Effectiveness, cost, and implications of forest haul road stream crossing structures and best management practices in Virginia
Morris, Brian Christopher
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Forest roads and stream crossings have the potential to be sources of sediment from forest operations. Recent litigation has renewed interest in furthering research related to forest road Best Management Practices (BMPs). Three legacy (100 year old) forest road stream crossings were monitored for suspended sediment for nine months before and six months after upgrading three unimproved ford crossings with one bridge, one culvert, and one improved ford. During construction, rainfall simulation was utilized to estimate the sediment contribution of each crossing with minimal BMPs (BMP-), BMPs equal to state recommendations (BMP), and BMPs beyond state recommendations (BMP+). Construction costs were recorded to quantify the change in cost with a change in BMP level. Three levels of rainfall simulation were used on each BMP treatment for each crossing resulting in 27 rainfall simulations. Water samples collected by an automatic sampler downstream of the crossings were analyzed for suspended sediment. Pre - and post- construction time periods were compared to assess how the improved crossings altered total suspended sediment concentrations downstream of the crossings. The number of stream crossings constructed per year in Virginia was also estimated using satellite imagery on 400 harvest tracts. Site visits were conducted on 240 harvest tracts where data were collected on the presence of crossings, the types of crossings, and the level of BMP implementation. Rainfall simulation experiments showed decreased sediment with increased BMP level and daily total suspended sediment concentrations measured over 15 months showed a decrease in mean daily sediment concentration after construction of the bridge and culvert crossings. There was no decrease in sediment concentration for the ford crossing. Statewide crossing construction and BMP implementation rates were estimated. Approximately 67% of the audited stream crossings were characterized as having BMPs that were equal to or beyond state recommendations. Increased BMPs and upgrading of stream crossings resulted in decreased total suspended sediment. However, increased BMP implementation also increased stream crossing construction costs. Effectiveness of increased levels of BMPs and the pre and post construction analysis suggests the improvement of a legacy stream crossing may reduce total suspended sediment concentrations.
- Doctoral Dissertations