CANACONA AND ITS RIVERS

The rivers of Galgibag, Talpona and Saleri have developed spits at their mouths over the years. This may threaten the identity of rivers, explains Dr F M Nadaf, an associate professor in Geography at Shree Mallikarjun College of Arts and Commerce, Canacona.

Dr Nadaf further said that a spit is a long narrow accumulation of sand, pebbles, or shingles with one end connected to the mainland and the other projecting out into the sea or across an estuary due to deposition by onshore drift. Geomorphologically, such features are very common to coastal areas.

Due to the increase in size of the spits, all the three rivers are becoming narrower. The latest satellite image shows that the mouth of the river Saleri is 18 meters, river Talpona is 30 meters and river Galgibag is 44 meters. In the past, these rivers had wide open mouths, Dr Nadaf pointed out.

If the present rate of deposition near the mouths continues, in the decades to come, these rivers will turn into lakes. The rivers are not only becoming narrower, but also becoming shallower.

The riverbed of these rivers is visible to the naked eyes during the low tide. This will have very serious impact on Canacona and its people. It will affect the agriculture and fishing activity, said the associate professor, adding if the mouths of the rivers are closed, the sea will not be able to supply saline water to these rivers and this will affect the rare mangrove ecosystem.

“Due to decline in the depth of rivers because of siltation, the water-carrying capacity of these rivers has and will decline further. Such situation would result in flooding and submergence of fertile agricultural tracks,” he observed.

Talpona, Galgibag and Saleri spit formations have matured and become solid projections over the years, he pointed out adding hence, there is an urgent need to de-silt rivers and scientifically treat the spit formations. Unscientific treatment will lead to serious ecological problems including gushing of seawater into the river thereby destroying the entire area.

Dr Joseph Rauto D’Souza, chief scientist, DST, is of the opinion that there is an urgent need to study these coastal formations microscopically by using remote sensing and geo-spatial techniques to avoid any disaster in the future.

“Over a period of time along and with a change in wind direction, the end of spits becomes a hook like structure, as observed at Galgibag River. These geomorphic zones are potentially highly vulnerable to sea-level rise which could cause the low-lying areas and associated tidal flats to be permanently inundated and lead to major erosion of the supra-tidal areas, which happened during the floods in Canacona on October 2, 2009,” he said.

During spring tide cycles low-lying areas of the spit, get completely inundated. Over prolonged time scales the sandy barriers have become stable and with sufficient sediment supply, will grow with a rising sea-level,” he said.

Talking about morphology features in rivers, the scientist said, “When the wave movement at times cannot go beyond the spit, due to break in the wave energy, under this condition a sheltered area is formed where silt is deposited and mud flats or salt marshes form.

This is a unique estuarine feature which is developed in the Zuari river, at the Agassaim village. Barrier spits are actually bars that cut off a small part of water inland; the body of water becomes a lagoon which is conspicuous at the Mandrem village beach”