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I I I I I I I I I I I I I I I I I I I The procedure used to determine the CUHP parameters is outlined in the Urban Drai nage and Flood Control Di st ri ct, Urban Storm Drai nage Criteri a Manua l. Recent modifi cat ions were app lied to the procedure as recommended by the UDFCD. The Phase B hydrology is the same as presented for the Phase A and FHAD Reports. Detailed documentation of the hydrologic analysis for Tucker Gulch is available at the office of the UDFCD separate from this report. Table IV-2 summarizes the drainage basin parameters and equations used for the CUHP model. TABLE IV-2 DRAINAGE BASIN PARAMETERS FOR CUHP* TUCKER GULCH - Kenneys Run - (mi2) (mi) (mi) (ft/ft) (Existing) (Future) Basin Area L l Slope la ~t C I It ~ ---{;a -p -a T-17 9.02 7.16 3.75 .06** 2% .55 .47 no change T-89 0.60 1.53 0.68 .055 10% .26 .27 23% .22 .31 C-12 1.16 2.97 1.46 .06** 3% .38 .34 4% .37 .33 C-3 0.32 1.14 0.44 .050 4% .25 .27 20% .19 .27 T-10 0.33 1.23 0.57 .039 20% .20 .27 24% .20 .30 *CUHP - Colorado Urban Hydrograph Procedure **Maximum slope of .06 was assumed for steep basins for use with CUHP. Ia - percent impervious area The hydrologic analysis for Kenneys Run involved dividing the major basin into 50 sub-basins and utilizing the E.P.A.'s Storm Water Management Model (SWMM) with modifications developed by the Missouri River Division, Corps of Engi- neers. The SWMM model was calibrated from a more general hydrologic analysis using the Colorado Urban Hydrograph Procedure. The results were checked for reasonableness and the condition of the existing drainage system was incorpor- ated into the final watershed routing. Minor revisions were incorporated into the SWMM model for the Phase B study by sub-dividing the East Fork watershed into two additional sub-basins to provide better definition of flows tributary to the planned detention basins. The two additional sub-basins are shown as Sub-Basins 49 and 50 on the Basin Boundary Map (Figures IV-I). A minor revi- sion was also made to the channel routing upstream of 24th Street on the West Fork to better represent the improved channel condition. The primary model revisions relate to the preliminary designs of the three planned detention facilities. The overall results were not significantly different than those reported in Phase A. Detailed documentation of this hydrologic analysis is also available at the offices of the Urban Drainage and Flood Control District. Table IV-3 contains a computer printout from the SWMM model listing the drainage basin and channel routing parameters for the improved drainageway and future basin conditions. CUHP Equations C = K (ll )0.18 t t ca S 0.24 o C = P K AO.15 P t in which, Kt = time coefficient related to Ia l = hydraulic length of basin in (miles) lca = centroidal length of basin in (miles) Flood Discharges t = C (ll )0.3 P t ca qp = 640 C P t P Tp = tp + 0.5 tu Qp = q A P S = average stream slope in (ft/ft) 0 Ct = unit hydrograph coefficient refl ecting time to peak P = peaking coefficient related to 1 a A = drainage area of basin in (mi.2) Resulting peak discharges for the improved and unimproved conditions are tabulated in Table IV-4. Flood discharge probability profiles for the 2-, 5-, 10-, and 100-year runoff events are shown in Figure IV-2 for Tucker-Gulch and Cressmans Gulch and Figures 1V-4 and IV-5 for Kenneys Run. Typical lOa-year flood hydr09raphs for Tucker Gulch and Cressmans Gulch are shown in Figure IV-3. Design hydrographs for Kenneys Run are shown on Figures IV-6 and IV-7. C = unit hydrograph coefficient reflecting p peak discharge t = time to peak of unit hydrograph from p midpoint of unit rainfall in (hours) qp = unit peak of unit hydrograph in (cfs/mi.2) tu = time of unit rainfall duration in (hours) Tp = time to peak of unit hydrograph in (hours) Qp = peak discharge of unit hydrograph in (cfs) IV-3