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assumed for the first 300 feet, and then shallow flow was assumed until intercepted by a <br />diversion channel (Haan, et al, 1994). The parameters used in these calculations are <br />presented in Table 2. Various velocity coefficients for overland flow used in these <br />calculations are presented in Table 3 (Haan, et al, 1994). Diversion channel flow was <br />modeled using the kinematic-wave method within HEC-HMS. <br />Per DRMS guidance, and consistent with the existing permit, the Probable Maximum <br />Precipitation (PMP) was selected as the design storm for the TDA in its reclamation <br />configuration. Both the general and local storm events, determined using procedures <br />detailed in the NOAA Hydrometeorological Report 55a (HMR55a) (Hansen, et al, 1998) <br />were considered, with the general storm being the most critical for the reclamation <br />configuration. The PMP general storm will result in 18.42 inches of rainfall over a 24 <br />hour period. It should be noted that the Colorado Office of the State Engineer is in the <br />process of preparing an updated Extreme Precipitation Analysis Tool (EPAT) to provide <br />more refined estimates of extreme precipitation events statewide. Although this tool is <br />not yet functional for the San Luis Valley, it is anticipated that it may be used in final <br />design of the TDA spillway and associated facilities. As such, the analyses and designs <br />presented herein are considered appropriate for cost estimating purposes with the <br />realization that the final design flows, and therefore designs, may vary from those shown <br />when EPAT becomes available for this area. <br />Figure 1 illustrates the final contributing upgradient watershed and subbasin boundaries <br />as well as the longest overland flow path for each subbasin. Storm water control <br />structures associated with the final reclamation configuration are shown on Figure 2. The <br />existing South Diversion will remain in place after reclamation, however this diversion <br />was designed to carry flows up to the 100-year event, and not the PMP event. Therefore, <br />it is expected that the South Diversion would overtop during events significantly larger <br />than the 100-year storm. <br />Storm flows in excess of the capacity of the existing diversion channels will flow on to <br />the reclaimed TDA surface where it will be routed to the reclamation spillway in the <br />north abutment of the dam. Calculations show that there is ample storage volume