1. High Level of Aquatic Habitat Potential - That flow regime which will 

 consistently produce abundant, healthy and thriving aquatic populations. 

 In the case of game fish species, these flows would produce abundant game 

 fish populations capable of sustaining a good to excellent sport fishery 

 for the size of stream involved. For rare, threatened or endangered 

 species, flows to accomplish the high level of aquatic habitat 

 maintenance would: ]) provide the high population levels needed to 

 ensure the continued existence of that species, or 2) provide the flow 

 levels above those which would adversely affect the species. 



2. Low Level of Aquatic Habitat Potential - Flows to accomplish a low level 

 of aquatic habitat maintenance would provide for only a low population of 

 the species present. In the case of game fish species, a poor sport 

 fishery could still be provided. For rare, threatened or endangered 

 species, their populations would exist at low or marginal levels. Tn 

 some cases, this flow level would not be sufficient to maintain certain 

 species. 



The final flow recommendation is selected from this range of flows by the 

 fishery biologist who collected, summarized and analyzed all relevant field 

 data for the streams of interest. The biologist's rating of the stream 

 resource forms the basis of the flow selection process. Factors considered In 

 the evaluation include the level of recreational use, the existing level of 

 environmental degradation, water availability and the magnitude and 

 composition of existing fish populations. The fish population information, 

 which is essential for all streams, is a major consideration. A marginal or 

 poor fishery would likely justify a flow recommendation at or near the lower 

 inflection point unless other considerations, such as the presence of species 

 of special concern (arctic grayling and cutthroat trout, for example), warrant 

 a higher flow. Tn general, only streams with exceptional resident fish 

 populations or those providing crucial spawning and/or rearing habitats for 

 migratory populations would be considered for a recommendation at or near the 

 upper inflection point. The process of deriving the flow recommendation for 

 the low flow period thus combines a field method (wetted perimeter/inflection 

 point method) with a thorough evaluation by a field biologist of the existing 

 stream resource. 



It is recommended that at least three and preferably five riffle 

 cross-sections are used In the analysis. The final flow recommendation is 

 derived by averaging the recommendations for each cross-section, or the 

 computed wetted perimeters for all riffle cross-sections at each flow of 

 interest averaged and the recommendation selected from the wetted 

 perimeter-flow relationship for the composite of all cross-sections. The 

 latter method is preferred. 



A study evaluating the wetted perimeter/inflection point method for small 

 trout streams was completed at the Cooperative Fisheries Research Unit, 

 Montana State University, as a thesis project (Randolph and White, 1984). An 



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