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In practice, the utility of a mat'ne:r.atical ;model lies in its ability <br />to precisely represent over-all behavior of natural systems, and their <br />response to changes in one or more system co;nponents. Accordingly, small <br />•" changes in s}•stem response not otherwise detectable throueh statistical <br />and regional analyses, can often be detected by careful simulation modeling. <br />1. Apotication and Use of t!odels <br />Jones and leaf (1975) have revie,:ed several models developed for <br />engineering hydrology. They vary widely in terms or' complexity and scope, <br />dependong on application. .411 are based on a practical engineering <br />approach lrhich achieves a balance betl,een: (1) theory, (2) available data, <br />and (3) operational objectives and constraints. The successful application <br />of each model depends tc so-.e extent cn empirical derivations of several <br />parzr.•eters and relationships, some of which are unique to the geographic <br />areas for which they ~:~ere originally derived. Accordingly, adaptation of <br />the yodels to other areas, in most cases, requires development of similar <br />er;:pirical relationships lrhich ref?ect nel•r conditions. <br />Recalling the six basic steps in the simulation approach mentioned <br />previousl}', model adaptation is based primarily on trial-and-error solutions <br />(Lumina) to obtain acceptable responses based on historic data. This <br />tuning procedure is repeated until satisfactory verification of observed <br />strearfla.; is obtained. <br />2. Subalyine Mater Balance ttcdel <br /> <br />It is emphasized that a ~:,odel should be well documented and applied <br />to watersheds of the same character for r,hich it was developed. One such <br />model, the "Subalpine 4later Balance ;'odel," ~•rs chosen to simulate v,ater- <br />sheds in the north Fork, since it bras developed and calibrated for the <br />high-elevation subalpine zone of the Central and Southern Rocl:y I.lountains. <br />This dynamic Hydrologic model 1•ras developed by the U.S. Forest Service, <br />and is specifically designed to simulate the hydrologic impacts of <br />uas15: (1) Nlnter Snob: aC'.J-1UIat1Cn, (L) the CnerC}' balGnCe, (3) snch•pack <br />condition, (~;) evapotranspiro:ior•, (5) sno;~mclt, and (5) resultant rater <br />yield on all co~binatiun:, of a•.~~!•'_t, ~,1~,;~~•, ~rlcvaliun, n~~'I lir;r•'.l ,~~•,rr <br />,. <br />