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Modeling Results for <br />Colorado River Basin States' Modeling of <br />Colorado River and Reservoir Management Strategies <br />Terminology <br />Abbreviations and Acronyms <br />CRSS Colorado River Simulation System — Reclamation's long -term <br />planning and operations model <br />CRSS -Lice A simplified annual version of CRSS. CRSS -Lite models <br />Powell and the Lower Basin only. CRSS -Lite preserves the <br />accuracy of CRSS but has a significantly shorter run -time <br />EOCY end -of- calendar -year <br />EOWY end -of -water -year <br />ISG -FEIS Colorado River Interim Surplus Criteria Final Environmental <br />Impact Statement, December 2000 <br />KAF thousand acre -feet <br />MAF million acre -feet <br />SIA -FEIS Final Environmental Impact Statement for the Implementation <br />Agreement, Inadvertent Overrun and Payback Policy, and <br />Related Federal Actions, October 2002 <br />Index Sequential Method <br />To represent hydrologic uncertainties during long -term policy studies, both CRSS <br />and CRSS -Lite use a technique known as the Index Sequential Method (ISM). <br />ISM utilizes the existing 90 -year natural flow record to create 90 different <br />hydrologic sequences, referred to as "traces" for each policy alternative. The <br />difference between traces is the start year of the historical hydrologic record. For <br />example, the first trace represents the actual sequence of historical inflows from <br />calendar year (CY) 1906 to 1995; the next trace starts in 1907 and proceeds in <br />order to 1995, with 1906 appended to the end to form a 90 -yr record; the last trace <br />begins in 1995, with historical inflows from 1906 to 1994 appended to the end to <br />form a 90 -yr record. For example, <br />• Trace 1: CY 1906 -1995 <br />• Trace 2: CY 1907 -1995, 1906 <br />• Trace 90: CY 1995, 1907 -1994 <br />By cycling through the full set of 90 hydrologic traces generated by ISM, a range <br />of probabilistic output can be generated and analyzed using standard statistical <br />techniques. The model can also be executed in single -trace mode to analyze the <br />affects of one particular inflow sequence, rather than a range of potential inflows. <br />32 <br />