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001306 . Draft Task 9 Technical Memorandum . 1. Assemble data for USGS gages 9245000 and 9245500. Gage 9245500 is located on the North Fork of Elkhead Creek immediately upstream of the confluence with the main fork and captures a total drainage area of21 square miles. Gage 9245000 is located on the main fork of Elkhead Creek immediately upstream of the confluence with the North Fork and captures a total drainage area of 64 square miles. 2. Extend the annual records for these gages using regression against the annual discharge at the USGS Maybell gage (9251000). The period of record for gage 9245000 is complete from 1954 to the present and indicates an average annual yield of approximately 41,000 af. The period of record for gage 9245500 is 1959 to 1974 and shows an average annual yield of approximately 12,500 af. The regression. . equations used to extend the records for the two gages on Elkhead Creek are as follows: Annual Discharge Annual Discharge Gage 9245500 extension: Gage 9245500 = 0.0374 * (Gage 9251000) -788.6 R2 = 0.909 Average annual error = 2.49% Annual Discharge Annual Discharge Gage 9245000 extension: Gage 9245000 = 0.0134 * (Gage 9251000) - 1432 R2 = 0.804 Average annual error = 2.43% For gage 9245000 synthetic data were generated over the years 1930 to 1953. For gage 9245500, data were generated for the periods 1930 to 1959 and 1974 to 1982. The synthetic annual values were combined with the actual annual data to develop a complete annual data set for the period 1930 to 1982. Once the extension of records from gage 9245500 and 9245000 was completed, these two records are combined to provide a total flow at the confluence of the North and Main forks of Elkhead Creek. Total annual yield at the point of confluence was approximately 51,000 over the period 1930 to 1982. It should be noted that, while this figure is not intended to represent virgin flow conditions, there are very few diversions above the confluence of the North and Main Forks of Elkhead Creek (Division 6 records indicate less than 200 acres of irrigated lands). 3. The confluence of the North and Main Forks of Elkhead Creek is located approximately 15 miles upstream of the existing Elkhead Dam and the drainage area captured by the two gages is approximately 85 square miles. Total drainage area above the site of Elkhead Dam is 2 ;.it ",,,",