Where rivers kiss: Effects of coastal erosion in Grande Riviere

The quiet village of Grande Riviere, on the northeast coast of Trinidad, is internationally recognised as a turtle-nesting site as varying species – including the endangered leatherback turtle – flock to its beaches every year.

The Grande Riviere beach is one of the largest nesting sites of the leatherback in the western hemisphere.

The village is also recognised for its high-quality cocoa and chocolate products, made from the country’s prized Trinitario cocoa. With several cocoa estates in the area and surrounding villages, turtle-watchers can also enjoy Bean to Bar tours with the Grande Riviere Chocolate Company and rest their weary bones after a long night at Mt Plaisir Estate Hotel, as all three businesses are situated on the Grande Riviere beach.

While tourists the world over swarm the community to get a taste of its natural beauty, it is not the only natural phenomenon the village experiences.

At least once every decade, the village is subject to intense flooding which wreaks havoc when the waters from two rivers that flow into the sea at the Grande Riviere beach meet head-to-head.

“The villagers say that two rivers, they have to kiss each other. They use that term,” the owner of the Mt Plaisir Estate Hotel, Piero Guerrini, told Sunday Newsday during a visit to the area.

On either side of the estate, there are two rivers – Grande Riviere and the Ferdinand rivers – which both run into the ocean.

In July, flooding caused by the river-shifting phenomenon came dangerously close to the beachfront property. Valencia East/Toco councillor Martin “Terry” Rondon and a team from the Sangre Grande Regional Corporation (SGRC) visited after heavy rain made the river overflow.

“There was a drop here (at the hotel’s edge, on the beach) of over 12 feet...but the river has found its way (and) the beach is recuperating.” During Sunday Newsday’s visit, it was observed that the sand had resettled, and the drop was only about four feet.

“Now (the sand) is starting to come back and most likely the next heavy storm, the water will level the beach again. That means all this sand here is fresh sand that will facilitate the next event.

“It’s just like Venice,” said the Italian-born hotelier, who has been operating in the area for 28 years. “You cannot avoid the water rising. When it rises, you have to be prepared for it. Of course, it will be better to have reinforcement, but that will cost a lot of money and it will encroach on the protected area and I don’t want to do that.”

He said nothing was done to reinforce the building.

“Honestly, I don’t want anything to be done. Yes, of course, I am worried, it will take a lot of work. and to do that work we will have to bring in heavy machinery on the beach again. and I do not agree with that.”

International fallout

In 2012, the Ministry of Works sparked an international incident after the river course diverted and the ministry tried to rectify the situation by using heavy machinery to manually shift the river to its original course.

The move resulted in the death of endangered leatherback turtles and hatchlings on the beach.

The Institute of Marine Affairs released a report in January 2013 – obtained online – afterwards, which concluded that the use of heavy machinery was inadvisable.

In a statement to Sunday Newsday on Thursday, the IMA said it visited the beach in November for its quarterly beach-monitoring exercise.

“Observations during this visit indicate that the beach is in recovery from the river-mouth-shifting event recorded in July,” said the statement.

“IMA technicians observed a small berm (a flat strip of land or raised bank bordering a river or canal) reformation and some in-filling in the previously eroded backshore areas. Natural recovery is expected within the coming months if conditions are consistent with the regular seasonal trends experienced at Grande Riviere.”

Guerrini said he is not expecting the same result next year and welcomes the idea of tourists returning to the beach for turtle-watching, one of the many industries severely affected by the covid19 pandemic.

“Next year, I don’t think we will have that problem. Hopefully, we will have a lot of turtles. The number of turtles has been steadily increasing over the last 25 years.”

The 2013 IMA report said in April 2012, it was observed that the course of the Grande Riviere River had been shifting westward, deviating from its normal path through the berm heading north.

“Progression of this shift continued producing a backshore (the part of the beach lying between the beach face and coastline) erosion channel of approximately 110 metres in length.”

It said expansion persisted until the ministry intervened in July 2012, when a sand dam was constructed to arrest the westward flow of the river.

The report also said the last river shift occurred in 2003.

It said up to January 2013, the backshore erosion channel persisted, and the IMA advised that the winter swells from December to February would superimpose higher-energy waves on the beach, returning the eroded sediment from offshore back onto the beach.

“While an exact time-frame for beach recovery was not given…it was noted that the beach will recover naturally over time.”

Research ongoing

In a statement to Sunday Newsday, coastal design engineer Nyoka Sinanan of the Ministry of Works’ Coastal Protection Unit said a report was done after the July incident.

It said the river had once again changed its course and posed a threat to backshore infrastructure.

“The Grande Riviere river was now flowing in an east-to-west direction before joining with the Ferdinand river (and) before emptying at a location west of its original river mouth position.

“It is strongly believed that the conditions observed are similar to that which happened in 2012 and 2003 in which the Grande Riviere river had shifted its flow in a westerly direction and created a new path behind the beach berm.”

The statement said the beach has been monitored since 2000 and seasonal erosion patterns have been noted.

“In general, research has shown that the north coast of Trinidad is subjected to seasonal wave activity which in turn affects the trends of erosion and accretion throughout the year.”

It said between May and October, the beach grows, owing to the lower-energy-wave conditions.

“During these months, sand is deposited on the beach by the waves and the wind, resulting in the growth and formation of sand berms.

“The berms provide additional protection to the backshore of the beach from incoming waves, but they also have the potential to impede the flow of the rivers. The river can channel through the beach whenever the conditions change.”

In this case, it said the sand deposits, combined with the large volumes of sediment brought down by heavy rainfall, would have blocked the river mouth, forcing it to create another exit point to empty into the sea. It said these changes have affected both the Grande Riviere and Ferdinand rivers.

“The exact mechanism is yet unknown, but it is theorised that the elevation of the mouth of both rivers would have been raised at heavy rainfall and high tides.

“When both the tides and the river flows subsided, neither the river flow nor the influence of the waves would have sufficient energy or pressure head to surmount the recently built-up river mouth area, and thus the water would take the path of least resistance to drain seawards, even if this path requires the formation of a new channel. This phenomenon is also seen in other locations in Trinidad.”

The statement said data gathered from monitoring the area suggests the natural river rerouting is a cyclic process with a return period of approximately nine to ten years, but it has only been documented in 2003 and 2012.

It said residents in the area have stated their concern and want the situation remedied to ensure the protection of their homes and businesses as well as its high eco-tourism value.

“The river diversion occurs due to natural events but introduces a potential threat to nesting turtles, eggs, and hatchlings.”

It said while in-filling of the river channel (when rerouted) is not recommended, extreme weather patterns associated with climate change may lead to changes in the process and/or its cyclical nature.

So the unit estimates the process may occur more frequently, or the river flow may grow heavier owing to more extreme rainfall.

“This can conceivably create a wider channel or one further inland, thereby posing a greater threat to properties or infrastructure on the backshore.”

It said the Coastal Protection Unit and other government agencies are working to provide both short- and long-term solutions, keeping in mind the ecological sensitivity of the beach.