Crossing Streams and Rivers

• Shallow Stream Fords
• Bridges

Stream and river crossings present a challenge to trail managers grappling with a mix of user challenge, safety, convenience, cost, and esthetics. At one end of the use spectrum, a bridge can allow people with disabilities, toddlers, and those new to the outdoors to experience the trail with little risk. But bridges are expensive. Wilderness visitors who expect a challenge may prefer a shallow stream ford. During high water these folks may opt for a tightrope walk across a fallen log. Each kind of water crossing has consequences for the recreation experience and the lands being accessed. Choose wisely from the spectrum of options before committing present and future resources to any given crossing.

Shallow Stream Fords

A shallow stream ford is a consciously constructed crossing that will last for decades with a minimum of maintenance (barring major flood or debris torrent) and will provide a relatively low challenge to users.

The idea behind a shallow stream ford is to provide solid footing, at a consistent depth from one bank to the other. Most fords are not designed to be used during high runoff, but are intended to be used when flows are moderate to low. A ford for hikers and "nontraditional" packstock (like llamas and pack goats) should not be more than 400 to 600 mm (16 to 24 in) deep (about knee high) during most of the use season. A horse ford (Figure 53) shouldn't be deeper than 1 m (39 in).

Figure 53—Build fords when the water is low.
Place stepping stones for hikers.

Fords should be located in wider, shallower portions of the stream. The approaches should climb a short distance above the typical high water line so that water isn't channeled down the tread. Avoid locations where the stream turns, because the water will undercut approaches on the outside of a turn.

The tread in the ford is level, ideally made of medium-sized gravel. This provides solid footing. The plan is to even out the flow through the ford so the gravel–sized material isn't washed away, leaving only cobble or boulders.

You can do this by arranging a level riprap of big rocks (like a miniature dam) or anchoring a log about 1 to 2 m (3 to 7 ft) downstream from the trail centerline. The idea is to evenly slow the water as it goes across the ford. This slowing effect can be enhanced by placing several rows of stepping stones or rocks upstream from the tread. These slow the water entering the ford and begin to even out the flow. Be sure these upper rocks are not too close to the trail to avoid a scouring effect.

On trails receiving motorized use, concrete planks or blocks placed in soft stream bottoms can strengthen the trail tread for a solid crossing.

Well–constructed shallow stream fords are almost maintenance free. Watch for deep spots developing in the crossing. Floods or seasonal runoff can wash away the approaches or parts of the dam. Debris can catch in the dam or stepping stone line and alter flow characteristics. Approaches can erode into jumpoffs or turn into boggy traps. Maintenance consists of retaining or restoring the design criteria of an even shallow flow with solid footing.

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