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• 12 <br />that once snowmelt begins, it continues until no snow is left. This second as- <br />sumption is not accurate for the study area. In the study area, snow will ac- <br />cumulate and melt throughout thn winter season. The first assumption is feasible <br />for small drainage areas, but becomes less feasible as the drainage area increases. <br />snowmelt runoff was first estimated for each area using the 10- and 25-year <br />seasonal precipitation. The 10- and 25-year seasonal precipitation ras determined <br />using precipitation-probability data presented in Chapter IV on climotologieal <br />information. The results of the snowmelt analysis are presented in Table 3. <br />C Comparison of the peak discharge estimated for snowmelt with that estimated for <br />a rainfall event shwa that the peak discharge due to a rainfall event is larger. <br />~' Thus, the peak discharge produced by a rainfall event will control for design of <br />structures for peak discharges. However, the wlume of runoff estimated for <br />• snowmelt is greater than that estimated for a rainfall event and snovmelt-runoff <br />Volume should be considered in the design of structures for runoff volume, spe- <br />cifically sediment ponds. In consideration of runoff wlume produced by snowmelt, <br />two important points should be kept in mind: (1) the assumptions made by the model <br />used to develop the baseline hydrograph; and (2) the wlume of runoff from snowmelt <br />occurs over a period of two to three months, whereas the runoff from a rainfall <br />event has a duration from one to three days. 71 discussion of use and application <br />of the snowmelt-runoff volumes for the design of sediment ponds rill be presented <br />in the final report entitled 'Determination of 8ydrologie Consequences.' <br />State regulations require design of sediment pond structures for runoff <br />wlume produced by a 10-year event. No other drainages or sediment control <br />structures require design for runoff wlume. Thus, no further estimation of <br />runoff due to snowmelt for the 2- or 100-year events was done. <br />• <br />