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Water Quality Assessment: Physical: Rock Size
The size of rocks on the bottom of a stream is very important. It affects the flow of water through a channel. Streams with a mixture of large and small stones tend to have increased turbulence. This leads to increased oxygenation of the water. Rock size may also affect the species of organisms that inhabit a stream.

Image showing a sample of rocks collected from Wheeling Creek.Typically, scientists measure the size of the rocks removed from the benthic sampler during the biological assessment. Scientists assume that the rocks are round and estimate their area as " ", where "r" is the longest distance across the rock. Another method is to photograph the rocks on a white pan and use video image analysis to calculate the exact area of each rock (see photo). Photo: Sample of rocks collected from Wheeling Creek. Photo courtesy of Dr. Ben Stout.

A lack of variability in rock size may indicate that a stream has been dredged at some point in the past.

 

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