Publication Summary

Selected timber harvest, new road construction, and haul road maintenance best management practices (BMPs) were evaluated to determine their effectiveness. Specifically, the study assessed whether the BMPs achieved state water quality standards pertaining to sediment-related water quality impacts during the first one to three years following the practice. This investigation focused primarily on surface and stream channel erosion processes. A case study, weight-of-evidence approach was used to assess BMP effectiveness. Measures of effectiveness included erosion and sediment delivery to streams, physical disturbance of stream channels, and the condition of aquatic habitats and biological communities.

To order a printed copy, call DNR at 360-902-1400. Ask for Pub. No. TFW-WQ6-99-001-115.

Selected timber harvest, new road construction, and haul road maintenance best management practices (BMPs) were evaluated to determine their effectiveness. Specifically, the study assessed whether the BMPs achieved state water quality standards pertaining to sediment-related water quality impacts during the first one to three years following the practice. This investigation focused primarily on surface and stream channel erosion processes. A case study, weight-of-evidence approach was used to assess BMP effectiveness. Measures of effectiveness included erosion and sediment delivery to streams, physical disturbance of stream channels, and the condition of aquatic habitats and biological communities.

Much of the 1992-1995 study period was characterized by below-average to average precipitation. Streamside buffers (Riparian Management Zones and Riparian Leave Tree Areas) were generally found to be effective at preventing sediment delivery and direct physical disturbances to streams. Ground-based harvest and cable yarding in the vicinity of streams without buffers was generally found to be ineffective or only partially effective at preventing sediment-related water quality impacts.

Practices for installing stream crossings for new road construction were generally found to be ineffective or only partially effective at preventing chronic sediment delivery to streams. Road drainage BMPs, specifically practices for installing relief culverts, were found to be effective at over half of the new road sites evaluated. Practices for construction and stabilization of cutslopes on road segments draining to streams were generally found to be ineffective or only partially effective at preventing chronic sediment delivery to streams, while fillslope construction (beyond the immediate area of stream crossing fills) was generally found to be effective. A very limited evaluation of practices for maintaining active haul roads found that these BMPs appear to be effective at minimizing sediment delivery to streams during light to moderate runoff events. However, the small sample size and lack of major storm events precludes drawing firm conclusions regarding this BMP category.

Various factors influencing the effectiveness of the BMPs are described. General recommendations are provided for improving ineffective and partially effective BMPs to ensure a high confidence of achieving water quality standards by preventing or minimizing chronic sediment delivery to streams and avoiding aquatic habitat degradation.