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<br />EM 1110-2-1406 <br />5 Jan 60 <br /> <br />the determination ,}f .ehe water equivalent of the snowpack, for use in forecasting total volume of <br />runoff during the melt season, 1fethods <if formulating seasonal runoff forecasts, however, aTe <br />not within the scope of this manual. <br /> <br />1~05. PROBLEM OF SNOW HYDROLOGY. A knowledge of certain hasic physical relation- <br />ships is required for tbe intelligent application of snoW hydrology, Since the atmosphere constitutes <br />the immediate source of the earth's moisture supply and nlso regulates the energy exchange within <br />a. iHlsin which in tun g;OVCfIlS snow.melt rat.('sl the scicBce of meteorology is particularly important. <br />Physical principles underlying energy exehan:.':" to the sno\\-pa"k, both from the atmosphere and <br />from the sun, as well as effects of tl", atmosphere on radiation exchange, must be generally understood, <br />In the application of SI1-CW hydrology to the computation of ba,in snowmelt, it is usually <br />necessary first to consider each melt component at a point, under stated conditions of environment. <br />In this regard, the r"lationships may be expressed by mathematical formulas, with constants of <br />proportionality given in the form of coefficients_ Having determined point values from laboratory <br />experiments, the next ~tep consists of utilizing these vulu(ls to determine amounts and distribution <br />over a basin area, considcring variations in environment, as \vcll as in time. This involves pro- <br />cedures which are much less exact Hnd less rigorous dum is the case ,vit,!J point evaluations. It is <br />necessary to deal with basin avcragf'S in major subdivisions of topography and also to deal wiLh <br />averages in time. These requirements lead to the use of indexes to represent basin averages from <br />individual point measurements. Indexes may range in use from simple two-variable relationships <br />to complex multivari"ble st"tistieal "nalysis, <br /> <br />2 <br /> <br />e <br /> <br />e <br /> <br />e <br />