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<br />French Creek <br /> <br />710 cfs <br /> <br />OR~f1 <br /> <br />Illinois Gulch <br /> <br />330 cfs <br /> <br />sawmill Gulch <br /> <br />120 cfs <br /> <br />Methodoloqy <br /> <br />Water surface elevations for the 100-year flood were computed <br />through the use of the U.s. Army Corps of Engineers HEC-2 step <br />backwater computer program (Corps of Engineers, 1982). <br /> <br />The stream distances along the Blue River are measured from <br />Cemetary Road. The stream distances along all tributaries of the <br />Blue River are measured from their confluence with the Blue River. <br /> <br />The starting water surface elevation for the Blue River was based <br />on culvert flow computations and a weir flow determination for the <br />component of flow overtopping Valley Brook Road. A similar <br />computation was performed on French Creek to obtain the starting <br />water surface elevation. On Sawmill Creek, the starting water <br />surface is based on inlet control condition for the storm sewer <br />which conveys flows from beneath Peak Avenue and Ski Hill Road to <br />the Blue River. Illinois Gulch initial starting water surface <br />elevation is based on the water surface level of the Maggie Pond <br />during a 100-year flood. <br /> <br />There are numerous culverts on the Blue River and, its three <br />tributaries studied. At most of these culverts, the design charts <br />in "Handbook of Steel Drainage and Highway Construction" (American <br />Iron and Steel Institute, 1971) and "Concrete Pipe Design Manaual" <br />(American Concrete Pipe Association, 1985) were utilized to <br />determine the water surface immediately upstream of the culvert. <br />In cases where the roadway was overtopped, weir flow calculations <br />were applied to determine the amount of overtopping. Hydraulics <br />of the vertical pipe spillway on French Creek just above Magnum <br />Bomum Drive were computed using procedures from "Design of Small <br />Dams" (U.S. Bureau of ReClamation, 1987). <br /> <br />Data <br /> <br />Besides the hydrology, other major data required for analyzing the <br />flood levels are cross-sectional geometry and flow resistance. The <br />sources for each of these data category are described below. <br /> <br />The cross-sections and geometric data such as culvert sizes, <br />inverts, bridge dimensions, and roadway elevations were obtained <br />from a variety of sources. The original FEMA study information <br /> <br />29 <br />