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000930 FINAL MEMORANDUM TO: FROM: SUBJECT: File November 8, 1996 Meg Frantz Task 3.06 Yampa River - Develop return flow data set for aggregated nodes Introduction This memo describes the approach and results obtained under Task 3.06 Develop return flow data set for aggregated nodes. The objective ofthis task was as follows: Specify the modeled timing and location of return flaws resulting from diversions by the aggregated irrigation structures, and prepare the Statemod .rtn, .dly and.dds input files. Approach and Results Aggregated Irrigation Return flow Locations Based on an inspection of the aggregated irrigated land locations, return flow locations were assigned to the next downstream node for each of the aggregated irrigation structures modeled. Aggregated Irrigation Return flow Timing Based on an inspection of the aggregated irrigated land . locations, return flow timing was estimated to be the same as that used for most other irrigation structures in the Yampa River Basin. This return flow pattern (Table 1) is presented below. Month 1 2 3 4 Total Table 1 % Returned 75.5 17.5 5.5 U 100 Accordingly, no changes were made to the Phase 2 .dly file, which contains the return flow pattern tables. As it creates the .dds file, watright sets the return flow location for each diversion to the next downstream node, unless an entry in the .rtn file indicates that returns re-enter the stream at a different site. In all cases, returns from aggregated nodes should be modeled as returning to the next downstream node. Therefore, the Phase 2 ,rtn file was not modified; nor did the .dds file have to be regenerated. DN.c72-101-061kmc SOIr'LE