The mean discharge for a 70-year period of record at the 

 USGS gage located 16 miles below Clark Canyop' Dam (at Barretts) 

 was 424 cfs. Discharges ranged from 69 to 2', 720 cfs. The 

 historic peak flows occurred in late May to mid-June. Since 

 1964, flows at this gage reflect regulation by Clark Canyon 

 Dam. 



Cross-sectional measurements in reach #2 were made in a 

 540-ft subreach located at river mile 78. Seven cross-sections 

 were placed in a riffle-pool sequence containing an island 

 (Figures 8, 9 and 10) . 



Gallatin River 



The free-flowing Gallatin River (Figure 11) originates at 

 Gallatin Lake in Yellowstone National Park at an elevation 

 of 8,8 34 ft. It flows north for approximately 115 miles to 

 Three Forks, Montana where it joins the Madison and Jefferson 

 rivers to form the Missouri River. The Gallatin River drains 

 an area of about 1,800 square miles, all above an elevation of 

 4,000 ft. Most of the drainage basin above 5,000 ft is 

 covered with coniferous forest and located within Yellowstone 

 National Park and the Gallatin National Forest. The drainage 

 basin below 5,000 ft consists primarily of the Gallatin val- 

 ley, one of the richest agricultural regions in Montana. 



Reach #2 of the Gallatin River encompasses a 34-mile 

 section located within the Gallatin valley between the 

 mouth of the East Gallatin River (river mile 12) and the ■ ■ 

 mouth of the Gallatin canyon (river mile 46) near Gallatin 

 Gateway. As the river leaves the canyon, flow is confined 

 to- a single channel. Mean channel width at this point is 

 approximately 151 ft. As the river progresses through the 

 Gallatin valley, the flow becomes braided into 3-4 channels 

 with the main channel shifting from year to year. Mean chan- 

 nel width in the lower valley is approximately 6 47 ft. 



The streambed at the mouth of the canyon is approximately 

 20% boulder, 70% cobble and 10% gravel and sand. In the 

 lower portion of reach #2, the streambed is approximately 

 50% cobble and 50% gravel, sand and silt. 



Fish cover in the upper valley consists primarily of 

 overhanging, rooted, bank vegetation and large instream 

 boulders. Fish cover in the lower valley is composed pri- 

 marily of Cottonwood log jams and debris piles. Rooted vege- 

 tation is of lesser importance due to the unstable, erodable 

 banks. The large instream boulders of the upper valley are 

 absent in the lower valley. 



15 



