Graduate Thesis Or Dissertation

Sediment Transport Prototypes : Novel Methods to Disconnect Forest Roads from Streams

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  • Unpaved roads are a critical form of infrastructure in forested landscapes but also a potential source of fine sediment that can degrade sensitive ecosystems nearby. Improved management of aggregate road surfacing can reduce sediment generation, lengthen its useful life span, reduce maintenance costs, and more importantly, mitigate the impacts of road sediment on hydrologically connected ecosystems. This study investigated three road construction treatments and evaluated their performance based on runoff water quality, aggregate load distribution, and practicality of widespread application. Treatments included an aggregate-only control (no treatment), a biomass waddle-type filtration bale, and a geotextile-wrapped filter sand berm with a geogrid underlay. Two different aggregate varieties were used totaling six road treatment sections. The biomass filtration bale provided no discernable filtration benefit from road aggregate sourced runoff. The geotextile-wrapped sand filtration berm produced variable results in the field, but follow-up laboratory testing indicated a substantial reduction in effluent turbidity. The geogrid reinforcement effectively reduced subgrade stress and increased aggregate bearing capacity. Testing took place on a reconstructed unpaved forest road test track in Dunn Research Forest, Oregon, USA. A worst-case sediment scenario was produced with simulated rainfall and heavy truck traffic to mimic wet-weather timber hauling. Ditch runoff was collected to determine filtration effect of each road treatment and surface aggregates were testing for degradation through time to determine rate of sediment generation. Field testing was performed during June and July, 2015. Data analysis is ongoing and preliminary findings are presented herein. Hydrologic relationships and aggregate degradation rates are consistent with contemporary research. These agreements provide a metric for validating the highly-controlled experimental design. Investigators are currently developing recommendations for new best management practices employing the use of geotextile materials in unpaved forest road construction as a means of improving water quality of runoff, and aggregate performance.
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