Coastal Erosion – an analysis

Context

Recently a study report published in scientific Journal Nature Climate Change says that Climate change poses an existential threat to the world's sandy beaches.

Background

• Coastal erosion is the wearing away of land and removal of beach sediments by high winds, drainage, wave action, wave currents, and tidal currents. Coastal morphodynamics studies the erosion and sediment redistribution in coastal areas. It is caused by corrosion, hydraulic action or abrasion.
• Coastal erosion can be either a:
  • rapid-onset hazard (occurs very quickly, a period of days to weeks)
  • slow-onset hazard (occurring over many years, or decades to centuries).
• The beaches and shorelines in India serve multidimensional needs such as seaport for maritime commerce, space for residential & commercial structures, recreational purposes etc.
• Developmental activities along the coastline have increased and the trend is expected to continue in the decades to come.  Similar to any other maritime country, India’s long peninsular region constantly battles erosion.
• The developmental activities are often carried out without a clear understanding of the coastal dynamics. This leads to a long term, in the worst cases, permanent damage particularly to the local communities.
• According to the Ministry of Environment, Forest and Climate Change (MOEFCC) 40% of India’s coastline is subjected to high, medium or low coastal erosion.

What is the need for prevention of Coastal Erosion?

• The coastal regions where land and water meet are ecologically dynamic and sensitive regions, as marine and coastal ecosystems continuously impact on each other.
• These regions have a rich ecosystem such as mangroves, water bodies, seaweeds coral reefs, fisheries and other marine life, and other coastal and marine vegetation.
• These ecosystems protect the region from saline winds, cyclones, tsunami waves etc., promote carbon sequestration and promote biodiversity as well as provide raw materials for a number of manufacturing activities. Hence, this is an alarming situation for us to overcome from the coastal erosion.

Causes of Coastal Erosion

• Wave energy is considered to be the primary reason for coastal erosion.
• Natural hazards like cyclones, thermal expansion of seawater, storm surges, tsunami etc due to the melting of continental glaciers and ice sheets as a result of climate change hamper the natural rhythm and precipitate erosion.
• Strong littoral drift resulting in sand movement can also be considered as one of the major reasons for coastal erosion.
• Dredging, sand mining and coral mining have contributed to coastal erosion causing sediment deficit, modification of water depth leading to longshore drift and altered wave refraction.
• Coastal erosion has been sparked by fishing harbours and dams constructed in the catchment area of rivers and ports reducing the flow of sediments from river estuaries.
• Heavy rainfall can enhance the saturation of soils, with high saturation leading to a reduction in the soil’s shear strength, and a corresponding increase in the chance of slope failure (landslides).

Status of Coastal Erosion in India

The Ministry of Earth Sciences that monitors shoreline changes along the Indian coast states that:

• About 89% of the shoreline of Andaman and Nicobar Island is eroded by the Bay of Bengal.
• Goa has the highest percentage of stable shoreline.

• With 62% of its coast gaining land, Tamil Nadu has gained the newest shoreline.
• Example:
  • A major portion of the beach between Someshwara Rudrapade and Uchila looked as if it had been washed away.
  • Hundreds of people living in coastal Kerala at Aliyarpalli, Marakkadavu, Murinjazhi, Puthuponnani, Azhikkal, Veliyankode, Thannithura, Palappetty and Kappirikkad evacuated their houses following the threat of sea erosion.
• Length of the coastline of India including the coastlines of Andaman and Nicobar Islands in the Bay of Bengal and Lakshadweep Islands in the Arabian Sea is 7517 km.
• Length of Coastline of Indian mainland is 6100 km which is surrounded by the Arabian Sea in the west, Bay of Bengal in the east, and the Indian Ocean in the south.
• The long coastline of India is dotted with several major ports such as Kandla, Mumbai, Navasheva, Mangalore, Cochin, Chennai, Tuticorin, Vishakapatnam, and Paradip.

Why did the Eastern coast see more erosion than the Western coast?

• The eastern coast of India saw more soil erosion than the western coast as the Bay of Bengal sees rougher waters than the Arabian Sea.
• The eastern coast sees a lot of rain which keeps the seas rough through most of the year.
• Besides the Southwest Monsoon (June to September), the eastern coast also witnesses the Northeast Monsoon from October to December and brings rain to coastal Andhra Pradesh and Tamil Nadu.
• The eastern coast underwent more erosion due to frequent cyclonic activities from the Bay of Bengal in the past three decades, compared to the western coast, which remained largely stable.

Impact of coastal erosion:

Immediate Effects 

• Removal of small islands. 
• Loss of beach sediments. 
• Destruction of existing habitats of shore flora and fauna.
• Weakening and destruction of sea walls, revetments, bulkheads and other coastal defences. 
• Loss of agricultural land. 
• Deposition of sediment on productive lands. 
• Damage and destruction of jetties. 
• Damage and destruction of boat-launching facilities, septic tanks, water tanks, and building foundations. 
• Disruption of communications caused by the collapse of seafront, bridge, road, and railway foundations. 

Secondary Effects 

• Loss of income for those who are dependent on coastal areas.
• Reduction of protection against future storms. 
• Creation of unstable cliff slopes. 
• Pollution of beaches caused by broken sewer lines. 
• Silting and invasion of saline water behind breached defences.  
• Flooding of land areas behind breached defences. 
• Scarcity of drinking water 

 Control Methods

• Hard-erosion controls
  • Hard-erosion control methods provide 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 life span of a seawall is 50–100 years and the average for a groyne is 30–40 years. Because of their relative permanence, it is assumed that these structures can be a final solution to erosion.
• Soft-erosion controls
  • Soft erosion strategies refer 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 a means of preserving a building foundation.
• Relocation
  • Relocation of infrastructure or housing farther away from the coast is also called a managed retreat. The natural processes of both absolute and relative sea-level rise and erosion are considered in rebuilding.
• Improving vegetation along the coastline, which is important for improving slope stability and providing shoreline protection.
• Using Geosynthetic tubes that are being used along the coast in Odisha.
• Building out into the sea, low walls or barriers called groynes to check drifting.
• Making use of indigenous knowledge of local communities before decision making concerning developmental projects along the coastline.

Conclusion

National Centre for Coastal Research (NCCR) has found that nearly one-third of the country’s coastline is severely eroded. We continue to lose more of our coastal areas to climate change. The government and the people must make use of the traditional knowledge in addition to the scientific methods to mitigate the impacts of climate change on our coastal areas.