Estimation of Extreme Storm Surge for the Chennai Coast using Delft3D

This study carried out a numerical modelling of storm surges for historical tropical cyclones that crossed the Chennai coast, the northern part of the coastline of Tamil Nadu, India. An extreme value analysis was made based on the peaks-over-threshold (POT) method to calculate extreme storm surge estimates for different return periods. The area's bathymetry was generated from the National Institute of Oceanography (NIO) sea-floor data derived from ETOPO5 (the earth's surface that integrates land topography and ocean bathymetry). Historical storm tracks in the vicinity of the study area were selected from the database. These storm tracks were used to generate temporally and spatially varying wind and pressure fields using the Holland method. Cyclones considered for the simulations are from a 35 year period, ranging from 1977 to 2012. Cyclones of significant intensity that occurred in the vicinity of Chennai were selected for modelling. The Delft3D modelling software was used for the analysis. The domain considered for the study was generated on a rectilinear grid of size 540 km × 670 km covering the coastline from Nagapattinam in Tamil Nadu to Diviseema in Andhra Pradesh with 1.35 km × 1.65 km as the size of each grid cell. The water level calculated by the Delft 3D-FLOW module by solving the shallow water equations (SWEs) was extracted from the model over the entire domain at constant intervals and was monitored. The maximum surge in the water level at the Chennai coast was reported as the storm surge value for each cyclone. Results showed that Chennai is highly vulnerable to cyclones. A one-in a-100-year cyclone can produce a storm surge of 1.0 m, which can pose severe hazards to the city, since the topography is very low.This study will assist officials in preparing for a disaster of this enormity.