This is a discussion of the BMP guidelines for Streamside Management Zones (SMZs).

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.

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