Globally, coasts are subjected to varying degrees of shoreline changes, erosion and accretion (SEA) activities which may be for short- or long-term. Sand erosion may exist in one area while there would be accretion elsewhere so that an equilibrium is maintained along the coast.
But there are sites where these processes may be lopsided and affect the safety and livelihood of the people living along the coasts. Being in a dynamic marine environment such phenomena are expected and we cannot stop the progression but need to could protect the coasts.
India has a coastline of 7,500 km (9 coastal States and nearby island groups) and 26% of the total population reside along the coasts. Reportedly, 15% (1,144 km) of India’s coast is eroding resulting in a loss of 3,680 hectares (ha) of land while 4,042 area has been gained through accretion.
According to the National Centre for Sustainable Coastal Management, Goa’s 105-km long coastline, from Querim (Keri) in the north to Polem in the south, is 35% is rocky, 20% stable and has 27% erosion and 17% accretion. The consequences of SEA are worrisome especially as Goa depends on beach tourism and fishery.
In March 2023, the Indian Space Research Organisation identified 21.7 km of the coast and 28.8 ha area to be eroded, while accretion was noticed along 7.1 km that resulted in addition of 13.6 ha of coastal area. Effectively, Goa lost about 15.2 ha of area with severe erosion observed along the Candolim-Calangute stretch. Perhaps this may be due to the sunken merchant vessel ‘River Princess’ that had remained grounded for more than 12 years and drastically altered wave and sediment movements.
The reasons for SEA are due to enhanced wave activities, frequent tropical cyclones of varying intensities, climate change, sea-level rise, and human interferences. River sand mining changes the littoral drift of sands as noted at Khandepar, Chapora, Tiracol rivers and at Keri, Morjim and Coco beaches.
The other important reason for SEA is the long shore transport of the sediments during the south-west or summer monsoon between June and September and north-west or winter monsoon from October to December. The former severely affects the west coast while the latter is confined to the east coast. During monsoon there is beach erosion while post-monsoon beach building commences and these processes repeat annually.
The coastal States have taken different steps to protect themselves by means of anti-erosional methods such as using tetrapod, gabion walls, retention walls, and geobags. The Water Resources Department of Goa constantly takes steps to limit erosion by the above methods. These techniques are not fool-proof but significantly reduces the SEA, depending on the site and intensity of oceanographic processes.
Considering the materials, cost and time involved in protecting the coasts, we could explore use of cheaper and locally available materials. It is a common sight to see coconut groves and trees along the coasts. The roots hold the sands and lessen the erosion and because the trees sway with the wind they do not get easily uprooted except during severe stormy or cyclonic conditions. The adaptable coconut trees should be encouraged to be grown along the coasts as the trees and the fruits are used in coir, jute, food, and artefact making industries.
The coastal people could benefit by consuming and selling coconuts and using the branches for roofing and to make broomsticks and tree trunks as rafters.
In Goa, as elsewhere, there is always a demand for tender coconut water as a thirst quencher, increasingly used for its nutritional value as well as an ingredient for food and desserts. Most Goan families daily use at least one coconut and it would be much more in restaurants. Just imagine the thousands of ‘shells’ (colloquially used here to mean the exocarp, mesocarp and endocarp, that are parts of a coconut) that are generated at the end of a day! Have you ever wondered what happens to the shells and how and where are they disposed of? The shells are not easily biodegradable, takes more than a year to decompose and occupy (especially the tender coconuts) a large space in the landfills. The carelessly discarded shells clog the drainage channels.
Perhaps we could use these tough and long-lasting resources in a sustainable way to protect our coasts! A concrete wall could be constructed with shells embedded with their empty side facing the sea while the husks could be placed in the interstices. The wall could be covered with fine-meshed galvanised steel wires so that it would be sturdy enough to bear the impact from the waves and trap the sands. The dimensions of the walls ie, height, thickness and length could be determined after studying the height and movement of the waves. The cost of such a seawall built at site would be less expensive than for example tetrapod, which need to be fabricated elsewhere and transported to the beach.
The Goa government could have coconut shell collection and sorting centres from where the WRD could source them to construct the seawalls. On a trial basis, seawalls could be built along a part of the mouth of rivers and between Candolim and Calangute and between Mobor and Cavelossim where intense erosion prevails.
If the above novel suggestion works successfully, then it could be replicated along other coastal areas of India. Wind and waves would find seawalls of coconut shells and husks, tough nuts to crack!
(Sridhar D Iyer is Chief Scientist (retired), CSIR-NIO, Dona Paula, Goa. Anthony Viegas is Associate Professor and Vice-dean (Academic) School of Earth, Ocean and Atmospheric Sciences, Goa University, Taleigao Plateau, Goa.)