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I I I I HYDROIDGIC AND HYDRAULIC DETERMINATIONS Flood CharacterisU.cs I I Tallman Gulch Tributary No. during rainstorms does the tributary are caused by rainstorm runoff. 1 is have an intermittent stream. measurable flow. Flood Only flows Hydrologic Anal YSiE~ I I I II I A hydrological analysis of flows in Tallman Gulch Tributary No. 1 was done by Emmons, Henry, Meisenheimer and Gende, Inc. (EHMG) (see Ref. 2) The 10-year and 100-year peak flows were calculated by EHMG for the Hidden River Subdivision whose lower boundary lies approximately 0.6 miles upstream of the mouth of Tallman Gulch Tributary No. 1. The drainage area upstream of the Hidden River Subdivision lower boundary is 0.9 square miles. Because the drainage area at the mouth of this tributary is only 0.2 square miles larger, EHMG's hydrological analysis is applied to the study reach without alteration. I I I I I I The methodology applied by EHMG was the Colorado Urban Hydrograph Procedure (CUHP) as described in Urban Drainage and Flood Control District's (UDFCD) Storm Drainage Criteria Manual (Ref. 9). Important assumptions were 1:,% impervious area and a 100-year rainfall of 2.9 inches. (1 hour storm). CWCB has calculated the 50-year peak flow using the CUHP. The 500-.year peak flow was extrapolated from a plot of the 10-, 50-, and 100-year peak flows on log probability paper. Flows determined by E~~G and CWCB and used in this study are as follows: I 4 Peak Flows for Tallman Gulch Tributary No. 1 near the Mouth Recurrence Interval (years) 10 50 100 500 Peak Flow -[efS;- 184 368 579 990 EHHG Inc. It should be noted that the were presented to the Town and were subsequently approved. hydrologic calculations performed by of Parker for review by Hydrodynamics, A plot of the frequency discharge curve for Tallman Gulch Tributary No. 1 is shown in Figure 1. I