Development and Application of a GIS-based sediment budget model Paper by Ramos-Scharrón, C. E. & MacDonald, L. H. (2007). Development and application of a GIS-based sediment budget model. Journal of Environmental Management, 84(2), 157-172. Presented by Matthew Whitehead, Environmental Studies, GEOG 370 25 February 2008

Sedimentation Issues in the Caribbean Islands Problem: Poor planning and landuse practices has expedited the sedimentation of many water bodies in the Caribbean islands. Increased sedimentation has caused the degradation of coastline ecosystems and reefs. Unpaved roads and rampant development seem to be causing much of the increased sedimentation. Hypothesis: Areas near unpaved roads and other land disturbances experience more sedimentation problems then undisturbed areas. The development of a GIS-based sediment budget model will be able to accurately determine sedimentation problem areas.

Methods: developing and implementing a GIS-based model Data collection: Used 82 erosion pins along 4 stream reaches to measure the stream bank erosion to the nearest millimeter. Sedimentation do to treethrow was measured by finding the volume of sediment in rootwads and estimating the number of treethrow events. Sediment fences were installed to measure the amount of sediment production. Creation of the Model: A GIS-based model was created called The Saint John’s Erosion Model (STJ-EROS). In this model the user is prompted to input data and the model does several calculations based on the data to determine the sediment budget is for a defined area. A map of the study area, St. John island in the US Virgin Islands, the shaded areas are the study basins.

Flowchart of the STJ-EROS model

Results The STJ-EROS model proved to be very accurate in determining sediment yields on Saint Johns Island. Using the model it was determined that at all 3 basin sites 80-85% of the sediment yield comes from unpaved roads. The model showed that paving 10% of the unpaved roads in the Lameshur Bay basin would reduce sediment yields by 50%.

Sediment Budget Maps Produced by STJ-EROS

Conclusions Unpaved roads proved to be the main contributor to sediment in river basins in the Saint Johns area. STJ-EROS is a useful tool that can find the specific location of sediment sources. With it’s pinpoint accuracy STJ-EROS is a good tool for determining were money needs to be allocated for stream restoration and paving roads.