Flash flooding, from extreme rainfall is one of the major natural disasters affecting Jamaica and other small island states of the Caribbean. Flooding in Jamaica is mainly riverine, coastal and depression with the major coastal towns being affected owing to their location on low lying areas. Such localization is driven by increase in urbanization and tourism along the coastal areas. The present work aims in a broad discussion of the flooding in Jamaica with special reference to riverine flooding of Port Maria, the capital of St Mary, one of the parishes lying in the high rain zone of the island and being affected by repeated events of flooding. Analysis of the extreme rainfall event of November 23rd–24th, 2006 shows that it exceeded the 30 yr annual rainfall of the area and the 100 yr return period as calculated from 30 yr annual rainfall data for the island. The Port Maria river lacks a gauging station to monitor flow data and flood discharge peaks. Several methods are used to calculate the run-off in such small ungauged catchments. In this study the Soil Conservation Systems Curve Number (CN) method was used to calculate the run-off from the measured rainfall data using empirical equations. Results show an unprecedented high of 13–14 inches affecting the buildings and other infrastructures, leading to the collapse of a newly constructed bridge over the river Port Maria. The town continues to get flooded from intense short duration rainfall continuing to affect life and property. Flood plain maps exist for the larger watersheds of the island but smaller yet flood prone ones have not been mapped so far. Hence this becomes very important to create a floodplain map showing the extent of the runoff from rainfall with respect to the buildings and other infrastructures of the area. The present work thus aims in creating a spatial distribution map of the runoff from the rainfall measurements aiding in developing a no build zone for this and for other low lying coastal areas of the island.

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