OUTDOOR CORNER: THE STRAIGHT STORY ABOUT OUR STREAMS

Over the last several decades our streams have been degrading at an accelerated rate.

This has largely been due to poor stream and watershed management practices such as timber clearing, bulldozing, some farming practices, urbanization, strip mining, etc. As a result, Missouri has one of the highest erosion rates in the United States. However, one of the most destructive and misunderstood "stream management practices" is channelization (stream straightening).

In the 1940s it was thought that channelization was the solution to problems like streambank erosion, flooding, and slow land drainage. During that time the U.S. Army Corps of Engineers even assisted in channelizing some Missouri streams. We have learned since then that channelization actually creates more erosion and flooding problems than it solves. In addition, channelization has a devastating effect on fish and wildlife.

One of the first laws of physics states that for every action there is a reaction.

Unfortunately, streams react poorly to channelization. When a stream is straightened, a long, meandering channel is replaced by an unstable shorter one. A shorter channel increases the streambed's gradient (slope) and the water velocity. The force of swifter flowing water increases streambed and bank erosion along the new unstable channel.

It also erodes the channel in an upstream direction (a process called "headcutting"). In addition, channelization promotes gully erosion in nearby fields and increases scour in upstream tributaries. The result of all this is even more loss of valuable streamside land than before. What remains is a stream that is characterized by high vertical banks, fast-flowing water, shallow depth, and a wide channel.

Channelization also increases the frequency of flooding downstream. Much of the sand, silt, and gravel which erodes from the straightened reach settles or falls out downstream. When the channel fills with this sediment, its water carrying capacity is reduced. This forces the water up against the streambanks and out into the fields which increases streambank erosion and flood frequency. As a result, downstream bottomland and structures such as roads, bridges, and buildings are affected.

Stream straightening also degrades water quality. Excessive erosion along the new channel leads to increased turbidity (muddiness), sediment load and, in some cases, water temperature. Groundwater recharge and wetlands are also affected by channelization. The increased runoff rate caused by the new channel decreases the ability of water to filter down into the soil. This lowers the groundwater table and drains adjacent wetlands. Wetlands are a streams natural mechanism to hold water and draining them contributes to increased flooding.

To make matters even worse, channelization destroys critical fish and wildlife habitat. A once long, meandering stream with riffles, deep pools, and instream cover (trees, rootwads, etc.) is now replaced by a short channel of uniform depth and width with no cover. Research has shown that this loss of habitat has an adverse impact on the fishery.

Remember, flooding is a natural occurrence along streams. It's also natural for a stream to meander across the floodplain by slowly eroding its banks. However, this lateral movement of the channel under natural conditions takes hundreds or thousands of years.

It is the accelerated streambank erosion caused by man's activities that we must try to stop. To solve stream related problems, we need to start working with the stream instead of against it. There are better alternatives than channelization that will reduce the problems of flooding and excessive bank erosion. Some of these alternatives include tree planting, willow staking, tree revetments, dikes, hard points and riprap.

However, the important thing a landowner can do to help reduce erosion and flooding problems is to establish and maintain a healthy wooded stream corridor (strip of land that borders a stream channel). To encourage landowners to establish these stream corridors the United States Department of Agriculture, through the Conservation Reserve Program (CRP), is providing cost-share assistance and annual rental payments for landowners willing to plant trees on cropland and pasture land along streams.

If you would like more information concerning streams or the CRP program contact the Missouri Department of Conservation at (573) 290-5730.

Brad Pobst is an aquatic services biologist with the Missouri Department of Conservation.