Hydrographs .• ' 



The final minimum flow recommendations derived from the 

 trout standing crop and flow data for the five reaches are 

 compared to monthly mean, median and 80% exceedence (percentile) 

 flows in Figures 30 through 34. The percentile flows by month 

 of the minimum recommendations are given in Table 22. A brief 

 discussion of this data follows. 



M adison River - Reach #1 



Siammary flow statistics for a 29-year period of record 

 were derived from data collected at the USGS gage below Ennis 

 Reservoir (near McAllister) . Throughout this period flows 

 at this gage reflect regulation by Ennis and Hebgen reservoirs. 



The absolute minimum recommendation of 900-1,100 cfs is 

 available in at least 9 of 10 years for the months of August 

 through December, and at least 7 of 10 years for the months of 

 January through April. Overall, the absolute minimum is 

 readily obtainable during the low water months of August through 

 April. 



On a monthly basis, the most desirable minimum of 1,200- 

 1,400 cfs is available in at least 4 of 10 years. The most 

 desirable minimum is generally obtainable in average and above 

 average water years. 



The Montana Power Company, operator of Ennis and Hebgen 

 reservoirs, presently has an informal agreement with the Mon- 

 tana Department of Fish, Wildlife and Parks to provide a mini- 

 mum flow of 1,100 cfs at the USGS gage below Ennis Reservoir. 



Madison River - Reach #3 



Mean monthly flows for a 9-year period of record were 

 derived from data collected at the USGS gage above Ennis 

 Reservoir (near Cameron). Due to insufficient records, only 

 the mean monthly flows are available for comparison. Flows 

 at this gage reflect regulation by Hebgen Reservoir. 



The absolute minimum recommendation of 650 cfs is less 

 than the mean monthly flows for all months. The absolute mini- 

 mum flow appears to be readily obtainable during the low water 

 months of August through April. 



The most desirable minimum of 1,150 cfs was greater than the 

 mean monthly flows for five of the nine low water months, sug- 

 gesting that the most desirable minimum is probably unobtain- 

 able in other than above average water years. 



The Montana Power Company presently has an informal agree- 

 ment with the Department of Fish, Wildlife and Parks to provide 

 a minimum flow of 600 cfs at the USGS gage near the mouth of 

 the West Fork (Kirby Ranch) 



68 



