Discussion of Flow Recommendations 



A policy of the MDFWP when deriving flow recommendations for unregulated 

 mountain streams supporting fish is to prohibit flow depletions in winter. 

 The justification for protecting winter flows is primarily based on the fact 

 that winter is the period most detrimental to trout survival in mountain 

 streams exposed to icing and other severe weather conditions. For these 

 streams, the harsh winter environment ultimately limits the numbers and pounds 

 of trout that can be maintained indefinitely by the aquatic habitat. Winter 

 flow depletions would only serve to aggravate an already stressful situation, 

 leading to even greater winter losses and the possible devastation of fish 

 populations. 



The fact that the flows in Montana's mountain streams are lowest in the 

 winter further justifies the policy of protecting winter flows. The assump- 

 tion that more water provides space for more fish has led to the well-accepted 

 conclusion that the period of lowest stream flows is most limiting to fish. 

 The coupling of the low flow period with harsh winter weather conditions, as 

 occurs in Montana, greatly increases the severity of the stream environment in 

 winter. 



The recommended instream flows for German Gulch will preclude all water 

 depletions in winter (November through March) and some other periods as well. 

 This is demonstrated in Table 12, which compares the flow recommendations for 

 the Below Beefstraight Greek study site to the 10th, 50th and 90th percentile 

 monthly flows at the USGS gage located 0.5 miles upstream from the mouth. The 

 10th, 50th and 90th percentile flows provide a measure of stream flows during 

 a very wet, typical and drought year, respectively. 



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