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SPDSS Memorandum <br />Final <br />To: Ray Alvarado and Ray Bennett <br />From: LRE, Erin Wilson and Mark Mitisek <br />Subject: Task 3-Aggregate Non-Key Agricultural Diversion Structures <br />Date: March 20, 2008 <br />Introduction <br />This memo describes the approach and results of Phase 3 Task 3, Aggregate Non-Key <br />Agricultural Diversion Structures. The objective of this task was as follows: <br />Determine which non-key diversion and groundwater only structures should be grouped <br />together (aggregated) and decide where the node representing each group's aggregate <br />operations should fit into the river network <br />The SPDSS Historical Crop Consumptive Use analysis is based on the 1956, 1976, 1987, 2001, <br />and 2005 Irrigated Acreage coverages developed by Riverside Technology, inc. (RTi) for <br />SPDSS. Key surface water structures were determined and documented in Subtask 3.1 (Task 3 <br />Summary -Key Diversion Structures May 2007, revised March 2008). The spatial aggregation <br />of non-key surface water or conjunctive use structures and aggregation of ground water only <br />parcels was completed using tools in the CDSS GIS Toolbox developed in Task 18. Note that <br />throughout this memorandum, "surface water structures" means structures receiving surface <br />water. Surface water structures may or may not also use supplemental ground water. Ground <br />water only parcels only have a ground water source. <br />Background <br />The SPDSS Historical Crop Consumptive Use analysis (using StateCU) and subsequent water <br />resources planning model efforts (using StateMod) represents 100 percent of the crop <br />consumptive use in the South Platte and North Platte River basins in current years (both 2001 <br />and 2005 acreage coverages). Both models will be used for planning purposes, therefore <br />accurate representation of current water use, operations, and administration is important. <br />Key diversion structures were initially identified as diversion structures representing the <br />approximately upper 85 percent of net absolute decreed water rights within each Water District <br />in the SPDSS study area. The preliminary list of key diversion structures was then revised during <br />Phase 1 and Phase 2 of the SPDSS effort based on interviews with Water Commissioners and <br />Division 1 and 6 Engineer office personnel. These interviews discussed diversion structures <br />and/or diversion systems that should be included in potential future modeling efforts due to their <br />impact on basin operations. Diversion systems are defined as a group of key diversion structures <br />on the same tributary and operated in a similar fashion to satisfy a common demand. <br />Page 1 of 19 <br />