Coastal Erosion

In News

• Recently, the Ministry of Earth Sciences informed the Lok Sabha that of the 6,907.18 km long Indian coastline of the mainland, a significant area is under varying degrees of Coastal erosion.

About

• The National Centre for Coastal Research, Chennai, an attached office of the Ministry of Earth Sciences has been monitoring shoreline erosion since 1990 using remote sensing data and GIS mapping techniques.
• About 6,907.18 km long Indian coastline of the mainland has been analyzed from 1990 to 2018.
• Another organization under the MoES, the Indian National Centre for Ocean Information Services (INCOIS), has prepared and published an atlas of Coastal Vulnerability Index (CVI) maps for the entire coastline of India at a 1:100000 scale.
  • It uses data on sea level rise, coastal slope, shoreline change rate, coastal elevation, coastal geomorphology, tidal range and significant wave height.

Key Findings

• Percentage wise assessment
  • About 34% is under varying degrees of erosion, while 26% of the coastline are of an accreting nature, and the remaining 40% is in a stable state.
• State wise assessment:

• In terms of percentage, West Bengal, located on the eastern coast of the country, with a 534.35 km-long coastline, suffered erosion along about 60.5% of the coast (323.07 km) over the period from 1990 to 2018.
• This is followed by Kerala on the west coast, which has 592.96 km of coastline and 46.4% of it (275.33 km) faces erosion.
• Tamil Nadu, with a long coastline of 991.47 km, recorded erosion along 42.7% of it (422.94 km).
• Gujarat, with the longest coastline of 1,945.60 km, recorded erosion along 27.06% (537.5 km) of it.
• In the Union Territory of Puducherry, with a 41.66 km-long coastline, about 56.2% of its coast (23.42 km) recorded erosion.

Factors causing Coastal erosion

Coastal erosion may be caused by hydraulic action, abrasion, impact and corrosion by wind and water, and other forces, natural or unnatural.

• Hydraulic action: Hydraulic action occurs when waves striking a cliff face compress air in cracks on the cliff face.
  • This exerts pressure on the surrounding rock, and can progressively splinter and remove pieces.
  • Over time, the cracks can grow, sometimes forming a cave.
  • The splinters fall to the sea bed where they are subjected to further wave action.
• Attrition: Attrition occurs when waves cause loose pieces of rock debris to collide with each other, grinding and chipping each other, progressively becoming smaller, smoother and rounder.
  • Scree also collides with the base of the cliff face, chipping small pieces of rock from the cliff or has a corrasion (abrasion) effect, similar to sandpapering.
• Solution: Solution is the process in which acids contained in sea water will dissolve some types of rock such as chalk or limestone.
• Abrasion: Abrasion, also known as corrasion, occurs when waves break on cliff faces and slowly erode it.
  • As the sea pounds cliff faces it also uses the scree from other wave actions to batter and break off pieces of rock from higher up the cliff face which can be used for this same wave action and attrition.
• Corrosion: Corrosion or solution/chemical weathering occurs when the sea’s pH (anything below pH 7.0) corrodes rocks on a cliff face.
  • Limestone cliff faces, which have a moderately high pH, are particularly affected in this way.
  • Wave action also increases the rate of reaction by removing the reacted material.
• Secondary factors
  • Weathering and transport slope processes
  • Slope hydrology
  • Vegetation
  • Cliff foot erosion
  • Cliff foot sediment accumulation
  • Resistance of cliff foot sediment to attrition and transport
  • Human Activities
• Tertiary factors
  • Resource extraction
  • Coastal management

Way Forward/ Control methods

• Hard-erosion control methods:
  • It provides a more permanent solution than soft-erosion control methods.
  • Seawalls and groynes serve as semi-permanent infrastructure.
  • These structures are not immune from normal wear-and-tear and will have to be refurbished or rebuilt.
  • It is estimated the average lifespan of a seawall is 50–100 years and the average for a groyne is 30–40 years.
• Soft erosion strategies:
  • It refers to temporary options of slowing the effects of erosion.
  • These options, including Sandbag and beach nourishment, are not intended to be long-term solutions or permanent solutions.
  • Another method, beach scraping or beach bulldozing allows for the creation of an artificial dune in front of a building or as means of preserving a building foundation.
• Living Shorelines
  • The solutions to coastal erosion that include vegetation are called “living shorelines.”
  • Living shorelines use plants and other natural elements.
  • Living shorelines are found to be more resilient against storms, improve water quality, increase biodiversity, and provide fishery habitats.
  • Marshes and oyster reefs are examples of vegetation that can be used for living shorelines; they act as natural barriers to waves.
• Relocation
  • Relocation of infrastructure any housing farther away from the coast is also an option.
  • The natural processes of both absolute and relative sea level rise and erosion are considered in rebuilding.
  • Depending on factors such as the severity of the erosion, as well as the natural landscape of the property, relocation could simply mean moving inland by a short distance or relocation can be to completely remove improvements from an area.

Source: TH