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,. In this model, the highest estimated runoff tram snowmelt is 0.36 inches on March 4th, well below the 1.4", 10-year, 24-hour event used in our hydrologic models. Using the 10-year average has a tendency to levelize the peaks in snowfall and temperature and therefore the model loses some credibility. In consideration of this weakness, a second model was developed using that year that most closely represents the average year ta snowfall. The winter of 1986-87 with a snowfall of 76.8" most closely approaches the 10-year average of 78.3". The second model (Attachment 2.6) uses actual snowfall, equivalent moisture and degree-0ay data for 1986- 87 and a value of K = 0.12 in the equation M = KD. In order to check the validity of the value for K, the CMLRD inspection report for March 1987 was pulled to check for a documented observation of snow depth. On March 19, 1987 Mike Long and Jeft Deckler reported "approximately 3-0 inches of snow covered the site" (see Attachment 2.7, March 1987 Inspection Report). This seems consistent with the model for this same period. A lower value of K would add to the modeled snowpack while a higher value would subvact. The model indicates that a 3"~" snowpack would be probable in [he form of new snow with old wrote[ snowpack having melted during the previous weeks. In the second model, the highest estimated runoffs from snowmelt were 0.68 inches on April 20 representing the immediate melting of a 7" snow event and 0.72" on February 14. These values are also well below the • 1.4", 10-year, 24-hour event used in our hydrologic models. Predicting the runoff from snowmelt has not received the rigorous treatment in the literature that rainfall has. The "art" o[ prediction of snowmelt runoff is much less sophisticated and somewhat subjective when site specific data and history is not available. The degreeday method neglects evaporation which can be as high as 2.1" of snowpack per month (Clyde) and oversimplifies the effect of temperature (e.g. 12/9/90 shows 0 degree days although the temperature reached 49° on [ha[ day). Based on the models developed using the methodology described, it appears that a snowmelt event exceeding 1.4" in 24 hours is unlikely. Given Trapper's excellent compliance record and some extraordinary reclamation measures [o control erosion and runoff, we feel that our current rainfall event assumptions are valid and should remain valid until our performance in the field shows otherwise. •.