Mumbai: At least 55 hectares of coastal land of Devaghar, in Raigad district equalling more than five Azad Maidans have been lost to the sea over the past three decades, a remote sensing analysis of the region has found.
A 1.5-kilometre-long shoreline in the region around Devaghar beach has significantly receded — to the extent of 300-500 metres inland — between 1990 and 2022, resulting in the loss of various ecosystems, including mangroves, mudflats, small creeks and sandy beaches, the analysis led by Deepak Apte, director, Srushti Conservation Foundation (SCF), found.
Apte, who also serves as chairman on the Union environment ministry’s expert appraisal committee on Coastal Regulation Zone (CRZ) and Infrastructure, Ports and National Highways, and his team from SCF conducted a remote sensing analysis over the past several months using images from NASA and the US Geological Survey’s Landsat Program. Data going back to 1990 was analysed using the Google Earth Engine which revealed the extent of geological changes.
The analysis follows years of anecdotal reports from locals in the area.
The shoreline erosion, noted since the 1990s, has also caused large-scale death of mangrove patches. “It is not possible to quantify the extent of mangrove loss because the resolution in older images is not very good, but we can tell that it is significant because today, the mangroves at Devaghar are very patchy and don’t grow in large swathes as they once did,” said Apte.
Casuarina plantations which extend along the north-south belt on Devaghar beach were also found to be at risk due to this phenomenon. “Beach-side plantations are being destroyed due to continuous loss of sediment resulting in the erosion of the shore and change in sediment profile from a clay-silty dominated seascape to coarse sand dominated seascape,” SCF’s analysis said.
What’s more, the rate of erosion has increased markedly since 2005, after the construction of a vehicular bridge across the Bankot Creek which adjoins this area, began. “This seems to have sped up a slow process which has been going on since the 1990s. When Cyclone Nisarga made landfall near Devaghar in June 2020, it resulted in the destruction of nearly five hectares of mangrove land. The scale of damage could have been averted had the rate of erosion been slower. Some of these patches are now recovering, but large tracts of mangroves are already on the verge of death,” Apte said.
Large-scale sand mining in recent decades in Bankot creek could be one reason for the increased pace of shoreline erosion. Though this requires further study, unregulated sand mining has been seen to facilitate erosion in several areas along the Maharashtra coastline, like Alibaug and Mandwa, Apte said.
Researchers have warned that this is not an isolated phenomenon, and emphasised on the need to carry out similar assessments along the entire coastline of Maharashtra. “Climate change related sea-level rise will further worsen the situation. The Government should commission a study to seek solutions to deal with the changing seascape. We are currently doing ad hoc interventions which will only worsen the situation and increase erosion in the long-run,” Apte said.
Surendra Thakurdesai, a coastal geomorphologist at Ratnagiri’s Gogate Jogalekar College, who reviewed SCF’s findings at HT’s request, said, “Erosion has definitely occurred, but the cause can’t be pinpointed with the data which has been presented. It need not be connected to a global phenomenon like sea-level rise and could be more due to some local factors, but this needs to be studied further. Some common causes which could be responsible include a shifting in shore-parallel currents in the area, construction of bunds by people to prevent entry of sea water inland, changes in the outline form of coastal protection walls, a new jetty in vicinity, or dredging of a nearby creek channel.”
The analysis in Devagarh beach is part of an ongoing study by SCF — a non-profit involved in conducting conservation research — to examine the nature and extent of land-inundation in coastal Maharashtra, due to various geomorphic and environmental processes.
Last year, SCF had released an assessment of shrinking creeks and waterways along the Mumbai Metropolitan Region due to excess siltation, and succession of mangroves over 60sq.km of agricultural land along Karanja Creek due to ingress of saline water.
Coastal erosion is monitored by the Maharashtra Maritime Board, and studies have been conducted nationally by organisations like the National Institute of Ocean Technology (NIOT) and the National Centre for Coastal Research, but localised data for specific regions is scarce. A recent NIOT analysis of shore erosion suggested 25.5% of Maharashtra shoreline eroded with varying degrees between 1990 and 2018.