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<br />.-'. <br /> <br />0015P <br /> <br />, <br />, <br /> <br />A. BACKGROUND <br /> <br />Reclamation acting for the Secretary of Interior is called upon, in consultation with the Basin <br />States, to make determinations as to the availability of water for pumping or release from Lake <br />Mead to satisfy consumptive use. As water orders by the Lower Division States are exceeding <br />7.5 MAP, and there are numerous proposals being developed for criteria to address concepts of <br />surplus, shortage, banking, there is increasing need for tools which increase understanding of <br />Colorado River operations, and which facilitate interaction and communication. One of the tools <br />which help in this process are computer models which simulate river operations and allow <br />concerned parties to try different ideas and quickly review the effects. <br /> <br />Reclamation has been developing these computer models to simulate the Colorado River. One <br />of the models that is particularly quick and easy to run is the CRSS-ez Annual Colorado River <br />System Simulation Model (CRSS-ez Model). For exercises which focus on exploring alternative <br />concepts, and developing an appreciation for the Colorado River system, the quick turn around <br />model allows users to more readily "think as you go," creating graphs and data to explore <br />questions and observations as they arise. An in-depth discussion and documentation of the <br />procedures used in the Model can be found in Reclamation's April 1996 Users Manual. <br /> <br />For several years, Reclamation has been using CRSS-ez, presenting graphs of the data from the <br />model runs, and facilitating discussions between and among concerned parties, While the model <br />is a simplified operations model that is quick and "easy" to run, understanding the results, <br />deciphering what they mean and/or imply, and facilitating good communication remains <br />challenging. Statistical and hydrologic terms like probability, standard deviation, time step, <br />stochastic, cumulative probability, critical period of record, wrapping around the hydrologic <br />record, and 1000 traces get tossed about as parties discuss and debate what the data and graphs <br />suggest. The complicated nature of the resource, the Law of the River, and the data increases the <br />difficulty in articulating issues and communicating concerns. The easier to understand, and <br />more clear Reclamation can present the data, the more opportunity there is for the discussions to <br />identify and focus on the key elements relevant to the issues. We may not get people to agree, <br />but hopefully we can remove much of the scientific baggage, such that people clearly understand <br />what they are disagreeing about. With that intent, this document will attempt to add further <br />clarity and understanding to the graphical data produced by CRSS-ez simulations by discussing <br />how the graphs were produced, and stepping though some examples. <br /> <br />B. CRSS-ez MODEL OVERVIEW. <br /> <br />The CRSS-ez Model is a simplified approximation of the Colorado River reservoir system. Of <br />the 60 MAP of Colorado River reservoir storage, SO MAP controlled within two reservoirs. The <br />reservoir system being dominated by the operations of Lake Powell and Lake Mead lends itself <br />to a simplified model for approximating the effects ofIong term operational concepts. As <br />shown in Figure 1, the CRSS-ez model simplifies the 12 reservoir system into three reservoirs <br />and approximates the operation using annual data (rather than more detailed hourly, daily, or <br />montWy data). <br /> <br />1 <br />