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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 f100dhaZdrds 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, ~nd
<br />
<br />This report cont~i ns ti'lO reI ated dfidlyses: an overall floodplain
<br />~n~lys is for the three creeks (Cedar Creek, Montrose Mroyo, 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 lOO-year recurrence interval flood, as well.
<br />The urban drainage analysis 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 the study streams. The urban analysis will facili-
<br />tate planning for the total urban drainage system, whereas the overall
<br />floodplain analysis relates tc planning for the three major str eams.
<br />This report is organized in the order the analysis was performed.
<br />The first (introductory) section contains the background info rma.tion.
<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 />drainage analysis.
<br />Thethirdsectionofthisrepnrt "Reseorchandllistoryof
<br />Floo~ing", describes the research approach, the <lnilable hydrolo~ic
<br />dH~, Mid a hrief Il;~t()ry Of flo<>ding in th~ M0ntrose ~r.,~.
<br />
<br />The report data inclUd€S flooded arl."a r:I<lpS dl."lineatingthelOO-
<br />year flood boundary, flood profiles and typical floodplaincrosssec-
<br />t ions showing the peak water surfoce elev~t ions for the 10., 50., 100.
<br />and 500-yearfrequency floods.
<br />B. Authorization
<br />
<br />co.
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<br />"to devise and formulate mettlOds, means and plans for
<br />bringing about the greoter utilization of the waters of the
<br />state and the pre~ention of flood damages therefrom and to
<br />designate and approve storm or floodway runoff channels or
<br />b<lsins,ancttomukesuchctesignationsavaiJabletolegisla-
<br />tive ~dies of cities and incor~orated towns; to county
<br />planning com'nissions; and to boards of adjustment of cities;
<br />i ncor~ordted towns; and \:ount ies 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 regulJtions...
<br />"to establ ish, re9uldt~, restrict, and 1 imit SlJcll uses on or
<br />along any storm or floodwater runoff channel orbasin,as
<br />such storm or floodwater run-off Channel orbdsin has been
<br />des i~nated and approved by the ColoradO ~'ater Conserv~tion
<br />BOMd, in order to lessen or avoid the haZJrds to persOIlS and
<br />dalilage to property resulting fro," the accur.,ulation of storm
<br />or f1oodw~ters..."
<br />
<br />The fourth section "Hydrologic Analysis", descri bes the appro~ch
<br />and methods used to define the precipitation i'lhich results in the
<br />runoff and flooding. Hydrology deals with the moisture source: the
<br />amount and pattern of ~recipitdt ion, sub-basin runoff relationships,
<br />and how the flow gets to the stream in question or points 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 tile study strea.n, i.e.,
<br />the "".echanics"cf the flow process. The first part of this fourth
<br />sectic'1 d~d'S wit~ the hJ'd~ol()s:.y of ~he three st~dy st~Od~ j~v~l'l~d 'n
<br />
<br />as stated in Sect ion 30~28.111 for COlJnty ~overn"l('nts and Section 31-
<br />23-301forrnunicipal govern"l€nts of the CnloradoRevised Statutes 1973.
<br />Tl1erefore. ~pon officia I approval of thi 5 report by tt,e Colorado
<br />\;'aterConservationBOdl"d, thedredS described as being i"undatedby tile
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<br />The terms "Intermediate Regional Flood", "100-yearflood",and
<br />"one-percent flood" can be used i nterchangeab ly as they ~re all
<br />defi ned by ~he S<l','Je type of flood l'yent (see G 1 OSSdry). However,
<br />to avoid confusion the term "IOO-ycdr flood" \1i11 tleusedexclu-
<br />sively throughout this report.
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