Caribbean - The dynamic coastline of Trinidad's Grande Rivière Beach requires coastal zone planning

This post was first published on the Cari-Bois Environmental News Network on behalf of Trinidad and Tobago's Institute of Marine Affairs’ (IMA) Oceanography and Coastal Processes Department. An edited version of the post is republished here as part of a content-sharing agreement.

Located on Trinidad’s north coast, Grande Rivière gets its name from the large river that empties into the Caribbean Sea at the eastern end of the curved beach which, at approximately 1.2 kilometres (about 3/4 of a mile) in length, provides an important habitat for marine and coastal wildlife.

The beach is one of the most important nesting sites for the leatherback turtle(Dermochelys coriacea), which has been designated an Environmentally Sensitive Species in Trinidad and Tobago. These turtles have also been declared vulnerable on a global scale, by both the International Union for Conservation of Nature (IUCN) Red List and World Wildlife Fund (WWF).

For residents of the area, Grande Rivière beach contributes to their socioeconomic well-being, as it provides a landing site for fishing vessels. The surrounding forest also attracts tourists, as it is home to a wide variety of birds, including the endangered Blue-throated Piping-Guan, locally called Pawi.

The Turtle Village Trust (TVT) and the Grande Rivière Nature and Tour Guide Association (GRNTGA) both list ecotourism as the area’s main income generating activity, thanks to the estimated 15,000 tourists, both local and foreign, who visit the community every year.

Understanding beach erosion

The accumulation of loose sediment on beaches provide protection from waves, currents, and tides, and are in a constant flux of erosion and accretion.

Erosion, however, can have significant impacts on coastal infrastructure, making the issue significantly consequential to the lives and livelihoods of individuals, communities, and even entire countries.

Coastal zone planning and management can help preserve beaches’ integrity and ensure that the services can be maintained for continued use.

Sediment flow and erosion at Grande Rivière

With the passage of time, meteorological events have created conditions that resulted in changes to the course of the Grand Rivière River and as a result, the movement of sand along the beach. In October 2022, for example, it was observed that the river had begun shifting westward.

This widening of the river mouth led to the removal of sand from the berm, causing the easterly and westerly sections of the beach to be completely separated. The large volume of sediment that was removed caused damage to coastal infrastructure, and posed a threat to the March 2023 turtle nesting season.

While these mass erosion events are drastic, they are part of a natural process of sediment cycling along the shoreline. With time, the sand would naturally be replenished — unless, under extreme turbulent sea conditions, the sediment were to be washed too far offshore.

The westerly end of the beach is in a state of dynamic equilibrium, where there is no net loss of sand, and the backshore area is stable thanks to the resistant cliffs that are characteristic of Trinidad's north coast. Meanwhile, the eastern section of the beach, especially the berm close to the mouth of the Grand Rivière River, experiences frequent changes in sediment elevation.

Beach accretion usually happens between the months of May and October, when wave energy is low. Conversely, sediment is carried offshore from November to March, when wave energy is high. (Turtle nesting season typically runs from March through September each year.)

The winter swells experienced during the months of December through February create larger waves that reach up to two metres (6.5 feet) in height, and allow the offshore sediment to be redeposited onto the beach as part of the natural sediment cycling process.