Recovery of eroded beach over a one-year period on Jamaica's north-east coast.
IN ADDITION to the seasonal erosion caused by storms, the slow rise in sea level described in our previous article means that the oceans are gradually encroaching on the land, and the beaches are retreating landwards as a result. The amount of retreat varies with the local conditions. On a steeply rising shoreline the rate of retreat is relatively low. On very flat lying shores, the rate of retreat can be very high.
It is possible to forecast a likely rate of shoreline retreat for any particular part of the coast, using tested modelling methods and by choosing the most likely rate of future sea level rise. In our studies we have made one or two preliminary estimates that suggest there will be at least a 30-metre retreat of some of the flatter lying Jamaican beaches by the end of the century, due to sea level rise alone.
This long-term retreat of the shoreline has implications for deciding the amount of setback that should be recommended. Diagram B illustrates the position. If a setback is determined solely on the erosion expected from a storm of given strength, the distance will be progressively underestimated as conditions are extended into the future, because sea level rise is not taken into account. With the prospect of the rate of sea level rise accelerating in the future it is not probable, but certain, that beach erosion and shoreline retreat will continue, probably at a faster pace.
Marine Geology Unit mgu@uwimona.edu.jm
