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I I I I I I I I I I I I I I I I I I I were actually lowered, increasing travel time and storage from existing conditions (see Summary Tables for HEC-2 models Exist, As-Built, Appendix 2c,d), Manning's "n" was varied from section to section according to the type of vegetation encountered, These values were computed by actually measuring sections of the wetted perimeter composed of different types of vegetation, Specialized wetland consultants, as well as various pictorial references (Ref, 6, 7) were consulted to determine a reasonable roughness value for the density, stature and depth of flow for each type of vegetation (Fig, 8). These values were encoded using the NH card for each section through the UCBRP, Flows through the area were varied according to the split flow analysis (Fig, 5c, Table 3), The adjacent Skunk Creek channel was assumed to be running full, and no flows were added to the Boulder Creek floodplain from this source, Cross sectional area used in the flow computations was limited in some sections with reference to the plan view of the site in order to reflect the effective flow, Section 16,1 was encroached from the right to the berm connecting pond three to four, This, in conjunction with the previously mentioned limitations on sections 14 and 16 which describe the Foothills Parkway bridge more accurately reflects the flow of water over the intersection of Arapahoe and Foothills, Section 19,01 was encroached on the right to limit flows passing over the berm between ponds one and two, Sections 19,2 and 20,0 were encroached on the left to restrict flows to pond one, The variable ELSED (X3,2) was used to restrict all pond sections. The area below the normal pond water surface was not used in the flow computations. 3.2.6 Results A rigorous analysis of the flooding situation along the study reach has been performed to determine the extent of flood protection provided by the construction, A complex situation exists above the Foothills Parkway bridge, where three hydraulically independent floodplains converge, Numerous methods were employed to develop an understanding of the interaction of these flows as they mix before going under Foothills Parkway bridge or over the intersection of Foothills and Arapahoe, A one-dimensional model such as HEC-2 is not capable of describing the effects of flows shifting back and forth between overbank and channel, i,e" a variable energy grade line across the section, various efforts were made to describe the amount of flow from the Research Park which overtops the intersection of Foothills Parkway and Arapahoe Avenue, It is apparent that part of the Research Park spill (2,500 cfs) will cross Love & Associatesl Inc. Page 11