Sediment delivery ratios from forest road networks and harvesting operational features by physiographic region in the southeastern United States

Abstract

Mechanized forest harvesting and associated access networks can accelerate soil erosion. Forestry best management practices (BMPs) for water quality are used to minimize soil erosion from forest operations and to trap eroded materials on-site before stream entry. Sedimentation provides multiple threats to water quality, but research indicates that BMPs are generally effective at reducing erosion. However, BMP effectiveness for reducing sediment from specific operational features (skid trails, decks, harvest areas, stream crossings, and haul roads) and regions is insufficiently quantified. Sediment delivery ratios (SDRs) are needed to evaluate efficiencies and effects of BMPs. SDR is the ratio (or percentage) of eroded sediment that reaches streams. Soil erosion modeling and sediment trapping were applied to 183 operational features on 58 recent harvests across the Mountains, Piedmont, and Coastal Plain regions of Virginia and North Carolina to determine SDRs. For all regions combined, mean SDRs were highest for stream crossings (34%), followed by skid trails (21%), haul roads (16%), and decks (4%). Harvest areas, not including access features, had SDRs averaging 11%. SDR values were weighted by areas, and the highest weighted SDR was for the Coastal Plain (19%), followed by the Mountains (13%) and Piedmont (6%). The overall average SDR for all regions and operational features across the southeast was 12%, which corresponds with previously reported values. The highly variable SDRs were influenced by site conditions, climatic factors, and a wide range of BMP implementation across sites, yet reasonable estimates were developed. Major recommendations include additional emphases regarding stream crossing, skid trail, and Streamside Management Zone (SMZ) BMPs.