both irrigation and fertilization of cropland, increased 

 salinity, and a potential for decreased dissolved oxygen 

 levels associated with an increase in algae growth. 



The tradeoff between instream uses, such as power 

 generation, and irrigation uses has become an important 

 issue, as power demand occasionally exceeds hydropower 

 system capacity even though system capacity has increased. 

 The lands currently under irrigation will probably be 

 maintained, given the large capital investment associated 

 with irrigation development. However, in addition to any 

 other development costs, future irrigation developments may 

 only be justified if the net benefits exceed the lost value 

 of power generation and other interests associated with 

 depletions. For the Columbia River Basin, this would mean 

 that the net benefits of irrigation are greater than $4 per 

 acre-foot consumed (see next section) . 



HYDROPOWER 



As a headwater state, Montana is an important con- 

 tributor to the regional hydropower system of the Columbia 

 River Basin. The average quantity of water flowing from 

 Montana at the Montana-Idaho state line is about 26 million 

 AF per year, of which about 16 million AF per year flow in 

 the Clark Fork. The Montana water contribution (total flow 

 minus 8.3 million AF entering from Canada) is about 57 

 percent of the upper Columbia River flow and 11 percent of 

 the average annual streamflow at the mouth of the Columbia 

 River (Wright Water Engineers and DNRC 1982) . 



There are four hydropower dams on the Clark Fork 

 mainstem and three hydropower facilities located on major 

 tributaries in Montana. The mainstem dams contain very 

 little storage capacity and have little influence on seasonal 

 discharge patterns. Two major storage projects on the 

 Flathead River system, Kerr and Hungry Horse dams, do have 

 potential to alter seasonal flows in the Clark Fork. A 

 description of the basin's major hydropower facilities and 

 their operations is pfoyided in Table 2-8. 



System Operation 



The organizational structure of the Columbia River 

 hydroelectric power system has evolved over a period of 40 

 years. Although utilities in many parts of the United States 

 have formed interconnected power pools on a regional basis, 

 the degree of integration among major producers and consumers 

 in the Northwest is unusual. 



2-11 



