High-Resolution Erosion and Accretion Mapping to Identify Critical Areas along the Indian Coast

Overview

The identification of critically eroding areas is essential for coastal protection measures and to protect the coastal infrastructure and livelihoods. With this objective, a joint programme on the demarcation of composite hazard lines was undertaken by the National Centre for Sustainable Coastal Management, (NCSCM), Ministry of Environment, Forest and Climate Change (MoEF&CC) and the Survey of India (SoI) all along the Indian coast. SoI demarcated hazard lines account for the extent of flooding on land due to water level fluctuations, sea level rise and shoreline changes - erosion or accretion - occurring over a period.

These shoreline changes corroborate significant variations, indicated by erosion and accretion, on the coast due to evolving climatic and anthropogenic influences. This clearly envisages a baseline framework for policy formulation and developing strategies for coastal management.

Vision: To identify critical eroding areas and determine potential flooding on the Indian coast by mapping shoreline changes due to erosion or accretion.

Objectives

y To prepare shoreline change maps using high-resolution satellite imagery y To determine shoreline position using different shoreline proxies. y Calculating long-term shoreline change rates to calculate erosion/accretion status.

Stakeholders involved

NSCSM, SoI, coastal states and UTs, various government departments and the fishermen community. Solution and Implementation

The implementation of shoreline change has provided input for Integrated Coastal Zone Management Plan in West Bengal to facilitate coastal development and reduce beach erosion.

11 sets of high-resolution satellite imagery have been used to prepare shoreline change maps, as depicted in the following table:

Year

1990 1997 2000/2001 2003/2004

2005/2006

2007/2008

2009/2011

2011/2012

Source

Landsat IRS 1C/1D Pan IRS 1C/1D Pan IRS 1C/1D Pan IRS P6 LISS IV IRS 1C/1D Pan IRS P6 LISS IV IRS P6 LISS IV Cartosat 1 Worldview1 Worldview2 Quick Bird GeoEye Aerial Photo

Resolution

30 m 5.8 m 5.8 m 5.8 m 5 m 5.8 m 5 m 5 m 2.5 m 0.5 m 2 m 2.4 m 2 m cm GSD

This was followed by determining shoreline position using different shoreline proxies, including vegetation line, berm line, high water line, structures, dune vegetation line and rocky coast. Finally, long-term shoreline change rates were calculated using Digital Shoreline Analysis (DSAS), taking Linear Regression Rate for every 200 m transect interval perpendicular to the coast from the baseline to calculate erosion/accretion status.

The results were categorized into eight classes as “Zones of erosion/accretion” as follows:

High Accretion Medium Accretion Low Accretion Stable coast Low Erosion Medium Erosion High Erosion Artificial coast (Eroding coast) Rocky coast > 5m/yr +2 m/yr to +5 m/yr +0.5 m/yr to +2 m/yr -0.5 m/yr to +0.5 m/yr -0.5 m/yr to -2 m/yr -2 m/yr to -5 m/yr < -5 m/yr