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Operations within specific Districts determine the number of key structures and diversion <br />systems. Most Districts have a relatively small number of diversion system structures. <br />Exceptions to this general rule are discussed below: <br />• Water District 23 -Absolute water rights from many ditches within South Park have <br />been aggregated and assigned to and administered at 20 stream gages within the District. <br />SPDSS modeling will represent the water rights from the 149 individual structures at the <br />18 gages. <br />• Water District 48 -Many diversion systems within the Laramie River basin are <br />recommended due to the number of large ranches that are irrigated by multiple ditch <br />systems. <br />• Water District 80 -Similar to the Laramie River basin, several diversion systems are <br />recommended due to the number of large ranches that are irrigated by multiple ditch <br />systems. <br />More information regarding these Districts and others within the SPDSS study area can be found <br />in the individual Water District meeting notes developed in Task 3. <br />As presented in Table 1, the percentage of total decreed surface water rights associated with the <br />key structures vary by tributary but, in total, account for approximately 84 percent of the total <br />decreed surface rights anticipated to be included in the model (e.g., not including seeps, drains, <br />reservoir outlets, etc.) in the South Platte. The percentages of total water rights associated with <br />key structures within the Water Districts range from about 21 percent (District 23) to about 99 <br />percent (District 4). Key structures and diversion systems account for about 99 percent of the <br />total 2001 irrigated acreage assigned to structures in the South Platte basin. <br />The total irrigated acreage identified in the 2001 assessment for the South Platte is over 910,500 <br />acres. Over 167,000 acres are assigned to ground water sources only. The associated well rights <br />will be explicitly represented in both the consumptive use and surface water modeling efforts. <br />The remaining acres are assigned to surface diversion structures and may also be supplemented <br />with ground water. Figure 1 shows the breakdown of key surface water, non-key surface water, <br />and ground water source only acreage for the South Platte River basin. <br />Where to find more information <br />^ The Water District 3 Meeting Notes prepared for SPDSS Task 3 -Identify Key Diversion <br />Structures contains additional information on the selection of key structures and the <br />representation of diversion systems. <br />^ The SPDSS Irrigated Acreage Assessment GIS coverages for 1956, 1976, 1987, 2001, and <br />2005 are available on the CDSS WEB site. <br />^ Surface water irrigation structures not represented as "key" and parcels irrigated only with <br />ground water are modeled in aggregate groups as documented in Task 3 -Aggregated <br />Non-Key Agricultural Diversion Structures. <br />