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8888 Legend Flood Level 8887 _ 1800 cfs WS 100yr D 100 year 8886 .. D 50 year ~ WS 50yr c 8885 .. _ 25 year 0 WS 25yr D 10 year ~ > 8884 Cross- ill WS 10yr [jJ 8883 . Section WS 5yr 8882 . WS 2yr 8881 0 5 10 15 20 25 30 35 Station (ft) (left) Figure 2.2.13. Overtopping of Windy Gulch culvert cross-section (right) Figure 2.2.14. Flooding caused by Windy Gulch culvert Entrance to Army Corps Flume The Army Corps constructed large levees to guide flood flows into the masonry flume. Flooding originating from Windy Gulch may circumvent the levees and flow towards downtown Creede. However, flooding and overbank flows caused by Willow Creek should re-enter the forebay upstream of the levees, and HEC-RAS modeling indicates that flood-flows from Willow Creek should be contained by the levees and enter the masonry flume. Figure 2.2.15 shows a closer view of the approach levees and the results of the flood water surface elevation modeling. Survey points along the top west edge of the levee are also shown as well as the distance from the survey point to the water surface elevation of the 100-year flood (shown in yellow). For the 100-year flood, a three-foot freeboard is maintained to the top of the constructed portion of the levees. Just beyond the north tip of the constructed levees, a small dip does exist that has slightly less than a 3-foot freeboard (2.77 ft). The Army Corps requires a three-foot freeboard to recognize that 100-year flood flows will enter the masonry flume. It is noted that flood levels are often rounded to the nearest 1 foot in typical flood studies. However, a small modification to the approach levees or channel configuration to guarantee this 3-foot freeboard, and mitigation of the 100-year flooding problem at the Windy Gulch culvert may be needed for the Army Corps to recognize that structures in downtown Creede are not located in the floodplain. 2-26