INTRODUCTION 



The vetted perimeter and discharge relationships for selected channel 

 cross-sections are a useful tool for deriving instream flow recommendations 

 for the rivers and streams of Montana. Wetted perimeter is the distance along 

 the bottom and sides of a channel cross-section in contact with water (Figure 

 1). As the discharge in a stream channel decreases, the wetted perimeter also 

 decreases, but the rate of loss of wetted perimeter is not constant throughout 

 the entire range of discharges. Starting at zero discharge, wetted perimeter 

 increases rapidly for small increases in discharge up to the point where the 

 stream channel nears its maximum width. Beyond this break or inflection 

 point, the increase of wetted perimeter is less rapid as discharge increases. 

 An example of a wetted perimeter-discharge relationship showing a well-defined 

 inflection point is given in Figure 2. The instream flow recommendation is 

 selected at or near this inflection point. 



The MDFWP developed in 1980 a relatively simple wetted perimeter predictive 

 fWKTP) computer model for use in its instream flow program. This model 

 eliminates the relatively complex data collecting and calibrating procedures 

 associated with the hydraulic simulation computer models in current use while 

 providing more accurate and reliable wetted perimeter predictions. 



The WKTP computer program was written by Dr. Dalton Burkhalter, aquatic 

 consultant. 1429 S. 5th Ave., Bozeman, Montana 59715. The program is written 

 in FORTRAN IV and Is located at the computer center, Montana State University, 

 Bozeman. Direct all correspondence concerning the program to Fred Nelson' 

 Montana Department of Fish, Wildlife and Parks, 8695 lluffine Lane, Bozeman, 

 Montana 59715. 



1-1 



