St. John erosion study : Final report to the Water Resources Research Institute-University of the Virgin Islands : 1 March 1998 to August 1999

Macdonald, Lee; Ramos-Scharron, Carlos

Even though these previous research efforts have provided some information on runoff and erosion processes on St. John, a more intense and longer-term field study was needed to better quantify and understand the key processes and sediment sources. The current study responds to this need, and the main objectives were to: (1) measure runoff, sediment production, and sediment delivery rates from undisturbed areas; (2) measure sediment production and sediment delivery from unpaved road surfaces, fillslopes, and cutslopes; (3) construct empirical models to predict sediment production and delivery from undisturbed areas, unpaved road surfaces, fillslopes, and cutslopes; (4) quantify runoff rates and sediment transport through the fluvial system at various scales, and evaluate the role of land use on the observed sediment concentrations; (5) develop a GIS-based empirical sediment routing model for St. John, and evaluate its performance against other commonly-used models; and (6) educate the public about erosion processes, and provide specific strategies to minimize the potential adverse effects of anthropogenic sediment sources. This report will describe the field and laboratory work conducted in St. John between June 1998 and August 1999. Field work that took place during this time period can be divided into three main categories, and these are: precipitation and runoff response; sediment production and delivery from roads and hillslopes; and sediment transport through the fluvial network at scales ranging from low-order sub-catchments to higher-order watersheds. Since the funds from the current project helped to trigger other funds that allowed us to continue the project for an extended 1999-2000 field season, the emphasis of this report is on the design and data collection. Hence the following sections first outline the general approach of the study, site selection, and field and laboratory methods. This is followed by as summary of the work performed in the field and in the lab, construction of the GIS coverages for developing a sediment routing model, and our efforts to disseminate the preliminary results and educate the public about local erosion problems. The final section discusses the preliminary analysis of data collected during the first part of the first field season.