Controls on sediment production from an unpaved resource road in a Pacific maritime watershed

Unpaved resource roads have the potential to produce large amounts of sediment and can negatively impact water quality and aquatic ecology. In order to better understand the dominant controls on sediment generation from unpaved resource roads, we did 23 large-scale rainfall simulation experiments on a road section in the Honna Watershed, Haida Gwaii, British Columbia, Canada. The experiments were performed with different rainfall intensities (4-52 mm/h), with and without traffic. Precipitation intensity was the dominant control on the amount of sediment generated from the road surface; the total mass of sediment increased linearly with precipitation intensity. The number of passages of loaded logging trucks during an experiment was the second most dominant control on the total amount of sediment generated from the road surface. Elevated sediment concentrations in road surface runoff persisted for 30 min following the passage of loaded logging trucks during low intensity (<8 mm/h) rainfall events and for much shorter periods at higher rainfall intensities. The mass of sediment generated by the passage of a loaded truck increased with precipitation intensity. Passages of empty logging truck did not result in sediment pulses, except during very high rainfall intensities. Seven small-scale rainfall simulation experiments on other parts of the road, however, highlight the large spatial variability in sediment production from the road surface, suggesting additional experiments are required to better describe and predict sediment production from different road sections.