Stream Crossings: Trails… from a River’s Point of View

“I hear footsteps….”

There’s more to me than you might know...

• I am a river.
• I am dynamic, ever-changing.
• I am pleasing to the eye and to the ear.
• I cut through the earth.
• I meander across the landscape.
• I carry water, sediment, and debris.
• I adjust my shape to maintain balance among runoff, sediment, and slope.
• I provide critical habitat for unique and diverse communities of aquatic and terrestrial organisms.
• I am home to many species of fish, mollusks, insects, amphibians, mammals, reptiles, and birds.
• I provide transport routes to their areas of food, shelter, reproduction, and colonization.
• I change and evolve over time in predictable patterns.
• I tend toward stability unless disturbed.

Trails can harm me, or be my welcome companions; poorly designed, constructed, or maintained trail crossings can:

• Deliver polluted runoff and sediment to my channel.
• Divert, capture, or block my flow.
• Cause my channel to become unstable and disrupt transport of water, sediment, and debris.
• Impede or bar passage of fish, macroinvertebrates, and other aquatic organisms.
• Fragment habitat by creating impassable water depths, flow velocities, or jump heights.
• Impair or prevent access to food resources, refuge from unfavorable conditions, reproductive success, and new areas for colonization.
• Diminish biological diversity and species abundance.

I prefer solitude

• It’s best to keep your distance – avoid interacting with me; trails can be too close for comfort.
• Travel parallel to my course, rather than perpendicular to it.
• Select a path that’s higher, flatter, and drier.
• Leave a healthy fringe of vegetation -- riparian buffer -- between me and a trail.

But, if you must come near or cross me…

• Minimize the number of crossings.
• Cross where my channel is most stable – at a riffle or where my banks are solid rock.
• Use a bridge instead of a ford or culvert.
• Span as much of my active floodplain as possible, preferably at least twice my bankfull width.
• Use an armored ford instead of a culvert.
• If you must use a ford or culvert – minimize the width of the ford or length of the culvert.
• Mimic nature – don’t change width, depth, or gradient.

For culverts, use a natural bottom – don’t change the substrate. For fords, armor the crossing if the natural substrate consists of clay, silt, sand, or gravel. Use stones large enough to withstand scour during flood events.

• Size culverts to handle the largest expected flows and to allow a flood fringe to develop inside.
• Design the approach, to descend into and climb out of the crossing, at an 8% grade maximum.
• Provide grade reversals on both approaches to prevent water and sediment from entering the stream.
• Get runoff from the trail into the soil – use outslopes, dips, and waterbars. Avoid outside berms.
• Plan and design for possible failure of the crossing.
• Integrate other restoration activities into the design and construction of new or rebuilt crossings.

If you can do all this, we can peacefully coexist, but, there will be times when I will flood you...it’s natural!

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