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~ 00163S c , MODEL OPERATION CRITERIA Disclaimer Nothing in these Colorado River Simulation System (CRSS) model studies nor any of the related summary information is intended to interpret the provLsLons of the Colorado River Compact (45 Stat. 1057), the Upper Colorado River Basin Compact (63 Stat. 31). the Water Treaty of 1944 ~ith the United Mexican States (Treaty Series 944. 59 Stat. 1219). the decree entered by the Supreme Court of the United States in Arizona v. California, et al. (376 U.S. 340), the Boulder Canyon Project Act, (45 Stat. 1057), the Boulder Canyon Project Adjustment Act (70 Stat. lOS, 43 U.S.C. 618a), the Colorado River Storage Project Act (70 Stat. 105, 43 U.S.C. 620), or the Colorado River Basin Project Act (83 Stat. "885, 43 U.S.C. 1501). The CRSS Studies Three studies ~ere performed using, the CRSS computer model. One study ~ill be used to update the "Central Arizona Project Water Supply Study" which ~as last published in December 1984. This CRSS study used a natural flo~ hydrology data base representing the period from 1906 through 1985. Natural flo~ is both undepleted and unregulated, Additionelly~,this run used the 12-year most critical period from 1953 through 1964 for "602(a)" storage determination. T~o additional studies were performed at the request of the Colorado River Commission (CRC) of Nevada to analyze the impactS of a more adverse ~ater supply upon ~ater availability for the Robert B. ~riffith Water Project (SNWP) in southern Nevada. Both of these CRC studies use the more adverse hydrologic period from 1922 through 1985. The t~o CRC studies differ from one another in that one uses the 12-year most critical period from 1953 through 1964 for "602(a)" storage determination ~hile the other uses a 12-year 90 percent probability of exceedance or 10 percent probability of nonexceedance of flo~ represented by the period from 1955 through 1966. The hydrology for years 1920 and 1921 ~ere substi~uted for 1984 and 1985 hydrology to create a data base through 1985 for all three studies. The natural flo~ volumes for 1984 and 1985 are estimated to have been 24.1 and 20.4 million acre-feet (maf). respec,tively. The natural flo~ volumes for 1920 and 1921 are 21.9 and 22.7 maf, respectively. The Sum of 1984 and 1985 estimated flo~s is 44.5 maf, while-the sum of 1920 and 1921 flows ~as 44.6 maf. The rationale for using the 1920 and 1921 hydrology is that the data available for 1984 and 1985 are limited. provisional, and subject to change. Each of the three model runs was performed on a calendar year basis. The projected study period ~as 1986 through 2050 in all cases. Initial conditions of beginning reservoir contents for all studies corresponded to the Ja~uary 1, 1986 conditions, as described in the January 1986 24-month study entitled "Operation Plan for Colorado River System Reservoirs."