Development and application of a GIS-based sediment budget model.

Area of Science:

• Environmental Science
• Hydrology
• Geomorphology
• Geographic Information Systems (GIS)

Background:

• Accelerated erosion and increased sediment yields due to land-use changes pose critical environmental challenges, particularly in developing regions like the Caribbean.
• Predicting sediment production and delivery from disturbances like unpaved roads is crucial for resource managers, especially to protect vulnerable nearshore coral reef ecosystems.
• Rapid development in the Caribbean exacerbates land disturbance, necessitating spatially explicit tools for impact assessment.

Purpose of the Study:

• To develop a Geographic Information System (GIS)-based sediment budget model for quantifying watershed-scale sediment yields.
• To evaluate the specific effects of unpaved roads on sediment delivery rates in three distinct watersheds on St. John, US Virgin Islands.
• To compare model-predicted sediment yields with existing empirical data and sedimentation rates.

Main Methods:

• Development of the St. John Erosion Model (STJ-EROS), an ArcInfo-based program utilizing empirical sediment production functions and delivery ratios.
• Integration of user-adjustable input routines and calculation routines that incorporate data from nine layers to estimate sediment yield from various sources (roads, slopes, banks, etc.).
• Application of the STJ-EROS model to three St. John watersheds with varying land development levels to simulate natural and current conditions.

Main Results:

• Predicted sediment yields under natural conditions ranged from 2 to 7 Mg km⁻² yr⁻¹, significantly increasing to 8 to 46 Mg km⁻² yr⁻¹ under current development.
• Unpaved roads were found to increase sediment delivery rates substantially: 3-6 times in Lameshur Bay, 5-9 times in Fish Bay, and 4-8 times in Cinnamon Bay.
• Model predictions for both undisturbed and current conditions align well with measured sediment yields and observed bay sedimentation rates.

Conclusions:

• The STJ-EROS model effectively quantifies watershed-scale sediment yields and demonstrates the significant contribution of unpaved roads to increased erosion and sedimentation.
• The model's adaptable structure and user-friendly interfaces allow for its application in other regions to assess the impact of various land uses on sediment dynamics.
• Findings underscore the need for effective land management strategies to mitigate sediment runoff and protect sensitive marine ecosystems like coral reefs.