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The WRRI Trout Cover Rating Method


Trout cover, an important habitat component resulting from the geomorphological characteristics of a stream channel, the streambank interface with the riparian community and the streamflow, has in the past often been overlooked in the course of instream flow studies, primarily because its measurement was considered too subjective and standard procedures did not exist. The primary objective of this study was to continue to test the WRRI Cover Rating Method and adapt it as necessary to larger streams.

Trout cover can generally be described as object-oriented, having a water depth of at least 0.5 feet, a point water velocity of less than 0.5 feet per second, and a mean water velocity of less than 1.0 feet per second. Brown trout were found to be more cover-oriented than are brook or Colorado River cutthroat trout.

A significant positive relationship was found to exist between the amount of cover available and the standing crops of brown trout. For measuring available cover in smaller streams (average discharge less than 100 cfs), the basic WRRI Cover Rating (WCR) Method is recommended. For larger streams, the modified WCR Method (including a "deep-water" factor) is best suited. Step-by-step instructions for the use of these methods are presented in the Appendix.

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