Table 33. Comparison of the optimum instream flows derived 

 from the IFG Incremental Method u-s'ing both the 

 mean and bottom (0.8 of the depth) velocities in 

 the water column. 



Reach 

 Madison(#l) 



Gallatin(#2) 



Big Hole(#l) 



Life Stage 

 and 

 Species 



Adult brown trout 

 Adult rainbow trout 



Adult brown trout 

 Adult rainbow trout 



Adult brown trout 

 Adult rainbow trout 



IFG Methodology 

 Optimum Instream Flow(cfs) 



Mean Bottom 

 Velocity Velocity 



1,100 

 1,100 



4x200 

 375 



700 

 900 



2. 



The probability-of-use curves on file with the IFG and 

 used in this study were primarily developed from data 

 collected on smaller streams and creeks. These curves 

 may not adequately describe the preferences of trout 

 inhabiting the larger waterways. It is also possible 

 that one set of curves cannot be applied to all rivers, 

 Curves may have to be developed on a river or regional 

 basis . 



3. 



Cover, a variable influenced by flow and shown in many 

 cases to be highly correlated with standing crops of 

 trout, should be incorporated into the IFG method. 



The Montana Department of Fish, Wildlife and Parks does 

 not plan to utilize the present IFG method in its instream 

 flow program for the rivers of the state. The method, how- 

 ever, may be valid for the smaller waterways. The field data 

 needed to apply the IFG method to streams and creeks are being 

 collected concurrently with the data needed for the wetted 

 perimeter methods. The IFG method will be used if proven ap- 

 plicable to the smaller waterways. 



97 



