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Substitute Supply Plan /or the I r_ Fvanct ADorenatw r)neratinn Diversion records for the South Rock Creek Ditch aze summazized in Table 3A. Table 3A indicates that for the period from 1965 to 1994, the ditch diverted an average of 842.0 acre-feet per year, with the total amount of water in the dry year of 1978 equaling 874.0 acre-feet. Table 3A shows that the average diversion rate for the ditch (1965 to 1994) was 4.4 cubic feet per second (cfs). The historic consumptive use of the South Rock Creek Ditch was estimated using historic irrigated acreage based on aerial photographs, interviews with past and present irrigators, the District 36 Water Commissioner, a field inspection, and analysis of diversion records for the ditch. Aerial photographs taken in 1974 and 1988 show that approximately 78 acres of pasture grass were historically irrigated by the South Rock Creek Ditch. However, this 78 acres includes approximately 9.5 acres of wetlands. Therefore, a total of approximately 68.5 acres of pasture grass are claimed in this plan (see Drawing 2). This acreage is consistent with the information obtained from the historic irrigators and the Water Commissioner. Dry-up of this historically irrigated land will occur in 1997. The Penman-Monteith method was used to estimate the net consumptive use associated with the historic irrigation of pasture gross by the South Rock Creek Ditch. This method was chosen over the Jensen-Raise method in that it uses more site-specific information. The Jensen-Raise method was used in regional decrees for the Graff Ditch (Case No. 81CW160) and the Ruth Ditch (Case No. 84CW284). The Graff and Ruth Ditches are located on Willow Creek, approximately three miles south of Maryland at an elevation of approximately 8,800 feet. The priorities and historic uses of these rights are very similaz to those for the South Rock Creek Ditch. Climatic data used in the Penman-Monteith analysis were adjusted from the Green Mountain and Dillon weather stations. Using this method, the estimated dry yeaz net consumptive use is 1.62 acre-feet per acre. This compares favorably with the value of 1.61 acre-feet per acre decreed in Case Nos. 81 CW 160 and 84CW284. Based on the proposed dry-up of 68.5 acres described in this plan, the estimated dry year historic consumptive use from the South Rock Creek Ditch is 111.0 acre-feet. The historic consumptive use by month is summarized in Table 4A. 681-025.110 Wright Water Engineers, Inc. Page 7