This story was written by Christopher Alexis and Isabelle Chen on behalf of the Institute of Marine Affairs’ (IMA) Oceanography and Coastal Processes Department.
Located on Trinidad’s north coast, Grande Riviere Beach gets its name from the large river that empties into the Caribbean Sea at the eastern end of the beach.
Spanning approximately 1.2 kilometres in length, the beach is curved and provides an important habitat for marine and coastal wildlife.
The beach is also 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 the International Union for Conservation of Nature (IUCN) Red List and World Wildlife Fund (WWF).
For Grande Riviere residents, the beach contributes to their socioeconomic well-being as it provides a landing site for fishing vessels and the surrounding forest attracts tourists given it’s home to a wide array of birds including the endangered Blue-throated Piping-Guan (Pawi).
The Turtle Village Trust (TVT) and the Grande Riviere Nature and Tour Guide Association (GRNTGA) both list ecotourism as the area’s main income generating activity.
An estimated 15,000 tourists, both local and foreign, visit the community every year.
Understanding Beach Erosion
Beaches are characterised by an accumulation of loose sediment that extends from the low water line (the limit the sea level reaches at low tide) to the first significant change in topography (land surface) or permanent vegetation.
They provide protection from coastal processes (waves, currents, tides) and are in constant flux of erosion and accretion (gradual growth through sediment layering).
Overtime, the average beachgoer may observe that beaches get narrower or wider, steeper or gentler in slope, or stay the same all the time.
But beach erosion can have significant impacts on coastal infrastructure such as jetties, commercial property (hotels and guesthouses) and residential properties.
Therefore, the issue can be consequential to the lives and livelihoods of individuals, communities and even entire countries.
For these reasons, the need arises for coastal zone planning and management as they can help preserve the integrity of beaches and maintain the services beaches provide for continued use.
Understanding sediement flow and erosion along Grande Riviere Beach
Overtime, meteorological events have created conditions that resulted in changes to the course of the Grand Riviere River and movement of sand along the beach.
For example, it was observed in October 2022 that the course of the Grand Riviere River had been shifting westward.
This shifting and widening of the river mouth led to the removal of sediment (sand) from the berm, and the easterly and westerly sections of the beach were completely separated by the wide river mouth.
The large volume of sand removed resulted in damage to coastal infrastructure and posed a threat to the turtle nesting season in March 2023.
While these mass erosion events are drastic, it is a natural process of sediment cycling along the shoreline.
With time, the sand would naturally be replenished, unless the sediment is washed too far offshore due to extreme turbulent sea conditions.
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 due to the resistant cliffs, characteristic of the North Coast.
The eastern section of the beach – especially the berm close to the mouth of the Grand Riviere River – is dynamic and experiences frequent changes in sediment elevation.
Beach accretion is usually between May to October, where sand accumulates on the beach when wave energy is low.
Conversely, sediment is eroded and carried offshore between the months of November to March when wave energy is high.
The winter swells experienced during the months of December through February create larger waves that reach up to 2 meters and allow the offshore sediment to be returned onto the beach.
This is the natural sediment cycling process.
The hydrology of the river also influences beach erosion.
During the rainy season, with increased precipitation, river discharge is increased leading to increased volumes of water, and increased velocity which causes the river to erode and transport more sediment from the beach into the offshore area.
In recent years, with more frequent extreme rainfall events, the river mouth has been known to widen or change course which leads to larger sections of the beach being eroded.
Managing coastal erosion along Grande Riviere Beach
The Institute of Marine Affairs (IMA) has been monitoring Grande Riviere Beach for over 20 years.
The institute’s investigations at the beach include past events where extensive volumes of sediment were removed from the beach and carried offshore.
It has been observed that the offshore sediment returned to the beach over time (weeks to months).
But the exact time-frame for replenishment is uncertain, as it relies on marine and meteorological conditions.
With climate change influencing more frequent and intense storms, and sea level rise, engineering solutions must be considered to mitigate erosion.
Traditional hard engineering coastline protection measures such as construction of sea walls, or redirecting rivers, such as the Grande Riviere, need to be closely evaluated, as Grande Riviere is an ecologically sensitive area.
In 2012, 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 of the bay, where the river caused extensive erosion.
The sand translocation exercise led to the destruction of turtle nests, eggs and hatchlings.
The unfortunate scenario highlighted the need for caution in moving forward with such works especially in ecologically sensitive areas.
Decisions on interventions should be based on scientific data with respect to the coastal dynamics at Grand Riviere Beach.
Taking into consideration the ecological importance of the area, as well as knowledge of the natural sediment cycling that accounted for past erosion events, a ‘No- Action’ plan should be adopted, wherein the sediment would be allowed to return naturally, and any potential damage to the natural environment would be reduced.
Recalling similar events that were witnessed in Grande Riviere in 2002 and 2012, coupled with the historical IMA dataset, natural recovery allowed the beach to revert to its previous condition in a few months.
This underscores the importance for proper coastal zone planning.
It is important to identify and delineate coastal areas into land and sea-use zones with identified permitted and prohibited conditional uses.
This can aid in planning and management of the coastline and adjacent areas and can reduce coastal vulnerability associated with changing weather patterns, coastal erosion and sea level rise.
Grande Riviere, a high energy beach, is constantly changing and subject to oceanographic and meteorological forcing factors.
With Grande Riviere Beach being an ecologically sensitive area, it is not recommended that hard engineering structures or beach nourishment be used to curb the coastal erosion taking place.
These human interference can have negative consequences to this key environmental site.
The natural sediment flux of the beach has shown in the past that the sand will naturally be replenished over time with the ambient conditions.
Proper coastal zone management and planning need to be implemented in the Grande Riviere area so new infrastructure will not be threatened by the imminent erosion of sediment.
Information dissemination about the significance of sustainable coastal zone planning is of utmost importance for areas such as Grande Riviere and by extension the entire coastline of Trinidad and Tobago.
