By Christopher Alexis and Isabelle Chen
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.
The hydrology of the river also influences beach erosion. In the rainy season, river discharge is increased, creating larger and speedier volumes of water that cause the river to erode and transport more sand offshore. Recently, with the advent of more frequent and extreme rainfall, the river mouth has been known to widen or change course, leading to larger sections of the beach being eroded.
Managing the area's coastal erosion
The Institute of Marine Affairs (IMA) has been monitoring Grande Rivière Beach for over 20 years, observing how extensive volumes of sediment have been removed from the beach and carried offshore. The sediment is returned to the beach over weeks and months, depending on marine and meteorological conditions.
With climate change and sea level rise influencing the occurrence of more frequent and intense storms, engineering solutions offer a real opportunity to mitigate erosion.
Traditional hard engineering coastline protection measures, like the construction of sea walls or the redirection of rivers, should be closely evaluated, especially in ecologically sensitive areas like Grande Rivière.
In 2012, for instance, the Drainage Division of the Ministry of Works and Transport constructed a sand dam for the diversion of the river channel. Heavy machinery removed sand from the western side of the bay and translocated it to the eastern end, where the river had caused extensive erosion.
The exercise led to the destruction of turtle nests, eggs and hatchlings — an unfortunate scenario that highlighted the need for caution in moving forward with such works, and for heightened awareness about the requirements of operating in ecologically sensitive areas.
A case for ‘No Action’
Decisions affecting coastal dynamics should be based on scientific data. Considering the ecological significance of Grand Rivière Beach, as well as knowledge of the natural sediment cycling that has accounted for past erosion events, a “No Action” plan should be adopted — sediment being allowed to return to the beach naturally reduces potential damage to the environment.
The historical IMA dataset, and the fact that similar events were witnessed in Grande Rivière in 2002 and 2012, show that natural recovery allowed the beach to revert to its previous condition in just a few months.
This underscores the importance for proper coastal zone planning — delineating coastal areas into land and sea-use zones, with identified permitted and prohibited conditional uses. Such an approach can aid in the planning and management of the coastline and adjacent areas, and reduce coastal vulnerability associated with changing weather patterns, erosion and sea level rise.
It is not recommended that hard engineering structures or beach nourishment be used to curb the coastal erosion taking place at Grande Rivière, since this type of human interference can have negative consequences to this key environmental site.
The introduction and implementation of proper coastal zone management and planning, as well as education in this regard, is critical for new infrastructure not to be threatened by the imminent erosion of sediment — not only in Grande Rivière, but along the entire coastline of Trinidad and Tobago.