1. Paradise Threatened: Land Use and Erosion on St
Paradise Threatened: Land Use and Erosion on St. John, US Virgin Islands
Paper by: L.H. MacDonald, D.M. Anderson, and W.E. Dietrich Environmental Management, 21(6):
Presented by Kelly Anderson, Environmental Studies, GEOG 370, March 1, 2010

2. Problem, Hypothesis, and Goal
Problem: Development of new roads, businesses, and vacation homes are leading to increased erosion and sedimentation in nearby marine environments.
Hypothesis: Erosion is most prevalent in areas of containing unpaved roads and parking areas.
Goal: Identify sediment sources, construct model for predicting road surface erosion, evaluate erosion consequences, and recommend minimization methods.

3. Methods, Data, and Test Field observations
Unpaved roads. Drainage channels clogged with sediment.
26 measurements at different road locations wide range of gradients
Main focus: gradient and contributing area  determine energy available for sediment transport
Mapped road segments
E = A x S  incorporated into GIS-based road surface erosion model (ROADMOD)
Fish Bay and Lameshur Bay  US Geological Survey (USGS) operated automated discharge and suspended sediment stations
Fish Bay: rapid development
Lameshur Bay: undisturbed, VINP

4. Results Fish Bay Lameshur Bay
16 km of roads  total road surface erosion rate of 390 m³/yr. By assuming a sediment density of 1500 kg/m³, this converts to nearly 600 t/yr.
Lameshur Bay
1.4 km of roads  65m³/yr or 100 t/yr
Main issue: amount of sediment that reaches the coast  mangroves, reefs, beaches..
Sediment delivery rate to water (scale 1-0). Use ROADMOD.
Fish Bay: >60 tons/km²/yr (road surface erosion quadruples normal sediment yields)
Lameshur Bay: 50 tons/km²/yr.
Recommendations: erosion control measures, silt fences, road pavement regulations, waterbar installation, etc…

5. Map of St. John and USVI National Park, Contour Map of Lameshur Gut
Contour map of sediment depth in the Lameshur Gut detention basin in January Shaded area represents area of sediment deposition; sediment depth contours are in centimeters.
Map of St. John and Virgin Islands National Park. The USGS gauging stations are located near the mouth of the
ephemeral streams (guts) flowing into Fish Bay and the eastern bight of Lameshur Bay.