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<br />CHAPTERIl
<br />INTERPRETATION AND USE OF REPORT DATA
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<br />1. T"bl~-6, "Flood Fr~qu~ncy, Elevation and Discharge Data,"
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<br />2. flooded Area Plates I through 10, (IOO~y"ar hequency flood o:lly).
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<br />A. Flood Frequency and Discharge
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<br />l. FloOd profiles On Plates II t;Hough 15, (10-, 50-, 100-, and 500-y~a.
<br />frequencie,).
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<br />This report ~as prepared to be compatible with the H.B. 1041 designation,
<br />Federal Emergency Management Agency (FEMA) flood insurance rate studies, and
<br />can be adopt~d by local governments for regulation purposes. The 5-, 10-,
<br />50-, 100-, and 500-year frequency flood events were used in the analysis.
<br />These flood event probabilities mal' also be represented as having a 20, 10,
<br />2, 1, and 0.2 percent chance of being eq~alled o. exceeded ~n anyone glven
<br />year, respectively.
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<br />4. Typical Cross Sections onP1ates 16 and ]7, (5-, ]D-,50-,and 100-
<br />yea. fr"q~eneies).
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<br />The =cst i~portant use of the IDO-year flood data is fot the description
<br />of the floodplain and its land use regUlation. Th~ Colorado Seate statutes
<br />considet the lOO-year flood as the flood event to be used in desig~ing and
<br />protecting all buildings and structures to be used for human occupancy. This
<br />level of flood protection has teceived nation-wide acceptance.
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<br />The flood profiles ~ay be used in areas where controversy arise. oVer
<br />the 100-year flood elevation shown On the flooded area plates. Since the
<br />flood profiles give the elevstion at a specific point on the reference
<br />line, the high water elevations Can be conveyed to the ground. A number
<br />of control warkers are in place along the study reach which can be used
<br />for this putpose. The ~arkets consist of 3-inch dia~eter bras. caps set
<br />in concrete or a cap and rebar ~hich are stamped with appropriate identi-
<br />fication. The pertinent information and locations of the control markers
<br />are listed in Table-I. Furthet verification and more specific information
<br />concerning these control markers should be obtained fto~ the offices {see
<br />page vii} distributing the reports ptior to any a~tual surveys.
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<br />Infor~tion concctning ~re ftequent flood events is provided to allo~
<br />assessment of the tisks of flood da~ages during lesser floods. Minot roads,
<br />recteation facilities, and livestock structures may often be designed basad
<br />on floods s~aller than tbe IOO-year flood. A higher risk of damage mal' be
<br />acceptable for the design of these type of facilities.
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<br />C. FloodedAreas
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<br />B. FloodElellations
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<br />In Colorado th~ IOO-year flood has been selected to delineate and
<br />regulate flo<,dplsin.. Therefote, thc nooded area OIaps show the IOO-yca~
<br />floodplain boundary for St. Vrain Creek. The mapping has a 2-foot contour
<br />interval and a scale of I-inch equal to 400 feet. If needed, the floodplains
<br />produced hy other frequency floods could be teadily delineated On these maps
<br />usingthetloodptofilcs"ndinform;ltionlnTable-6. Tile flooded a,ea. for
<br />St. V~ain Creek arc presented On P tat cs I (hrough 10.
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<br />I.'ater sutface elevations for the 5-, 10-. 50-,100-, and500-ye"r
<br />flood for St. IIrain Creek can be found in four locat ion~ with in thi S report.
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<br />These locations are as follows:
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<br />The IOO-yeat tloodpl"i", as delinc<lted on ne flOOded atea maps, ",ccts
<br />tlw (cq"irt'm,'nts of House Blll ]1)1,1. U;>0t\of.ficialdesignationoftni..re?On
<br />by the Colorado Water Conservation Board. the d(ea outl ined on the "'a~. ",ay
<br />~o tegulated by local officials.
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