Locating and Projecting Hydrologically Induced Forest Road Vulnerabilities

Forest roads—unless receiving regularly spaced maintenance operations—deteriorate over time due to cumulative traffic-induced and weather-enhanced rutting, braiding, puddling, flow channeling, flooding, roadbed erosion, and washouts. The rate of this deterioration depends on a variety of factors, among which are: 1) traffic loads and timing by season and weather, 2) roadbed and construction practices including soil substrates and materials used, 3) frequency and intensity of storm and snowmelt events, and 4) terrain-determined amounts of water remaining and flowing towards, along and away from roads and associated trails. This article reports on a road-segment study focused on indexing, modelling, verifying and mapping image- and terrain-determined road vulnerabilities as revealed through surface imaging and digital elevation projections. Road damage indexing, applied to a 12 km forest road before and after repair, ranged from image-recognizing no damage (0) to rutting (1), braiding (2), puddling (3), and flooding (4). This index was subsequently related to DEM-generated 1-m resolution rasters referring to road-focused: 1) depression depth, 2) slope, 3) upslope flow accumulation, and 4) terrain and depth-to-water projected rut occurrence probabilities. Through regression analysis, it was found that these rasters accounted for up to 82% of the observed road-generated damage index variations. As shown, the resulting model appears to be useful in mapping likely traffic- and weather-affected forest road vulnerabilities and related damage occurrences region-wide.