August 11 – 17, 2017Vol. 19, No. 10

Road Crossings Are Frequently Stream Barriers

This culvert seems large enough to allow a stream channel to form in the bottom.

by Dale Finseth

As towns, road associations and land owners continue work on their roadways this summer and fall, the sites where they cross streams need special attention. Usually this involves installing or replacing a culvert and sometimes a bridge. There seem to be two primary issues:

  1. The culvert is too small. With changes in how severe a rain storm may be, the culvert may no longer be large enough or it has become "pinched." Or, given changes in land use upstream, the stormwater runoff may have increased and overwhelms the current culvert.
  2. The current culvert was installed without attention to habitat protection. Fish and other aquatic animals can't use the stream to move up and downstream. The culvert creates high water velocity or may be "perched" so that animals, usually fish, are not able to travel upstream to other parts of their habitat.

Road crossings are, by their nature, restricted points in a stream's path to downstream. Ideally the water would move slowly enough and through a wide enough channel to maintain an environment conducive to aquatic animal passage. But a road crossing's "choke point" can alter the natural flow and action of the stream. Both the stream environment and its water quality can be effected.

Occasionally the road crossing is a bridge. Usually a bridge is better than a culvert because the water flow is more gradual and the stream bed beneath the bridge is closer to a "natural" channel. But in the case of a culvert, they may be too small and/or too steep. Wildlife is unable to cross the barrier. Or they may be so damaged that critters, and certainly fish, can't travel through them. The classic is a culvert where the water runs out the lower end, drops a couple feet and scours out a large hole beneath the outlet. That is a "perched" culvert.

The fix for such barriers is usually replacement. The replacement is nearly always larger and installed deeper. Replacement is expensive: The initial installation cost can be higher, but the improved life span of the properly sized culvert makes the cost more realistic as a long term investment, and the vast improvement for aquatic plants and animals upstream can be priceless!

It is estimated that about 40% of a watershed's area may be impaired because water flow is hampered by culvert barriers. A program called Stream Smart helps people identify stream barriers, judge their impact on the stream habitat and identify prospective fixes. They sponsor workshops around the State. The LakeSmart Program has begun to incorporate Stream Smart practices into their program, and the Maine DEP has offered grant funds targeted at culvert replacement. Contact Maine DEP or your local watershed association if interested.

Remember . . . the objective is improved water quality. Managing the waterways for native plants and animals is a big part.

Conservation Too columns are written by staff at by the Kennebec County Soil and Water Conservation District in Augusta. For more information about the district and its projects, call Dale Finseth at 622-7847, X 3 or visit