Are we playing Russian roulette with Mandovi's flow?

SRIDHAR D IYER

It is 25 years since the first casino, Casino Carnival, began its operation in Goa in 1999 onboard a yacht in the Mandovi River. Down the years, several casino vessels (CV) anchored and some quietly sailed away or were replaced. What began as a single CV has now gone up to six. In July 2023, Goa's chief minister had assured that permission would not be given to more offshore casinos. Let us hope for the best.

“Offshore” is a misnomer as several petitions in the Bombay High Court at Goa argued that “offshore” means 12 nautical miles (22 km) off the coast. Perhaps the CV could be aptly called as “river casinos.”

A few years back the government-of-the day wanted the CV to move beyond the Aguada sandbar but this never saw the light of the day. This is because, the CV owners were apprehensive of increasing cost, maintenance, rough sea and whether people would have the stomach to take a ride on speedboats to the CV. 

In December 2016 an amendment was made by the Goa cabinet that defined “offshore” as “any designated location in the sea, river and estuary within the jurisdiction of the Captain of Ports, Government of Goa."

Some years back, there was hullaballoo when some politicians and the civil society were up in the arms against the casino culture and its harmful outcomes on the people of Goa.

Furthermore, the argument that Goa’s economy could be augmented by way of license and visitors’ fees did not have much takers. This is because of the expected side-effects of tourists visiting the CV as Panjim does not have the carrying capacity to cater to hordes of floating population.

 As the 80-km-long Mandovi River traverses from the Western Ghats and meets the Arabian Sea at the Miramar beach, it transports a huge volume of materials that range from boulders at the source to coarse sands in the mid-stream and fine sands, silt and clay at the river’s mouth.

The gradation in material size is due to breakdown of rocks, loss of transporting energy by the river, slope of the river bed, bends and knickpoints along the course, density and settling rate of the materials, amongst others.

These aspects lead to deposition of sand to varying extents along the banks of the rivers and near natural obstacles such as islands, sandbars, rocks, etc.

Another factor that affects deposition is the tidal action that occurs twice a day and during the non-monsoon period the seawater enters through the river’s mouth (4 km wide), travels upstream up to 50-60 km, and makes the river water salty.

Generally, nature acts in such a manner that as the river flows and erodes its banks at one site simultaneously sand accretes at another and thus, an equilibrium is maintained along the river’s course.

But there may be natural and/or anthropogenetic factors that might disturb the balance. The former could be during intense monsoon, floods, tidal bore, rise in sea-level, geological features and so forth. The latter are human-made structures like fishing jetties, ferry wharfs, bridges, and barrages, fishing and leisure vessels all of which would hinder the river’s flow.   

Let us see if the CV, anchored at the lower reaches of the river influence, the sediments (characteristics and movement) and the subsequent sand accretion-erosion of the Mandovi banks and at the river’s mouth at Miramar Bay.

During a normal fluvial process, the sediments move to the river’s mouth where a sand spit or bar may form or the sediments move into the sea. In recent years, an extensive shoal has formed on the left bank (as one looks westward) of the Mandovi and opposite the old Goa Medical College (GMC).

A shoal is a naturally submerged sandbar, sandbank, or gravel bar consisting of consolidated sand. The shoal rises from the bed of an adjacent waterbody such as a river. Shoal is used to refer to a submerged sandbar, bank, or ridge, that rises near the surface of a waterbody and is a navigational threat.  

When the sediment-laden water gets diverted due to reduced velocity of the river, sand accretes to form a shoal. In the lower reaches of the river, two reasons could be ascribed for the lessened velocity: fishing trawlers anchored at Betim and Malim and the CV.

The trawlers are anchored on the right bank while some of the CV are either in the midstream or near the left bank of the river. Hence, the velocity of the water current is reduced, laterally diverges and during this process sand deposition might occur.

Interestingly, the CV and shoal are less than 500 m distance apart. Once the water current crosses the CV, it maintains its natural course but since much of the sediments have been deposited, the water starts to erode the right bank at the lower reaches of the river. Hence, there is sand accretion near the old GMC and erosion at Reis Magos-Verem and Coco beach (Nerul), leading to a state of equilibrium along the river’s course.   

During the above process, the sediment characteristics varies from the shoal to Miramar. The medium to fine sands instead of been transported and deposited at the mouth, are replaced by silt and clay brought in from the sea.

Although this is normal during monsoon but post-monsoon these could remain in place and over-time cover a large area and hamper the movement of the river sands. The repercussion would be felt by the Miramar beach which, in the long run may be significantly deprived of sands and the beach would be rapidly eroded.

Due to weakened downstream currents there would be sand accumulation at the Bhagwan Mahavir Children’s Park, the shoal might grow beyond the Youth Hostel, lateral extension of the shoal may constrict the width (presently ~3 km) of the river and the river’s course could be altered.

The incoming tide would push the sands upstream but as their transport is hindered by the CV hence, during low tide the sediments would settle in the shoal.

If the shoal grows, it could also affect the movement of barrages and trawlers that may run aground in the sandbar and/or at the Miramar Bay.

Due to changes in the sedimentation style the area between GMC and ferry wharf could become vulnerable. The boulders dumped near the Yog Setu and the Mandovi promenade also influence the Mandovi’s flow and sediment deposition.

Another factor for the shoal formation is the flow of sewage from the St. Inez Creek which is also affected by the tidal currents. The outflow-inflow from the creek impedes the course of the Mandovi and subsequent sand deposition. 

The changes in the sedimentation and the pollutants (advertently or inadvertently released from the CV, barrages, trawlers, cruise vessels) would get trapped in the shoal; would impinge on the ecology of the Mandovi River and result in low fish yields.

The shoal with prolific flora (mainly mangroves) and rich fauna needs to be studied. Presently the river water is slicing through the shoal and in the long run it may separate from the left bank and form a minor river island or a shoal complex.

Are we playing Russian roulette with nature by interfering with the natural flow and course of the Mandovi River, transport of the sediments and the riverine environment? Let us save the Mandovi, not only at the source but even during its tranquil flow to the sea.

And towards this end we must consider Mandovi’s “carrying capacity” and not create artificial turbulences by adding more and bigger CV, trawlers and leisure boats. Already the several constructions, completed and upcoming ones, from the New Patto bridge to the Children’s Park are playing havoc with the flow of the Mandovi.