How do you build a trail on 50-100% slopes of soft organic soils if the slope is under active plant restoration?
Autumn 2015, Nicoterra Trails and client began with a negotiated a contract to address the design challenges. We worked as sub-contractor to GardenCycles who was contracted to remove invasive plants; Himalyan blackberry, English ivy, clematis, Holly, et cetera then stabilize the slope with jute and stakes, lay new organics down and then plant native ground cover, shrubs, and trees. Their plant establishment work would occur over 3 years. I believed their success is our success!
We worked closely to identify the path before plant investments were made and created conditions for future irrigation via the path: mutuality. Steep slope angles required trails with long “running slopes”, functional cross-slopes, drainrock, outboard reinforcement, surface erosion control structures, and finally our choice tread material: 5/8″ minus (with lots of fines) granitic gravel.
To build tight circumference switchbacks we constructed stone steps. This entailed hauling 4,000 lbs of stone via a tensioned high-line system complete with timber tripods to each point. Stone steps were cut and fit and extra-reinforcement which included 5/8″ re-bar and cementitious material at these locations knitted the materials into a unit. In a section that warranted, we constructed a hand rail from beautiful Brazillian cherrywood and white oak posts.
Site Characteristics: 2 adjacent Seattle city lots pie-cut shaped on a north-facing aspect varying from 50-100%slope angles, evidence of slope creep, organic soils to 6″, silt loam subsoils without aggregate below, recently removed vegetative layer, mature conifers upslope and downslope off property
Methods: drafting of slope angles against proposed pathway making the most of the terrain, sustainable grades, and potential irrigation, compaction of backslope, full bench construction to 18″ trail tread, light on the land approach with hand tools, drain rock and double loop system. Trail length was approx. 300′
Conclusions: Winter rains against the graveled path enhanced tread compaction, drainage, and improved slope stability (observed). Coordinating work and objectives with GardenCycles and the client was most satisfying as we all knew of the vulnerability of a steep, unvegetated slope in winter in Seattle. This residential site is within a gulch of the Interlaken neighborhood of Seattle. Neighbors and clients may expand this effort, and if so, Nicoterra Trails is willing to aggrandize this effort.