7912

• UCREFRP Catalog Number: 7912
• Author: Tennant, D. L.
• Title: Instream Flow Regimens for Fish, Wildlife, Recreation and Related Environmental Resources.
• USFW Year: 1975.
• USFW - Doc Type: Billings, MT.
• Copyright Material: NO

Table 1

Instream Flow Regimens for Fish, Wildlife, Recreation and Related
Environmental Resources

Narrative Descf}.ption
of F1 ow~

Fisheries Recommended Base Flow Regimens
C1assificatio~ Oct.-Mar. Apr.-Sept.

200% of the average f10w3/
60%-100% of the average flow4/
I 40% 60%
II 30% 50%
III 20% 40%
IV 10% 30%
1 0% . 1 0%
10% of average flow to zero flow

..

Flushing or Maximum
Optimum Range
Outstanding
Excellent
Good
Fair or Degrading
Poor or Minimum
Severe Degradation

\.,

lIMost appropriate description of the general condition of the streamflow
for all the parameters listed in the title of this paper.

l!Roman numeral ratings for Fisheries Classification Systems like those de-
veloped for the States of Idaho, Montana, West Virginia, Wyoming, and the
De1awgre1~ivT4 Btgin2~omprehensive Study by the U.S. Fish and Wildlife Ser-
vice.' , , , The base flow regimens outlined above in columns
3 and 4 to maintain the respective desi~nated classes, are judged to be as
reliable and valid.as the classification systems themselves. These recommen-
ded flows generally apply very well to both cold and warm water streams.
Regimens should be reversed or altered to fit different hydrologic cycles,
like the Sa1monid streams on the West Coast, or to favor species like the
fall spawning brown trout. Flows may be refined further by specifically
matching them to vital periods of the life cycle of fishes, like migration,
spawning, incubation, growth, etc. Use of the Montana Method on spring
creeks or streams that have a very uniform flow year-around may provide un-
precedented low-flow regimens at the minimum or base flow levels.

liThe average flow will usually fill the active stream channel approximate-
ly 1/3 full or to the 1 ine of permanent terrestrial vegetation, while 3 times
the average flow wi 11 often fi 11 the acti ve channel apprOximyte1y to the
point of spilling out on the first bench of the flood plain. 5 Twice the
average flow will produce effective depths and velocities within the stream
channel for moving silt, sediment and other bed load material without doing
extensive damage to the banks and riparian vegetation. Twice the average
flow is a good maximum flow recommendation as well as a good flushing flow
(Fig. 1).

YOptimum is a nebulous term; however, this flow range covers that defini-
tion best for all the parameters of this paper collectively.

3