A recent field visit to Cavelossim peninsula revealed a 7- metre wide road, audaciously laid across a sand dune complex. The pathway traverses about 220 metres across the dune and another 200 metres along the frontal seaward pioneer dune.
Thus a 420 metres long road is built from the river side to the ocean front across an ecologically sensitive CRZ I zone.
Being a no development zone and utterly prohibited, such a roadway is tantamount to blatant violations of CRZ rules.
Inquiries with local villagers revealed plans to build a rubble sea wall to stop the accretion of sand at the mouth of river Sal.
Littoral currents transport excess sand along shorelines and ultimately gets deposited at river mouths in the form of spits. Navigation at the mouths of rivers is often hampered.
The origin of large sand shoals within the estuary is not known. The catchment of river Sal is not sandy; as such does not contribute sand. However, the monsoon erosion of the adjacent vertical cliff may throw some sand into the estuary. But it is highly likely, considering its large volume, that the sand within the estuary is transported from the sea into the estuary.
During monsoons, the coast of Goa gets a direct hit from the westerly sea waves.
As such, sand from the spit and at the mouth of river Sal can easily be pushed into the estuary.
Google Earth satellite images of January 2017, April 2015, April 2014 and February 2003 show distinct wave fronts that propagate into the estuary. Sand thus enters into the estuary through the 120- metre wide inlet.
Groynes or coast- perpendicular rubble walls are generally employed ( at prohibitive costs) to curtail the movement of beach sand into the rivers.
However such measures are mostly inefficient, and have drastic negative impacts on shorelines: accretion of sand on the up- drift side with consequent erosion on the downdrift side. Scientific publications have reported chronic sand erosion wherever groynes are constructed.
Consider these examples: ( a) Port activity at Chennai has taught haunting lessons. The untold chronic erosion on the Ennore side as a consequence of sand entrapment by the harbour breakwater groyne is a classic example.
The highway towards the north is virtually in water due to disruption of sand movement that has led to severe coastal erosion and collapse of the highway.
( b) The groyne of Kakinada port is another example; the village of Upadda, about 4 kilometres north of the port is suffering for than two decades; the sandy beach has vanished and several houses are engulfed by sea water. ( c) Similarly, the sea wall at Netravati river mouth at Mangalore has created untold miseries on Ullal side of the river; a fishing village is under threat of marine incursions due to chronic erosion at these sites. ( d) At Pondicherry, the beach disappeared due to a seawall on the southern part of the city. Such examples of disruption of sediment supply by groynes, with consequent sand starvation, are numerous.
Note that groynes are built by piling and dumping of large boulders in the form of a dyke into the sea. Such boulders / hard rocks are transported from elsewhere. This implies that rocky massifs are blasted to obtain boulders. What is the fate of such hinterland mountains? What happens to the villages or townships around such sites? What about the road transport and its impacts on roads and pollution by heavy trucks that ply on them? Therefore, can such projects be called sustainable? Also note that the ancillary activities around the groyne sites create uncontrollable negative impacts on the coastal areas. For example, the construction of the bridge at Tiracol / Keri spit, and the sea wall along the beach, has severely damaged the entire coastal belt of about 1.5 kilometres.
Construction material is scattered all over, the dunes are leveled and the coastal strip is now in shambles.
The issue therefore is whether such a rubble mound wall is indeed required at Mobor. Instead, an eco- friendly management solution to regulate accretion of sand at Sal estuary can be offered as follows: ( 1) Avoid the emplacement of the groyne altogether. ( 2) Restrict / manage the growth of the spit on an annual basis, by removing excess sand, preferably by manual methods, so that the spit is maintained at / up to a desired size / volume. ( 3) An effort can be made to fix the ‘ managed’ sand spit once the deposit attains maturity and a desirable dimension; elsewhere, evolving sand spits have been stabilised by appropriate plantations.
( 4) Surplus sand may be transported by small trucks and dumped at places where sand dunes are damaged; such an exercise will ensure beach nourishment and dune restoration, never before attempted in Goa.
( 5) Similarly, the large deposits of sand presently accumulated within the river / estuary of river Sal can be dredged up to a depth of 1- metre or up to a minimum depth as required by trawlers to navigate out of the river. ( 6) The dredged sand from the river / estuary should not be disposed into the sea; but instead this sand can as well be used to nurture the beaches and dunes along the Cavelossim – Velsao belt; beach nourishment is the need of the hour, not only in Goa but in the entire country.
In brief, A). Sand spits at river mouths are Nature’s playing fields as these features belong to the ocean domain; being highly dynamic, these geomorphic features keep shifting in space and time; as such, any human intervention on such fragile estuarine ecosystems is bound to prove counterproductive.
B). Groynes invariably require annual maintenance dredging to remove new sediment that gets deposited due to high sediment- laden river discharge, during monsoons for example.
C). There is no guarantee whatsoever that new sand will not come in via the sea, considering the monsoon related strong wave activity; in addition, erosion of the opposite shoreline, sandy coves and cliff is highly likely. D). Instead, the sand spit can be managed by simply ecofriendly methods described above; the growth of the spit can be restricted as desired. E).
Considering several such adverse cases in India alone, a new equilibrium may never be attained if this area is disturbed.
There is no doubt that the construction of such a massive structure at a highly dynamic spit system will induce more harm than good.
( Dr Antonio Mascarenhas is a ex- Scientist, NIO, Goa) hit such,
