Welcome to Eprints@IARI

Abstract

The influence of land use on runoff and soil loss was assessed on two small watersheds in the Eastern Caribbean island of St Lucia, under contrasting land management regimes. The data generated from these watersheds revealed that the soil losses from an intensively cultivated agricultural watershed were 20-times higher in magnitude than that of a forested watershed both for peak rainfall event and for total duration of analysis. This was due to higher surface runoff rates and exposure of soil to direct raindrop impact within cultivated areas. Whereas the forest canopy cover in combination with higher infiltration capacities of the forested land reduced the erosive runoff from the forest watershed and thus the soil loss. Moreover, the energy intensities of large storms in excess of 40 mm were estimated and found to range between 400 MJ mm haÀ1 hÀ1 and 1834 MJ mm haÀ1 hÀ1.1 Soil loss from the agricultural watershed was strongly correlated (R2 1⁄4 0Á85) to storm energy-intensity (EI30). However, the correlation of soil loss with the EI30 (R2 1⁄4 0Á71) was poor for the forest watershed due to the effect of canopy vegetation, which significantly reduced the energy of raindrop impact. Over the study period, cumulative soil losses were 10Á0 t haÀ1 for the agricultural site and 0Á5 t haÀ1 for the forest site.2 The largest storm observed during the study period resulted in erosion losses of 3Á78 t haÀ1 and 0Á2 t haÀ1 from the agricultural and forest sites respectively. The regression models were developed using the measured data for prediction of runoff and soil loss over the watersheds of St Lucia under similar conditions. This study contributed towards efficient watershed management planning and implementation of suitable water conservation measures in St Lucia.