When one thinks of shoreline change, immediately the sensitive topic of land loss comes to mind. Change, however, can be categorised into two main measurable outcomes - erosion (loss of land), and accretion (gaining land).  The determination of either of these processes is accomplished through the measurement of shift in the vegetation line along the shore from one year to the next.  While the impacts of erosion are more familiar, accretion may also pose difficulty for coastal users and marine life. These effects include: siltation of fish landing sites and ports, the smothering of benthic communities and sea grass beds, and a longer climb to the surface for turtle hatchlings on nesting beaches.

In 2010, the Institute of Marine Affairs (IMA) undertook a study to assess coastline change for Trinidad and Tobago, utilising 1994 aerial photography and 2000-2007 high resolution IKONOS Imagery. Satellite imagery and aerial photography allow for the efficient collection of data for the purpose of mapping the coastline with high accuracy.  Coupled with the use of Global Positioning Satellite (GPS) System mapping, the measurement of shoreline change can be definitively assessed.
Preliminary results indicate that there are areas of coastline change - either through erosion or accretion. While most of these changes are negligible, there are a few areas where the change is significant; southwest Trinidad is one of these areas. At Columbus Bay there has been considerable erosion. Corral Point, which forms the southern extent of this bay, has become so eroded that its definition as a 'point' is no longer applicable. Based on this initial assessment, a total of 5.05 hectares of land has eroded between 1994 and 2011 at a calculated rate of 0.3 hectares per year, over a shoreline distance of 0.45 kilometres. This differs from adjacent Punta Del Arenal, where 14 hectares of land have accreted over a shoreline distance of 3.83 kilometres at a rate of 0.82 hectares per year. Whether a relationship exists between the erosion at Corral Point and accretion at Punta del Arenal is still to be determined. 
In view of the severity of the erosion problem at Columbus Bay, the IMA will embark on follow-up research to determine the cause and to provide recommendations to help manage the problem. The proposed project will investigate the existing oceanographic conditions within the bay.   Numerical modelling techniques will be employed to calculate sediment transport patterns, utilizing data collected on the prevailing winds, waves, tides, currents and seabed topography.
Significant accretion was also measured at Barrancones Bay which is found at the southern end of the Caroni Swamp.  In this bay, approximately 42.38 hectares of land were colonized by mangrove forest between 1994 to 2007.  In contrast, erosion was also observed along the East coast, in Matura Bay and Mayaro Bay.  In Tobago, while some erosion was observed in Goldsborough Bay, accretion was noted on the western side of the Bon Accord Lagoon and on Sheerbird’s Point. 
This study highlights the dynamic and varied nature of coasts. In some areas there is erosion, in others accretion, and in yet others there is dynamic equilibrium (that is, no net change).    The information provided from the study will help researchers better understand the processes involved in shoreline change and guide decision-makers for improved management of our coastline.

Article by Adam Jehu, Research Officer, and Deanesh Ramsewak, Remote Sensing Officer, Institute of Marine Affairs Remote Sensing Lab