10/6/A-005 Supplemental Data

• Case Number: 10/6/A-005
• Stream Name: Morrison Creek
• Water Division: 6
• Instream Flow App - Doc Type: Supplemental Data

Results:
During my walk - through, I observed a number of trout, most appearing to be less than 10 inches
in length. Mr. Dequine indicated the predominant game fish was brook trout (Salvelinus
fontinalis), with lesser numbers of cutthroat trout (0iicorizynchus clarki) and rainbow trout (0.
mykiss). Stream flow was measured at 7.44 cfs (staff gage reading =1.35 ft), with conditions
being low and clear.
Channel stability based on the SR.I/CSE was rated as "fair" with an overall score of 101 ("fair"
range, 77 -114). Most Upper Bank attributes scored in the "good" category, while 9 of I 1 Lower
Bank and Channel Bottom attributes fell into the "fair" category. Of particular concern is the .
accelerated bar formation and stream bed deposition observed due to the apparent transport of
relatively large volumes of sand and finer gravels into the study reach from the upstream
Morrison Creek watershed. Sediment movement into the study reach from the Silver Creek
watershed appeared to be substantially less.
Habitat quality for most parameters in the EPA and Montana assessment procedures scored as
either `marginal" or "sub- optimal ". Of particular concern are the marginal ratings for "aquatic
structure as cover ", "channel flow status ", "riffle development", "benthic substrate ",
"embeddedness ", and "sediment deposition ". These ratings suggest the likely impairment of trout
resting areas, food production, and reproductive capacity due to the accelerated bar fonnation
and sediment deposition discussed above. Such conditions could be further degraded by future
water withdrawals. Overall, habitat quality was 60.5% of optimum based on the EPA procedure
and 55% of optimum based on the Montana protocol.
Instream flow recommendations following the CWCB protocol are based upon the hydraulic
criteria established by Nehring (1979). These criteria include maintaining a wetted perimeter of
at least 50% of the bankfull condition, an average cross- section depth of 0.39 ft for a channel the
width of MC, and an average cross - section velocity of LO fusee. Protecting sahnonids during the
summer season is accomplished by ensuring all three criteria are met while winter protection is
accomplished by meeting two of the three criteria (Roach 2008). Based upon these criteria and
our hydraulic modeling results for Transect 3, a summer instream flow of about 18 cfs and a
winter flow of about 4 cfs would be appropriate for trout protection on MC below the Silver
Creek confluence.
Conclusions and Recommendations:
My overall assessment of the Morrison Creek channel and the habitat provided is that current
conditions are well below optimum, with likely impairment of trout resting areas and cover, food
production and reproductive capacity. Such reduced habitat quality is due to the relatively high
volumes of sand and finer gravels being transported into the study reach from the upper MC
watershed. Future water withdrawals would likely degrade trout habitat quality even Ruther. A
watershed -based restoration effort by concerned landowners and agencies could prove beneficial
in reducing sediment loading to the system and improving trout habitat quality.
The instream flow recommendations presented above will provide some level of trout habitat
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Appendix B