FINAL CONSIDERATIONS 



Re sure to compare your instream flow recommend a t i oris to the water 

 availability. For Raged streams, many summary flow statistics, such as the 

 mean and median monthly flow of record, are available for comparison. For 

 ungaged streams, instantaneous flow measurements collected by various state 

 and federal agencies and simulated data are useful. The primary purpose is to 

 determine if the recommendation is reasonable based on water availability. It 

 is also desirable, for future planning, to define the period in which water in 

 excess of the recommendation is available for consumptive uses and to quantify 

 this excess. 



It is common for the low flow recommendations for many of the headwater rivers 

 and streams to equal or exceed the normal water availability for the months of 

 November through March. This is the winter period when the natural flows are 

 lowest for the year. These naturally occurring low flows, when coupled with 

 the adverse effects of surface and anchor ice formation and the resulting 

 scouring of the channel at ice-out, can impact the fishery. Consequently, 

 water depletions during the winter have the potential to he extremely harmful 

 to the ,-ilready stressed fish populations. For headwater rivers and streams, 

 it is generally accepted that little or no water should be removed during the 

 critical winter period if fish populations are to be maintained at existing 

 levels. 



The recommendations derived from the wetted perimeter/inflection point method 

 only apply to the low flow or nonrunoff months. For the high flow or runoff 

 period, flow recommendations should be based on those flows judged necessary 

 for flushing bottom sediments and maintaining the existing channel morphology. 

 This method, termed the dominant discharge/channel morphology concept (Montana 

 Department of Fish and Came, 1979), requires at least ten years of continuous 

 USCS gage records for deriving high flow recommendations, so cannot he applied 

 to most streams. 



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