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companion with the consumptive use entitlements. Representation of the return flow obligations <br />of the changed water rights is discussed further below. <br />Consumptive Ilse <br />Since approximately 95 percent of Aurora's water sources are consumable or reusable, it is <br />critical that a proper calculation of consumptive use of Aurora' diversions be made to allow that <br />reuse. Most of Aurora's consumption is at the residential level and is calculated as follows <br />1) Water deliveries for indoor use are assumed to be 5 percent consumed. This is a <br />commonly used percentage in the water resource community for sewered indoor uses. <br />2) Water return flows for most lawn irrigation are to be (Water Court Case No. 02-CW- <br />341 pending) calculated based on the commonly used "Cottonwood Curve" that <br />calculates deep percolation as a function of the application and the potential <br />consumptive use. <br />Water Supply <br />Aurora's water supply system has evolved from a few wells, through early 20th century contracts <br />with Denver Water to a fully independent (from Denver Water) and diversified system. Starting <br />in the 1960s and continuing into recent years Aurora has acquired irrigation water rights, <br />subsequently transferred to municipal use, in the upper South Platte River. In the late 1960s, <br />Aurora partnered in the development of the Homestake Project in the Colorado River Basin and <br />has also acquired interest in several transmountain diversion projects from the Colorado River. <br />Since the 1980s, irrigation water rights in the Arkansas River basin have been acquired and <br />changed to municipal use. Combined with the development of principal storage at Spinney Mtn <br />and Aurora Reservoirs and ground water sources, Aurora water supply has evolved into a <br />diversified and complex system. <br />Operation of Aurora's water resource system is very much influenced by where water exists in <br />the system and the opportunities to reuse consumable supplies. With Aurora's complicated <br />system of supplies in three major drainage basins which are regulated by major storage in each <br />basin, it becomes difficult to cast operations with simple rules. However, Aurora's order of use <br />of its water supplies generally operates along the following pattern, which is recommended for <br />use in the SPDSS planning model: <br />1) Upper South Platte Changed Water Rights (for direct use or to storage in Spinney Mtn <br />Reservoir), <br />2) Tarryall Basin Changed Water Rights (for direct use or exchange to Spinney Mtn <br />Reservoir), <br />3) Effluent Exchanges (to Cherry Creek wellfield, direct use, or to storage in Spinney Mtn <br />Reservoir), <br />4) 1964 South Platte Intake Water Right (for direct use), <br />5) Pumping from Aurora wells (Cherry Creek wellfield - if in priority) (for direct use), <br />6) Spinney Mtn Stored Water (from Upper South Platte changed water rights, Arkansas <br />Basin water sources, Colorado River Basin water sources) (for direct use), <br />7) Other ground water sources (non-tributary or Cherry Creek wellfield when replacement <br />water is available) (for direct use), and <br />8) Aurora Reservoir (for direct use). <br />City of Aurora Operating Memorandum 20 of 29 <br />