Aquatics

With the advent of the automobile, our road system became increasingly important in America's growth and prosperity.  However, it did not come without a cost to our aquatic habitats and the countless varieties of fish that depend upon them. We now understand that the roads built to accommodate human needs are often particularly harmful to fish.

The presence of a road may contribute to habitat degradation without ever crossing a body of water. The speed and quantity of water flowing over impervious roads during storm events increases water velocity and peak flow of nearby streams, altering their preexisting condition. Greater quantities of fast moving water can change the composition of the streambed and erode the banks of streams and rivers. These waters also carry toxins, trash, and sediments. Among the most common are oil, antifreeze, rubber, gravel, sand, and road salts. The effects of runoff can vary from sedimentation, straightening, erosion and channelization. For fish, this means a reduction in habitat quality as well as an overall loss in available habitat.

A road crossing a stream can cut a population of fish in to two separate populations. Structures designed to allow water to pass under roads often-present barriers to fish. These structures may channelize water making it difficult for fish to swim against them or may not provide water deep enough for fish to swim through them. For anadromous fish, this may be a disaster. Anadromous fish are those which enter river systems from the sea in order to breed. Fish like salmon need to be able to swim down river in order to mature at sea and back up the same rivers in order to reproduce.

With developments in science and technology, engineers have increased their ability to make accommodations for wildlife. Road building can be practiced in such a way as to minimize impacts to the surrounding environment. Engineers and scientists have designed a variety of methods to allow fish passage under roads where they cross streams.

Bridges, baffles, and culverts can be designed to allow the proper water depth and velocity necessary for fish to pass under roads. In Washington the State Department of Transportation and the Washington Department of Fish and Wildlife have been working together to correct more than 500 Aproblem culverts@ where the water depth is too shallow, the water velocity too high, or the outfall drop too far. In Oregon, 54 fish passages have been replaced or modified and over 130 miles of habitat has been restored or enhanced through the Oregon department of transportation. Similar efforts can be made to limit disturbance by new construction and restore streams that have already been disturbed.

Written by John Houssein

Recommendations

  • Existing roads can be retrofitted with appropriate or improved structures such as culverts, fish ladders, and baffles, designed to allow for fish passage.
  • Road building should be done in such a manner as to avoid disturbance, erosion, and proximity to water.
  • If new roads are absolutely necessary, new road designs should include the appropriate structures to allow fish passage, and should maintain a natural flow.