The Construction Process
At the heart of sustainable natural surface trail design is the principle of meandering with natural contours and traversing slopes perpendicularly at a rolling grade that does not exceed half of the grade of the side slope. Rolling grade design breaks the trail into a series of short watersheds; this minimizes both the volume and velocity of surface run-off from any given grade dip. We rely on the natural downhill flow of water and the filtration and buffering provided by existing vegetation. The tread is not level but rather is slightly out sloped to encourage the natural flow of water downhill; on bike-optimized trails, the tread is often in sloped, and the resulting camber both enables a smooth flow for riders and forces water to a gutter which diverts the water to the nearest drainage dip. Drainage dips which provide an outlet for more concentrated water flows are generally armored with native stone and channel water into a small Settling Basin in order to capture sediment.
Construction proceeds incrementally, with corridor cleared at the beginning of the day and all exposed soil stabilized through compaction and restoration of a thick cover of forest litter by the end of the workday. Construction begins by removing saplings (< 3” DBH) and shrubs from the trail corridor, as well as pruning limbs that protrude into the corridor. Leaf litter and organic debris are raked and blown uphill. The tread and a relaxed back slope are then shaped using small equipment (mini skid steer and compact excavator) and hand tools. All soil tilled by construction is used to shape the trail (averaging out grades, building grade crests, constructing switchbacks, etc.).
Once the tread has been graded, it is then mechanically smoothed and compacted. The native duff—equivalent to mulch—is raked and blown back downhill to cover all exposed soil, and one last pass reveals the narrow finalized tread. When there is not sufficient elevation change to exploit for natural storm water management, it is usually necessary to raise the tread, either by digging a swale and using the spoils to elevate the trail way or by constructing a wooden boardwalk. Swale-and-rise trail construction is very similar to building a Diversion Dike, with the primary difference that the dike or berm becomes the walking or riding surface. Vegetation from what will become the swale is first harvested; the swale (trapezoidal or parabolic in cross-section) is then dug; the raised tread is built up using the excavated spoils; and finally, the native vegetation is replaced in the swale to create a Vegetated Channel. As within sloped diversion channels, the outlet for the swale is a drainage dip located to take advantage of the natural runoff pattern at the site.
Trail construction is thus a linear process of Selective Grading and Shaping, which utilizes Slope Roughening and Scarification, while Grubbing is omitted when clearing the wider corridor for visibility and Temporary Seeding is used in the season to stabilize spoils. Because the linear disturbance is minimal, the surrounding forest provides a natural Vegetated Buffer/Filter Strip. The tread is sometimes paralleled by short Diversion Ditches or Vegetated Channels, which contain organic Check Dams. At critical sites, such as switchbacks, captured storm water is channeled across a drainage dip to a small Settling Basin.
Current Construction Progress
Construction started in the summer of 2019. To date we have completed nearly 29+ miles of trail, featuring fiberglass truss bridges and several scenic overlooks, wooden boardwalk, rock armoring, and miles of natural surface trail. We hope to finish the trail in fall of 2023, if the weather cooperates with us.
More miles will be added to the Dragon Trail next year. Make your gift to support the trail today!
