India’s Western Coastal Plains lies between the western part of the Deccan plateau and the Arabian Sea. The plains extend from the Kutch region in Gujarat to Kanyakumari, the southernmost tip of the Indian peninsula in Tamil Nadu, with the Western Ghats forming their eastern boundary. The place where the land meets the sea has been shaped by the waves and tides over thousands of years. In recent years, however, the beaches in the region have been slowly shrinking, with the sand washing away and the coastline changing.
To understand the changes taking place, researchers from the CSIR-National Institute of Oceanography, Goa, the Academy of Scientific and Innovative Research (AcSIR), Ghaziabad, and Bharathidasan University, Tiruchirappalli, conducted a detailed study of embayed beaches along India’s west coast. Embayed beaches are those that are tucked into bays, often nestled between rocky headlands. They have been facing increasing pressure from both a changing climate and human activities. The researchers aimed to understand precisely how these unique beaches are changing and what is causing it, examining the past three decades.
This research examines the morphodynamics, or the changes in shape and form over time, of these beaches. The team focused on twenty-seven specific embayed beaches along a roughly 200-kilometre stretch of coastline from Palshet to Shiroda Beach. To gain a better understanding of these diverse coastal features, they first classified them into three groups: those that are wide open and exposed to the full force of the ocean, those that are semi-exposed, and those that are more sheltered. They did this using a new method that looks at the beach's area and how much it curves inward into the bay. This classification is important because different types of beaches react differently to waves and storms.
Once classified, the scientists used a combination of hands-on fieldwork and satellite technology to track changes. For seasonal changes, they visited sixteen accessible beaches multiple times between February 2023 and September 2024, recording the temperature of each beach at various times of the year. They also used equipment, such as an optical level and a levelling staff, to measure the height of the beach surface at regular intervals during low tide. By comparing these measurements over time, they could calculate how much sand volume was gained or lost between the dry season (pre-monsoon) and the rainy, stormy season (post-monsoon). Their findings revealed a clear pattern: the beaches lost a significant amount of sand during the strong southwest monsoon waves (February to September) but regained some during the calmer months (September to February).
Waves generated by distant storms, called swells, can travel across entire oceans and significantly impact coastlines far away from where the storm occurred. |
To understand the changes that have occurred over decades, the researchers turned to satellite images from 1990 to 2023. Because beaches in this area are relatively narrow (50-100 meters wide), they required images with good detail, so they used Landsat data, which has a resolution of approximately 30 meters. They traced the outline of each beach in satellite photos from different years, ensuring consistency by using images taken under similar tide conditions. By comparing these outlines, they could see how the total area of each beach changed over the three decades. This analysis revealed a significant overall reduction in the area of many embayed beaches. While some beaches showed recovery or even gained some area (like Undi beach, which gained up to 62.5 meters), others experienced dramatic losses. Mirya beach, for instance, saw a maximum erosion of 81.72 meters!
Just looking at the area isn't enough to know if a beach is eroding or growing, however, as the sand can shift around within the bay. The researchers also performed a detailed analysis of shoreline changes. They used a method called Net Shoreline Movement (NSM) to calculate the distance the shoreline had moved at different points along each beach between 1990 and 2023. This gave them a more precise picture of where the coastline was retreating or advancing. This analysis confirmed that eight of the embayments, including Palshet, Hedavi, and Vengurla, are experiencing critical shoreline retreats. The long-term view confirmed that while beaches that might seem stable at seasonal or even yearly timescales are quite dynamic and unstable over longer, decadal timescales.
To understand what was driving these changes, the researchers examined several factors, both natural and human-induced. They analysed climate data going back to 1970, including sea level, tropical storms, wave power, and ocean swells. The data showed that regional sea levels have been rising (about 170 mm in Mumbai and 222 mm in Goa). They also found an increase in the frequency and duration of tropical storms over the Arabian Sea, which can generate powerful waves and surges. Wave power, a measure of the energy in the waves hitting the coast, has also shown an increasing trend over the decades, as has the frequency of long-period ocean swells originating from distant storms. These climate factors collectively contribute to more energetic conditions at the coast, increasing the likelihood of erosion.
But it's not just nature at work. Human activities also play a significant role. The construction of structures like breakwaters (walls built to protect harbours or coastlines) and jetties (structures extending into the water) can significantly disrupt the natural movement of sand along the coast. The study specifically noted that beaches with minimal human interference seemed to be primarily affected by climate factors. However, beaches like Mirya, Chiwla, Vengurla, and Shiroda, which have seen significant human-built structures and tourism development, showed more severe erosion.
Mirya Beach is a striking example; despite having a seawall built along much of its length, it has experienced substantial erosion, partly because the jetties built there have altered the natural flow of sand. This highlights how human interventions, although sometimes intended to protect, can sometimes exacerbate problems by interfering with natural coastal processes. The study concludes that the observed changes are a result of a complex interaction between natural forces and human actions, with human interventions often accelerating this transformation.
This research provides the first systematic classification of these specific embayed beaches in India. It also identifies which beaches are most vulnerable to erosion and helps understand the factors causing it, providing crucial information for coastal managers and planners. Understanding that these beaches are dynamic over decades, not just seasons, is key to effective management in the face of ongoing climate change.
This research article was written with the help of generative AI and edited by an editor at Research Matters.