ftAY ,9 - 2006 



simply stated, the need for new recruits decreases as the adult population 

 approaches the stream's carrying capacity. If this premise is correct, then 

 there is little justification for providing flows that attempt to maximize 

 the potential spawning, incubation, fry or juvenile habitat since high levels 

 of recruitment are not needed when adult populations are at or near the carry- 

 ing capacity. Adult habitat is the overriding consideration. 



On heavily fished streams in which overharvesting maintains the adult 

 population far below the stream's carrying capacity, the highest possible 

 level of recruitment may be desirable. In these situations, flows that maxi- 

 mize spawning, incubation, fry and juvenile habitat could be justified. How- 

 ever, it is our belief that the best option is to Initiate restrictive angling 

 regulations that limit the removal of adults rather than recommending a flow 

 management plan that attempts to maximize the production of recruits. Again, 

 adult habitat becomes the overriding consideration when formulating flow 

 recommendations . 



The recommendations derived from the trout standing crop and flow data 

 and the selected instream flow methods are Intended to satisfy the flow needs 

 of only the adult trout stage. The selected instream flow methods are designed 

 to meet this objective. Methodologies designed to address the flow needs of 

 other life stages are not evaluated in this paper. 



METHODS 



The standing crop estimates, which provide the data base for evaluating 

 the instream flow methods, were obtained using the mark-recapture method. 

 Trout were captured with a boat-mounted electro-fishing unit. Estimates of 

 standing crops by age-groups were calculated using computerized methods sum- 

 marized by Vincent (1971 and 1974) . 



Cross-sectional data for the three field methods were collected simul- 

 taneously to conserve field time. Cross-sectional measurements were made 

 using surveying and discharge measuring techniques described in Bovee and Milhous 

 (1978). 



Single Transect Method 



The single transect method involves the use of the wetted perimeter- 

 discharge relationship for a single riffle cross-section to derive flow recom- 

 mendations. 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 throughout the entire range of discharges. 

 Starting at zero discharge, wetted perimeter Increases rapidly for small in- 

 creases in discharge up to the point where the stream channel nears its 

 maximum width. Beyond this inflection point, the increase of wetted perimeter 

 is less rapid as discharge Increases. The flow recommendation is selected 



