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I I I I I I I I I I I I I I I I I I I OO~~~~ v.J~ Big Thompson River was processed by the model to estimate the quantity of water available to the City under its own direct-flow rights and through ownership of specific ditch company rights. A second model was used to estimate the availability of water from the CDT and Vindy Gap projects; this model included hydrologic factors representa- tive of the Upper Colorado River Basin, and operational constraints on CBT supplies such as fish flow releases and annual quotas. It also included the impact of senior water rights on Vindy Gap diversion rates and the impact of availability of storage capacity in Lake Granby to store Vindy Gap water. Both models were operated on the same time scale to generate a long-term monthly record of the quantity of water available to the City. Both models are described in more detail in Section 8 of this report and in the Technical Appendix. 2.4 EVALUATION OF SYSTEM YIELD The results of the previous steps produced a long-term (1000-year) monthly record of the total quantity of water available to the City. System yield and reliability were determined by using this 1000-year record of available water as inflow to the City's water treatment plant. For each month, the City demand was compared to the available supply. Any excess water in a given month was stored for future use subject to the following constraints: 1. Storage allowed under the City's storage decree. 2. Only Big Thompson River direct-flow water derived from ownership in irrigation/ditch companies could be stored. 3. Maximum storage at any time is limited to the capacity of the Green Ridge Glade reservoir (600 AC-FT). 4. Releases of stored direct-flow water are in accordance with the terms of the Transfer Decree. 5. The quantity of water taken for storage is in accordance with the terms of the Transfer Decree. 2-6