Reach #2 is markedly affected by man, most notably by 

 irrigation diversions. As the river progresses through the 

 valley, water is diverted for the irrigation of hay lands during 

 the summer growing season. The degree of flow reduction (de- 

 watering) depends on the annual discharge with more severe 

 dewatering occurring in low water years. A dewatering survey 

 in the summer of 1966 showed that 12 miles of reach #2 were 

 dewatered over 90% for 3-8 weeks (Wipperman 1967) . In some 

 years portions of the river are totally dewatered in late - , 

 July and August. 



The mean discharge for a 49-year period of record at the 

 USGS gage near the mouth of the Gallatin canyon (near Gallatin 

 Gateway at river mile 48) was 817 cfs. Discharges ranged from 

 117 to 9,690 cfs. This gage, which is upstream of all irri- 

 gation diversions, reflects the natural flow regime of the 

 river. The high water period normally occurs from late May i- , ■ 

 to late July with peak flows occurring in early June. :■" 



Water quality in reach #2 can generally be described as 

 good. Selected chemical properties of the river near Belgrade 

 in 1977 and 1978 are given in Table 3. 



Table 3. Selected chemical properties of the Gallatin River 

 near Belgrade, Montana in summ.er and fall, 1977 and 

 spring, 1978 (data from Bahls et al., 1979). 



i Summer Fall Spring Mean 



Specific Conductance '! ' 



(umhos (a 25 C) 319 - . - • - ' 



Total Alkalinity 



(mg/1 CaCO-j) 124 - - - 



Phosphate (PO4 as P in mg/1) .004 .005 .028 .012 



Total Phosphorus (P in mg/1) .010 .020 .037 .022 



Nitrate plus Nitrite 



(NO3+NO2 as N in mg/1) <.01 .09 .07 



T^mmonia (NH3 as N in mg/1) c-01 <..01 .02 



Kjeldahl Nitrogen (N in mg/1) .14 .08 .10 .11 



The water in reach #2 is comparatively cold except in 

 areas subject to extreme dewatering. The highest water temper- 

 ature recorded in 19 76 and 19 77 near the canyon mouth was 66 F 

 while temperatures as high as 78 F were recorded in dewatered 

 sections of the lower river (Nelson, 1977a) . 



19 



