Streamside Management Zones (SMZs)

Unit 1: Welcome to Streamside Management Zones

BMP guidelines recommend that a minimum of a 50 foot SMZ be left on both sides of a perennial and intermittent streams in order to filter sediment from overland flow, stabilize the stream bank, and to provide shade for stable water temperature. The SMZ extends out 50 feet from the edge of the streambank, measured horizontally.  BMP guidelines recommend that professional judgment be used when determining if an SMZ is necessary on ephemeral streams and other water bodies to protect water quality. BMP guidelines also recommend the use of professional judgment when determining if an intermittent or perennial stream may require an SMZ that is wider than 50’ to account for slope and soil type.

SMZ’s wider than 50’ may be needed on sites with one or more of the following conditions:
⦁ steep slopes adjacent to or very near the stream.
⦁ sites with highly erodible soils.
⦁ sites where there is going to be intensive soil disturbance near the SMZ.
⦁ sites with very little or no ground cover near the stream or SMZ.

BMP guidelines allow for selective harvesting within the SMZ.  A minimum of 50 sq. ft. of basal area should be left evenly distributed within the SMZ.  If you are not familiar with basal area, a general rule of thumb would be to leave about 50% of the crown cover, this will leave approximately 50 sq. ft. of basal area.

Unit 2: Perennial Streams

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.

Unit 3: Intermittent Streams

BMP guidelines recommend that a minimum of a 50 foot SMZ be left on both sides of a intermittent stream in order to filter sediment from overland flow 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.

Intermittent streams flow at least 30% to 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 an intermittent stream.

Unit 4: Ephemeral Streams

Whether or not an ephemeral stream needs an SMZ or not should be a site-specific determination made by a forester or other qualified professional.  Factors which may warrant a necessity for an SMZ on an ephemeral stream might include: soil type, slope of surrounding land, vegetative cover, and volumes of expected flows.  Some benefits of leaving an SMZ along an ephemeral stream include but are not limited to:

  • providing travel corridors and habitat for wildlife.
  • adds aesthetic quality to a harvest area.
  • soil retention and stabilization.

Ephemeral streams usually flow less than 30% of the year or just after rain events.  If the flow of the stream can’t be determined, the presence of 3 or more of the following characteristics may help identify the stream as an ephemeral stream:

Unit 5: Streamside Mangement Zones Quiz