Sediment delivery from bare and graveled forest road stream crossing approaches in the Virginia Piedmont

Abstract

Forest road stream crossing approaches, or the section of road immediately adjacent to the stream crossing, represent primary sources and nearly direct pathways for sediment delivery to stream channels. This research quantified sediment delivery rates associated with reopening abandoned legacy road stream crossing approaches and evaluated the effectiveness of gravel surfacing of the entire running surface in reducing sediment delivery at stream crossings in the Virginia Piedmont. Sediment delivery rates from five regraded (bare) legacy road approaches were compared to those from four completely graveled road approaches. Repeated measurements of road derived sediment trapped by silt fences were used to quantify sediment delivery rates from the road approaches for one year (Aug. 5, 2011–Aug. 5, 2012). Annual sediment delivery rates from the bare approaches were 7.5 times higher than those of the gravel approaches. Sediment delivery rates ranged from 34 to 287Mgha−1year−1 for the bare approaches and from 10 to 16Mgha−1year−1 for the graveled approaches. The highest sediment delivery rates were associated inadequate road surface cover and insufficient water control structures. These findings show that reopened legacy roads and associated stream crossing approaches can deliver significant quantities of sediment if roads are not adequately closed or maintained and that corrective best management practices (BMPs), such as gravel and appropriate spacing of water control structures, can reduce sediment delivery to streams.