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APPENDIX F-I <br />" HYDROLOGIC S1N~'JLATION h10DELING: <br />SUQALPINE WATER BALANCE MODEL <br />The modeling approach involves six basic steps: <br />(1) Construction of a dynamic mathe~~~atical model in which important <br />interactions bet+veen system components are defined. <br />(2) Programming and execution of the model over a period of time on <br />a digital computer. <br />(3) Co..~parison of model results against all pertinent available data. <br />(The regional approach can be effectively used for model <br />validation.) <br />(4) Revision (tuning) of the model until it is acceptable as a <br />representation of the actual system. <br />(5) Alteration of certain model components in order to represent <br />changes in the real system. - <br />The foregoing process is often called "simulation." Qecause the model <br />represents the real dynamic system, changes in system behavior can be <br />traced directly to their causes. <br />At each step in the above sequence, the prior steps often need to be <br />revised. The whole procedure is not unlike the development of an aircraft <br />or automobile, +vhere repeated design chanoes and testing ultimately result <br />in an operational prototype. <br />No model is "perfect;" not now, or ever, will there be "complete" <br />information about any natural system. t•loreover, there are no principles <br />to nuide the selection of model content. Failure to include the important <br />system variables in a model can destroy its validity as an operational <br />te?1. Accordingly, models should be constructed, used and interpreted by' <br />specialists who are familiar with the natural systems and understand <br />d}namic system analysis. <br />• <br />