Understanding Streams
by Bill Turner
Streams Program Coordinator
Most
people enjoy the captivating qualities of flowing water. But
streams are much more to us than enjoyable places to visit. We
rely upon them to drain the land, serve as water supplies and
to irrigate our crops, as well as for fishing and other recreation
The careful treatment of our streams is essential. To protect them we must understand how they work and what we can do to ensure they will continue to function properly.
Understanding begins with the realization that a stream is not just flowing water in an earthen channel; it also includes the watershed, floodplain and stream corridor.
Much like the parts of a clock, each of these land forms plays a role and all must work together for the stream to function properly. Protection and management of each is vital to a healthy stream.
The Watershed
The watershed is an area of land that drains into a stream. This includes both the surface runoff and groundwater. Because a stream is made up of drainage water it is a product of the land above it.
If the land is misused or pollutants are spilled, the receiving stream will be degraded. Although simple, the most important concept in stream management is that every stream is the product of its watershed and each of us lives in a watershed. Each one of us is linked to a stream regardless of our occupation or way of life. How we use the land is ultimately reflected in the condition of the stream.
Watershed management includes all of the land uses and activities of rural and urban living. Each watershed has its own runoff patterns which are dependent upon the types of plants and trees and the natural slope of the land.
A timbered or native grass watershed delivers its runoff slowly and over a long time period. Watersheds with a lot of timber clearing or the construction of many paved streets and parking lots allow water to run off fast, which results in larger, more frequent floods. Faster runoff increases erosion both on the land and in the stream channels below.
In urban areas floodplains make good locations for parks, ball diamonds, football and soccer fields, and industries which can withstand periodic flooding . In rural Missouri floodplains make good pastures or areas for growing timber products such as pecans and walnuts. Row cropping can be acceptable if the stream channel, and other channels that carry water during floods, are protected with a corridor of trees on both sides.
Most watershed changes speed runoff, but conservation can reduce their bad effects. Some landowners build terraces and use strip cropping. Towns use stormwater control measures, such as retention basins, to help slow runoff.
A natural watershed delivers some nutrients and sediment, such as soil, sand and gravel, to the stream. But some watershed practices increase these amounts to harmful levels. Row cropping of erodible land, careless handling of household and industrial chemicals, construction sites with uncontrolled erosion and strip mining pollute runoff waters and degrade the receiving stream.
Some Missouri farmers are doing a good job of maintaining runoff water quality by removing erodible land from production, but this is still a major pollution source. Reclamation of stripmined lands has also been effective and homeowners are becoming more conscious of the need for careful use and disposal of chemicals. An effort to stop poor land use and other polluting activities will result in healthier streams.
The Floodplain
This
is the relatively level area on both sides of the steam channel
that carries flood waters the channel cannot handle.
During a flood, the floodplain does much of the work for the
channel. If a floodplain is not allowed to work properly and
the channel is forced to handle more of the flow, the stream
will be eroded to a larger size.
In relatively undisturbed Missouri watersheds, floods large enough to require the use of the floodplain occur about every two years.
Good floodplains are important but because they do not function continuously, people tend to forget them. Poorly designed roads and levees that block floodwaters are often the result. These can speed up the stream flow by constricting it, which causes erosion.
Houses and businesses constructed in floodplains are subject o flood damage. These may not alter the functioning of the floodplain but sizable changes that do affect the floodplain, such as levees and dams, are often constructed to protect them.
Stream Checklist
Use the following checklist to gauge your past involvement in stream protection and as a way to identify those things you can do in the futures.
| Watershed Practices | Floodplain Practices |
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| Stream Corridor Practices | Stream Channel Practices |
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The overriding guideline to follow on stream channels is simple...protect them in their natural condition by keeping heavy equipment out of the stream and addressing streambank erosion when possible. These are some of the ways we can all become involved in protecting our valuable Missouri Streams. The Conservation Department will assist anyone who wants more information on stream management. For help please write: Streams for the Future Missouri Department of Conservation P.O. Box 180 Jefferson City, MO 65102-0180 |
Stream Corridors
The
strip of land bordering a stream channel is called a stream corridor
or riparian corridor. This is actually a part of the
floodplain, but because it is so important to the stream system
it deserves special consideration. A functioning stream corridor
is at least 100 feet wide and forested.
This wooded border benefits the stream and neighboring landowners by controlling erosion, filtering sediment, producing wood products and enhancing fish and wildlife habitat.
Healthy stream corridors control erosion and sediment in several ways. During a flood the streamside trees and brushy vegetation slow the water before it passes over the floodplain. This reduces erosion on bottomland fields.
Because the water is slowed within the wooded corridor it drops much of its sediment, gravel and sand within the stream corridor, rather than on bottomland fields or in backwater areas downstream. This corridor of trees also traps woody debris that would otherwise end up in folds. The tree canopy and underlying leaf layers of healthy stream corridors protect the soil from the direct force of falling rain and the forest floor acts as a sponge to slow runoff and reduce erosion.
Also, the root systems of those trees growing near the water's edge are vital to controlling bank erosion. A wide corridor of trees will ensure that banks are protected even when unusual flooding removes some streamside trees.
Fish and wildlife habitat are improved by forested stream corridors. These corridors provide many species with food, protection, travel lanes and nesting cover. Every part of the tree is important when it is living and after it has died.
Leaves shade the stream and keep it cool, and after falling they become an important part of the food chain. Branches produce nuts, berries and other foods and provide den cavities for birds and other wildlife. If the tree falls into the stream, it provides cover for fish.
Stream corridors also hold some of Missouri's riches soil, which is good for growing valuable hardwood trees. A planned timber harvest in the corridor means income for the landowner and a healthier forest.
The Stream Channel
Most
Missouri streams meander as they move down the valley.
They show two basic habitat types: pools and riffles. Good pools
are deep, slow moving and provide fish with cover and resting
areas. Riffles are shallow, with a faster flow. They are feeding
and spawning areas. Riffles are shallow, with a faster flow.
They are feeding and spawning areas. This is the natural way
in which water flows through Missouri streams.
Meanders, which are often called bends, are constantly changing because the force of the water moving around the bends removes soil and gravel from the bank and deposits it on an inside bend downstream. Channels develop over a long period of time and relatively small amounts of bank erosion occur during each flood.
But when a major change is made to any part of the stream system the channel must adjust and becomes unstable. We often see these adjustments in the form of severe bank erosion, large deposits of gravel or erosion of bottomland fields.
Shaping stream channels is often seen as a solution, but it usually causes more problems than it solves. Straightening stream channels, pushing gravel against eroding banks, removing gravel from the stream and dumping old cars and debris on banks are some of the ineffective things people do.
Channelization, or stream straightening, seems logical because the eroding bends are totally removed. however, the removal of the bends shortens the length of the channel, making it steeper than the original channel. Water flows faster causing the banks and bottom to erode. Additional erosion will result as the stream takes years to re-establish its natural meandering pattern.
Pushing gravel against eroding banks is a short-lived solution because the flood waters will eventually move the gravel downstream and the bank will again be exposed to erosion. Fish are hurt by sediment that clogs their gills and destroys their spawning habitat. Also, the stable stream bottom is disrupted and left exposed to erosion.
Too much gravel in streams can cause problems, but in most cases, not enough can be removed to have a meaningful effect on stream stability. Efforts should be directed at good watershed management to stop the influx of gravel.
Car bodies and other debris, dumped on the stream bank, do not work to stabilize the bank. Unlike tree roots, junk cannot hold the soil. Nor can junk armor the soil like a blanket of large stone. Besides being ineffective this method is ugly and causes pollution.
I have written about the need to protect our streams and the reasons for including the watershed, floodplain and stream corridor in this effort. But how do we do this? Where do we start and who is responsible for properly managing the components of a stream system?
First, remember we all live in a a watershed so we are all responsible. Whether we are city dwellers, suburbanites or farmers we can all change things by the way we manage the land. We can change the land we own, and we can ask our local governments to require good land management by the public, developers and their own employees.
