Parts of the 300-km shoreline of the State may be slowly eroding, with beaches such as Ullal losing more than 1 m of shoreline annually.
A total of 40% of 30 beaches along Karnataka’s coast face some form of erosion, shows a study conducted by researchers from the Department of Marine Geology in Mangalore University and the National Institute of Oceanography in Goa. The results, part of growing literature on the vulnerability of the coasts, were recently published in the International Journal of Sediment Research .
The researchers tabulated the changes in the shoreline between 1990 and 2016 through remote sensing and then applied statistical tools to determine the loss or gain in shoreline during the period. Bhavikeri in Uttara Kannada and Ullal in Dakshina Kannada are seeing a loss of more than 1.3 m annually (or, 33.8 m since 1990). Meanwhile, Yermal (DK) and Devbagh (UK) have seen their beach shorelines increase by 3.1 m yearly.
While there is a natural process of sediment removal (during monsoon) and accretion (natural river flow or non-monsoon periods), human activity has exacerbated erosion along the coast, said K.S. Jayappa, professor, Mangalore University, who authored the study along with K. Sowmya (Mangalore University), M. Dhivya Sri (NIO, Goa), and Aparna S. Baskaran (SRM Institute of Technology, Chennai).
“Breakwaters have been constructed around the entrance to ports, which affects the movement of sediment. This has led to accretion in beaches further up, while beaches down are experiencing erosion,” said Dr. Jayappa, adding that construction of these barriers end up pushing the problem elsewhere.
Compounding matters is the lowering of sediment from west-flowing rivers such as Nethravati and Swarna. “Lower amounts of sediment are reaching because of vented dams as well as sand mining in these rivers,” he said.
Previously, a study by the National Institute of Technology, Surathkal, which compared satellite images between 1972 and 2014, had shown that nearly 50% of the State’s coastline was highly vulnerable to erosion. In 2016, NIO Goa researchers stated that nearly 28% of the coast in Dakshina Kannada and Udupi coasts were critical and faced severe erosion.
Biowalls
To counter the erosion that threatens the vast number of houses in coastal areas, the State government is executing a seawall project — at a cost upwards of ₹200 crore — that will break monsoon waves.
However, these walls will either be washed away to the sea or shift the problem elsewhere, said Dr. Jayappa. “Instead of these walls, what should be set up is biowalls. The focus should be on strengthening of beaches with plantations at the fringes. These are known to be more efficient than seawalls, which cost more than the damage they are supposed to prevent,” he said.
