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<br />CONC1.US10N
<br />FEMA wUl continue eo u..e the tbed-bed IllOde18 to del!n..t.e the n.
<br />boundar!e' And detine th. tloo41n9 water aurtace .levation. ta~ the NAt
<br />Flood In,ur.no. Stl,1di... The oollllllJ.t:.tee cUd not 9ive l"BKA ~e model ,.1,
<br />criterie} hwever, the COllllU.tte. 414 reooll\lMlnd that then 18 a need to
<br />undertake an ettort to ol...lty n.tu.rAl river. in ta~ ot their hydreu
<br />geomorphologio.l. oharaoteri.tic. to prov!de lor aeltH.tion Clnd Applioati'
<br />Appropriate =od.l, that u.. appropttate con8tituent torml,11ation8 for ae
<br />di,ohar98, chanpel rou9hn..', and b6nk erodibility.
<br />
<br />8Od81. to predict the river tlood atage' along" the .rodibl. ch.nnel., and to
<br />know th. .v.il.bility of cl,1rrent .rodibl.-b.d .od.la. In additlon, lt 1, .1'0
<br />....ntl.l to FEMA'. hydrolo91't or hYdraUliO .n91ne.r' to have . par...t.r or
<br />. ..t at parameter' for~d from the phyalcal el...nta of flov .yat.. .ith.r by
<br />ti.ld ob.eTv.tion or by mathematic formul.tion, in order to provide the
<br />engin..t with. tool to .el.ct the ~.t DOd.l for the flood inaurance .tudy.
<br />
<br />EV~LUATION or EXISTING ERODIBLE-BED MODELS FOR FLOOD INSURANCE S~UO~
<br />In Al,1gu8t ot 1981, lEMA had a contr.ct with the NationAl Ac.d.~ ot
<br />Bci.nce (NAB) to evaluate the current exiatin9 erodible-bed .odele which can
<br />be used to compute the flood atage. at elevation. tor the National FlOOd
<br />Inal,1rance progr.m. NAS org.nized A .p.cial c~ttee re.pon.iol. tor the
<br />t.chnical evaluation. Thi. co~tt.e wa. cho..n to include expert. in river
<br />engineerlnq, hydraulic., hydrology and riv.r DOTphology and with regard for
<br />appropriate balance_ Or. John F. xennedy wa. the chairman at the co~ttee.
<br />Four modelera and eix model. were .eL.cted by the o~tt.e tor thi.
<br />.tudy.
<br />
<br />1.
<br />
<br />Dr. Ranjan Ariatburai - MOdel SEDIMENT (4H)
<br />
<br />2.
<br />
<br />Dr. Howard Ch.nq - Model Pluvial (II)
<br />
<br />3.
<br />
<br />Hydrologic Engineering Cent.r, U.S. Aray Corp_ at Engin.er. -
<br />Hodel KEC;-6
<br />
<br />4.
<br />
<br />Simone. Li . ~.aoci.te., Inc., Fort Collin8, Color.do _
<br />Hod.l8 HEC26R, KUWASER and UUWSR
<br />
<br />Three 8tudy rivera were aelected on the baai. ot hi8torically having
<br />experienced fl.ah-flood with appreciable river-bed chan~. and ch~nel
<br />migration during tlooda ch.racteriz&4 QY atabl., ccnf1ne4 channele and
<br />un'table, di.turbed channel.. Tho.e three te.t ~&. .ra,
<br />
<br />1.
<br />
<br />San Lorenzo River located in Santa Cru& COl,1nty in northern
<br />California,
<br />
<br />2.
<br />
<br />San Dieguito River locat.d in San Die90 COunty in .outharn
<br />Calitornia, .nd
<br />
<br />3.
<br />
<br />Salt River loc.ted in Har.copa County, ~izona.
<br />
<br />3.32
<br />
<br />':
<br />
<br />Co~tt.e'a concluaion..
<br />
<br />,. The prJ.nc1pal 4..ric1eno1e' of the erodible-bed. ll\Od.ele.
<br />
<br />.. uilreliable formulation ot the .ed.im.nt diacharge c.paoit
<br />How.,
<br />
<br />b. In.dequate tormul.tlon of the v.rlable frlction tactor 0
<br />e1'o41))1e-'be4 flow.,
<br />
<br />c.
<br />
<br />inadequate formulat1on of the machanic. of bed armorinq
<br />ttle1r ethct. on. .ediMnt...di.chuge capacity, triction t
<br />.Ad)
<br />
<br />d.
<br />
<br />inad.quate formul.tion of the mechanic. of bank .r08ion
<br />und.era.ininq.
<br />
<br />2.
<br />
<br />Th. efhct ot riv.r-bed deqrad&tion and .ggradation on water-I
<br />el.v.t.1on durinv flood p.....V. i. much araalbr than the efho'
<br />the uncert.int,ie. of chann.l rouwhn... or flow friotion faotoJ
<br />..dim.At input, an4 initial ohannel geom.try.
<br />
<br />3.
<br />
<br />The available input dat. on ~hannel Veom.try, bed-mAterial
<br />character1etic. generally are inadequate to permit tull utilil
<br />of the c.pabil1U.. ot erod.ible-bed modeb.
<br />
<br />..
<br />
<br />For 'the ,everely 41.turbed river. whioh have experienc.d .xtrt
<br />100.1 degradat.lon or &Vgr&4ation throuqh man'. intervention,
<br />ut.1U..aation ot uo41b1.e-be4 1D04e~. ught be una in flood in....
<br />. tud1e..
<br />
<br />5.
<br />
<br />Bacau.e of the d..f101enoi.. mentioned .bove, riqid.-boundary me
<br />ahould ~ utilized for f1004 1na~ranc. atud1.., and attention
<br />be directed toward ex~nlnV the .en.itlvity ot the.e model. 1
<br />~no.rt.lntl.. and variatione in chann.l rouCf'hn..., channel qec
<br />and chann.l 'lope.
<br />
<br />6.
<br />
<br />It 11 unlikely that & IIlOv.able-b.d model ",111 be forthcomin9 1
<br />apvl1cable to .11 typ.e ot: river.. In other worda, .I.ch 1lKl4e:
<br />be more depencSabl. tor the river of the type tor whloh it va.
<br />de",elope4.
<br />
<br />3.33
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