APPRAISAL OF METHODS _, , . ' •■■•■:. 



Single Transect Method ' :^ 



The wetted perimeter curve for a single riffle cross- 

 section provided acceptable absolute minimum flow recommenda- 

 tions for all five river reaches. Single, well defined in- 

 flection points were generally present and easily interpreted, i- 

 In addition to being a relatively consistent and reliable 

 method, it was also the most time and cost efficient of the 

 three field methods. -* ' ■' '• • -' 



The single transect method has other advantages. The 

 extra effort and uncertainties involved in the selection of ;, 

 representative subreaches and the placement of multiple cross-,- 

 sections are eliminated as are the need for large field crews 

 and elaborate boat operations. Data collection can generally 

 be handled by a crew of two since most riffles are wadable. -. r.- 



■ The defense of the single transect method before the non- 

 scientist as would occur in Montana's flow reservation process 

 is probably enhanced by its simple, easily explained, yet 

 scientific approach to flow recommendations. The results can 

 be graphically depicted; single inflection points are gen- ^ 

 erally well defined and recommendations easily derived. This 

 greatly adds to the credibility of the recommendations. Pic- 

 tures of the riffle cross-sections showing the area of ex- 

 posed bottom substrate at various flows can also be used to 

 great advantage. In general, the simplicity of the method 

 greatly enhances its persuasive capabilities before the non- 

 scientific community. j 



The consistency of the minimum flow recommendations de- 

 rived from the single transect method suggests that the 

 wetted perimeter curve for a given river bears some similarity 

 to the relationship between trout standing crops and flows. 

 Below the inflection point on the wetted perimeter curve, the . 

 capacity of the river to sustain adult trout greatly dimin- 

 ishes. Why the wetted perimeter would relate to the carrying 

 capacity is xinclear, particularly when standing crops reflect 

 a myriad of factors not common to all rivers nor of the same .• 

 magnitude. 



The inflection point may bear some relationship to the 

 area of bank cover. At the inflection point, the water begins 

 to pull away from the banks, bank cover is lost and the carry- 

 ing capacity declines. This premise probably has little ap- 

 plication to the rivers of the study area since instream 

 cobbles and boulders rather than undercut banks and submerged 

 and overhanging bank vegetation are the primary cover types. 

 The one exception is the Beaverhead River where bank cover is 

 exceptional. 



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