Paul Fernandes Times of India 23 Jan 12;
PANAJI: Quicker heating up of the coastal belt due to the capacity of concretized stretches to soak up heat contributes to enhanced beach erosion as the winds and waves batter the coast harder, a scientist has stated.
Tourism and development activities have triggered rapid urbanization of the coastal belt and, though it may sound unusual, they are a major factor causing faster beach erosion. "The concrete buildings, such as hotels, bungalows and tarred surface of roads and parking areas heat up faster because of high heat capacity, causing a phenomenon called heat island," says Alvarinho J Luis, a scientist at the national centre for antarctic and ocean research (NCAOR).
Speaking at a recently-held state-level seminar 'Weather and climate change in Goa after liberation', organized by department of physics, St Xavier's college of arts, science & commerce, Mapusa, the scientist said the heated surface in the coastal belt pushes the air into the upper atmosphere (convection) causing a low surface pressure below as compared to the similar conditions in the atmosphere over the sea.
The scientist, who is working on a paper to be published shortly, has compared data collected over a decade. He has used satellite-based data related to wind speeds and numerical models pertaining to sea level pressure and studied the contrasts between land and sea.
"This gradient (over a large area) between sea and land enhances the winds toward the land and increases the wave height via momentum transfer (tangential push) to the water," he said.
The increase in wind speed observed by satellites over the sea off Goa during the last decade (since 2000) has been significant (0.23±0.7 m/s per decade (r2=0.64, significant at 95% confidence level) (Figure 1).
An NIO scientist agrees, "The wind is a powerful agent for transportation of sand and even dry soil. In some African countries, the sand particles suspended in the air even block the sunlight," he said.
In Goa, water resources department has initiated various measures including erecting gabion structures to prevent denudation of beaches, but not with much success.
Coastal erosion is a worldwide phenomenon and many major centres of beach tourism, including Goa are expected to lose shoreline stretches in the future. But it was hardly known that higher wind speeds are triggered by heating up of the coastal belt due to development and concretization.
"The increase in the wind speed is a result of decrease in the sea level pressure trend over land when compared with that over the sea off Goa," Luis said.
In his assessment of the higher trend over land, the Luis states that it is a result of urbanization of Goa in the coastal belts due to a high demand for infrastructure, hotels, bungalows and tar roads.
The soaring waves crash on the sandy beach and carry away sand to the littoral zone. "Littoral currents flow parallel to the beach while rip currents flow perpendicular to the beach contour and move material out into the sea, altering the beach morphology" Luis said.
Sand bars are formed due to deposition of sand in the navigational channel due to high sediment load in monsoon. "The Aguada sand bar formation off the Miramar beach during monsoon is a typical example," Luis said.
Keri in Pernem, Anjuna in Bardez, Campal in Tiswadi and Talpona in Canacona talukas are some stretches which are heavily eroded. "About 20 years we could easily walk from Campal to Miramar beach, but now it is eroded and it is more visible near the light house," Agnelo Pinto, a resident said.
The eroded beach becomes vulnerable to further sea incursions. "As the topographic gradient of the beach decreases towards the land, it becomes easy for the sea water to intrude landward, thereby damaging sand dune vegetation, man-made structures," Luis added.
Though the rise in sea level is also increasing the influx of sea water once the coastline is eroded, wind-driven erosion is likely to be more dangerous. "Compared to the slow sea level rise (less than 1mm per year along the west coast), wind contributes a large chunk of mechanical energy to waves which are effective mechanism for coastal erosion," he further said.
The sea level rise has a time scale of century, but the wind forcing has a time scale of few years to a decade, Luis added.
Increase in sea level is another factor that contributes to influx of more water once the coastal line is eroded. Compared to sea level rise (less than 1mm per year along the west coast), wind contributes a large chunk of mechanical energy to waves which are effective mechanism for coastal erosion. Note that sea level rise is a slow process (time scale of century), while wind forcing has a time scale of few years to decade.
