Effects of logging road removal on suspended sediment loads and turbidity

Abstract

Poorly designed and unmaintained logging roads pose serious risks to aquatic ecosystems through sediment delivery from stream crossing failures and landslides. Redwood National Park (RNP) in northern coastal California has been implementing a restoration program for almost four decades, focused primarily on removing (decommissioning) abandoned logging roads on former commercial timberlands that were acquired by expansion of RNP onto large areas of cutover timberlands in 1978. Road decommissioning reduces sediment threats over the long term, however there are shorter-term impacts arising from ground disturbance that occurs when roads are removed. To better understand the magnitude and duration of sediment impacts, RNP conducted both onsite and offsite monitoring in a small watershed, Lost Man Creek, where nearly all legacy logging roads were removed from 2000 through 2010. Onsite turbidity increases were initially high at some locations, but diminished rapidly with time. Annual maximum peak discharge explained most of the variability in suspended sediment loads and turbidity at offsite gaging stations. Although restoration-driven increases in offsite turbidity and suspended sediment loads were likely detectable for part of the study period, legacy logging and natural sediment sources, triggered by larger storms, tended to confound the ability to quantify offsite effects with confidence. The year-to-year variability in road treatment intensity was high, and 2 consecutive years with high treatment intensity (2007 and 2008) likely caused concomitant, albeit brief, increases in suspended sediment loads. Since completion of restoration in 2010, sediment loads and turbidity have diminished rapidly despite the occurrence of the largest peak discharges of the study period, suggesting that the elimination of potential legacy sediment sources far outweighs sediment increases arising from road decommissioning.

Parent Publication

• Coast redwood science symposium—2016: Past successes and future direction

Citation

Klein, Randy D.; Ozaki, Vicki. 2017. Effects of logging road removal on suspended sediment loads and turbidity. In: Standiford, Richard B.; Valachovic, Yana, tech cords. Coast redwood science symposium—2016: Past successes and future direction. Proceedings of a workshop. Gen. Tech. Rep. PSW-GTR-258. Albany, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station: 203-214.