Physical Habitat

Fish need places in a stream to collect food, breed, take refuge from predators, and retreat from uncomfortably warm water temperatures; i.e. fish need good physical habitat. Habitat measures usually include: the availability of cover for fish such as woody debris, overhanging vegetation, and undercut banks; the composition of the stream bed; the variety of current velocities; the mixture of riffles, runs, and pools in the stream; and alterations to the bank and near-stream land areas.

Most of these parameters change with the change in streamflow, thus estimating the amount of the streambed covered with water can provide an estimate of the changes in habitat availability. As flows decrease the water pulls away from the river banks and their protective overhanging vegetation, banks, and debris. ("Channel Flow Status" -- the amount of streambed exposed--is estimated at a riffle near the staff gage by the volunteer gage reader.)

Channel Flow Status
15% wetted perimeter
Streambed completely covered:
(Channel Flow Status = 20)
Same riffle largely dry:
(Channel Flow Status = 1)
Stream habitats: riffles, runs and pools
Riffle on Elizabeth Run on Elizabeth
Riffle along Elizabeth Brook, Stow: Riffles are generally the fast, shallow sections of a stream where the water flows over partially submerged rocks and gravel and the surface is broken into small standing waves. Runs have a variety of streambed substrates - sand and gravel. A run or glide along Elizabeth Brook:
Runs or glides are deeper sections with moderate flow velocities where the flow is still visible, but the water's surface is smooth and unbroken. Glides tend to have slower flow velocities and fine-grained substrates - sand, silt, organic debris.
Pool on Elizabeth
Pool in Elizabeth Brook: Pools are deep and slow-moving. The surface is smooth and the current is generally not visible. Substrates are fine-grained-sand, silt, and organic debris.