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<br />: NTRODU CT I O~~
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<br />lUU-yearflood (Intermediate Regional FloOd)lcan be designated as
<br />flood hazard areas and their use regulated accordingly by the local
<br />agencies.
<br />C. Use of Report
<br />1. Format
<br />
<br />A. Purpose and Scope
<br />This re~ort was prepared to guide locd 1 officials in pl anning the
<br />use and regulation of the floodplain areas sue Ii that floodhaZdrds d nd
<br />futurefloodddlndgesdre',11nimized. It includes informotionon
<br />historical floods, ~xist ; ng factnrs which influence the flood hazard,
<br />the nature and extent of probable future f1 cods. as \~e 11 as an urban
<br />drainage analysis.
<br />
<br />This report was authorized by the Colorado ~ater
<br />Board in joint sponsorship with the City of Montrose,
<br />Montrose County.
<br />The Board's power and duty is
<br />
<br />Conservation
<br />ColoradO,and
<br />
<br />This report contains ti'lO related dfidlyses: an overall floodplain
<br />analysis for the three creeks (CedarCreek,MontroseMroyo, and Dry
<br />Cedar Creek), and an urban area draina~e analysis.
<br />TtJeoverall floodpldinanalysisfocusedonthethreestudy
<br />strea,"s: Cedar Creek, Montrose Arroyo, and Dry Cedar Creek. Water
<br />surface elevations were defined for the 10-, 50-, 100., and 500-year
<br />events. The floodplainooundary for the three study strearas was delin-
<br />eated for the 100-year recurrence interval flood, as well.
<br />The urban drainage analysfs focused on the urban area, and runoff
<br />deri ved from the urban area, as opposed to the draina~e conveyed
<br />through Montrose by tne study streams. The urban analysis will facili-
<br />tate planning for the total urban drainage system, whereas the overall
<br />floodplain analysis relates to planning for the three major str eams.
<br />This report is organized in the order the analysis was perforrned.
<br />The first (introductory) section contains the background info rmation.
<br />The second section describes the physical features of the study area:
<br />first, of the drainage basins and study streams for the overall
<br />floodplain analysis; and second, of the area covered in tile ,wban
<br />drafnaye analysis.
<br />The third section of this report "Reseorchandllistoryof
<br />Floo~ing", describes the research approach, the <lnilable hydrolo~ic
<br /><iH~, Mid a hrief h;~t()ry of flo<>ding in th~ M0ntrose ~r.,a.
<br />
<br />The report data inclUd€S flooded arl."a r:I<lpS dl."lineat1ngthelOO-
<br />year flood boundary, flood profiles and typical floodplain cross sec-
<br />tions showing the peak water surface elevations for the 10., 50. ,100.
<br />and 500-yearfrequency floods.
<br />8, Authorization
<br />
<br />...
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<br />"to devise and formulate mettlOds, means and plans for
<br />bringing about the greoter utflization of the waters of the
<br />state and th€ prevention of flood damages therefrom and to
<br />designate and approve storm or floodway runoff channels or
<br />basfns, and to make such designations avaiJable to legisla-
<br />tive ~dies of cities and incor~orated towns; to county
<br />planningCOJll1lissions; and to boards of adjustment of cities;
<br />incorporated towns; and t:Qunties of this state..."
<br />
<br />as stated in S~ction 37-60-106 (1) (c) of the ColoradO Revlscd Statutes
<br />1913.
<br />
<br />The cities, incorporated towns, and counties within the study area
<br />may provide zoning regulations...
<br />"to establ ish. regulat~, restrict, and 1 imit such uses on or
<br />along any storm Or floodwater runoff channel orbasin,as
<br />such storm or floodwater run-off channel or basin has been
<br />des ignated and approved by the ColoradO ~'ater Conservation
<br />80drd, in order to lessen or avoid the hazards to persons and
<br />dalilage to property resulting fro," the accur.,ulation of storm
<br />or floodwaters..."
<br />
<br />The fourth section "Hydrologic Analysis",describes the appro ach
<br />and methods used to define the precipitation i'lhich results in the
<br />runoff and flooding. Hydrology deals with tnemoisture source: the
<br />amount and pattern of precipitation, sub-basin runoff relationships,
<br />and how the flol'l gets to the stream in question or ~oints of interest.
<br />This is t~ be dist inguished from the hydraul ic analysis. which cxa<.1ines
<br />i'lhat happens to the water once it !las reached the study streM, i.e.,
<br />the ",,<cchanics"cf the flow process. The first part of this fourth
<br />sectic'1 d~d'S wit~ the hJ'drolos:J of ~he three st~dy ~trca~ j~v~l'l~d 'n
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<br />as stated in Sect ion 30~28.111 for county governlllents and Section 31-
<br />23-301forlllunicipal governlll€nts of the Colorado Revised Statutes 1973.
<br />Tl1ercfore. ~pon officirll rlpproval of thi 5 report by tl,e Colorado
<br />"'dter Conservat ion BOMd, the drCdS described as bein~ inundated by the
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<br />The terms "Intermediate Regional Flood", "lOO-ye~r flood", and
<br />"one-percent flood" can be ~sed interchangeably as they are all
<br />defi ned by ~he S<l,ne type of flood "yent (see G 1 05>ory). However,
<br />to avoid ,onfusion thctl!rm "IOO-year flood" \1i11 tleusedex,lu-
<br />siYely throughout this report.
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