Alvarinho Luis

The West India coast had an unwanted visitor in Cyclone Ockhi that caused sand erosion and ingression of water inshore along the coastal regions from Kerala to the north. It is the third and strongest storm of the north Indian Ocean cyclone season 2017. My breakfast companion – Herald – published pictures of sand erosion and water intrusion at many beaches, which prompted me to write article. In Pernem, nearly 30 shacks were reportedly damaged due to the cyclone. Media reported that the sandy beaches at Mobor, Majorda, Cavelossim, Benaulim in south Goa and Arambol, Morjim, Baga, Calangute in north Goa were the worst affected at a time when Goa is witnessing a peak tourist season which would culminate in December when of crowds will descend here for Christmas and to usher in the New Year. The major damage was reported to shacks, beach beds and other properties due to water intrusion inshore. This damage is in addition to the one that is already caused by humans by cutting of vegetation and leveling of sand dunes at many places for construction of permanent structures and encroachments. With the natural barriers flattened, the seawater ingress landward is easy during high tide and/ or storm surge, which further erodes the sand thereby, causing irreparable damage to the ecosystem such as uprooting of trees, damages to the structures, etc. 

What triggered the seawater to ingress higher-than-normal on beaches on December 3? It started with a higher sea level which was caused by piling up water towards the coast by strong winds. The amount of water piling up at the coast depends on the direction of the wind. The cyclone track was parallel to the west coast and came closest to about 200-300 kilometres off Goa on Sunday. As a result, the strong winds on the outer periphery of the cyclone were blowing north/north-northwest. So the wind stress on the sea surface caused large transport of seawater towards the west coast due to balance between pressure gradient and Coriolis force. On Sunday (3rd December) it was a supermoon – a full moon which reaches the point in the moon’s orbit where it is closest to the Earth. So the high tide on Saturday/Sunday was a few centimeters higher than normal which surged the coastal sea level and facilitated ingression of sea water into the shacks which were setup close to the high tide line. The strong cyclonic winds also enhanced the wave activity and caused large-scale erosion of the beach as well. 

 What facilitates the seawater to ingress to the backshore? The shore line consist of an offshore region which extends seawards from the low-tide line, the foreshore region between the berm crest (the elevated portion of the beach from the high tide line) and high tide line, and the backshore which hosts sand dunes and all types of vegetation such as Casuarina equisetifolia and creepers that gives stability and protects dunes from wind-related sand erosion and acts as a shelterbelt in the disposition of wind energy. The offshore zone is the most dynamic dominated by swells which support water sports, fishing, etc. Goa being a tourist destination there is a pressure on backshore, especially the sand dunes, to set up structures to cater to tourism-related and commercial activities which are mostly done in blatant violation of CRZ guidelines. In a global warming scenario, we have to position coastal structures and plan outdoor activities scientifically to mitigate potential threats from sea level rise and natural phenomenon like in cyclones and tsunami. Research papers suggest that the cyclone count and intensity have increased many folds globally, so we have to be prepared for reality by planning and positioning structures scientifically. The responsibility of GCZMA is paramount is taking wise decisions while granting licenses for structures in the CRZ, in consultations with all stake holders in the tourism industry and the scientific community. 

(Dr Alvarinho Luis is a senior Scientist researching on climate change at the Ministry of Earth Science, Govt of India, Vasco da Gama)