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Step 1: Preliminary Key Structures List <br />In Task 1.3 of the RGDSS surface water modeling effort, a preliminary list of key structures was <br />developed based on decreed water right amounts in each of the eight Water Districts in Division <br />3. The Data Management Interface (DMI) watright was used to access the State's database, <br />HydroBase, and develop initial listings of all surface diversion structures, reservoir structures and <br />instream flow rights in Division 3 as a whole, and then separately for each of the eight Water <br />Districts within Division 3. These structure and water right listings were ordered by descending <br />decreed amounts. For surface diversion and reservoir structures, the decreed amounts were the <br />total amount decreed to the structure under all rights (many of the structures have multiple water <br />rights). The listings also provided the cumulative percentages of each structure relative to the <br />entire Division and District, and the acreages irrigated under the different structures. The listings <br />are provided with the memorandum documenting Task 1.3 of the surface water modeling effort: <br />Develop Preliminary List of Key Structures. The listings were used as a starting point to identify <br />key structures. <br />An initial objective of the RGDSS study was to define a sufficient number of basin structures as <br />key such that a minimum of 75 percent of the total decreed water rights are modeled explicitly in <br />the surface water model of the Rio Grande. Approximately 170 surface diversion structures were <br />identified during Task 1.3 which comprise 75 percent of the total decreed water rights in Division <br />3. <br />For reservoirs, the initial list of key structures included those with decreed storage rights greater <br />than 5,000 acre-feet and known to be actively operated for water supply to agricultural users. <br />Eleven reservoirs met this initial criteria. These eleven reservoir comprise approximately 90 <br />percent of the decreed reservoir storage capacity in Division 3. All instream flow water rights <br />were considered key in these initial efforts. <br />Step 2: Flow Rate and Irrigated Acreage Cutoff <br />The watright DMI listings developed during Task 1.3 were used along with two specific criteria <br />to further evaluate the relative importance of individual structures. For surface diversion <br />structures, these criteria included: <br />• total decreed water right amount under the structure (>5 cfs); <br />• relatively large amounts of land irrigated under the structure (>250 acres) <br />In general, if a surface diversion structure or right met one or more of these criteria it was <br />considered key, and was carried forward in the evaluation process. Those structures not meeting <br />one or more of these criteria were considered non-key and will be represented in an aggregated <br />fashion in the Rio Grande surface water model. <br />The identification of key reservoirs was generally based on the sizes of storage decrees, and <br />additional information regarding whether the reservoirs were actively operated for water supply <br />or part of a system whose structures are key. Smaller reservoirs and stock ponds (e.g. less than <br />5,000 acre-feet) will be aggregated in the surface water model. <br />instream flow rights to be modeled explicitly include all those located on mainstem rivers and <br />other tributaries where detailed hydrology will be represented. Instream flow rights located on <br />tributaries not included in the model will not be modeled. <br />C:Acdss\Task6-2.doc Finalize Key Structures July 27, 1999 -Page 2 of 4 <br />