Monitoring sediment production from forest road approaches to stream crossings in the Virginia Piedmont

Abstract

Reopening of abandoned legacy roads is common in forest operations and represents a reduced cost in comparison to new road construction. However, legacy roads may have lower road standards and require additional best management practice (BMP) implementation upon reopening to protect water quality. Silt fences and elevation measurements of trapped sediment were used to quantify annual sediment delivery rates for reopened bare and existing gravel forest road approaches to stream crossings in the Virginia Piedmont. Additionally, rainfall simulation experiments were performed on reopened legacy road stream crossing approaches to quantify the cost-effectiveness of a range of gravel surface coverage for control of total suspended solids (TSS) concentration from road surface runoff during storm events. In the sediment trap study, mean annual sediment delivery for the reopened bare approaches (98 Mg ha-1 year-1) was 7.5 times greater than that of the gravel approaches (13 Mg ha-1 year-1). Problem road approaches were associated with inadequate water control (greater than 75 m between water control structures) and 90 to 100 percent bare soil conditions throughout the year. Median TSS concentration of road surface runoff (g L-1) for the Bare treatment rainfall simulations (2.34 g L-1; 90 to 100 percent bare soil conditions) was 1.8 times greater than Gravel 1 (1.32 g L-1; 25 to 50 percent gravel surface coverage) and 3.3 times greater than Gravel 2 (0.72 g L-1; 50 to100 percent gravel surface coverage). Gravel surfacing of the road approaches cost $10.27/m of road length for a gravel depth of 7.6 cm and local cost of $27.78/Mg ($25 per ton).