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I . I I I I I I I II I I I I I I I I I 002105 Hydrosphere's Colorado River Model December 29, 1993 Page 12 maximum annual capacity of 2,172 kaf in subsequent years. CAP demands that cause Ariwna's total depletions to exceed the States' entitlement of 2.8 maf can only be satisfied from "surplus" releases (see discussion in the following section). Central Arizona Project The state of Arizona's entitlement of2.8 mafper year includes from 1.44 to 1.49 maf for uses along the mainstream. The residual is allocated to the Central Arizona Project (CAP), which delivers water to south-central Arizona, including Phoenix and Tucson. The maximum CAP water use request in Hydrosphere's Colorado River Model dataset depends on which depletion level is being used. The 1968 Colorado River Basin Project Act specified that mainstem diversions under CAP would be junior to California's basic entitlement of 4.4 maf as well as to Nevada's entitlement and Arizona's non-CAP diversions. Thus, CAP's diversion is a junior one. Current operating policy is that under "normal" conditions, as declared by the Secretary of the Interior, CAP is entitled to divert sufficient water to bring Arizona's depletions to the state's entitlement of2.8 maf, or to the specified depletion level, whichever is lower. Additional supplies may be available to CAP if surplus conditions are declared by the Secretary of the Interior. Hydrosphere's Colorado River Model simulates three levels of CAP depletion: shortage, scheduled and surplus. In its standard configuration the "shortage" CAP delivery level is 450 kaf/yr, which conforms to the standard assumption used by CRSM. CAP deliveries are limited to this amount when a shortage is declared at Lake Mead (see discussion of shortage later in this document). When conditions at Lake Mead are normal, that is neither a shortage nor a surplus has been declared, the deliveries to CAP are limited to an amount that brings Arizona's total depletion to 2.8 maf. The USBR refers to this level of delivery as the "scheduled" level. CAP may receive deliveries in excess of the scheduled level when "surplus" conditions are declared by the Secretary of the Interior (a discussion of surplus quantification is in the following section). An assumption adopted by CRSM is that CAP will divert water up to the limit set by the system conditions (shortage, normal or surplus). Under surplus conditions, deliveries are limited by the capacity of its physical plant (3000 cfs). However, Hydrosphere's Colorado River Model allows lower depletion levels to be used, e.g., as part of the Severe and Sustained Drought project, CAP deliveries below even the 450 kaf minimum supply were used in some scenarios. Hence, alternative depletion assumptions such as these can easily be incorporated into the model. As the junior entitlement, the CAP entitlement is subject to the limitation discussed above. The policy regarding limitation of CAP deliveries is left to the discretion of the Secretary of the Interior and is thus subject to change. The standard assumption in Hydrosphere's Colorado River Model is that CAP would be cut back to its minimum level when the elevation of Lake Mead drops below the shortage elevation (see discussion of shortage in the next section). The shortage elevation used by the USBR, 1095 ft, is based on model analyses and was selected to protect power generation, which must be reduced when the surface elevation of Lake Mead reaches 1083 feet elevation. CAP would not be cut back further until conditions are such that insufficient water is available at Lake Mead to supply all of the higher priority entitlements and all of the CAP minimum supply. Diversions to CAP would be reduced, to zero if necessary, before any reductions are made to higher-priority entitlements. In Hydrosphere's Colorado River Model alternative assumptions can be specified for both the shortage delivery limit and the shortage elevation. Hydrosphere Resource Consultants 1002 Walnut Suite 200 Boulder, Colorado 80302