According to this matrix, the flow that maximizes the total available 

 habitat for adult brown and rainbow trout in reach //I of the Madison River is 

 24 .1 m /s. Similar matrices were constructed for the remaining study reaches. 



Non-Field Method 



For this method, the monthly flow recommendations derived from the trout- 

 flow data for the five study reaches are expressed as percentages of the mean 

 and median annual flows of record as derived from USGS gage records. The 

 purpose of this analysis is to determine if any general rules of thumb emerge 

 for the study reaches. Rules of thumb would provide a basis for evaluating 

 the applicability of instream flow methods, such as the Tennant method 

 (Tennant, 1975), which base their recommendations on a fixed percentage of 

 a historical flow of record. 



STUDY AREA 



Madison River 



The Madison River originates in Yellowstone National Park at the junction 

 of the Firehole and Gibbon Rivers and flows in a northerly direction for 240 km 

 to Three Forks, Montana where is joins the Jefferson and Gallatin Rivers to 

 form the Missouri River. The river drains about 6,475 sq km. There are two 

 man-made impoundments on the river: Hebgen Reservoir, located 2.4 km down- 

 stream from the park boundary; and Ennis Reservoir, located 101 km downstream 

 from Hebgen Reservoir. 



Flows in the lower 175 km of river are regulated by Hebgen Reservoir. 

 Hebgen Reservoir, built in 1915 by the Montana Power Company, stores water 

 for downstream hydro-electric generation. Water storage usually occurs 

 during the snow runoff period of mid-May to early July. Stored water is re- 

 leased to downstream reservoirs from October through December. 



Ennis Reservoir, built in 1908 by the Montana Power Company, has a rather 

 stable water level with little storage capacity of its own. Its primary 

 function is to create a head for the hydro-electric facility immediately below 

 Ennis Dam. 



Reach #1 encloses a 64 km section of the Madison River between the river's 

 mouth and Ennis Reservoir. The channel in the lower 42 km of reach itl gener- 

 ally exceeds 91 m in width and is braided, forming many islands and side chan- 

 nels. Boulder, cobble and gravel comprise the bottom substrate. Weed beds 

 are also common. Depths rarely exceed 1.2 m. Well-defined riffle-pool areas 

 are absent. The immediate floodplain is vegetated with willow, alder and 

 numerous cottonwoods. Gradient averages 3.0 m/km. 



The upper 22 km of reach #1 lie within the narrow Bear Trap Canyon. The 

 river within the canyon is characterized by turbulent riffle-run areas inter- 

 spersed with pools and large boulders. Gradient averages 4.0 m/km. The dominant 



