Exploring Streamside Management  Zone

At Weldon Brook WMA, the minimum allowed SMZ width was placed between a regeneration harvest and this stream.

Submitted by Steve Kallesser CF

An interesting study was published in Forest Science that addressed the width of Streamside Management Zones (SMZ) within riparian areas.  SMZ are addressed in NJ’s BMP manual as areas where management activities can occur, provided an absolute minimum of mechanized activity.

The study looked as sediment trapping given four regimes:

  • 25′ SMZ with no selective harvesting
  • 50′ SMZ with selective harvesting,
  • 50′ SMZ with no harvesting
  • 100′ SMZ with no harvesting

Interestingly, all four management regimes gave the same outcome: being able to capture all of the sediment that entered the SMZ from adjacent harvest areas that included site preparation treatments.  One caveat was that each and every regime failed to capture sediment in “blow through” areas caused by channelized flows of water.  These small gullies were only active during extreme rain events, and all of the sediment that ended up in the stream was accounted for by these “blow throughs.”  The study concluded that SMZ width of any size greater than 25′ was adequate, but emphasized that such gullies, usually associated with road water control, should be addressed in harvest planning.  The study is worth reading simply for the introduction, which provides an excellent synopsis of the history of SMZ study and formulation of regulations.

To read more, click here.