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<br />May 20,1992
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<br />fi ",.- - 2. A~socict~s, Inc.
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<br />Dr. 101m Liou, P.E., P.I ..S.
<br />Federal E=eency Management ^sency
<br />Region vm - Denver Federal Center
<br />Building 710. Box 'Z'i2l'i7
<br />Denver, Colorado 80225-0267
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<br />Mr, Ken Bruch
<br />Ql)' Manager
<br />Cil)' Hall
<br />:roo We., Main
<br />Florence, Colorado 81226
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<br />REF: 8924F - OAK CREEK LMMP - FLOODW A Y
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<br />Dear John and Ken:
<br />
<br />During our May 13dl meeling, the lllethodology \\sed to d.eu:nDine the FEMA lOO-year floodplain
<br />fOT Oak Creek was presented to representatives from the City of Florence (City). FEMA, the U,g,
<br />A.'my Corps of En8;ineer~, and concerned citizens. The method.ology used in our analysis was
<br />generally accepted by aU panics, At the time of the meeting, the floodway had not yet been
<br />detennined. llowever, based upon our cursory review of the hydraulic model, the fioodway for
<br />Oak Creek would bI~ significantly wider in places than the currently I1;gulated floodway, The City
<br />expressed some cOllcern over the increase in the floodwllY. Thus, lI.S agreed in o\lr meeting, the
<br />enclosed drawings show the cun-ently regulated floodway taken fmm the 1984 FIS and an
<br />approximate flood~/ay compute\! u'om the LMMP HEC.2 hydraulic model. The purpose of the
<br />comparison is to illustrate the potential difference in the twO floodways,
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<br />The LMMP floorlway was delineated using the LMMP HI-:C.Z modeL lIS a single model as opposed
<br />to the three models presented in the May 13 meeting. The floodway shown on the drawings was
<br />delineated based 011 the melhodoLogy discussed in the May 13 meeting, A Single model assumes
<br />the water sulface is leveL over the width of the floodplain and thatllll portions of the floodplain are
<br />hydraulically conMetec!. Thus. the basp. water surface used in the calculation of the fioodway is
<br />not the Sllme as thai: computed using the tllree SCpllrll1e models. The flOOdway ~.iteria for FEMA is
<br />a maximum of a Cine-foot rise in the lOO-yell! water surface, The LMMP floodway shown is
<br />simply a fIrst cut '~stimate using a sinele modelllpproaeh, As seen, in some places along the
<br />channel, the twO fl()odways are significantly different.
<br />
<br />This lnfonnation c,n the approximate flOOdway should be used as a starting point for discussions
<br />50 that llI\ agreement can be reach~ between the City of Florence and FEMA lIS to how to procted
<br />with the LMMP SUlUY for Oak Creek within the City.
<br />
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