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In general, non-key structures that are currently active are included in aggregates and exhibit one <br />or more of the following characteristics: <br />• Active structures (CIU indicates active) that currently (in the period since 2001) <br />divert for irrigation <br />• Sparse or no diversion records during the 1950 to current digitized (2006) year <br />SPDSS study period <br />• Diversion source is a small tributary that will not be included in the water resources <br />planning model <br />• Relatively small acreage, generally less than 100 acres <br />Each water right associated with a well assigned to irrigated acreage will be specifically included <br />in the StateCU and StateMod analyses. However, for modeling purposes, it is appropriate to <br />group well only lands regionally. This effectively reduces the number of individual acreage <br />groups served only by ground water only from greater than 4,500 to around 85, and allows more <br />efficient simulation of both the StateCU and StateMod models. <br />Approach <br />The following approach was used to determine aggregated irrigated structures and aggregated <br />ground water only parcels in the South Platte River basin. <br />1. A single coverage for both surface and ground water aggregates was created by dividing <br />water districts into subsets that were based on the location of non-key irrigated lands, <br />confluences, designated basins, stream gage locations, and the alluvial ground water <br />boundary. <br />2. The coverage was assigned a unique SW and GW only ID. The non-key surface water <br />aggregates and ground water only aggregates were assigned nine character identifiers that are <br />made up of the Water District, ADP (Aggregate Diversion Platte) or AWP (Aggregate Well <br />Platte), and a unique Aggregation ID. For example O1_ADP001 indicates a surface water <br />aggregate located in Water District 1, while O1_AWP001 indicates a ground water only <br />structure located in Water District 1. <br />3. The ArcMap CDSS Tools toolbox was used to spatially aggregate irrigated land using the <br />"Aggregate by GW Parcel" and "Aggregate by SW Structure" tools under the Aggregate <br />Menu. <br />• The "Aggregate by GW Parcel" was used to combine irrigated lands with ground water <br />as the only source within each Aggregate ID. The irrigated land coverage for each year <br />(1956, 1976, 1987, 2001, and 2005) was run independently and resulted in four output <br />tables of Aggregate ID, Parcel ID, and Parcel acreage. These tables are in a comma <br />separated format and can be used directly by StateDMI in creating StateCU and <br />StateMod input files. <br />• The "Aggregate by SW Structure" was used to combine active non-key surface water <br />structures within each Aggregate ID. The irrigated land coverages for recent years (2001 <br />and 2005) were run independently and resulted in two output tables of Aggregate ID, <br />WDID, and total acreage. <br />Page 2 of 19 <br />