Streamside Management Zones

Background: What is an SMZ?

Streamside management zones (SMZs) are land and vegetation areas next to lakes and streams where management practices are modified to protect water quality, fish, and other aquatic resources.  These areas are complex ecosystems that provide food, habitat and movement corridors for both water and land communities. Also, because these areas are next to water, SMZs help minimize nonpoint source pollution to surface waters.

The width of a streamside management zone (SMZ) varies with slope, soils, and other conditions, as well as the stream's designation as intermittent or perennial.


Streamside management zones help to:

Filter sediment and nutrients from runoff.  As runoff water moves through plants and the organic matter, it slows and drops sediment that has been carried along.  This settling process keeps sediment and nutrients from flowing into streams and lakes.  It also allows plant roots to take up the nutrients that have dissolved in the runoff and soaked into the soil, further reducing the amount of pollution flowing into lakes and streams.

Allow water to soak into the ground.  Trees and plants, leaves and twigs slow surface runoff, allowing the water to soak into the soil.  This helps to reduce peakflow levels in streams and replenishes the groundwater that helps maintain lake levels and stream flows.

Stabilize streambanks and lakeshores.  Trees and plants along streambanks and lakeshores reduce soil erosion because their roots hold the soil together, making it more difficult for waves, currents, and runoff to wash the soil away.  Plants also lessen impact of raindrops on exposed soil, decreasing erosion.

Shade streams. In most cases, plants and trees along streambanks are necessary to shade streams, keeping the water from becoming too warm for aquatic life in the summer.

Provide food and habitat for aquatic organisms.  Fallen leaves, twigs, and other organic debris from trees are the base of the food chain for aquatic organisms in small forest streams.  Aquatic invertebrates which graze and shred these materials are eaten by small fish, which are in turn eaten by larger fish as well as mink, kingfishers and other wildlife.  Large woody debris provides hiding cover for fish, both predator and prey.  Depending on its location, large woody debris affords shelter from excessive currents and forms scour holes valuable to sport fish species such as bass, crappie and catfish.

Agricultural and Urban Areas

Streamside zones are as valuable in agricultural and urban settings as they are in the forest. Runoff from cultivated fields, as well as city streets and lawns, contain sediment, pesticides, and fertilizer.  Plants in streamside zones filter out these contaminants, reducing the amount of pollutants entering waterbodies.  All streamside zone landowners should maintain or restore streamside management zones.  Do not allow livestock to graze in SMZs. 


Definitions

Lake -- A still waterbody that:

  • is navigable
  • has an ordinary high-water mark
  • has a bed that indicates "reasonably permanent" surface water.

Stream -- A watercourse that:
  • has an ordinary high-water mark (bank full condition)
  • has bed and banks
  • flows at least periodically
  • has an easily identifiable beginning and end
  • does not lose its character as a watercourse even though it may break up and     disappear temporarily and reappear downstream.

Figure 4-1.  Ordinary high-water mark for a lake and a stream.
  (Adapted from Minnesota Department of Natural Resources, 1989.)



For the purpose of this document two types of streams are recognized.

Perennial streams flow throughout most of the year.

Intermittent streams usually flow only during wetter periods and are therefore pooled or dry much of the year.  Intermittent streams must be protected because they import nutrients and food organisms into perennial streams and lakes and may become important spawning habitats during wetter times of the year.

The ordinary high-water mark is the point on the bank or shore up to which the presence and action of the water is so continuous as to leave a distinct mark whether by erosion, destruction of land vegetation, or other easily recognizable characteristic.  It is the bank full condition.

Note: Lakes and streams (perennial and intermittent) are identified on current USGS topographical maps (7.5 minute/1:24,000 scale).

Best Management Practices for Streamside Management Zones

Locate roads outside the SMZ unless necessary for stream crossings.  For stream crossings, follow recommendations in the Stream Crossings section of Forest Roads.

Locate landings outside the SMZ.

Do not move slash into or pile slash within the SMZ.  Keep slash out of lakes and stream channels and away from areas where it may be swept into the water.

Minimize soil exposure and compaction to protect ground vegetation and the leaf layer.

Harvesting should be done so as to purposefully regenerate the forest while maintaining adequate vegetative cover to protect the site.

Operate wheeled or tracked harvesting equipment within the SMZ only when the ground is dry or frozen.  If the ground is not dry, restrict equipment use to roads and stream crossings while working within the SMZ. 

BMPs for Lakes and Perennial Streams

The SMZ for these waters is a strip of land running along the shoreline of lakes and on each side of streams.  It begins at the ordinary high-water mark and extends a minimum of 50 feet landward, and to a greater distance on steeper slopes.

BMPs for Intermittent Streams

The SMZ for these streams is a strip of land on each side of the stream, beginning at the ordinary high-water mark and extending a minimum of 25 feet landward.



Recommended minimum streamside management zone widths between
disturbed areas and water courses.


   Slope of land between                                              Minimum SMZ width in feet
disturbed area and stream
           (Percent)                                                             Intermittent          Perennial

                 0                                                                           25                        50
               10                                                                           45                        90
               20                                                                           65                      130
               30                                                                           85                      170
               40                                                                         105                      210
               50                                                                         125                      250
               60                                                                         145                      290

Note: On steep slopes or on areas of highly erodible soils, you should widen the SMZ.  Source:  Tennessee's BMP Guide.

Figure 4-2.  The two streamside management zone categories.

Back to Main Page
Previous
Next