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<br />D, HYDRAULICS <br /> <br />The SWMM program then routes the hydrographs from one sub-basin to the next along drainage <br /> <br /> <br />routes or reaches. The reaches can be a stonn sewer, channel, street flow, or a combination of the <br /> <br /> <br />various types of reach elements, Figure 5 shows a schematic drawing of the SWMM routing, and <br /> <br /> <br />Figure 6 provides the design points and reach elements used in SWMM. Table 4 supplies the <br /> <br /> <br />characteristics of each drainage reach, <br /> <br />Table 5 provides the peak flow for each return period along each drainage reach and design point <br />in the City of Aspen, In general, these drainage reaches correspond to the major drainage facilities <br />(stonn sewers, streets, and channels) in Aspen, The exceptions are the reach along Garmisch Street <br />from Hopkins to Main and the reach along Mill Street from Main to Bleeker, Flow along these <br />reaches will be discussed in the following section. <br /> <br />E. DRAINAGE SYSTEM CAPACITY <br /> <br />The existing drainage system conveyingrunofffrom Aspen Mountain and the City to the Roaring <br />Fork Riveris comprised of stonn sewers, streets (serving as open channels), and open channels, <br />The SWM1v! model provides a general flow analysis from Aspen Mountain and through the City <br />of Aspen, To provide a greater level of detail and a better analysis of the existing drainage <br />facilities within the City, the SWNlM drainage reaches were further subdivided within the City, <br />The reaches defming the existing City drainage facilities are shown in Figures 7 and 8. Each of the <br />major drainage facilities in Aspen is designated by a letter, <br /> <br />Since the flow rate could not be detennined directly from the SWMM output for some of the <br />drainage facilities (Garmisch Street from Hopkins to Main and Mill Street from Main to Bleeker), <br />the flow along these "sub-routes" was detennined indirectly, The unknown flow at a point in a <br />basin can be detennined fr~m the known flow downstream of the location and the drainage areas <br />at the desired location and at the downstream location. This relationship is shown below (USBR, <br />Flood Hydrology Manual, 1989): <br />Q *A 0.' <br />Q I 2 <br />2 = A 0.5 <br />I <br /> <br />4 <br /> <br />I <br /> <br />,_,lee <br />