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it <br /> The model bases parameters on the City topography maps and hand level surveys <br /> for selected hydraulic controls. Instrument surveys of sensitive features such as <br /> extended weirs, levees, channels, and flow splits have not been undertaken. <br /> However, the study does indicate where such efforts would be more important. <br /> The model does not simulate a local storm, but the regional event assumed by the <br /> Corps. Some of the West Valley flow paths particularly along Dry Creek Ditch <br /> No. 2 would probably be dominated more by an intense local storm than by spills <br /> ' from South Boulder Creek. <br /> Ultimately we believe that refined South Boulder Creek hydrology complying with <br /> regional and NOAA practices will result in larger flows than those indicated herein. <br /> SPECIFIC NOTES AND ASSUMPTIONS <br /> The SWMM model elements cannot simulate flow in both directions, such as may <br /> very well occur through the Viele culvert under the on ramp from Foothills to <br /> Highway 36 eastbound. Due to this and the likely breach of the lower levee, spills <br /> from South Boulder Creek are assumed to first discharge through the local 48-inch <br /> culvert under the on ramp to its capacity, with the remaining flow traveling west to <br /> the Viele channel and offline storage upstream of the ramp. <br /> ' The Anderson Ditch culvert under the on ramp and freeway was assumed to be 25 <br /> percent plugged based on our observations. <br /> The Anderson Ditch culvert may consist of an 8-foot by 4-foot concrete box culvert <br /> at the upstream end and switch to either a double 54-inch RCP or double 48-inch <br /> RCP at the downstream end. To simplify the calculations a single 8-foot by 4-foot <br /> culvert was assumed for the entire length. <br /> The exact outlet configurations of the Viele side channel storage and of the Table <br /> Mesa storage were not known. The best information available was used in the <br /> model. The outlets should probably be surveyed and the correct discharge storage <br /> relationships used. <br /> The size and route of the existing storm sewer running along Foothills Parkway has <br /> ' not been verified. The initial model assumes a 2-foot diameter pipe discharging to <br /> the west storage at Foothills and Baseline. <br /> The Thunderbird Lake at Pawnee Drive and Mohawk Drive was ignored for flood <br /> control purposes as directed by the City. <br /> ' The area to the west of Foothills Parkway and Baseline Road along Inca Parkway, <br /> Mohawk Drive, and the surrounding area have storm sewers that appear to <br /> IV - 3 <br />