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<br />,0, <br /> <br />Mr. Rex A. Burns <br />~ November 24, 1976 <br />.page two <br /> <br /> <br />more strin~ent than the requirements of the criteria <br />"2Zf-"55.1-2U and. 24-65.1-204" (Empha.sis supplied). <br /> <br />It would therefore seem that the very clear meaning of the <br />quoted sections is to the effect that local governments can adopt <br />regulations which are more stringent than those set forth in the model <br />regulation adopted by this board, but cannot adopt regulations which <br />are less stringent. On February 26, 1975, this board adopted a model <br />floodplain regulation pursuant to the specific statutory direction <br />above quoted. This regulation contains the information which you <br />requested in your memorandum and which is hereinafter summarized. <br /> <br />listed in Sections <br /> <br />. <br /> <br />In the model regulation promulgated by this board, we define <br />a floodplain as being an area in and adjacent to a stream, which area <br />is subject to flooding as a result of the occurrence of an intermediate <br />regional flood. In preparing the model regulation, we fully recognized <br />that there is a variable degree of danger in the various areas which <br />might be inundated by an intermediate regional flood. For that reason <br />we divided a floodplain into two possible zones, one being designated <br />as a floodway zone and the other being designated as the low hazard <br />zone. A low hazard zone is defined as that area of a floodplain in <br />which the waters of an intermediate regional flood will not exceed a <br />depth of one and one-half feet. <br /> <br />In applying the above criteria to a number of floodplains <br />which had already been delineated within the state of Colorado, we <br />determined that in every case the low hazard zone was only a very small <br />part of the total floodplain, and that along some reaches of a given <br />stream there was no low hazard area. If there is no low hazard area, <br />then an entire reach of a stream within the floodplain falls within <br />the definition of the floodway zone, and in such cases the terms flood- <br />plain and floodway zone become synonymous. <br /> <br />We also recognized that the occupation of an area where the <br />water depth would reach one and one-half feet could also be hazardous <br />if the water attained sufficient velocity. The model floodplain <br />regulation therefore provides that no structure can be placed in a low <br />hazard zone where the water can be expected to attain a velocity <br />greater than three feet per second unless adequate floodproofing to <br />withstand such velocity is provided. In summary, the o~ly actual <br />requirement that this board has is the identification of a floodplain <br />that would be inundated by an intermediate regional flood (IOO-year <br />flood). We have made provision for the identifioation of a low hazard <br />area for the convenience of local authorities in administering flood- <br />plains. As a general rule therefore, we believe that the low hazard <br />areas of a floodplain ~hould be identified as a part of the floodplain <br />study. The management of such low hazard zones, if any, is then within <br /> <br />. <br />