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<br />considered as a qualitative value rather than an absolute value, The model results should be <br /> <br /> <br />viewed as showing that the buildings will cause the water surface elevation to increase <br /> <br /> <br />significantly rather than the buildings will cause a 4,5 foot increase in water depth, Figures <br /> <br /> <br />9 and 10 show the area south of Mill Street without the development constructed and with <br /> <br /> <br />th", development in place, respectively, By comparing these two contour maps, the increase <br /> <br /> <br />in depth and area of increased depth is readily apparent. The depth of flow north of the <br /> <br /> <br />proposed development would increase from 1.5 feet to 5.5 feet. <br /> <br />C, SNOWMELT ANALYSIS - NATURAL ONLY <br /> <br /> <br />1. Introduction <br /> <br /> <br />Snowmelt from Aspen Mountain in the Spring and early Summer causes flow and sediment <br /> <br /> <br />problems in the City of Aspen, Usually the magnitude of the flow associated with snowmelt <br /> <br /> <br />is relatively small but of a long duration. As the sediment-laden runoff encounters the <br /> <br /> <br />relatively flat slopes in the City, the sediment settles out of the flow and is deposited in the <br /> <br /> <br />stream, channels, streets, and storm sewers, The quantity of sediment is relatively small in <br /> <br /> <br />comparison to the mud floods and mudflows previously discussed, These flows and deposits <br /> <br /> <br />constitute more of a maintenance problem as opposed to the risks of property losses and loss <br /> <br /> <br />of life that the mudflows and mud floods produce, <br /> <br />2, HEC-I <br /> <br />a, <br /> <br />Introduction <br /> <br /> <br />FLO-2D cannot calculate the runoff due to snowmelt, and the equations used by <br /> <br /> <br />FLO- 2D to estimate sediment transport (as opposed to mud floods or mudflows) are <br /> <br /> <br />not valid on steep slopes such as those found on Aspen Mountain, HEC-I, written <br /> <br /> <br />by the Corps of Engineers, can calculate the runoff associated with snowmelt, but <br /> <br /> <br />it has no sediment transport capabilities, <br /> <br />'. <br /> <br />HEC-I can produce estimates of snowmelt by two different methods: the degree-day <br /> <br /> <br />method and the energy-budget method, The degree-day method was chosen mainly <br /> <br /> <br />due to the availability of the data for use in the model. The input data needed for the <br /> <br /> <br />degree-day method is the temperature as it varies over time, In this case, it is the <br /> <br />17 <br /> <br />, <br />, <br />'I <br /> <br />, <br />I <br />.,j <br />" <br />''I. <br />