will lead to increase water
level due to back water flow in flood situation will arise between Garudeshwar weir and SSD. Conventional flood
frequency analysis, involving log-normal, Gumbel’s, and log-Pearson type III (LP3) distributions, was used to calculate
extreme flows with different return periods. The peak floods from frequency analysis were input into HEC-RAS model to
find the corresponding flood levels expected along river reaches extending through SSD dam to proposed Garudeshwar
weir. Results obtained with HEC-RAS model were used in combination with ArcGIS to prepare floodplain maps for
different return periods. Through floodplain maps, areas that are vulnerable to flooding hazards have been identified.