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" " IV. Ft.OOOPLAINIIlFOR}IATIOll SOQ-y"..."event The 500-year flood event is useful in making the public ...~...r" that floods larger than the 1aO-year flood ~n and do ocour. aeoause an individual is living outside the lOa-year flood boundary does not mean that he te oompletely safe from flooding_ The 500-year flood event oan alao be used tor regulating high risk develo~nt8 within the flood plain such as nuclear power plants or the Dtorage or Manufacture of toxic or "xploalve materials. The 10-, 50-, 100-, and SOO-year flood event" """re used a" the flood fre- quencies for this flood plain analysis. Thus, the data developed in this report ..ill be compatible not only for t'aqul"tlon P'J"p"su and H.B. 1041 designations, but aleo for FederaL Emergency ~nagement Agency flood insurance rate studies. These various flood events have an average occurrence of once in the n~r of years as indicated. For example, the 100-year flood occurs, on the average, once in a 'OO-year period and has a one percent chance of being equaled or exceeded in any given year. The particular uses for the various flood evonts in addition to those stated above are aa follows. I I Upon official approval of this report by the COlorado water Conservation Board, the area outlined by ths 100-year flcod boundary will be designated a flood plain area and may be regulated accordingly by the local officials. The flood profiles may be used in areaa where controversy arises over the 100-year flood boundary on the flood plain boundary figures. Since the flood , profile figures give the elevations and distanoe or stationing fr~ a known point. the high water elevations can he surveyed on the ground to alleviate any discrepancies on the base map. SUrvey control markers exist in the field in the vicinities of both drainage paths 4S indicated in Figure 1. 10- and 50-Year Events Information regarding theee more frequent events is especially useful for future engineering studies and land use planning purposes related to minor road systems, Minor channel improv~nts, the location of parks and recreational facilities. agricultural l~nds, and appurtenant structures. ~Qr struct~res and uses of this type on the smaller tributaries and in areas where the high risk of structural fail~re Is econo~cally feasible and the ha~ard to life and property nonexistent, the uee of the ~re frequent events may be considered. Extent of Flooding The areas inundated by the 100- and 500-year flood events for the Lola Fark Tributary and saBtern Flow path are outlined in Figures 1S and 19. The 'OO-yeilr flood in the upper reaches ot the L:>la ParJ< Tributary will be fair ly well confined within a 150-foot-wide band directly affecting only two houses. Velocities here average about four fps. Between Highway 60 (Broad Street) and Elm Street, ponding occurs behind the highway embankment. Flood waters spread oVer the wide, tlat area bound by ~rriett ~venue on the eaat and a diagonal line from Elm Street between Irene and Josephine ~venUe5 to the intersection of Kathlnen hvenue and Broad Street on the west. Sixteen ho~s, the fire stil- tion. and several ~ercial businesses will be inundated. The pond reduces flo... veloeiel" below one font l"'r "econ" (fp8) allowlng"edl"'''ntt ."Bettl""ut all' docutll.ented in previous floods. Flood depths reach up to four f",et Boutheast of the intersection of Josephine ~ven"e and Highway 60. Flow overtopping Highway 60 will spill into a 1J_aere tow area bound by the Great Western &ailroad embankment on the north and east and Highway 60 on the south end ~st. The hydraulic analysis assumed the Thompson and Platte Ditch to be flowing full leaving ov"rtopp!ng of th" Great Western ~i1road 100-YearEvent The 100-year floo<1 ~v"nt. ""'y al.", be "Red for engin....ring de...!gn pu..po..os whera a lower riBk of failure than the 10- or 50-year fiood is dA..i....". nowever, the most important use of the 100-year flood event 11es In the flood plaln designation and land use regulation as set forth in the state statutes. 'l'~e .:>lOate ot Colorado oonsiders 10;'.. IGO-y".u (r"'l.""""y fl<><><l.... me fl<XJ(] event to be us..d in ~signing and protecting structur..s and dwellings for h"",anoccupatioll. Therefore, "II flood plain regul"Uons are baeed upon the 100_y"ar flood. ~lso, the are.. which would be inundated by the 'OO-year flood ""'y be <i<llln....ted as an are4 of state interest u set forth in H.B. 1041 (the state'slandusebilll.