IRRIGATION 



The Water Resources Division of the DNRC uses a land 

 classification system to determine the suitability of land 

 for irrigated agriculture. The system separates arable lands 

 into three classes based on soil type and climate. Class 1 

 represents land with the highest potential productivity; 

 Class 2 lands are of intermediate potential; and Class 3 

 represents irrigable lands of the lowest value. Table 4-1 

 lists the arable acres in each class for seven subbasins of : 

 the Clark Fork drainage. 



TABLE 4-1. 



ESTIMATED ARABLE LAND IN SUBBASINS OF THE 

 CLARK FORK 



Subbasin 



Land Class 

 1 2 3 



(acres) (acres) (acres) 



Total 



Arable 



Acres 



Upper Clark Fork 



Flint-Rock Creeks 



Blackfoot 



Middle Clark Fork 



Bitterroot 



Flathead 



Lower Clark Fork 



950 



27,531 



48,722 



4,386 



6,471 



12,419 



44,754 



7.186 



160,752 

 45,893 



121,614 

 51,442 

 60,807 



180,065 



111.666 



210,424 

 45,893 



126,000 

 57,913 

 73,226 



252,350 



118.852 



Total 



28,481 



123,938 732,239 



884,658 



Source: DNRC Land Classification System Database. 



These figures represent the upper limit of irrigation 

 development imposed by soil, topographic, and climatic 

 factors. The number of potentially irrigable acres is 

 reduced when economic factors, such as water delivery costs, 

 are considered. For example, Elliott (1986) estimated that 

 only about 13,300 acres could actually be irrigated 

 profitably in the upper Clark Fork, which is approximately 6 

 percent of the arable acreage shown in Table 4-1 for that 

 subbasin. Further study is required to determine if economic 

 factors would have the same effect on other parts of the 

 Clark Fork Basin. 



Water availability is another major constraint on future 

 irrigation development in the basin. The DNRC (1988a) 

 evaluated the irrigable lands identified by Elliott (1986) 

 and found that water was not available throughout much of the 



4-4 



