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systems, the San Luis Valley Drain, the Empire Canal, the Richfield Canal, the Lowland Ditch <br />and direct flow. The source of water diverted by ditches in the lower areas is noted and recorded <br />in State records. <br />Use of direct flow water rights in District 21 typically occurs during the period April 1 through <br />October 31. However, variations in climatic conditions may often result in minor extension or <br />shortening of this "irrigation season." <br />District Commissioners are aware of several diversions structures and canal systems that have <br />physical capacities that are less than their total decreed water rights. For example, many of the <br />structures with relatively junior "flood" rights cannot physically pass the full amount decreed. <br />Included would be: <br />• Alamosa Creek Canal <br />• Valdez Ditch <br />• North Alamosa Ditch <br />• Terrace Main Canal <br />• Scandanavian Ditch <br />• Alamosa Spring Creek Ditch <br />• Lower La Jara Ditch <br />est. cap. = 70 cfs <br />est. cap. = 60 cfs <br />est. cap. = 55 cfs <br />est. cap. = 70 cfs <br />est. cap. = 30 cfs <br />est. cap. = 40 cfs <br />est. cap. = 25 cfs <br />Commissioners indicated that examination of historical diversion records may well be the best <br />indicator of actual capacities of diversion structures on the River. <br />Key Structures <br />To assist in the development of a surface water model of the Rio Grande as part of the RGDSS, <br />discussions with District 21 Commissioners included the identification of "key" diversion <br />structures. Key structures were defined as those that significantly effect water rights <br />administration in the District. The criteria that were used to identify key structures included: <br />• total decreed water right amount under the structure (greater than 5 cfs); <br />• water right priority, either senior or swing rights as identified by the water <br />commissioner during the interview; <br />• relatively large amounts of land irrigated under the structure (250 acres and <br />greater); and <br />• represented in previous modeling efforts. <br />A list of all structures within District 21 is provided as Attachment 2. Fora 5 cfs cutoff, 73 key <br />structures exist in District 21 that represent approximately 99% of the decreed rights in District <br />21. Also, the last column of Attachment 2 includes a descriptor that explains why a structure that <br />appears to meet one or more of the above criteria was not considered key. <br />Drainage and Seepage Ditches <br />Several drain and seepage ditch systems have been constructed within District 21. Drains have <br />been constructed in several areas to both convey unwanted water away from potentially <br />productive lands and to salvage return flow waters for additional use. Many of these drain <br />systems have been decreed with water rights for irrigation purposes. Major drains and seepage <br />ditches within District 21 include: <br />C:Acdss\D21_Mem.doc District 21 InterviewJuly 2, 1999 -Page 4 of 8 <br />