FLOOD10401 - Laserfiche WebLink

Home Browse Search

I I I I I I. I I I I I I I I I I I I I A second expression is the following equation modified from the original equation initially proposed by Hathway: Te = ((2Ln)/(3*S^0.5))^0.47 Where:Tc = Time of concentration (minutes) L = Channel length (feet) S = Mean slope of the basin n = Manning's roughness coefficient Final Te values were determined by adding travel times for the various conveyance elements to the initial overland flow time. Six major detention structures have been included in the hydrologic model. These structures are North and South Catamount Reservoirs, Crystal Creek Reservoir, Manitou Reservoir, lake Moraine, and Big Tooth Reservoir. Smaller detention structures were not considered in the hydrologic analysis because the effects of such structures would not be seen on the mainstream of Fountain Creek. These facilities do not have a dedicated flood control function and as such provide only incidental alteration of flood flow release. Routing of flow in the hydrologic model was accomplished using the Muskingum- Cunge method. Th is rout i ng techn i que is a new method of hydrograph rout i ng available within HEC-l version 4.0. Parameters used in this method for each individual reach or sub-basin include the length, slope, Manning's roughness coefficient, type of channel, bottom width of the channel, and channel side slope. Within the HEC-l computer program, rainfall is input and runoff is calculated for each individual sub-basin. Definition of rainfall and runoff information is described in more detail in following sections of this report. This runoff is either combined with runoff from another basin, routed through a reach, or routed through a detention structure, to establish discharges at various points throughout the Fountain Creek basin. Combination points are denoteq by "DP" and a numerical value (i .e., DP27) within the HEC-1 input data. Where DP is a abbreviation for design point and the numerical value is a location identifier. Channel and reservoir routing is denoted by "RT" and a numerical value (i.e., RT 131). Similar to the combination points, the RT is an abbreviation for routing of flow and the numerical value is a location identifier. At all design points a minimum of two and a maximum of five hydrographs were combined to determine the outflow hydrograph at that specific point. Design point peak flows for the Fountain Creek mainstream are presented in Tables 4.7-4 and 4.7-5. Design point hYdrographs for select locations along Fountain Creek are presented in Figures 4.7-1, 4.7-2 and 4.7-3 for existing and future conditions. 4.0-12