PREDICTING ROAD SURFACE EROSION FROM FOREST ROADS IN WASHINGTON STATE

Erosion from forest roads can be a large source of sediment in watersheds managed for timber production.  In Washington State, timberland owners and tribal, state, and federal resource managers cooperatively developed methods to quantify road surface erosion as part of their Watershed Analysis Methods in the 1990’s.  Since that time, these methods have been further refined and integrated into a GIS model (SEDMODL) and an updated Washington Road Surface Erosion Model. 

The Washington Road Surface Erosion Model is a database tool that allows users to calculate average annual road surface erosion and sediment delivery to channels in a standardized manner.  The model is intended for use on forest roads in Washington State, and can be applied on a variety of scales, ranging from a single road segment to all roads within a watershed.  The model is designed to interface with a GIS system if such spatial data information are available.  The analysis can be carried out at 4 different levels, depending upon the purpose of the analysis and the amount of detail of data available for the roads: 

Level 1 – Screening.  Assessment tool for determining relative sediment input using little site-specific information.  Useful for screening road system to prioritize field work. 

Level 2 – Planning-level Assessment.  Assessment of erosion and delivery appropriate for use during road maintenance planning or sediment budgeting using minimal site-specific information. 

Level 3 – Detailed Assessment and Scenario Playing.  Detailed assessment of erosion/delivery using field-verified data on each road segment.  Ability to determine reduction in sediment delivery resulting from potential road maintenance or Best Management Practices (scenario playing). 

Level 4 – Site/Segment Level Monitoring.  Ability to track changes in road segment attributes and erosion/delivery resulting from road maintenance or BMPs through time. 

The user has the ability to update road records through time as new information for the roads becomes available as a result of field inventories or improvements in the roads resulting from maintenance or BMPs.  Users can specify past, present, or future dates for calculation, allowing resource managers to determine changes in road inputs through time.