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I I I I I I I I I I I I I I I I I I I General generally 500 to 800 feet wide downstream to l36th Avenue. The street does not create much backwater but the floodplain widens out to 1,200 feet south of l36th Ave. along the west side of the Quail Crossing Subdivision. Approximately 150 cfs flows between houses and into the street right of way at the northwest corner of the subdivision. Flood flows follow the street for 1400 feet before rejoining Quail Creek below Ka1amath Street. Additionally, most of the streets in the west side of the subdivision would experience shallow flooding during the 100-year event. FLOODPLAIN DESCRIPTIONS Flood Hazard Area Delineation Maps showing the limits of the 100-year floodplain are contained in the Appendix. Sheets 1 through 13 pertain to the Quail Creek basin whereas Sheets 14 through 24 cover the McKay Lake basin. Computed water surface profiles for the 10- and 100-year flood events in the Quail Creek basin are shown on Sheets 25 through 32. Similar information for McKay Lake basin is depicted on Sheets 33 through 35. Tables 10 and 11, which follow this section, present floodplain and floodway reference data related to specific cross sections utilized in the hydraulic modelling of the Quail Creek and McKay Lake basins, respectively. Quail Creek and Tributaries Tributary "A" joins Quail Creek at the upstream side of Osage Street. At least 20 houses in this subdivision are subjected to some degree of flooding during the 100-year event. Shallow flooding and street flows place many more structures very close to the floodplain. The floodplain widens out to 1000 feet just upstream of Huron Street due to backwater effects. Shallow flooding occurs north of the Huron Street/136th Avenue intersection and continues in a northeasterly direction. Generally, the floodplain is 300 to 500 feet wide through the subdiv- ision. The Quail Creek floodplain is very well defined at the upper end east of 124th Street. In the 0.7 mile reach above the Sunny Side Estates Subdivision the floodplain widths vary from 50 to 250 feet. Approximately 700 feet east of l24th Street a small farm pond having a surface of one acre would be inundated, Flood flows cross Equity Ditch at the confl uence of Quail Creek and Tributary "0" and follow the natural channel that has historically been used as an irrigation ditch. Within the Sunny Side Estates Subdivision, 2 houses and other structures are in the 100-year floodplain. The irrigation ditch breaks away from the natural drainageway about 0.4 miles west of Lowell Boulevard and, in the past, has provided water to West Lake. Since the irrigation ditch is assumed to be at capacity, shallow flooding in the backyards of the homes on the east side of the subdivision returns to the natural drainageway of Quail Creek. The small culvert under Lowell was assumed to be completely blocked during a 100-year event, as were all the culverts in the study reach with the exception of those that are part of the improved channel through the Quail Crossing Subdivision. Below Huron Street the floodplain is 1000 to 1600 feet wide. Elevations are consistent throughout the area due to backwater caused by Bull Canal and the adjacent maintenance road. Approximately 200 cfs crosses the unpaved extension of l36th Avenue toward the north and east at a depth of about one foot. Shallow flooding occurs at a depth of approximately one foot from this point downstream to where it combines with McKay Lake Basin backwater upstream of 1-25. Between Bull Canal and 1-25 the floodplain is 600 to gOO feet wide measured to the Quail Creek/McKay Lake Basin boundary. For purposes of hydraulic analysis, downstream flows were assumed to remain within their respective basins. The floodplain west of Lowell is approximately 1,300 feet wide. Downstream of Lowell is a large pond at which Tributaries "B" and "c" join Quail Creek. The pond was assumed to be full when the 100-year event occurred. The floodplain is 1,300 to 1,500 feet wide through the pond. Below the pond the floodplain is Following the above stated assumption, flows over 1-25 were computed, assuming the effects of the road embankment only and not including the concrete median barrier. Upstream of 1-25, the backwater effects of the median barrier were accounted for in the floodplain delineation. Approximately 1230 cfs would top the highway toward the south and east at depths of one to two feet. The remaining 2500 cfs would cross the highway at a depth of approximately one foot and would continue toward Big Dry Creek. Quail Creek, along 136th, has a very sma 11 19