MODELING ROAD SURFACE SEDIMENT PRODUCTION USING A VECTOR GEOGRAPHIC INFORMATION-SYSTEM

Field investigations indicate that unpaved roads are the largest sedim ent source on St John, US Virgin Islands. Cross-sectional measurements of eroded road surfaces were used to establish an empirical relations hip to predict annual road surface erosion as a function of road gradi ent and contributing drainage area. A model (ROADMOD) for estimating a nd mapping average annual sediment production from a road network was developed by combining this empirical relationship with a series of ne twork algorithms to analyse road data stored in a vector geographic in formation system. ROADMOD was used to estimate road surface erosion in two St John catchments with very different road densities but similar land cover, topography and soils. Unpaved roads were found to increas e sediment production in the more densely roaded catchment by a factor of three to eight, and in the less-roaded catchment by a factor of 1. 3-2.0. Turbidity measurements in the receiving bays of these two catch ments are consistent with model predictions and observed sediment deli very processes. Although this model was developed specifically for St John, it can easily be adapted to other locations by substituting a lo cally derived predictive equation for road erosion. Model assumptions, limitations and potential improvements are discussed. (C) 1998 John W iley & Sons, Ltd.