OTHER USES FOR THE WETP OUTPUT 



The wetted perimeter/inflection point method, as previously described, is the 

 primary method the MDFWP is presently using to derive instream f 

 recommendations for the waterways of Montana. The WETP program and output can 

 also be used in other ways for deriving recommendations. Some of these uses 

 are discussed in the following examples. 



Pa ssage of Migratory Trout 



Many streams, particularly those in northwest Montana, provide important 

 spawning and rearing habitats for migratory salmonids. Efficient stream 

 ows are needed not only to maintain the spawning and rearing habitats but 

 .lso to pass adults through shallow riffle areas and other natural barriers 

 while moving to their upstream spawning areas. carriers 



Trout passage criteria relating to stream depth have been developed in Oregon 

 and Colorado (Table 1). These criteria, when used in conjunction with the 



nows° C exUl rifflG areaS ' C3n ^ USGd t0 derlve - lnl »™ P- 

 W IHli'f/f eX . ample ' P ft aS f Sa 8 e "iterla developed by the Colorado Division of 

 W lid fe for streams 70 ft and wider indicate that the minimum average depth 

 needed to pass trout through riffles is 5-0 6 fr Tfc a „ , -7 u 

 Tobacco River (Table 2) shows that the^-ver.^Vpth f« sTf iJWf It 

 cross-sections exceeds 0.5 ft, the approximate minimum average depth required 

 for pass age, at a flow of approximately 120 cfs. A flow of at lest 

 is therefore recommended during the spawning period to facilitate the Passage 

 of adult trout to upstream spawning areas. Passage 



Table 1. Trout passage criteria (from Wesche and Rechard, 1980). 



Species 

 Large Trout 

 20 inches 



Source 



Thompson 



1972 



Minimum 

 Depth (ft) 

 0.6 



Average 

 Depth (ft) 



Where 



Developed 



Oregon 



Other Trout 

 20 inches 



Thompson 

 1972 



0.4 



Oregon 



Trout 



(on streams 

 20 ft or 

 greater) 



Colo. Div. 

 of Wild. 

 1976 



0.5-0.6 



across 



riffles 



Colorado 



Trout 



(on streams 

 10-20 ft 

 wide) 



Colo. Div. 

 of Wild. 

 1976 



0.2-0.4 



across 



riffles 



Colorado 



7-1 



