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Stream Anatomy — Stream Bed

Find out more about geomorphology

Stream or Fluvial Geomorphology:
The study of how the geological features and shape of the stream channel change over time.
Find out more here.

Stream bottom (substrate) is the material on the stream bottom.

Substrate types include:

  • Silt/clay/mud. This substrate has a sticky, cohesive feeling. The particles are fine. The spaces between the particles hold a lot of water, making the sediments behave like ooze.
  • Sand (up to 0.1 inch). A sandy bottom is made up of tiny, gritty particles of rock that are smaller than gravel but coarser than silt (gritty, up to ladybug size).
  • Gravel (0.1-2 inches). A gravel bottom is made up of stones ranging from tiny quarter-inch pebbles to rocks of about 2 inches (fine gravel - pea size to marble size; coarse gravel - marble to tennis ball size).
  • Cobbles (2-10 inches). Most rocks on this type of stream bottom are between 2 and 10 inches (between a tennis ball and a basketball).
  • Boulders (greater than 10 inches). Most of the rocks on the bottom are greater than 10 inches (between a basketball and a car in size).
  • Bedrock. This kind of stream bottom is solid rock (or rocks bigger than a car).

(Text from USEPA Stream Habitat Walk. )


Upper Kingsbury Creek


Trout require silt free gravel for egg-laying.