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<br />CONCLUSION <br />riMA will continue to use the fixed-bed models to delineate the floc <br />boundariea and 48fin. the flooding water aurface elevations for the Notte <br />Flood In8uranc. StucU... The colllllLittee did not give IBM the I1'Odel ..lee <br />criteria, however, the committee did recommend that there is a need to <br />undertake an eftort to classify natural rivers in terms of their hydrauli <br />geomorphological cbaracteristies to provide for selec~ion and 4pplicatior <br />appropriate model. that use appropriate constituent formulations for 8e~ <br />di8charqe, channel roughne.s, and bank erodibility. <br /> <br />models to predict the river flood stages along the erodible channels, and to <br />know the availability ot current erodible-bed. IllOdeU. In .d.dition, it .b .lao <br />essential to FEMAls hydrologist or hydraulic engin.ers ~o h.v. a par.=eter or <br />a set of parameters formed from the phy.ic.l .le..nts of flow ey.t.. either by <br />field observation or by mathematic tormulation, in order to 9rovide the <br />engineer with a tool to select the beat model tor the flood inaurance study. <br /> <br />EVALUATION OF EXISTING ERODIBLE-BED MODELS FOR FLOOD INSURANCE STUDY <br />In August of 1981, rEMA had a contract with the National Academy at <br />Science (NAS) to evaluate the current existing erodibl.~bed ~del. which can <br />be used to compute the flood stages of elevation. tor the National Flood <br />Insurance program. NAS organized a ep.cial committe. re.pon.ible tor the <br />technical evaluation. This committee was chosen to include experts in river <br />engineering, hydraulics, hYdrology And river morphology and vith regard tor <br />appropriate balance. Dr. John F. Kennedy vas the chairman of the committee. <br />Four modelers and six models were selected by the committe. for this <br />study I <br /> <br />1. <br /> <br />Dr. Ranjan Ariatburai - Model SEDIMENT (4") <br /> <br />2. <br /> <br />Dr. Howard Chang - Model Fluvial (II) <br /> <br />J. <br /> <br />Hydrologic Sngineering Center, U.S. Army Corps at Engin..rs - <br />Mooel HEC-6 <br /> <br />4. <br /> <br />Simons, Li & Associates, Inc., Fort eollins, Colorado - <br />Models HEC2SR, KUWASER and UUWSR <br /> <br />Three study rivers were selected. on the basis ot hi.torically h.ving <br />experienced flaeh-flood with appreciable river-bed chang.. and chann.l <br />migr.tion during floods characterized by stable, contined channel. and <br />unstable, disturbed channels. Those three t..t c.... ar.. <br /> <br />,. San Lorenzo River located in Santa Cruz County in northern <br />California/ <br /> <br />2. San Dieguito River located. in San Diego County in south.rn <br />California, and <br /> <br />3. Salt River located in MaracOpa County, Arizona. <br /> <br />J,32 <br /> <br />Committee's conclusions, <br />Th. prinoipal deficienci.. ot the erodible-bed ~del., <br /> <br />1. <br /> <br />2. <br /> <br />unr.liable formulation ot the sediment discharge capacity <br />tlow., <br />inadequate formulation of the variable friction tactor ot <br />erodible-~d flOW., <br />inadequate tor~lation ot the mechanics of bed armoring an <br />their ett.cta on .e41aent-4i.oharqe capacity, friction tac <br />.na, <br />inadequate formulation of the machanics of bank er08ion an <br />underaining, <br />Th. effect of river-bed degradation and aggradation on water-.u <br />el.vation ~ring flood p....g. i. much smaller th.n the ettect. <br />the uncertainti.s of channel roughne.. or tlov friction tactor, <br />sedim.nt input, .nd !nitial channel geQmetry. <br /> <br />.. <br /> <br />b. <br /> <br />o. <br /> <br />d. <br /> <br />J. <br /> <br />The available input data on channel geometry, bed-material <br />charact.ristics generally are inadequate to p.rmit full utili~a <br />of the capabilities of erOdible-bed Dadels. <br />For the ..v.r.ly dist.u.rbed rivera which have experienced extrem. <br />looal degoradation or aggradation thro\l9h man's intervention, <br />utilization ot erodible-bed mod.l. might be used in flood tnaur, <br />.tudi... <br />Becau.. at the deficiencies mentioned above, rigid-boundary modi <br />8hould be utiliz.d for flood insurance .tud~es, and attention ~ <br />be d1X'ect.d to",.r4 $JtULin.1ng the aensitivity of the.. lQOde1s to <br />unc.rtaintie. and variations in channel rouqhne.., channel goeom <br />and channel slope. <br />It is unlikely that . moveable-bed model will be forthcoming- th <br />applicabl. to all typ'. of river.. In other words, ..ch model <br />be more dependable tor the river ot the ty~ for vhich it was <br />develo98d. <br /> <br />4. <br /> <br />5. <br /> <br />6. <br /> <br />J,JJ <br />