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Keeping the Connection

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Published on: Jun. 2, 2005

Last revision: Nov. 19, 2010

Usually, the only time floodplains—the flat or low-lying areas next to streams—come to our attention is during floods. When rising waters are not threatening property or lives, it's hard to remember floodplains exist, much less how important they are to the health of our streams.

As they meander through valleys, streams naturally create their own floodplains. No heavy equipment or detailed project plans are needed!

These low-lying areas are called floodplains because they naturally flood when water levels top the stream's banks. This function of collecting excess water is important. It reduces the amount of water that surges downstream.

Flowing water contains a lot of energy. The faster it flows, the more erosive and damaging it can be. Floodplains allow water to spread out and slow down, reducing its potentially destructive force.

Although much of the water that disperses into floodplains eventually returns to the river, some of it soaks into the ground. The amount of infiltration that takes place depends on soil types, land use and vegetation. Water that soaks into the ground doesn't race downstream, where it can cause damage. As a bonus, floodplain infiltration helps recharge our groundwater supplies.

As the water that enters a floodplain slows, the sediment it carries drops out. Each flood brings more sediment, enriching and deepening the soil.

Forests in floodplains are used by wildlife more than any other habitat type. These areas are home to mammals, reptiles, amphibians and insects. Many fish species also use flooded areas for spawning, nursery sites, feeding and refuge.

Vegetation, leaves, twigs and other organic material washed from the floodplain add nutrients to the stream system. These materials form the base of a stream's food chain, providing forage for insects and crustaceans. Just as a stream nourishes its floodplain, a floodplain nourishes its stream.

Signs of Disconnect

Given the importance of floodplains to streams, and the natural interaction of the two, it seems ill-advised to separate them. Yet we've found many ways to disconnect streams from their floodplains.

For example, many of our streams are lined with levees. These embankments contain the flow of streams and keep the water out of the floodplain. Levees often protect urban, industrial or agricultural areas, but at a price. Depending on the height of the levees, their distance from the stream and whether they constrict both sides of the stream, they interfere in some way with the natural function of the floodplains.

Simply clearing vegetation from the floodplain reduces its ability to

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