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<br /> <br />In response to the Division's Preliminary Adequacy Review, RN-02/PR-02 Trapper Mine, #C-81-010, item 2 <br />(runoff from snowmelt), the following information is submitted. <br />Four sources were researched in an effort to address the Division's snowmelt concerns. These sources <br />included <br />1) Snow Melling Characteristics by George T. Clyde, August 1931, <br />2) .9n t7utline ojlhe 77iermadynamics ojSnow-Melt, W.T. Wilson, 1941, <br />3) Analysis ojHigh Rates ojSnow-Melting, Phillip Light, 1941, and <br />4) 77u National Engineering Handbook, Section 4, Chapter I1, Estimation of Direct Runoff From Snowmelt. <br />While all of these references contained useful and/or interesting information, onty the National Engineering <br />Handbook described a method for which we have data. Far that reason, the Degree-Day Method described <br />in this reference was used. <br />A description of the Degree-Day Method is included in Attachment 2.1 which is a copy of the fourth source <br />referenced above. BrieOy, the method uses the equation: <br />M=KD <br />• where M =the watershed snowmelt in inches per day <br />K = a constant that varies with watershed and climatic conditions <br />D =the number of degree-0ays for a given day. <br />A degree-day is a day with an average temperature one degree above 32°F. <br />Since a National Weather Service station exists at Trapper Mine (Station Index No. OS-1932-2), we have <br />good data regarding high temperatures, low temperatures, snowfall and equivalent moisture on a daily basis. <br />As a result, a snowmelt model can be constructed as descrbed in Attachment 2.1. <br />Attachment 2.2, Historical Data, summarizes snowfall and equivalent moisture data for November through <br />April for the last ten winters beginning with November 1982 and ending with April 1992. A daily average for <br />this 10-year period is shown. Similarty, Attachment 2.3 shows degree-0ay data for the same periods as well <br />as the daily average. Weather station data are provided for reference as Attachment 2.4. <br />Two models based on this data were developed. The first model (Attachment 2.5) uses the 10-year average <br />data. The first three data columns in the model are data from Attachments 2.2 and 2.3. The fourth data <br />column, Snowmelt Potential, is the calculated 24-hour runoff in inches using the equation M = KD and <br />assuming a remaining water equivalent at least equal to the snowmelt potential. In this model, the value K <br />= 0.12 was used. This value is twice the value of 0.06 that describes a condition of north facing slopes of <br />open country (see Attachment 2.1). The value of K = 0.12 is admittedty subjective but will be defended in a <br />• subsequent paragraph. <br />