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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />Sloans Lake Flood Routing <br /> <br />Hydrographs <br /> <br />The hydrologic investigation for the Sloans lake Basin included the <br />study of storage and outlet characteristics of Sloans Lake to determine <br />the impact of the Lake on the design floods. Curves designating stage <br />vs. discharge for the outlet structure and stage vs. storage for the <br />Lake were developed. Flood routed hydrographs through Sloans Lake for <br />the design storms of 5-, 10-, 25- and 100-year recurrence intervals <br />were also developed. This study revealed that the peak overflow values <br />at the outlet structure discharging into Sub-basin A3 for the four design <br />rainfalls were as follows: <br /> <br />Design storm hydrographs ~ere computed for a 2 hour duration at each of the <br />design points (except for Point A) for the four storm frequencies (5-, 10-, <br />25- and 100-year) under cons[deratlon for the projected total development <br />condition. These hydrographs, developed In accordance with the Colorado Urban <br />Hydrograph Procedure as outlined In the Runoff Section of the Urban Storm <br />Drainage Criteria Manual were used to determine peak design flows for each sub- <br />basin and design point within the study area. Graphical Illustrations of these <br />hydrographs are presented In Figures B-1 through B-15 In Appendix B. <br /> <br /> Water Surface'~ Total Sloans Sloans Lake Sloans lake <br />Storm Flood Flood Out 1 et Overflow <br />F req uency E levati on Oi scharge CarCi ty Olscharfe <br /> ( ft) (cfs) cfs) (cfs <br />5-year 5309.35 32 32 0 <br />I O-yea r 5309.79 34 34 0 <br />25-year 5310.04 48 36 12 <br />1 OO-yea r 5310.43 166 38 128 <br />*Sloans Lake overflow elevation is 5,310 (top of bike path). <br /> <br />Hydrographs at the Colfax Avenue/Federal Boulevard interchange (Sub-basin A) <br />were not developed due to the lack of any dralnageway point-of-concentratlon <br />for runoff flows. Peak flows in Sub-basin A were approximated by summing the <br />Sub-basin Al flow and that portion of flow from Sub-basins A2 and A3 which is <br />diverted to Sub-basin A. Two assumptions Inherent to this procedure Included: <br /> <br />I. The peak flows from the contributory sub-basins (AI, A2 and A3) <br />occur approximately at the same time; <br /> <br />2. The local raInfall in the Immediate vlc[nl ty of the Interchange is re- <br />latively Insignificant. <br /> <br />- FLOOD PLAIN EVALUATION - <br /> <br />A summary of peak flood flows for the projected total developed condition for <br />each frequency Is also provided on the Discharge Probability Curves shown on <br />FIgures B-16 through B-18 In Appendix B. <br /> <br />Upon completion of the hydrologic Investigation, a flood plain evalua- <br />tion was made on each of the dralnageways within the Basin for each of <br />the storm frequencies and conditions. The evaluation procedure involved <br />the use of the Corps of Engineers HEC-2 Water Surface Profile Computer <br />Program. This program was developed by the Corps of Engineers at the <br /> <br />A summary of the peak flows at each of the design points for each frequency is <br />presented In Table 2. <br /> <br />8 <br />