A comparison of flash flood response at two different watersheds in Grenada, Caribbean Islands

Grenada is one of the susceptible areas to flooding. It is due to the high intensity of rainfall in each year and Grenada often hit by hurricanes and tropical storms. Flash-flood often occur in Grenada, specifically in two areas (Gouyave and St. John's watershed). Both of them have different characteristics. Gouyave watershed represents rural area, whereas St. John's watershed is an urban area. This paper aims to understand the flash-flood response of Gouyave and St. John's watershed in different return periods. It is emphasized that urbanization is an important factor related to flash-flood. This paper uses quantitative methods with flood modelling using OpenLISEM software. Input data to develop flood modelling are DEM (Digital Elevation Model), saturated hydraulic conductivity (Ksat), initial soil moisture, surface roughness (Manning's n), and random roughness. The result shows that St. John's watershed is more sensitive and has higher response to flash-flood than Gouyave. St. John's watershed is more urbanized which decreases water infiltration. So, it increases the potential run-off and flash-flood events become more massive.