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<br />Evaluation of Existing Mathematical Fluvial Models <br />for National Flood Insurance Studies <br /> <br />by <br /> <br />John Liou 1 <br /> <br />'!'he prilaary objective af this investigation was to determine whether <br />river-bed degradation 4u.ring flood passage has an effect on flood stage <br />that should be inoorpo~ated into the calculation of flood-~one li.tts. <br />The ancilliary questiOQ is whether flood-zoning studies should make use <br />of flood-Bta..ge predictJ.on IIQdels which incorporate river-bed IIObility and <br />degradation/aqqradatlOtl, instead of utilizing fixed-bed ao4e18, which <br />have been eliP10yed ber*tofore. 'l'he study involved application of six <br />flow- and sedJAent-roatin9 ~la for alluvial streuas to *tudy reaches <br />of the &an LoreQZO, sa.. DieCjUito, and Salt Riven, for which relatively <br />COGIplete input data V8t'e aft11able. 'i'he developen of the individual <br />.odela: were CCDai.si~d to perforw. the numerical st.ulations using their <br />.....la. <br /> <br />FrOll. the resultA of 1:be studies, it vas exmclu4e4 that the effect. of <br />riftr-be4 degradation &ftd a99%'adation on vater-eurface elevatlon 6J.ring <br />flood passage is -.cb ..-Uer than the effeeta of the uncertainties of <br />channel roughness or flow friction factor, MdUlent input, and initial <br />channel qeoMtJ:y. Moreover, the available 1npu.t 4ata on cba~l <br />qe<*etry, be4-tlateri&1 cbaracterbtlcs, etC., ~nerally are inadequate to <br />penit full utilization of t:he capabilities of erod1ble-~ ~ls. <br />Therefore, except iD eas.. of ....rely 4.laturbed r1 vera which have <br />experienced extre.e loc&l degradation or aggradation through IUD' Ii inter- <br />vention, utilization Of erodible-bed ~ls instead of fixed-bed .odels <br />cannot be justified in flood-insurance atudies. <br /> <br />BACKGROUND OF NATIONAL FLOOD INSURANCE PROGRAM <br /> <br />For decades, the aatiQnal response to flood d.1suter8 vas ejenerally <br />lla1.ted to building flood. <xmtrel workll (daas, le~s, seawalls, etc.) and <br />providinq disaster relief t:o flood vict.ias. 'l'his approach did not reduce <br />lOS8es or diecoura.ge WW'is~ ~~nt and in some instances actually <br />encouraged a4ditiooal devet.op.ent. 'l'o ~d the problea, the public could <br />not buy flood coveraqe froll insurance co.lP<<nlea, and buildlnq techniques to <br />rilllduce flood daaage to new construction were often overlook.ed. In the face of <br />mounting flood losses and !escalating coets to the general taxpllyers, Congress <br />created the National Flood. Inaurance Progra. (NFIP) in order to llitigate <br />future 4aaage and provide protection. for property ownen aqailUJt potential <br />"loases. Congress estabUshed the NFIP with the passage of the National Flood <br /> <br />'Pe4eral z.erqency Manaq<eWlent Agency ae9ion VIII, t>enver, <br />Colorado. <br /> <br />3.29 <br />