Erosion Hotspots along Southwest Coast of India

Abstract

The south west coast of India consists of beaches and cliffs which support a highly dense costal community. Coastal erosion is confined to southwest monsoon season when the waves are rough. Seawalls and groins are the major management strategies adopted for coastal protection along Kerala coast. Erosion hotspots are identified from extensive field work carried out during the southwest monsoon season in 2013 and 2014. These hotspots are mostly dependent on the morphology and coastal structures. Identified hotspots are down drift side of mudbanks, fishing gaps, down drift sides of coastal structures including harbor breakwaters, locations of slumping seawalls, mining sites, wave over topping sites and piecemeal maintenance locations of seawalls. Tidal inlets are also vulnerable spots of coastal erosion. Highly viscous fluid mud formation that surface during southwest monsoon in the nearshore of the southwest coast is known as mudbank. It acts as wave dampening structures and triggers beach accretion and erosion in the mudbank region and its vicinity. Migration of seasonal tidal inlets which get opened during southwest monsoon induces erosion in the adjoining areas. Gaps within seawalls for facilitating traditional fishing are known as ‘fishing gaps’ towards which a pressure gradient develops pushing wave/swash into the gap accelerating erosion. In many places frontal beaches seaward of seawalls have disappeared bringing wave breakers closer to seawalls. Scouring at the base of seawalls accelerates slumping. Wave overtopping and flooding of the coastal zone landward of seawalls are also the resultant of high waves breaking very close to seawalls during southwest monsoon. Downdrift sides of harbor breakwaters are erosion hotspots because of the lack of proper Morphological Impact Assessment and mitigation plans for the expected shoreline changes. Seawalls have to abruptly end at some locations alongshore which cause ‘end erosion hotspots’. Maintenance of damaged seawalls is not well planned based on proper designs since most of the repair works are taken on piece meal basis and as emergency measures. The result is uneven shape of seawalls which itself weakens the protection measures making them highly vulnerable to erosion. The paper tries to understand the processes leading to erosion hotspots and propose measures to manage the hotspots