Sediment delivery from unpaved actively-used and relatively un-trafficked forest roads are one of the most common sources of impairment to aquatic ecosystems. Hence the objectives of this study were to: 1) compare the variability in erosion rates from actively used and relatively un-trafficked timber harvest roads across multiple water years in Railroad Gulch; 2) identify segment scale controls on road surface erosion and road-to-stream connectivity; 3) develop storm-based and annual segment scale models to predict road sediment production and compare the accuracy of these models to WEPP: Road; and 4) estimate road-related sediment loads to streams.
Between 2014 and 2019 mean plume lengths were four meters for active roads and two meters for inactive roads, whereas mean rill lengths were three meters on inactive roads and two meters on active roads. Only plume deposition proved significantly greater (α \u3c 0.01) on active roads compared to inactive roads.
The annual-based multiple regression model over-predicted sediment production by 28 percent and the storm-based underpredicted by 37 percent. WEPP: Road underestimated annual sediment loads by 95 percent. Segment-scale sediment production is significantly correlated (α \u3c 0.01) to the slope*area of a road segment, increased rill length (m), percent bare soil, and summed storm erosivity (MJ mm ha-1 h-1).
Sediment production rates for active and inactive roads in Railroad Gulch ranged from 0.0 kg m2 yr-1 to 4.8 kg m2 yr-1. Since between one and two percent of active road lengths and between four and nine percent of inactive road lengths were connected between WY 2017 and 2019, an estimated five Mg and nine Mg of sediment would have delivered to the East and West Branch Railroad Gulch, respectively
