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<br />0~ <br />---------=-; ,- '-" <br /> <br />;;;;0"/- <br /> <br />"J. ,.;~..3SCC:C~~S) Inc.. <br /> <br /> <br />': " <br /> <br />August 3, 1992 <br /> <br />~';';' ~=,"~ '-3:-:;'-:''0'" ;::. <br /> <br />_ _ _ 0 .~ - <br />.. ,~'" ,c... .~ _ <br /> <br />: C' ., '-~ j' ':::: C'':.::~ :::::2 S : - :.:: <br /> <br />-"_o_,,^, <br /> <br />Mr. Tor.) Smith <br />Michael Baker Jr., Inc.. <br />::,601 Ei,enhower Avenue <br />~:uite 600 <br />Alexaacria, Virginia 22304 <br /> <br />REF: 8924D . OAK CREEK FLOODPLAIN ANID FLOODW A Y . FLORENCE, <br />COLORADO. F'EMA LMMP CONTRACT NO. EMW.90-C.3132 <br /> <br />Dear Mr. Smith: <br /> <br />Love & Associates, Inc. is currently updating the floodplain and flood way for Oak Creek in <br />Florence, Colorado under FEMA's Limited Map Maintenaace Program. The study reach for Oak <br />Creek extends from the confluence with the Arkansas River to the irrigation ditch crossing <br />upstream of the Denver aad Rio Grande Western Railroad (D&RGW). This smd.y was prompted <br />by the rl~cent re-eva1uation of the hydrology for Oak Creek at the confluence with the Arkansas <br />IUver which was prepared this spring by the U.S. Army Corps of Engineers. The re-evaluation <br />reduced the 100-ye:ar peak flow from 22,500 cfs to 16,000 cfs. Love & Associates, Inc. has <br />prepared a detailed hydraulic aaa1ysis for Oak Creek usill,g the updated hydrology. <br /> <br />Due to the complexities in the evaluation aad delineation of the floodplain and floodway for Oak <br />Creek, we originally requested a meeting with FEMA Central Office personnel aad their <br />technical consultants Michael Baker, Jr. Engineers to discuss the hydraulic ,Ulalysis and the <br />options for the delineation of the floodway. However, at your n:quest, in lieu of a meeting we <br />Ere sen(ling you the enclosed information regarding the hydraulic aaalysis. Due to budget <br />constrairlts, before we proceed with the fmalization of the floodplain aad floodway, we request a <br />review of the work to date aad comments regarding how to proceed with th(~ delineation of the <br />floodway. <br /> <br />Floodplain <br /> <br />~:he following is a brief discussion of the hydraulic analysis for Oak Creek. The draft lOO-year <br />floodpl,in is shown on the attached drawings for tlll~ study reach. The HEC-2 input aad output <br />,Ie givea in Appendix A aad are on the enclosed floppy disk. <br /> <br />South of the D&RGW, at the upstream study limit.. 2,940 cfs of the total 16,000 cfs flow splits <br />from the main ch~.nnel aad flows east along the irrigation ditch alignment. This split flow <br />becomes hydraulically disconnected from the main channel. The: main channell flow is reduced <br />by 2,940 cfs which leaves approximately 13,060 cfs in the main channel upstream of the <br />D&RGW. At the railroad the 13,060 cfs is split as follows: 4,250 cfs is conl/e:yed thtough the <br />bridge opening; 8,310 cfs is conveyed over the railroad o:acks, and 500 cfs splits to the east along <br />the railroad. The flow split to the east (500 cfs) combines with the 2,940 cfs :flowing along the <br />