Changes in stream flow, sediment load, and erosion or deposition on the streambanks will cause the stream to seek a new balance.  Increasing paved areas or removing vegetative ground cover in the watershed will reduce the infiltration of rainfall and cause more runoff from the land.  This leads to higher stream flows with an increased capacity to scour streambeds and undercut streambanks.  Soil erosion from adjacent lands will cause increased sediment build up if the stream flow is insufficient to carry the load of soil (sediment) along the stream.

For those of you who live in urban or suburban areas, it is likely that your stream channel has or is in the process of adjusting to increased runoff by eroding deeper and/or wider.  Many urban streams which have eroded their banks so that the channel can carry greater flows will have lost the streamside vegetation that helps control bank erosion.

Fish and Wildlife Habitat Values
of Streams
A healthy aquatic population in a stream depends on maintaining a variety of suitable habitats, adequate food supply, and clean water.  Fish and the aquatic organisms on which they feed require a mixture of habitats such as fast-flowing riffles, deep pools cool water, rocks, snags, and overhanging vegetation.  Streamside vegetation is important to wildlife because it provides a food supply, shade to cool the water, and cover for roosting, resting, nesting, and protection.

Stream Vegetation Zones
Different natural vegetation zones adjacent to the stream should be considered when selecting an appropriate streambank stabilization technique.  The typical natural zones of a stable streambank community are shown in Figure 2.  These vegetation zones are distinguished by site conditions such as shape, steepness, soil make-up of the bank, variations in stream water depth, duration of flow, bank seepage, and flow rate.

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