If remedial measures are not taken urgently, there is every chance that in five years the surging waves of the Arabian Sea will start snapping at the edges of the Adani-controlled Thiruvananthapuram International Airport.

Already, the aggressive sea has smashed more than half the Shanghumugham road that runs very close to the boundary wall of the Airport.

Before Cyclone Ockhi hit in 2017, a popular sandy beach some 20-25 metres long had stretched between this road and the sea. That sandy leisure haven of city folks has long been devoured by the sea.

The vanishing of the Shanghumugham beach is just a small episode of what looks like a large disaster in the making. A latest study has found that the sea has taken away approximately 2.62 square kilometres or nearly 650 acres from the Thiruvananthapuram coast alone in 14 years (from 2006 to 2020).

 

West coast in danger
The study - 'Assessment of coastal variations due to climate changing remote sensing and machine learning techniques: A case study from west coast of India' – investigated coastal erosion, coastal accretion, and shoreline changes along the 58-km stretch from Pozhiyoor in the south to Anchuthengu in the north in Thiruvananthapuram district. This dangerously vulnerable stretch includes popular tourism spots Kovalam, Veli and Poovar.

The study, led by E Shaji, the head of the Department of Geology, University of Kerala, will appear in the September issue of the international multidisciplinary journal, Estuarine, Coastal and Shelf Science. Besides Shaji, the team included senior faculty of the Department of Geology and Department of Computer Science of the Kerala University and the National Centre for Earth Science Studies.

This is also the first study that used machine learning techniques along with remote sensing data to analyse the coastal variation of India’s west coast.

 

Vanishing sandy beaches
The study has detected the highest erosion from Poonthura to Veli, within which falls Shanghumugham, and Veli beach to Kadinamkulam. “These areas require special attention,” the study says.

The highest erosion rate obtained under the study is 10.59 metres per year at Pozhiyoor, at the southernmost tip of the Kerala coast bordering Tamil Nadu. This means, every year, an area larger than the width of a volleyball court disappears from the Pozhiyoor coast.

However, the study has found that the rate of erosion is more aggressive between Pozhikkara and Veli which includes the Shanghumugham Beach. This is because the maximum average erosion of about 4.73 metres per year is seen between this stretch. In other words, a slice of beach more than half the width of a volleyball court is lost every year along this 16-km stretch of the coast.

The other highly eroded areas include Vettuthura, Puthenthope, Pulluvila and Kochuthura, all of them densely populated coastal areas.

 

Fraction of land taken, returned
There has been accretion, too. The study observed that “high to very high accretion” occurs at river mouths and estuaries, where the river meets the sea. For instance, the northern side of the Neyyar river mouth at Poovar. Similarly, high accretion (2–3 metres per year) is seen in Karumkulam area, northern side of Poovar, and at north of the Adimalathura estuary.

“These areas get sediments from the Neyyar River and northward drift distributes the sediments to these locations,” the study said. It also detected more accretion at Vizhinjam, and this the study attributed to the Vizhinjam sea port construction and the natural rocky cliffs on the north of Vizhinjam, which act as groynes or 'pulimuttu', a bridge of sorts slightly above the water but constructed perpendicular to the shore.

Poonthura area, too, has relatively high accretion as the Killi river contributes sediments to the sea. “There are five groynes constructed in this area and the accretion is also observed in between these groynes,” the study said. Similarly, in the Valiyathura area the erosion rate is minimal due to the presence of about 15 groynes.

Nonetheless, when compared to erosion, accretion is woefully insufficient. If the entire stretch lost 2.62 square kilometres (nearly 650 acres) of land in the last 14 years, only 0.7 square kilometres (173 acres) were restored through the deposit of sediments. “The sediment supply is not enough for the coast to recover from the attacks that began from the 2004 tsunami,” the study said.

 

What to expect in five years
Using machine learning techniques, the study has also devised a prediction model. By 2027, the study predicts that the major erosion activity will be in the 30-km northern stretch of the coast from Shanghumugham and Anchuthengu.

In this long stretch made up of innumerable beaches, the erosion will be 7-8 metres a year; the sea, in short, will snatch away nearly the width of a volleyball court along this stretch every year.

 

Causes of erosion
The primary reason for the coastal erosion is the sea level rise and monsoon impact, the study observed. “The coast is eroded mainly due to high intensity waves during monsoonal and post-monsoonal seasons,” it said.

As for the aggressive erosion rate, the study blamed “lack of sufficient sediment supply from the river to the sea, increase in wave height and swell waves”. The less sediment supply may be due to dredging activities in the river, sand mining, trapping of sediments by dams, and change in land-use pattern.