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Contents
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Introduction
Coastal Areas are of vital importance. According to the UNEP, ~37% of the world’s population lives within 100 km of the coast. Coastal areas support a lot of economic activities including international trade and fishing. According to the OECD, ~90% of global trade occurs through marine route. Coastal areas have witnessed accelerated developmental activities and rising human population. The developmental activities have put tremendous pressure on the fragile coastal environment. The trend is same in India with coastal cities like Mumbai, Chennai, Kolkata, Kochi, Vishakhapatnam etc. witnessing tremendous growth and expansion. This has given rise to new challenges including accelerated coastal erosion. There is a need to counter the menace of coastal erosion and to protect the coasts, using both the traditional approaches and also using the new, innovative soft measures like dune rehabilitation.
About Coastal Erosion
A coastline is a complex series of interlinked physical systems in which both offshore and onshore processes are involved. Coastal Erosion is one such physical process.
Coastal Erosion refers to the loss of land, long-term removal of sediment and rocks along the coastline due the action of sea-waves, currents, tides and other impacts of storms. It involves wearing away and redistributing solid elements of the shoreline as well as sediment. Erosion occurs when the material being removed, for deposition elsewhere, exceeds the rate of supply finally resulting in the landward shifting of the shoreline.
Source: USGS
Waves are the main cause of coastal erosion. Wave takes birth in the mid-ocean and moves towards the coast. 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.
Wave energy is the result of three factors: (a) Speed of the wind blowing over the surface of the sea; (b) Length of fetch (i.e., the distance of sea over which the wind has been blowing); (c) Length of time that the wind has been blowing for. Waves are the major factor in determining the geometry and composition of the beaches. The action of waves dictates the processes of removal and addition of material/sediment on the coast.
Coastal sediment accumulates by process of accretion. Coastal erosion and accretion are natural processes that cause gradual to abrupt changes in coastlines over time and are instrumental in defining coastal landscape. These processes can occur in reaction to both small-scale phenomena like storms, frequent wave action, tides, and winds, as well as large-scale events like glacial or orogenic cycles, or tectonic movements that induce coastal land subsidence or emergence.
History of Coastal Erosion in India
Coastal erosion is an extensive and multi-dimensional problem for a vast country like India. Kerala is worst affected State by coastal erosion in India. In the original assessment in the 1960s, about 57% of the coastline was identified as vulnerable. Anti-erosion measures have been undertaken in the State from the nineteenth century. An assessment made in the late 1980s indicated that almost 85% of Kerala’s coastline was undergoing erosion.
Later, it was found that Karnataka and Maharashtra were also affected badly by sea erosion. The problem in other States was found to be in patches/coastal pockets depending on various factors.
The first anti-sea erosion measure in Puducherry was initiated by the French in the early 1920s when a 1.75 km long retaining wall was constructed along the urban coastline in Puducherry.
Source: Yojana November 2022
Causes of Coastal Erosion
The shoreline/coastline (the boundary between land and sea) keeps changing its shape and position continuously due to dynamic environmental conditions. Various developmental projects in coastal areas lead to diverse coastal hazards like soil erosion, seawater intrusion, coral bleaching, shoreline change, etc.
Natural Causes
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 for any reason, 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.
The natural variation in the supply of sediments to the coastline from the river can affect the erosion of the coastline.
An increasing sea level will promote shoreline erosion. Such erosion is higher in the littoral coasts consisting of finer sediments, as compared to coasts consisting of coarser sediments.
Subsidence is a regional phenomenon that lowers the surface area in a specific region. It also contributes to coastal erosion, the rate may vary as per the factor causing this subsidence.
Catastrophic events like severe storms, tidal surges, and cyclones cause the sea level to rise to abnormal heights and cause severe erosion.
Human-induced 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 includes ports/harbours works, coastal defence structures, river regulation works, dredging aggregate extraction/ sand mining, oil/gas exploration (in the form of long-term subsidence) etc. that impact sediment transport.
Coastal activities can also directly or indirectly result in beach erosion e.g., (a) Building houses via land reclamation or within sand dune areas has a long-term impact on coastal processes and sediment stability; (b) Harbours often have shore-perpendicular/inclined breakwaters (permanent structure constructed at a coastal area to protect against tides, currents, waves, and storm surges), which obstruct the long-shore transport of sand and cause accretion on the up-drift side, and erosion down drift; (c) Groynes (It is a rigid hydraulic structure built perpendicularly from an ocean shore or a river bank, interrupting water flow and limiting the movement of sediment) and jetties and other structures on the coast/ shoreline interfere with long-shore sand transport and can result in erosion when these are ill-designed; (d) The mining of sand/gravel along beaches and in the surf zone will cause erosion by depleting the shore of its sediment resources; (e) Coral mining and other means of spoiling the protective coral reefs also cause coastal erosion and beach degradation. The production of carbonate sand stops due to the killing of the corals and the protective function of the reef disappears; (f) Dredging of harbours, navigation channels leads to loss of sand and disturbs sediment equilibrium; (g) The removal of dune vegetation and mangroves causes exposure of the low-energy shorelines to the increased energy and reduced sediment stability. This further promotes erosion of coastal zone.
Climate Change
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. The low-lying areas along the coast are likely to be prone to salinisation due to seawater intrusion (surface and ground).
Protection Measures for Coastal Erosion
Coastal preservation measures slow natural or man-made coastline erosion over time. Nature offers many protective measures. Headlands, reefs, coastlines, dunes, etc. show nature’s coastal defence.
There are non-structural, structural and a mix of both measures to check coastal erosion. A combination of hard and soft options has become more popular for optimum results because they have weaknesses when used singularly. Many coastal protection schemes have failed and resulted in environmental and socio-economic problems owing to improper design, construction, and maintenance. They were often only implemented locally in specific places or within jurisdictional boundaries, rather than at system boundaries that reflect natural processes.
Brief description of these measures is given below:
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: (a) Artificial nourishment of beaches; (b) Coastal vegetation such as mangrove and palm plantation; (c) Sand bypassing at tidal inlets; (d) Dune reconstruction/rehabilitation.
Non- structural measures like adaptation to natural coastal processes (by using large setback distances, relocating vital structures, etc.) and moderation of coastal erosion (by stabilising coastal slopes, tripping the waves, etc.) should be used before employing hard structural measures.
These measures have limitations. While artificial nourishment of beaches 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. These solutions influence the coastal processes to stop/reduce the rate of coastal erosion.
The structural measures used for coastal erosion prevention include seawalls, off-shore breakwaters, groins/groynes/spurs, offshore reefs, and artificial headland.
Source: Wikimedia Commons
Out of the above measures, seawall is popular and generally used in almost all maritime regions.
Hard solutions cause erosion and needless accretion, are expensive, and can reduce the site’s economic worth by making it less appealing. Soft solutions are not quick-fixes and need time to be successful in the medium to long term.
Combination of the Structural and Non-Structural Measures
Combining structural and non-structural measures improves efficacy and efficiency. The combination creates a sustainable and affordable coastal protection system. Some of the common approaches of combinations are: (a) Combining beach nourishment with artificial headlands/groynes; (b) Revegetation with temporary offshore breakwaters/ artificial reefs.
Using a combination of beach nourishment and groynes/artificial headlands promotes the trapping of the downdrift movement of the sediment, thus reducing downdrift erosion. This also reduces the frequency of renourishment.
Initiatives to Check Coastal Erosion
Coastal Management Directorate, Central Water Commission (CWC), Department of Water Resources, River Development & Ganga Rejuvenation have undertaken a project entitled, “Shoreline Change Atlas of the Indian Coast” along with the Space Applications Centre (ISRO), Ahmedabad.
The Indian National Centre for Ocean Information Services (INCOIS) had prepared and published an atlas of Coastal Vulnerability Index (CVI) maps for the entire coastline of India.
‘Coastal Management Information System‘ (CMIS) has been initiated to collect data on coastal processes towards coastal protection measures.
National Centre for Sustainable Coastal Management aims to promote integrated and sustainable management of the coastal and marine areas in India for the benefit and wellbeing of the traditional coastal and island communities.
Integrated Coastal Zone Management Plan is a process for the management of the coast using an integrated approach, regarding all aspects of the coastal zone, including geographical and political boundaries, in an attempt to achieve sustainability.
The Coastal Regulation Zone (CRZ) Notification was issued in 1991 under the Environmental Protection Act, 1986, by the Ministry of Environment, Forest and Climate Change (MoEFCC) to regulate activities in coastal areas.
A National Strategy for Coastal Protection along with guidelines has been framed for all Coastal States and Union Territories by the MoEFCC.
The Flood Management scheme of Ministry of Jal Shakti, includes anti-sea erosion schemes.
Way forward
According to the Fifteenth Finance Commission, the National Disaster Management Authority (NDMA) and the Ministry of Home Affairs may adopt appropriate regulations for erosion mitigation measures. Both the Union and State Governments may develop a policy to cope with the widespread displacement of people caused by coastal and river erosion.
In addition, the Commission has provided specific recommendations for “Mitigation Measures to Prevent Erosion” under NDMF (National Disaster Mitigation Fund) and “Resettlement of Displaced People Affected by Erosion” under NDRF (National Disaster Response Fund).
Conclusion
As a result of globalisation, the diverse and culturally productive coastal ecosystems such as mangroves, coral reefs, sea grasses, and sand dunes are under threat from growing anthropogenic activity. To ensure sustainable development, these coastal ecosystems must be protected. It is critical to analyse the interplay between various activities carried out in coastal zones. This will ensure prudent, long-term development of the coastal zone while protecting the environment and ecology.
Syllabus: GS I, Important Geophysical phenomena, Geographical features; GS III, Disaster and Disaster Management.
Source: Yojana November 2022
