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<br />. '. '. <br /> <br />I. <br />II. <br />III. <br />IV. <br /> <br />Introduction <br />Generalized SPS Est1lates tor SIIIall Dra1J:I8Ce B&lI1J1s <br />SPS Estimates tor IArge Draillage Bu1J18 <br />Projects tor 'Which SPF Eat1JDl.tes are Re~u1red. <br /> <br />e <br /> <br />1-03. SHX:IFICATIONS OF A STANDAKI PROJECT STO!I( (Abbrev. "SPS). <br /> <br />a. The "sttlZldb.rd project storm" ",otimate tor a particular <br />drainage area mo. se~BO" vf year in "hich sno"-melt is IlDt a _Jor COl18ider- <br />atioD should repre~er.\. the ClOst severe fiood-produciug raintall depth-area- <br />duration relationship Me: isohyetal pattern ot any storm that 18 considered <br />reasonably character!..\. 1C of the region in \/bich the drainage bas1D is lo- <br />cated, giving consiOe~a"ion to the runoft characteristics and existence ot <br />water regulation st.rtJct.u..."s in .the basin. In d,1riving standa.rd project <br />storm rainfall est1m8te~ ~pplicable to oebsond and ~reas in "hich melting <br />sno" may contribute u ~ul:",t=t.ia,'" 'volUllle of runotf to the standard project <br />flood hydrograph, lli>P''Qi'" .a,e aJlo"anceo fvr SllO" melt are included with <br />and consiclered ad a part of tne ~o;andard projec& stonn raintall quantities <br />in computing the SPF hydror,raph. Where floods are predominatly the resul't <br />of melting sno". the SPF eot.uno.te io based on est1lllates of the most critical <br />combinations of SDO", temperature and vater losses considered reasonably <br />characteristic of the region. <br /> <br />. <br /> <br />b. The te= "s\:;olra" :J.6 used 1;.1 'r. broad sel18e to _an IIIIY <br />period or sequence of rain:lall events that _y contribute to critical t100d <br />events in the particular drainuge o.>.sil1 under study. <br /> <br />c. The te:r:n "re61011" uS used above 18 construed to 1Dclude the <br />area surroundiug the given basi:.1 1<:1 "l11ch stOl'lll producing tactors are sub- <br />stantially comparable; i.e., the geooral area vithin vh1ch meteorological <br />intluences and topography are sufficiently alike to permit adjustment ot <br />storm data to a COllllllO.:' bas1s of comparison vith practical degree ot <br />reliability. Such a "regi.:m" includes a very large area in the eastern <br />halt of the United States \/be;:oe relief i3 generally IIlOderate, IlI1d relatively <br />small areas in certain sections of the vp.stern ihllted States "\lere extreme <br />topography is encountered. <br /> <br />e <br /> <br />d. A genere.l comparison ot "'Y;'"'1Ill storms ot record in the <br />region, supplemented my m~,eor~lv6ical 1nves,igations, serve as a basis 1D <br />selecting ra1D1'all cri .eria '~o' repre&",nt the IOlOst severe storm that is COD- <br />sidered "reasonably cnarac',e.-iatic" ot a rellion. Certain stOl'lU ot extra- <br />ordinary severit:r -:r be ..U;u1nateo. &S too unU8U&.1 IlI1d extreme to "arrant <br />adoption as the standar~ ~roJ~c~ storm. <br /> <br />1-04. ST~ :r~~~ i':WOD \AobNV. US"") <br /> <br />a. In genen.l ttll'lll8, the atanciArd plXlJect tlood llIaybe c1et1Ded <br />&8 a hydrograph repre,,,!,,,t":J6 ~-tt trooa ttA atlODdard project ston! (llI1d!or <br />lDO" melt) as deri..",.. ";; '9<-.'-(;'.''''9;1 1-0:;... T"ue SPF _y have more thlm & <br />lingle peak it thede doN .he .-esult ot runoff tl'OlIl the SPS. <br /> <br />2 <br /> <br />-- <br />