BMP guidelines recommend that a minimum of a 50 foot SMZ be left on both sides of a perennial stream in order to filter sediment from overland flow, stabilize the stream bank, and to provide shade for stable water temperature. Other benefits of leaving an SMZ include but are not limited to: providing travel corridors and habitat for wildlife, adding aesthetic quality to a harvest area, and possibly reducing your property taxes.
Perennial streams flow at least 90% of the year under normal conditions. If the flow of the stream can’t be determined, the presence of 5 or more of the following characteristics may help identify the stream as a perennial stream:
- The stream shows evidence of a well-defined channel.
- Water pools are present even during dry conditions.
- The channel is almost always sinuous (winding, snakelike, etc.). The degree of sinuosity is specific to physiographic regions. For example, in geographic regions that have mountainous terrain, the channels are less sinuous.
- Fluctuating high water marks (flood prone width) and/or sediment transport are evident. Indicators of a flood prone zone parallel to a stream course are sediment deposits, sediment stained leaves, bare ground, and/or drift lines.
- There is evidence of soil and debris movement (scouring) in the stream channel. Leaf litter is usually transient or temporary in the flow channel.
- Wetland or hydrophytic vegetation is associated with the stream channel. However, perennial streams with deeply incised or “down-cut” channels will usually have wetland vegetation present along the banks or flood-prone zone. Examples include sedges, rushes, mosses, ferns, and the wetter/riparian grasses and woody species.
- Streams are commonly identified as solid blue-lines on USGS topographic maps and as solid black lines separated by one dot on NRCS soil maps.