- A coastline is a complex series of interlinked physical systems in which both offshore and onshore processes are involved. Coastal Erosion is one of these physical processes, wearing away and redistributing solid elements of the shoreline as well as sediment, normally by such natural forces as waves, tidal and littoral currents, and deflation.
- Erosion occurs when the material being removed, for deposition elsewhere, exceeds the rate of supply finally resulting in the landward shifting of the shoreline.
- The developmental activities have put tremendous pressure on the fragile coastal environment and about 20% of the Indian population resides in the coastal area.
- Around 15% of India’s coastline has been eroded. Kerala is the state which is worst affected by coastal erosion in India. Around 85% of the state’s coastline is identified as vulnerable to erosion. Karnataka and Maharashtra are also affected badly by sea erosion.
Causes of Coastal Erosion
- The causes of erosion are either natural or man- made. Sometimes, it is a combination of both natural and man-made factors.
- While the former is a relentless process that is often impossible to resist, the latter is often due to ill-planned activities and can certainly be contained, or even reversed.
- Natural factors influencing coastal erosion are waves, winds, tides, near-shore currents, storms, sea level rise, etc.
- The combined action of different processes on the coastline like waves and tides maintains the stability of the shoreline. If the sediment supply to a section of beach is reduced due to littoral drift/sea level rise or constant impact of waves, it can cause severe erosion.
- Waves are the main cause of coastal erosion. Waves bring an enormous amount of energy to the coast that is dissipated through wave breaking, generation of currents, water level changes, and movement of sediment, turbulence, and heat.
- Another major factor promoting coastal erosion is the sea level rise. Coastal erosion is facilitated by a rising sea level that brings wave action to progressively higher levels and permits larger waves to reach and break upon the shore.
- Another factor is the phenomenon of subsidence. Subsidence is a regional phenomenon that lowers the surface area in a specific region. It impacts the coastline in a way similar to sea level rise, however, the rate may vary as per the factor causing this subsidence.
- Also, catastrophic events like severe storms, tidal surges, and cyclones cause the sea level to rise to abnormal heights and cause severe erosion.
- Most of the human-induced erosion is due to human interventions in the natural transportation process as well as in the sediment load of the rivers.
- Human activity may be enumerated as coastal defence structures, river regulation works, dredging aggregate extraction/sand mining, oil/gas exploration, and ports/harbours that impact sediment transport.
- Sand removal above replenishable quantities from the coast upsets the longshore sand transport budget and can result in erosion.
- Coral mining and other means of spoiling the protective coral reefs will also cause coastal erosion and beach degradation.
- Vegetation is important for maintaining/improving the sediment slope stability and consolidating the sediments by trapping the sediments. The removal of mangroves due to man interventions reduces sediment stability. This further promotes erosion of the coastal zone.
- The phenomenon of Climate Change has recently emerged as an important determinant in the coastal environment. Coasts are sensitive to sea level rise, changes in the frequency and intensity of storms, increases in precipitation, and warmer ocean temperatures.
- In addition, rising atmospheric concentrations of carbon dioxide (CO2) are causing the oceans to absorb more of the gas and become more acidic. This rising acidity can have significant impacts on coastal and marine ecosystems.
Coastal Protection Measures
- Non-structural Measures:
- The Non-structural measures aim at the dissipation of the wave energy by mirroring the natural forces and maintaining the natural topography of the coast. These measures are also called soft solutions. Some of these are:
- Artificial nourishment of beaches;
- Coastal vegetation such as mangrove and palm plantation;
- Sand bypassing at tidal inlets;
- Dune reconstruction/rehabilitation.
- These measures have limitations. While artificial nourishment of beaches (a process by which sediment, usually sand, lost through erosion is replaced from other sources) is complicated and costly, mangrove plantation is possible only in marshy land and in semi-tropical or tropical conditions.
- Structural Measures:
- The structural measures, also known as the hard structural/engineering measures, use physical structures constructed near the coast to prevent or restrict water from reaching the potential damage areas.
- The structural measures used for coastal erosion prevention include seawalls, revetment, off-shore breakwaters, groins/groynes/spurs, offshore reefs, and artificial headland.
- The hard solutions offer a wide variety of disadvantages like causing unnecessary accretion at points, being expensive, and also, at times, spoiling the economic value of the site by making it look less beautiful.
- In terms of the soft solutions, it may be noted that these are not quick-fix solutions and they take time to be effective and these are effective only in a medium to long-term perspective.
- To optimise the long-term positive impact of prevention measures, many combinations of soft and hard solutions can be selected.
- Coastal erosion is an extensive and multi-dimensional problem for a vast country like ours. Efforts are being made to counter the menace of coastal erosion and to protect our coasts, using both the traditional approaches (using hard structures like a seawall, etc) and also using the new, innovative soft measures like dune rehabilitation.