percent of total marketing receipts for agricultural 

 production in the region. The agricultural sector, in turn, 

 accounts for approximately 1 percent of total income in the 

 region and employs about 5 percent of the work force. In 

 some counties, however, agriculture accounts for as much as 

 9 percent of county income and 19 percent of employment. 

 Irrigation not only increases average production but also 

 stabilizes production during drought periods. Thus, 

 irrigation has had a stabilizing effect on the livestock 

 industry and agriculture in western Montana. 



The value of irrigation to each operation depends on 

 many site-specific factors and is estimated to range between 

 $5 and $60 per acre-foot (Frank et al. 1984). Based on the 

 low-end estimate of 230,000 irrigated acres and a crop 

 requirement of two AF of water per acre (MDA 1987) , the total 

 value of irrigation to western Montana lies between $2 

 million and $28 million per year. 



The cost of irrigation to western Montana cannot easily 

 be quantified. The direct costs associated with irrigation 

 and crop production are not necessarily costs to Montana or 

 the Pacific Northwest. Most of the needed labor, equipment, 

 and material can be purchased in western Montana or in the 

 Pacific Northwest. Therefore, while irrigation is a cost to 

 the individual farmer, workers, retailers, and manufacturers 

 in the Pacific Northwest benefit from this business. 

 Irrigation depletions affect other beneficial uses such as 

 fish and wildlife habitat, water quality, and recreational 

 opportunities. Each new depletion can also further reduce 

 hydroelectric generating capabilities. These impacts 

 represent the primary costs of irrigation to the region. 

 Approximately 1.5 to 2.0 AF per year are consumed for every 

 acre irrigated (MDA 1987) . In most of western Montana, 

 depletions should tend to be on the lower end of this range 

 given high elevations and relatively high rainfall, which 

 reduce net irrigation requirements. However, in some areas, 

 such as the Flint Creek and Rock Creek drainages, the soils 

 are quite porous and require more water to derive an 

 irrigation benefit. Based on a range of 230,000 to 400,000 

 acres of irrigated cropland in seven of the Clark Fork sub- 

 basins, total consumption is estimated to range from 345,000 

 to 800,000 AF per year. 



The cumulative impacts of water quality degradation in 

 the Clark Fork Basin associated with irrigation are not 

 quantified and will be difficult to quantify in the future. 

 However, general water quality impacts are known to include 

 increased sedimentation from streambanks and overland runoff, 

 decreased channel stability and headcutting, increased water 

 temperature related to decreased streamflows, increased 

 nutrient levels that occur as a result of a combination of 



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