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Trail Construction and Maintenance Notebook

Trails in Wet Areas (continued)

Turnpikes (continued)

Rocks or logs can be used for retainers. Rocks last longer. If you use logs, they should be at least 150 mm (6 in) in diameter and peeled. Lay retainer logs in one continuous row along each edge of the trail tread. The logs can be notched to join them, if desired. However, in some species notching may cause the logs to rot faster (Figure 43).

[diagram] Notched retainer log
Figure 43—Notched retainer log.

Anchor the logs with stakes or, better yet, large rocks along the outside. Inside, the fill and surfacing hold the retainer logs (Figure 44).

[diagram] Sapling stake
Figure 44—Try this old Alaska trick if your stakes
tend to work up out of boggy ground.

Firm mineral soil; coarse-grained soils or granular material; or small, well-graded angular rock are needed for fill. Often it is necessary to haul in gravel or other well-drained material to surface the trail tread. If good soil is excavated from the ditch, it can be used as fill. Fill the trail until the crown of the trail tread is 50 mm (2 in) or a minimum of 2-percent grade above the retainers. It doesn’t hurt to overfill to begin with, as the fill will settle.

Construct a dip, waterbar, or a drainage structure at each end of the turnpike where necessary to keep water from flowing onto the structure. Keep the approaches as straight as possible coming onto a turnpike, to minimize the chance that stock or motorbike users will cut the corners and end up in the ditches. Turnpike maintenance, especially recrowning, is particularly important the year after construction; most of the soil settling occurs during the first year.

Causeways

A more environmentally friendly relative of the turnpike is the causeway, essentially a turnpike without side ditches (Figure 45). Causeways filled with crushed rock have been successfully used throughout the Sierra Nevada and elsewhere to create an elevated, hardened tread across seasonally wet alpine meadows. Often multiple parallel paths are restored and replaced with a single causeway. Causeways create less environmental impact than turnpikes because ditches are not used and the water table is not lowered. The risk is that in highly saturated soils the causeway could sink into the ground, a problem that geotextile can help prevent.

[diagram] Causeway
Figure 45—Causeways create an elevated, hardened
tread across seasonably wet areas.

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