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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:
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.
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