MATERIALS AND METHODS 



The standing crop estimates, which provided the data base 

 for evaluating the four instream flow methods, were obtained 

 using the mark-recapture method. Fish were captured with a 

 boat-mounted electrof ishing unit. Estimates of standing crops 

 by age-groups and confidence intervals were calculated using 

 computerized methods summarized by Vincent (1971 and 1974). 



Cross-sectional data for the three field methods were 

 collected simultaneously to conserve field time. Cross- 

 sectional measurements were made using surveying and discharge 

 measuring techniques described in Bovee and Milhous (1978) . 

 Major equipment used to collect this data included a Wild NAKl 

 automatic level, a 25-foot telescoping fiberglas level rod, 

 300 and 500-foot canyon lines and rod-held Gurley type AA 

 current meters. For unwadable cross-sections, the current 

 meter was suspended from a crane mounted on a 10- foot fiber- 

 glas boat. The crane was provided by the USGS, Helena, Mon- 

 tana. The USGS also provided much of the summarized flow data 

 presented in this paper. 



Single Transect Method 



The single transect method involved the use of the wetted 

 perimeter-discharge relationship for a single riffle cross- 

 section to derive instream flow recommendations for each of the 

 five river reaches. Wetted perimeter is the distance along 

 the bottom and sides of a channel cross-section in contact 

 with water. As the discharge in a stream channel decreases, 

 the wetted perimeter also decreases, but the rate of loss of 

 wetted perimeter is not constant over a given range of dis- 

 charges. Starting at zero discharge, wetted perimeter in- 

 creases rapidly for small increases in discharge up to the 

 point where the stream channel nears its maximum width. Be- 

 yond this inflection point, the increase of wetted perimeter 

 is less rapid as discharge increases. The instream. flow 

 recommendation is selected at this inflection point. 



The capacity of a river to sustain fish populations is 

 assvuned to decrease proportionately with the decrease in 

 physical habitat. Wetted perimeter, which is one of the 

 physical parameters least affected by flow reductions, was 

 arbitrarily chosen as an index of the physical condition of 

 the river habitat. It is reasoned that once the rate of loss 

 of wetted perimeter begins to accelerate other physical 

 parameters such as mean depth, maximum depth, mean velocity 

 and cross-sectional area have already shown substantial de- 

 clines. Fish population and wetted perimeter relationships 

 have not been documented in the literature at present. This 

 approach assumes such relationships do exist. 



