2.12 Stream Temperature and Buffers

Buffers can help maintain cooler water temperatures in small streams if the vegetation provides adequate shade on the water surface. This can be beneficial for coldwater aquatic species and for water quality.

Stream shade is comprised of topographic shade provided by nearby hills, bank shade, and vegetative shade. Streams with vegetation removed usually have undesirable summer temperature increases from 5 to 11°C. Aspect, channel morphology, and groundwater input may affect temperatures more than buffers.

Key Design Considerations

  • Incorporate topography and bank shade in the design.
  • Trees and shrubs provide the most shade but unmowed or ungrazed grass buffers can provide shade on streams less than 8 feet in width.
  • Buffer shading effectiveness decreases as stream width increases.
  • Windthrow may be common in buffers retained after timber harvest and wider buffers may be necessary.
  • Buffers may need to be wider (150 to 1000 ft) to maintain other microclimatic factors (e.g., soil temperature, humidity).
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