RGDSS_Task8-8_HistoricMonthlyModel_BaseflowCheckandSimulationRuns

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Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 5% 5% 5% 5% 8% 15% 20% 15% 7% 5% 5% 5% Water consumption by municipalities also varies over the course of the year in response to differences in the types of use. Water consumption is typically highest during the summer months because of outdoor lawn and garden watering practices. In other areas of Colorado, outdoor municipal water use has been estimated at roughly 75 percent consumptive with an overall (outdoor and indoor) consumption rate of between 50 and 60 percent (Metropolitan Water Supply Investigation, Colorado Water Conservation Board, 1999). By contrast, these same studies estimate water consumption during winter months at between 5 and 10 percent of water used. The following municipal water use efficiencies have been used in the surface water model: Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 5% 5% 5% 5% 25% 50% 50% 50% 25% 5% 5% 5% Rio Grande Compact In the Phase la and Phase lb surface water model, the Rio Grande Compact was simulated in a simplified manner as a diversion demand with zero consumption at the lowest point on the Rio Grande. The demand for this "diversion point" was set to the historical flows at the CO - NM state line; the water right was the most senior in the basin; and the returns from this diversion were modeled as occurring immediately and just downstream. Actual administration of the Compact by Division 3 occurs throughout the year and every 10 days during the irrigation season through a complex routine involving forecasted inflows, deliveries to- date, and if necessary, curtailment of Colorado water users. Addition information concerning administration of the Rio Grande Compact can be found in a memorandum documenting discussions with the Division 3 Engineer. Two new operating rules have been developed for StateMod to better reflect actual administrative practices. These two rules, which simulate Compact delivery requirements of the Conejos River and Rio Grande as non-consumptive instream flows, are functional in the Phase lc surface water model. The Compact operating rules are turned on beginning in 1969, which is the year the Compact was first administered under current practices. Surface Water Efficiency Enhancement The Phase lc Surface Water Model incorporates revised water use efficiencies that were developed by the RGDSS Consumptive Use Contractor. The revised efficiency estimates were developed in consideration of more detailed information on canal lengths, water loss rates, cropping and water application techniques, and are discussed in a memorandum documenting Task 8.2 of the Surface Water Model development. The Consumptive Use Contractor identified maximum application efficiencies for all structures depending on water application technique. For lands using flood irrigation techniques, a maximum application efficiency of 60 percent was recommended. A maximum application efficiency of 85 percent was recommended for sprinkler irrigation. Overall surface water efficiencies were estimated as follows: C:Acdss\Task8-8.doc Phase lc Model September 27, 2000 -Page 5 of 17