Small islands often make great case studies when considering the flow of sediment and it is easy to see the effects that the seasons and the overriding currents associated with them have on the shoreline of Cousin Island, a Special Reserve managed by Nature Seychelles.
As the monsoons change from the South-East (June to September) to the North-West (October to May), so too does the predominant wind direction. Wind is the primary energy source that drives waves.
At the moment waves are hitting the Northern side of Cousin. As the wave hits the beach it will either pick up or deposit sediments depending on the energy the waves. The fact that the wave energy is now being focused on the opposite side of the island means that any sediments on the windward side of the island will be picked up and moved down the shore and deposited on the beaches located on the leeward side of the island where the wave energy is least.
The roots of vegetation get exposed and the leaves burnt by salt sprays
These biological actions result in dramatic changes in the beach profile, these changes can make life on Cousin Island challenging at times, especially when you factor in tides which can be the difference between whether the main beach is accessible or not.
Cousin Island is open to the public Monday to Friday between 10:00 am and 1:00 pm, with visitors being ferried from their boats from 10:00-10:30am and back from 12:00-12:30pm. If these times coincide with a low tide and an awkward beach profile it can be virtually impossible to access the beach, without risking the boats’ engines, propellers and hull.
More importantly, the health and safety of the visitors and that of Nature Seychelles’ staff is of paramount concern. This is due to the fact that the low tide exposes or in some cases barely covers the razor sharp coral skeletons located just off the beach. However, the wardens on site are very experienced and know the island and the waters around it very well. This local knowledge often allows Cousin Island to continue to operate without incident even during these tidal difficulties.
During low tides the razor sharp coral skeletons located just off the beach are exposed
The dynamic ever changing nature and shape of the beach can cause other issues on the island with tree roots and building foundations becoming exposed, the sediment provides support to the structure and without that support they may fall down.
Low tide and the movement of sediments often reveal the beaches’ jagged edge, which consist of trees and debris once washed up on shore or claimed by the erosion, only to buried again by the moving sands. The wardens have to pay close attention to the coastal trail which is used daily by visitors. Due to the erosion this trail is slowly subsiding into the sea and at high tide, waves can inundate the trail with sea water.
Cousin Island is a protected marine reserve and important bird area, and as such affected minimally by human activities, the changes witnessed are purely natural patterns, which change from year to year. As such, the problems faced this year may be nonexistent next year or potentially even more challenging but only time will tell.
By Sam Hope
Chief Warden, Cousin Island Special Reserve