Aust WM

Brown KR

Dolloff A

Hession C

McGuire KJ

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Kristopher BrownMike Aust, Kevin McGuire,Cully Hession, Andy DolloffPresented at the Symposium on Forestry BMP Effectiveness in the Eastern USMay 12, 2014Effectiveness of best management practices to reduce sediment delivery from reopened legacy roads at forest stream crossingsForest roads at stream crossings• Sediment delivery potential is greatest at the road-stream interface• Issue has sparked legislative debates about CWA permits and NPSP status of forest roadsReopening legacy roads and potential impacts to water quality Legacy roads may have inadequate BMP implementations Common problems include poor grade control, insufficient water control structures, and concomitant bare soilNeed to document the efficacy of BMPs to reduce sediment delivery from roads… How?Turton et al. (2009)Robichaud and Brown (2002) Objective: Quantify annual sediment delivery rates for reopened (no gravel) and graveled stream crossing approachesField study 1: Sediment trapping Objective: Quantify event-based surface runoff and sediment yield for reopened approaches with diverse intensities of BMP implementationsNo gravel10-19% coverLow gravel34-60% coverHigh gravel50-99% coverField study 2: Rainfall simulation14% cover 47% cover 63% coverSediment trap sites at theReynolds Homestead= study siteSite Bare 3 after a thunderstorm on 22-Jun-2012.Plan view of two idealized stream crossing approaches.Road approach study sitesRepeated measurements of sediment deliveryBare approaches were 7.5X greater than gravel(from Patric, 1976)Problem road segments• Surface runoff traveled 75 and 130 m between the nearest water control structure and the silt fence• 90 to 100% bare soil conditions throughout the year287 Mg ha-1 year-1 85 Mg ha-1 year-1BMP audit score vs. annual sediment deliveryField study 1 conclusions• Legacy roads may require additional measures to protect water quality upon reopening• Findings support  contemporary BMP recommendations to:– gravel the entire stream-crossing approach– place a water control structure at least 7.6 m before the stream crossingField study 2Rainfall simulation Objective: Quantify event-based surface runoff and sediment yield for reopened approaches with diverse intensities of BMP implementationsNo gravel10-19% coverLow gravel34-60% coverHigh gravel50-99% cover14% cover 47% cover 63% coverGravel costGravel cost  ($) = Mass (tonnes) X $27.56/tonneMean cost for Low Gravel = $91.77; High Gravel = $183.54Sediment yield was reduced by:• Successive rainfall events• Increasing surface coverSediment-reduction efficacy of gravelMedian TSS concentration for the No Gravel treatment was 2.6 and 3.5X greater than that of the Low Gravel and High Gravel treatments, respectivelySiteSediment yield(mg m-2 mm-1)Gravel cost($)Sediment yield difference from No Gravel(%)No GravelLow GravelHigh GravelLow GravelHigh GravelLow GravelHigh Gravel1 1458 351 233 100.96 201.92 -76 -842 350 850 158 81.42 162.84 143 -553 1867 374 158 104.22 208.44 -80 -924 3072 699 144 81.42 162.84 -77 -955 728 71 156 94.45 188.90 -90 -796 709 309 100 84.68 169.36 -56 -86BMP effectiveness is site-specific.However, sediment yield decreased with successive gravel treatments in 4 of 6 sites.BMP audit score vs. event-based soil erodibilityRainfall simulation study conclusions• Reopened approaches represent significant sources of sediment delivery to streams• Judicious and low-cost BMPs can be used to protect water qualityOverall conclusions• Road planning is important!• Gravel surfacing and adequate water control structures can improve problem roadsQuestions?

Effectiveness of best management practices to reduce sediment delivery from reopened legacy roads at forest stream crossings

https://ir.canterbury.ac.nz/bitstream/10092/15630/2/KRB_Roads_12May2014.pdf

Effectiveness of best management practices to reduce sediment delivery from reopened legacy roads at forest stream crossings

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