SPDSS_Task3_AggregateNonKeyAgDiversionStructures

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Comments and Concerns • Key and aggregate structures represent 100 percent of the acreage and associated crop consumptive use in the South Platte and North Platte river basins in current years (2001 and 2005). The procedure used to aggregate non-key structures is automated, therefore can be easily updated if key structures are redefined, new coverages are added, or additional information becomes available and existing coverages are enhanced. • Aggregation allows the development of a planning tool to focus on key structures likely to be important in future planning efforts, yet provides basin wide totals of current diversions and consumptive use. The data centered modeling approach, including the CDSS GIS toolbox, allows revisions or refinements to the aggregation process to occur relatively efficiently. • Aggregated acreage for years when irrigated acreage mapping does not exist will be estimated using the approach described in the Task 71 -Estimate Historical Acreage memorandum. • Non-key surface water structures that have no acreage in 2001 or 2005 (but had acreage in earlier years) generally have a historical or inactive CIU code; have no recent diversion records; and/or have no active water rights and are not included in the aggregates. The historical use associated with these structures will be included in the Water Resources Planning Model in the baseflow gain/loss term. • There are 167 structures being excluded that have historical acreage but no current acreage, therefore inaccuracies are introduced to the historic consumptive use estimates. This is considered reasonable because the acreage and associated consumptive use are small compared to the amount represented. The historic structures not included make up approximately 0.4 percent of the total basin acreage in 1976, which underestimates basin- wide consumptive use in 1976 by approximately 5,000 acre-feet. Page 4 of 19