the Beaverhead #2 reach showed an inflection • point at about 



200-225 cfs (Nelson, 1977) . This 200-225 cfs inflection point, 

 which compares favorably to the 225 cfs derived from the IFG-4 

 curve, would suggest that the present WSP curve is grossly 

 inaccurate . 



There is still some question as to which of the models 

 generated the more accurate wetted perimeter curves. Based on 

 the study results, the IFG-4 predictions are judged better 

 than those of the WSP model. However, the best model would 

 be one that uses a stage-discharge rating curve approach using 

 three or more calibration flows to directly predict rather than 

 approximate the wetted perimeter at a flow of interest. This 

 wetted perimeter predictive model is presently being developed 

 by the Montana Department of Fish, Wildlife and Parks for 

 use in its instream flow program. This model will eliminate 

 the uncertainties associated with the wetted perimeter predic- 

 tions of the two models used in this study. 



< 



91 



