The northern most coastal landscape of Goa of which Tiracol estuary is a prominent ecosystem, has been under attack for a variety of reasons: a resort that has been proposed atop the cliff, a bridge at the mouth of the estuary, a new minor port in the making on the other side of the border, and recently, plans to dredge the river mouth. Always considered as the most pristine coast of Goa, the kind of activity planned, and presently underway, is rather scary.
The northern side of the estuary is marked by the Tiracol headland; this section of the coast is rocky and characterised by majestic cliffs, atop which the fort is located. A narrow sandy beach is found at the base of the fort wall. The present navigational channel runs close to the rocky shoreline. On the southern side, the Keri beach culminates into a sandy spit which is the most remarkable geological feature of Tiracol estuary.
A cursory look at the Google Earth (GE) images of the last 10 years reveals that the orientation and the area of the spit keep changing drastically. The following geomorphic features can be identified if a time series analyses is attempted:01/2006: A wide sandy beach can be identified; spit is elongated, pointing towards the river mouth; 01/2008: Spit becomes a thin elongated lobe pointing NE, and a wide beach is seen; 01/2010: Spit is thick, broad, trending NW; newly built sea wall is visible; 05/2012: the spit virtually disappears as sand is driven into the river mouth; 02/2013: Spit and beach disappear completely; only sea wall is visible; 04/2014: New spit enclosing water body emerges, trending northward; only a narrow beach is noted; 04/2015: A very narrow beach is seen; the sea wall is distinctly seen; the spit is pointing NE towards and into the river; 12/2015: the sandy feature has sort of rounded and curved towards the river side.
In addition to the sub-aerial sand spit, several (submarine) sand shoals also occur at the mouth of the river Tiracol, as evidenced by the breaking of waves further offshore. These shallow deposits appear to be all the more dynamic as compared to the sub-aerially exposed spit. It is a combination of these features that may create navigational hindrances.
Of the seven rivers of Goa, characteristic sand spits are found only at the mouths of five smaller estuaries: Tiracol, Chapora, Sal, Talpona and Galgibaga. At all these sites, the spits evolve in a southerly direction, except at Keri where the sand deposits are advancing towards the north.
Along the beaches of the world, sand is in a constant state of mobility. When sea waves break at an angle to the coastline, a shore-parallel current is created. This process is called littoral drift. In Goa, sand is mostly transported in a southerly direction, as evidenced by spits that grow southwards. But in the case of Keri beach, the movement of sand occurs northwards. Therefore, the sand deposit at Keri keeps extending in a northerly direction, and into the Tiracol estuary.
The observations above clearly indicate that the Tiracol estuarine/river mouth comprises an area that is extremely dynamic in nature.
Most of the Indian rivers that intersect the coast are marked by spits. In Goa, the longest spit is found at Betul; it is about 200 metres long. Along the west coast of India, almost all rivers develop spits, albeit small in dimensions. In comparison, the sand spit at Kakinada in Andhra Pradesh is about 17 kms in length and with a maximum width of 1.6 kms in the northern part. The Kakinada sand spit is the longest and the most spectacular one in India, and one of the longest in the world.
Should spits be allowed to grow? Can such features be colonised? Is it necessary to remove these sand deposits? What is the remedy if navigation is hampered? What is the fate of sand that may have to be removed? These are some of the pertinent questions that need to be addressed as such fundamental issues form the basis of coastal management. Therefore, any human interference in such a delicate geological set up has to be avoided at all costs for the sake of coastal stability in general and the beach – dune systems in particular.
The spit at Tiracol is presently under assault. A road bridge is under construction precisely at a place where such structures should be banned. Nowhere in the world has a bridge been emplaced at the mouth of an estuary, on a dynamically active sand spit, only a couple of metres away from the mighty ocean. Although this author is a party to the bridge approval as a member of GCZMA, the committee was shown that the bridge would be built upstream of the ferry point. What actually happened is totally different; the bridge columns are fixed on the spit, right at the mouth of the river. All the relevant issues raised by this author were overruled. Therefore, the decision to construct a bridge across a beach – dune – spit complex is rather absurd, as such an idea is rarely heard of.
In summary, sand spits belong to the ocean; being highly dynamic in nature, these features keep changing in space and time. Any human intervention on such fragile estuarine ecosystems is bound to prove counterproductive, more so in the case of Tiracol bridge that is simply not needed.
(Dr Antonio Mascarenhas is a former Scientist, NIO, Goa, and Member of GCZMA and GSBB)
