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. . . ,,'" :f (~- ,"':j "it "t". BASALT PROJECT HATER SUPPLY Present Water Shortap;es Presently irrigated project lands normally have an adequate water supply during the spri.ng runoff period. This runoff' rapidly falls to less than the ideal requirement later in the irrigation season. Project irrigators usually divert excessive amounts of t~ater to their land dur- ing the spring runoff period as they attempt to store moisture in the soil to alleviate later water shortages. Streamflows and resultant irri- gation shortages vary from year to year and annual ;Tater supplies are not evenly distributed among the various service areas o:f the project or to the various :farms within a service area. On the basis of diversion requirements shown previously in this chapter and past diversion records, the relationship of present water supplies to the water requirement of' the presently irrigated land i.s developed in the table on the following page. The usable water supply :from Cattle, COUlter, mld Mesa Creeks and their tributaries is estimated to be the natural :flow of those streams during the irrigation season plus 30 percent of that flow to allow for reusable return flows. The table sho;Ts that the present average annual water requirement is 20,100 acre-feet. The present wat.er supply us able wi thin the ideal demand pattern averages 13,800 acre-feet. Thus "ateI' shortages average 6,300 acre-feet annually, or about 31 percent. of the ideal requirement. The shortages differ somewhat by areas, averaging 30.8 percent for lands in the Cattle Creek service area, 21.5 percent for lands in the Sopris area, and 36.9 percent for the Carbondale area lands. Maximum annual shortages for these areas during the 1946-60 study period were 66.9, 69.2, and 79.2 percent, respectively, all of which would have occurred in 1954. Since some records SilO" more ,mter diverted than "8.S available in the stream, further studies !ne;)' show the shortages to be even larger than indicated above, especially in the Cattle Creek area. Project Water Operation Stu~ Operating assumptions A simulated project operation study was made on a month-by-month basis for the 15-year period 1946-60. The study "as made on the assump- tion that "ateI' required above project canals ;Tould be supplied by exchange. It was also assumed that owners of existing "8.ter rights would be willing to limit their diversions to the ideal requirement in order to permit more efficient use through project development of high flows in excess of the ideal requirement. 29