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<br />3.2.2.3 Flow Spill Upstream of Foothills Parkway <br /> <br />There are three approximately 18- x 5-ft Reinforced Concrete Box culverts (RCB) below <br />Foothills Parkway. These culverts have limited conveyance capacity and cannot pass the <br />entire flood peak for the 50-, 100-, and 500-year events. The City has indicated it is <br />unlikely future channelization or bridge improvements can or will be made at Foothills <br />Parkway to increase conveyance below the Parkway and make it possible to completely <br />pass the flood peak of these events. As a result, after consultation with the City, it was <br />decided to recognize the spills as part of the flood situation of Wonderland Creek, model <br />the spill, and use flood peak estimates in the HEC-RAS with the spill to define the <br />hydrology of the Creek downstream of the spill. <br /> <br />Spill discharges were modeled using lateral weirs in HEC-RAS. One lateral weir <br />upstream of the Foothills Parkway culverts (labeled 4619 in HEC-RAS) was used to <br />simulate spill flows from the south (right) bank of the Creek. Spills are summarized in <br />Table 9. <br /> <br />Table 9. Summary of Spill Discharge (cfs) Upstream of Foothills Parkway, <br />Wonderland Creek LOMR <br /> <br /> 50-Year Event tOO-Year Event 500- Year Event <br />Discharge in the <br />Channel Just 1460 2190 5330 <br />U stream of the S ill <br />Spill Discharge 210 430 2385 <br />Leavin the Channel <br /> <br />Spill discharges leaving the channel sheetflow to the south following ditches and roads, <br />and flowing through parking lots, entering Goose Creek slightly upstream of its <br />confluence with Wonderland Creek. The spill is confined topographically by railroad <br />tracks to the west and Foothills Parkway to the east. The spill was additionally examined <br />using normal depth calculations. Only shallow flooding is expected in this area. <br /> <br />3.2.2.4 Road and Path Crossings <br /> <br />There are sixteen road crossings of Wonderland Creek within the study area. The road <br />crossings range from small culverts to one bridge. During floods, steams commonly <br />transport debris through the City. To address the potential increase in flood elevations <br />upstream of road crossings caused by debris blockage, the City requires the conveyance <br />of road crossings with potential for debris blockage be reduced. Table 10 identifies the <br />debris blockage for road crossings along Wonderland Creek approved by the City. <br />Blockage is modeled in bridges and culverts by lowering the low chord of the upstream <br />cross section of the opening to reduce the opening by the percent blockage in Table 10. <br /> <br />-23- <br />