ADB to help check Karnataka coast erosion

ADB to help check Karnataka coast erosion
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First Published: Mon, Jun 30 2008. 06 42 AM IST
Updated: Tue, Jul 01 2008. 12 51 PM IST
Mangalore: Every monsoon, giant waves crush houses on the Ullal-Kotepura coast near Mangalore in southern Karnataka, and the sea advances a few metres, eroding the coastline.
“I have seen so many fishermen’s houses destroyed every year,” says Mehmood Moosa, a fish boat owner in Kotepura. “Some 15-20 years ago, we had a one-and-a-half km wide beach. Now we have only 50m.”
The Asian Development Bank (ADB) plans to do something about it. The Manila-based bank will fund a pilot project to check coastal erosion in the region, even as some scientists express doubts on the efficacy of this.
Some 40km of Karnataka’s coastline has sea walls of concrete and boulders built along the shore, half of which scientists say are already unstable.
For the Ullal beach, ADB is considering three options, says B. Nagendra Kumar, coastal protection works engineer on the bank’s technical assistance mission. These include submerged breakwaters, sea walls and T-shaped structures extending from the shore line which break waves, also known as T-groynes. The pilot project is likely to be implemented by the public works department.
“Submerged breakwaters is a good option with comparatively lower side effects on neighbouring beaches, as it does not obstruct the littoral drift,” says K.S. Jayappa of the marine geology department at Mangalore University who has studied the phenomenon off the Karnataka coast for over two decades. Littoral drift is the drifting of marine sediments in patterns parallel to the beach that is due to the actions of waves and currents.
Submerged breakwaters are structures built in the shallow waters parallel to the shore that break waves and reduce their impact on the shore. It has been implemented in US and Canadian beaches, and scientists say it is the most natural way to ease erosion.
“But this too will make waves converge on neighbouring beaches, thereby gradually eroding them further,” Jayappa, however, points out.
Seawalls and T-groynes, on the other hand, will have significant erosion effects on neighbouring beaches as they block the littoral drift, he said. A T-groyne or sea wall would protect Ullal but obstruct the littoral drift southwards and erode the adjacent beach.
The Ullal pilot is part of a larger ADB project to suggest engineering solutions for coastal erosion across the western states of Maharashtra, Karnataka and Goa. ADB is ready to lend Rs850-1,000 crore to ease coastal erosion along the western shoreline of the country, said Union government officials closely associated with the initiative who did not wish to be identified as they are not authorized to speak to the media.
Most scientists are sceptical about engineering structures for coastal management. “Erosion and accretion are natural cyclic processes. It is better to leave the beach to natural processes without any human interference,” says A.C. Narayana, professor at the Centre for Earth and Space Sciences at University of Hyderabad. “Underwater breakwaters will work for a few years but it will be at the cost of eroding neighbouring beaches.”
Studies have also shown that breakwaters—a popular measure along the Karnataka coast—may protect the immediate beach concerned, but would cause severe damage to adjacent areas. Breakwaters are stone or concrete structures built from the shore extending into the sea to prevent a beach from washing away.
Jayappa and G.T. Vijaya Kumar’s study named Coast Dynamics Related to Engineering Structures and Management Issues, published by the Indian Association of Sedimentologists in 2003, says, “The breakwaters at Old Mangalore Port are serving the purpose with which they were constructed but they have also been responsible for the present severe erosion problem in Kotepura (as they block the littoral drift).” The study also revealed the erosion in Kotepura is accentuated by building sea walls, breakwaters, small dams across the neighbouring river and due to sand mining on riverbeds and beaches.
The ADB report on the Ullal project is likely to be submitted in December. “Once they submit it, we will comment on it,” said a Karnataka public work official, who did not wish to be named as the project was still in a “fluid” state.
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First Published: Mon, Jun 30 2008. 06 42 AM IST