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A quantitative modeling analysis of water availability in the Colorado River Basin, the "Big <br />River" context, requires a competent water resources model that adequately represents the <br />physical and institutional features of the basin. The best available model for this type of study is <br />the CRSS model {Riverware implementation) maintained by Reclamation. The CRSS model has <br />a reliable representation of the current operating rules far the reservoirs and Lower Basin <br />contract deliveries, but does not represent the features of the Colorado River Compact and the <br />Upper Colorado River Basin Compact. Despite this shortcoming, the mast cost-effective means <br />of conducting the requested study will be to adapt CRSS. <br />Approach: <br />8.1 Summarize Key Issues. - Review key legal and operating procedures that may be <br />relevant to the study and the interpretation of study findings. Write a memorandum <br />summarizing the review. <br />8.2 Approach - Assess available methods far evaluating water available to Colorado under <br />the terms of the compact. Prepare a written recommendation for an approach. Submit <br />this to CWCB for review and meet with CWCB staff and State legal counsel, or others <br />able to provide input an the legal significance on the approach, to discuss the <br />recommendation. Based on comments from CWCB prepare a working recommendation <br />for an approach. Submit this to CWCB staff and State legal counsel, ar others able to <br />provide input on the legal significance on the approach, for further review. Based an <br />comments from CWCB prepare a final approach. The cost estimate assumes that two <br />review cycles will be required. <br />8.3 Compact-Constrained Data Set and Modeling Methods - Based on the approach <br />developed in Subtask 8.2 and the work conducted in Tasks 6 and 7, prepare data and <br />model methods quantify water availability to Colorado. The cost estimate assumes that <br />the current Riverware implementation of the CRSS model will be used for the basin-wide <br />analyses, with simplified approaches to representing curtailments to the Upper Basin as a <br />whole. Rather than modify the CRSS model to implement terms of the Upper Colorado <br />River Basin Compact, the water availability results from the CRSS model will be post- <br />pracessed to determine curtailments to Colorado. The cost estimate also assumes that the <br />same hydrology model, methods, and sequences used in the intro-state (StateMod} <br />analyses and developed in Suhtask 7.9 will be used to generate inflow ensembles to the <br />basin-wide model. Finally, the cost estimate assumes that depletion estimates within <br />Colorado will be estimated for a given flow ensemble based an the total consumptive use <br />calculated by the StateMod models, and the relationship between that detailed estimate of <br />depletions and the nominal level of depletions normally used in CRSS will be used to <br />adjust depletions in other Upper Basin states to more realistically reflect depletions <br />during dry spells. <br />8.4 Generation of Curtailment Amounts - Using the approach and methods developed in <br />Subtasks 8.2 and 8.3, generate ensembles of curtailment amounts. Use the modeling tool <br />Colorado River Water Availability Study Scope 25 81281200$ <br />CRWAS Phasel Contract Scope EX A Final <br />