While construction of port and harbour and breakwaters had affected the natural movement of sand along the coast, sand and clay mining and construction of vented dams across the rivers had reduced the arrival of sand deposits into the sea, the study said.

The study, undertaken by Reader in the department K.S. Jayappa, and research scholar Avinash Kumar, was published as an article in a recent issue of International Journal of Environment Research.

The report said that the movement of sand from north to south was more than the one from south to north on either side of the New Mangalore Port and the old port. Construction of breakwaters to provide a deep channel for vessels to move in and out of ports, was acting as a barrier for movement of sand.

Sand mining

Quoting a 2003 document, the study said that about 10 lakh tonnes of silica sand and 30 lakh tonnes of clay were being removed from the riverbanks and alluvial plains a year. “Sand is dredged both legally and illegally from beaches, estuaries, and in the upstream for various developmental activities. Illegal sand mining at the Someshwar beach, Netravati-Godavari estuaries, and in the upstream has been going on for years. This direct loss of material has affected the dynamic equilibrium of the beaches and led to erosion,” the study said.

Mr. Jayappa told The Hindu on Friday that the Government of Kerala had banned illegal sand mining. A huge quantity of sand mined here was now being transported to Kerala, he said.

Owing to the construction of vented dam at Thumbe, Joyikallu and other places across the rivers to provide water for industries, drinking, and irrigation purposes, a major portion of the sediment was withheld during the fag end of monsoon, and post-monsoon seasons. As a result, the sediment supply had been drastically reduced. Deforestation, urbanisation, and infrastructure development had major impact on coastal environment by accelerating the erosion rates, the report said.

The study is said to have indicated that the decline in annual average rainfall was also a contributing factor. The rainfall during 2001-05 was much below the normal in all the taluks of the district. This led to reduction of sediment input to the beaches, it said.

Topography changes

The researchers studied the topographic map prepared by the Survey of India for the 18-km stretch of the coast between Panambur and Talapady in 1967, and compared it with the satellite images obtained between 2001 and 2005 by the Hyderabad-based National Remote Sensing Agency.

It was found that the shoreline had extended into the sea by 10 to 120 metres whereas it receded by 10 to 260 metres. The shoreline between Panambur and Tannirbhavi had recorded net accretion of about 10 to 29 acres between 1967 and 2001. However, this stretch registered net erosion of three acres between 2001 and 2005.

The study observed that construction of seawalls (using large boulders) had resulted in shifting the location of sea erosion. Mr. Jayappa said that the construction of seawalls was a waste of public funds, and the Government should look at options such as green walls — planting rows of Casurina trees and growing creeper called Biloba. He was happy that this idea mooted by his department 10 years ago was being taken up by the Western Ghats Task Force.