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I I I I I I I I I I I I I I I I I I I Erosion control in the form of riprap was designed and placed with Bear Creek Fling NO.1. A copy of the design calculations from "Final Drainage Study, Bear Pag,3 2 Sep'iember 8, 1992 HYDROLOGY The hydrology used for Bear Creek Tributary No. 5 was taken from the Jefferson County FIS Table 1, Summary of Discharges. A copy of this table is included in Appendix A of this study. The 10-, 50-, 100-, and 500-year peak discharges for the tributary within the reach of study is 150, 320, 380 and 660 cfs, respectively. HYDRAULICS At the time the Flood Insurance Study was completed, the drainageway was a fairly deep channel with steep side slopes and sloping easterly through the area of study at approximately a 3.4 percent gradient. Between the time that the FEMA mapping took place, 1977, and the time the FIS was adopted by Jefferson County in 1988, the storm sewer was constructed in several phases by different parties. The storm sewer system which conveys flow in the tributary, currently consists of 60 inch and 84 inch reinforced concrete pipe at a gradient of approximately 4 percent. The alignment within Block 3 of the Bear Creek Filing No. 2 begins downstream of South Zinnia Street, follows the alignment of West Auburn Place right-of.way and easl3ment, then ieaves Block 3 at the westerly property line between lots 23 and 24, the City of Lakewood Corporate limit. A copy of the storm sewer as,built plan as provided by the owner is included in Appendix D. Also included in Appendix D is a copy of Sheet R3 of the construction pians for Bear Creek Village Subdivision Filing No.1 which shows the extension of 30 LF of 84 inch RCP and outlet erosion protection. The existing storm sewer system was analyzed at the upstream end utilizing FHWA culvert charts assuming inlet control which was then ver~ied with the computer prol~ram "Storm Drain Analysis" developed by the County of Los Angelos. The analysis shows that the 10" 50- and 100-year peak discharge flows are contained within the pipe. The 500'year peak discharge flow will overtop West Yale Avenue with approximately 280 cfs flowing overland through Block 3 and the property to the west in the City of Lakewood. Normal depth calculations were done at sections through Block 3 to determine the extent of the Overland 500-year flood boundary. The computer program "Storm Drain Analysis" was used to determine the flood pro/i1es in the pipe for the 10-, 50- and 100,year storm events. The hydraulic caleulations, including output from "Storm Drain Analysis", is provided in Appendix B. A pian view of the study area showing the 100- and 500-year flood boundaries and a profile showing the 10-, 50-,100- and 500-year flood profiles are included in Appendix C.