Aspen 1997 WCPlan - Laserfiche WebLink

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The study concluded that the water rights held by the City are sufficient to meet projected demands, that the raw water conveyance systems and water rights are of sufficient capacity to meet the full range of anticipated water uses and that the City's treatment plants have adequate capacity to meet expected water demands. However, due to a lack of raw water storage facilities, area streams cannot support all the diversions without adverse effects. The effects would occur with diversions during critically dry periods and could result in impacts to in-stream flow conditions necessary to protect fisheries in Castle and Maroon Creeks. Because the City has a policy of protecting these in-stream values and this situation will worsen over time with the addition of new water service and development, the study evaluated alternative means of addressing these deficits in water supply. It should be noted that in some cases the impacts to stream flow may be greater if the City does not elect to provide service, since the alternative is often an independent water system which may not respect the in-stream flow values to the same extent as Aspen. From a hydrologic standpoint, potable water shortages are expected during only critically dry periods . such as those occurring in 1977-1978. The critical months, considering both potable water demands and available streamflows, are late winter (February - March) and late summer (September). Water shortages are expected to occur on the average of one in tens years. During the landscape irrigation season (May - early September), streamflows are generally more than sufficient to meet the needs of the potable water system. Figures 1 and 2 show the relationship between available supply and projected potable water demand for a critically dry water year. Figure 2 shows the effect that both increased supplies and demand side management are expected to have on water availability with the maximum potential expansion of commitments to serve areas outside the City limits at buildout. Shortages in the potable water system would not be expected to occur in even the driest year of record if the City wished to exercise its rights to deplete streamflows below the minimum level recommended by the Colorado Water Conservation Board. In effect, additional supply improvements and conservation measures sought by the City will have the effect of benefitting streamflows, rather than reducing actual potable water shortages. Shortages in the raw water distribution system are expected on a more frequent basis than in the potable system. A higher priority is placed on satisfying in-stream flow needs and potable water supply needs than on delivery of raw water for irrigation. Reductions in water deliveries from the raw water systems are also more frequent as a result of lower stream conditions which physically limit -the amouilt of water \vhicn enters lhe -heatlgate. of each- dItch at the point Df diversion. Shortages in the raw water systems occur on average once in 3 years. The expected shortages typically occur during the latter portion of the irrigation season, from late August through September. The timing and duration of expected water shortages throughout the potable water system is an important factor in considering which water development and conservation measures best meet the City's needs. For instance, reduction of water demand during the peak portion of the irrigation season (July) does little to reduce the frequency or duration of water shortages since this is the time when surface water availability in area streams is generally at its maximum. Even in critically dry years such as 1977, there was sufficient water in Castle and Maroon Creek during the middle of the summer to satisfy expected water demand at buildout.Similarly, it should be recognized that 5