|
<br />~ser's manual. The hydraulic mdius w", comput~d [or typ;cal cros,"scct;ons of the drainagc",ay and
<br />uscdin Fqu.11;(\n2todet~rmincManning's"n".
<br />
<br />of imperviou' ar~a within a ,ub-watershed. Thc .<ub.watcrsheds with substantially higher or lowcr
<br />u,,;t rTlnoff mtes were checked to on~llre tbat the CUI IP ,ub-watcrshed parametc", juslified the runoff
<br />
<br />Cxi,tingsyslem.fotlheb",ditlcn"wmut;JlI,\,u"dclingindudcd,,11 S1ructurcs that arecurrellUy III
<br />place,~tnlcturesthatarenp"etedtobeconslructcdin thenearordist'ntflltureaspanoflhePlum
<br />Cred Outtail Systcms Plan arc not included in the !la,din" nm, 'These fUlure facilities will be
<br />modeled as parToflhealtcmalivc, cvaluatioll phase. The SWMM rouling olement:; for thc sludy area
<br />arc sllown on Drawing~ 15 through 20, Tile SW",lM routing demenls for thc off-site area are shown
<br />on Drawing 21, A schematic of the rouling e1~mem~ for the West section of the study ~rea is
<br />presenled io figures 2 through 6, A ,chcmalic oftl1erout;ng elements for theS oUlheasl section of
<br />the study area is shown in figure:; 7lhrough 9, A schematic of the routing e1emenls for the East
<br />seelion ofth,. study area i'providcdby Figures 10 through 14,aod a ,ehemalicoflhero\lling
<br />elemems for the off.,ile area;:; presemed in Figure IS.
<br />
<br />valu~s
<br />
<br />fhop_ak IOO.year runoff values forlho future land use condition, will bc us cd as lhe basclincmodcl
<br />formasterplann;ngandfloodplamdcl;neation,
<br />
<br />It;s imponant to oote that these flows assume that sedimenl is nOt suspended in the l1ow, Suspended
<br />sediment can significantly iner~asc Ihe flow volume and thus Ihe now rale. During the 1965 fl""d
<br />on Plum Creek. the bed wa, scoured several feet, which wO\lld probably have created a high
<br />eoncet\lraliol\ of:;\l:;pended sediments during the flood event,
<br />
<br />I
<br />,
<br />,
<br />
<br />Sample S\l,iMM illpm files for the West section ofllle 'ludy 'rea, tho Southeast section of the s!lld}
<br />area. and the East s~ction oflhe sludy area arc included in Appendix S, The off-sile routing is
<br />inclodedintbesestudyareatnodcls,
<br />
<br />E. MOIWl.lNr, Il.fSl'L TS
<br />
<br />rilc o<nput from SW~lM i, a bydrogrJph at each ,je,igTl point and routing eloment. Tahles 16. 17.
<br />"t\d l~ provide the peak rUlloffaleadL de,ign point and routing clement in lhe '!IIdy are,,', \Vesl
<br />S(;~tiOT1. Southoast soclion. Jnd the [:lSI section. r~speelivdy, T<lblc 19 sU"'nl"rizes lhe 100.ye'lr
<br />peak runoff \:IILle. at s"\'eral key lo~ations at\d e"mpare~ the flow values to Ihosc \,lilized bv the
<br />Federal hm"rsell~Y Management Agency (FEMA) for llood insurance administr:llioo purpo'o>
<br />
<br />(FE:MA. !9Cl3), T:Jbl~ ~O 00'''''''''''.' l!'~ !~"'"V ,,~ '.',",,"! !'bt\ Cr~,k!'.:; "Iim"t~d by n:MA i', iI.~i
<br />
<br />e.:imat"d hy lhil srudy. For the IOO-year eve"l. the flow used by FEMA und tile !low suggested f<1l'
<br />use ill Ihi:! ,tud)' are relali\'ely similar (within 15%), FE:>lA used the SCS synthetic hyd'o~'apli
<br />procedure with" 24-h(lur ~Wnl\ JuratioT\ and a Type IlA raiot;11] distriblll;t\t\.
<br />
<br />fhe unit runoff (cfs/a,"o) "f Ihc ;Oil-year n"", for e~ch 'LIb. watershed was comp'ucd to lho
<br />LJllp"rviou,nc" <>1 \he Illt"re land use e'ltlall",ns 10 CMC"K tor iI\COTlSI~lenc;es '" the nLn"IT
<br />"obd,'linn' f;~llc~, I ~ t -: "'" I ~ ~"" .,1" rhi, ,:.""':'''i~''', I"r 'h,: IJ.,'.". ;ecl;,,~ "f I!~~ >'t""y ':""':.
<br />
<br />t!,~ Suulb<'~'l ,;c~t'.m ofthc ,wd\' area. and lh~ rast .'ccli"n of the ,mdy arco. re'pe~live!v in ~e,,,,.,.:\i.
<br />it \\,-",Id~" "~pectcd tllal (he !In;l r\H1"tTw<'uld mnc~s~ rrq\("l".'[1~lly" illl~" it\~reas";n the poroom
<br />
<br />,
<br />
<br />6
<br />
|