sport fish in reach #1 in descending order of abundance are mountain whitefish, 

 rainbow trout and brovm trout. 



The mean flow for a 39-year period of record at the USGS gage near the 

 UDStream boundary of reach //I was 49.9 m /s. Flows ranged from 6.0 to 270.6 

 m /s. 



Cross-sectional measurements in reach //I were made in a 123 m subreach. 

 The lowermost of five cross-sections was placed in a relatively deep con- 

 striction and the uppermost in a wide, shallow area containing weed beds. 



Reach //3 encloses a 47 km section of the upper Madison River between river 

 km 116 and 163. This reach consists of turbulent riffle-run areas inter- 

 spersed with large boulders. The channel averages 68.0 m in width. Depths 

 rarely exceed 1.2 m. Boulder, cobble and gravel comprise the bottom substrate. 

 The gradient averages 5.1 m/km. The floodplain is vegetated with grasses 

 mixed with willow, alder and an occasional cottonwood and conifer. The 

 dominant sport fish in descending order of abundance are mountain whitefish, 

 rainbow trout and brown trout. 



Two USGS gages closely bound reach #3. The mean flow for a 13-year _ 

 period of record at the USGS gage near the downstream boundary was 40.6 m /s. 

 Flows ranged from 7.8 to 250.2 m /s. The mean flow for a 67-year period of 

 record at the gage near the upstream boundary was 28.3 m /s. Flows ranged from 

 0.1 to 289.0 m /s. 



Cross-sectional measurements in reach //3 were made in a 99 m subreach. 

 The lowermost of five cross-sections was placed in a wide riffle area and the 

 uppermost in a narrower run. 



Beaverhead River 



The Beaverhead River originates at the outlet of Clark Canyon Reservoir, 

 an irrigation storage facility constructed in 1964, and flows 129 km before 

 joining the Big Hole River to form the Jefferson River. The river drains about 

 12,950 sq km. 



Reach ill encloses a 26 km section of river between river km 103 and Clark 

 Canyon Dam (river km 129). The average channel width is about 25 m. Gradient 

 averages 2.5 m/km. The streambed primarily consists of cobble and gravel. 

 Submerged and overhanging willows and undercut banks provide much of the trout 

 cover in this reach. Flow is confined to one or two channels consisting pri- 

 marily of riffle-pool areas. The dominant sport fish in descending order of 

 abundance are mountain whitefish, brown trout and rainbow trout. 



The flows in reach //2 are completely regulated by Clark Canyon Dam. 

 From October through March, Clark Canyon Reservoir stores water for the up- 

 coming irrigation season. Releases into the river are minimal during this 

 period. Irrigation releases occur from April through September. The diversion 

 of irrigation water begins at the downstream boundary of reach #2. The major 



