Distribution Restriction Statement
Distribution Restriction Statement
Distribution Restriction Statement
I. IRTRODUCTIOB
1..01. :REFERENCES.
2
b. IDtiltration loaaea aaa'UIDI!d ill coarputiD& I"UDDt1' traa tb.e SPS
ahould correspond to thoee considered reaaoDAbly likely to occur duril::lg
at.oraa ot nch MgD.1 tude, estillated on the buia of dat.a obt&ined fl"'CCI the
~ a ot ra1Dt&l.l-I"UDot1' relatiooa 1D -.jor tlooda ot record.
3
which hyd.rographa tor periods antecedent tc and subsequent to a 8tazulard
proJect 8tom ot 120-houre duration are represented by tlovs actually
observed 1D the baaiD, V1th such adjustments as •Y be deemed appropriate
after a seaeral study ot flood and storm characteristics tD tbe resion
involved.
5
b. '!'be tena "deaigD. tl.ood" or "reservoir daaigD tl.ood" ~
be applied to tbe .:>at aevere tlood that a particular reservoir -.y be
capable ot cODtroll.iDs UDder u adopted plan at ope:rat1cm but auch uase
baa little value except 'Where the reservoir ia provided pr1-.r.lly tar
pl'Otect1cm at damage centers near tbe dam. Uaual.ly selection at the tlood
control al.lacation in a reservoir 1a gavemed by c:cmaideration ot tlood
coDtrol ettecta at several locaticma downatre1111, involviDg the &D&l.ysia
ot a m.iber at t1ood aituationa. Accardagl.y, application ot the tem
"design flood" or "reservoir 4eaisn flood" should be l.1mited to tboae
caaee 1D vbich the tem is actually 1Ddicative of the baaia tor a tlood
control storage allocation, .,re detaUed criteria being specified tor
other cases.
6
II. GERERALIZED BPS ESTIMA1'C) FOR SIW.L DRADIAOE BASIJI3
2-ol. ODDAL
7
b. Plate 2. SPS IDdez Ra1.Dfill. '!'be i.oh,.,-tea oa Plate 2
repreaat the •z1•n awraae depth o~ ra1Dtall 1a 24 houre over 200
square ld.l.ea 4Dr1Jag the RaD4ard proJect ato:na, vhich is equal to approzi-
•te~ Jto to 6o percent ot the •z1•• possible raiDtall :bldicated OD
Plate l, V1th a seDI!T'&l. average ot about 50 percent. Plate 2 vu prep&Nd
by rec!w:illg iaoh,eta em Plate 1 to 50 percent ot orJ.ciD&l ftl.uea 8Dd re-
ahapillg the 1aoh,eta ill certa1D regione by .oc!erate amounts to ccmtom
V1 th npplelleDt&r)" etudiea ot raiDt&l.l. cbarac:ter1at1ce ill thoae regiou
Dv1Dg c!eYelopDent lltudiea a1a1lar charta wre prepared tor Hlected anu
rtmeiDS t1"'0Il lO to 20,000 square llilea IIDd ato:na 4urat1ou trcm 6 to 96
houn. It vu tOUDd that depth-area-c!uration ftl.uea tor these several
charta bore a reaecmabl;y ccmaistent relat1cmah1p to ~uea shown on
PlAte 2• Accord1J:Isly, Plate 2 vas adopted ae the "SPS I.Dclez RaiJI.:t'&ll. •
chart, the use o~ vh1cb is expl..aiDed here1Datter.
8
r. Plate 6. Qeneftlized Depth•Are&..Curt"88 1 24-Rour RainteJ.l.
Cona1der1ng all atorma tabulated in Plate 5, the 24-bour values ot Icdex
Rainta.U Ratios (i.e. Percent ot Index Raintall) were &rr'U6ed 1D order or
A1m1p1ah1Dg maguitude tor each ot the areu 4ea1gDated 1n the column head-
iDS• or Plate 5. Tbe DUIDber ot Index R&in.:t'all Ratios exeee41J::ag vartoue val.uea
vaa detenai.Ded ~md converted to percent ot the total D'UIIber of atonu at.u41ea
(approx. !too). The curTe on Plate 6 dedcnated u "M&xiwn ObHr¥ed" vaa
o"btai.Ded by plottillg the higbeat value or lDdex ltaiJd&ll 8at1o ror each
area aDd draViDS a smooth cune to envelope the plotted points. The aet of
curve• mmiber lE, 5E, and lOE vas obtail:led by plottilll ror each selected
area the values ot IDdex RA1n1't&ll Ratio equalled or ezceeded by l percent 1
s percent_. and 10 percent, respecti'nlly, ot the total JNIIber or n.l.uea.
For purpose ot compariaon, the set ot curv'eS deaipated u lA, 5A, lOA,
25A and 50A were obtained by plotting the • • ot tbe Ja1cbeat l percent,
5 percent, lO percent, etc. , ot the Index :Ra1Dr&l.l Ratioa for the Mlected
areu.
9
J. Plate ll. '!'me-Distribution ot Mar'•• 6-Hour SPS Ra1Dt&ll
Azlalyaes ot maJor storms approachi.Jlg SPS 111teneitiee over areas ot a tev
hundred square ailea or larger ahov that the rate ot raini"&ll ie uaually ·
t&irl,- uniform duri.Dg the ••z1•• 6-hour period ot the atom, Vith exc::ept1on
ot 1Dte1"111ttent abort-period variations which ueual.ly produce only aaJ.l
ftriationa in atream-tlov rates at dovnatream po111ta atter ftl.ley eto1'88e
.baa 1110dulated loc&l Yariations 1Jl eurtace :ruDOt'f'. R&W'all rates during
leee 1Dtenae 6-hour period.e ot the storm are seaeral.ly more erratic , md
ma:r tollov any 41t'f'erent sequences and rate chazJ&ee 1D 41t'f'erent eto:naa.
!ovever, studies 1D41eate that aa8UIIZption ot UDitorm :l"'L1l1tall 1Dteneities
duriDg eucceaaive 6-hour periods ot the SPS, Yitb exc::eption ot the -.ziJI:NII
6-br. period ot SPS eatiJiatea applicable to lllll&ll d.rainase baaina, votl.ld
give satisfactory tlood discharge estimates it reasonable conservatism 1a
exercised in est1m&t1ng inf'iltration losaee and unit hydrographa. In
order to usure sate eatilllates ot peak d1ecbarsea to be expected trom SPS
rainfall over dra1DB45e areas lese than approximately 300 square llilee on
the avel"'&Se 1 the max1Jm1D! 6-bour rain1"all ot the SPS should be broken dow
1Dto shorter unit perioda and higher 1Dteneit1ee assumed tor the aborter
intenale ac:cord.i.Ds to criteria presented on Plate 11.
10
(3) Arrlt.Da• the 24-hour SPS r&i.D.t&l.l. ftl.uea 4ete:rw.1De4 in
.tep (2} 1D a MQ.uence taYOrablA to pro4ucticm ot critical I"UD.Otr at proJect
l.ocaticma UD4er ccuideratiaD, 'MH4 Gill a ,_.nl appra1Ml ot ~lac1c
COD4.1tiou 1D the proJect buiD.
ll
(1) LtDee 1 to 5 eatabliah the 1Ddex raiDtall and the
upit'Dde and ti.JDe a.rrangement ot 24.-hour rainfall amounts that vould be
obtaiDed for the entire basin Vithout reduction tor the tact that the
ato~ isohyeta do not conform to the shape of the basin.
l2
• "t'.... ~-
:nu:as•• 1A t.opo&ra~ are MJor tact.ora t.o be t.aka. 11at.o o_.14erat10D, it.
1• appropnate to e.tiJI&te tM •Y1•• »:robabl.e ~ ~ tor 1oM
'buill 'b7 cou14er1JII optS.. ea.b1Dat.1au of cnt.Mal ~1111
factor. D4 -~ tbe BPI' ~ ia eqW. ~ to pezwat ot tbe
• r ! w n pzooMble 41ac:bal'lea. Tbia approziat1• ia 'bue4 Clll tbe '!ODCl'WI!OC
~t CJ'1t1c&l. cca41t1ou c• be a.tel'ld.De4 tra ~ ot ..teorolocic&l.
e4 tcrposrapbic uatluacea, 11bereu a .ubetatial peno4 ot ~oro•
locte&l neoJ'de &re requincl to detend.M ~ a na=n1- ~ tloo4
JII"'cbM:SDs tact.on ...tilll 8W .,ecU'lc:B,_..
13
III. SPS ES'l'IMA.T!S POB LARJE DRAJlWlE BASDIS
3-o2. EXAMPLE: SPS tsTIMATE FOR CUMBERLA!ID RIVER ABOVE OLD HICKORY
DAM SITE (ll, 700 SQ. MI.).
l~
( 3) 'l'hb 11.-t ot 19 •torae vas referred to the R1droaaeteo-
roloa1c&l Section of the Weather Bwoeau for an opinion reg&rd:tJ:I,g tnASpoa1-
bil1ty and for an eati.Jaate of adjustmeat req,uired. 'l'vo tl"BA8poaitiona of
the 5,000 aq. 1&1. center area of each atom were couidered, one traaapoai-
tion beillg mo4e to the lover Cumberland baa in (center at ClarksVille 1 TenD. )
&Dd the other to the Upper baain (center at Bumaide, 1<:7·) 'l'he ti'8Aipoa1-
tiOD a4ju.tment fe.cton .tu.nUahed by the \leather Bureau are listed 1D tbe
5th ADd 6th columna of Table A, Plate 15.
(8) Criteria tor tbe preparation ot the SPF Series tor tbe
ctra1nage area above 014 Bickor,y, Tenn. 1 wen eetabl11hed 1ll the .amaer
expla1De4 1ll paracraph 3..02 !·
(2) Flova tor the 15-day period tJ'OIIl 23 Me.r to 7 Apr were
computed tram raintall-excess estimates derived !rom the selected 120-hour
standard project ato~ vbich vas based on a transposition or the 23·27 Mar
1913 sto~ (OR 1·15) as discussed 1n paragraph 3-02 b.
l7
IV. PJilJECTS lOR WHICB SPP E8'fDIA1'IS A!! :aQtJIR!!D
a.-o1. ODERAL. '1'he pu.rpose to be Hrftd by SPP' estiatea are c11s-
cuaae4 'br1e~ 11\ p&r~~Srapha l-o6 u4 1-QB. Ill aaae cuea tbe BP!' eatmate
•1' baw a -.jot" bearS.Ds Oil Hlectioa. o~ the c!edp tlDo4 ~01" a part1cul.a1"
project, vtle:reu 1D other cues the ellt~te -1 sene 0Dl7 u an 1Dd1cat1cm
ot th~ }J&rti&l. degroee ot protection proposed tot" the project. SP!I' estimates
are uaet\U 1D comaect1on vith practically all fiood control iDTeatig&tiona
but to reduce the vork required 1D project lltu41ee 1 prep&l'ILtion of SPP'
estimates is required only tor those projects 1D vbieh the proposed c!es1gn
flood is "'ore thaD one of eet~ted 25-year trequene1. To further reduce
the vork 1D~1Ted, approximate eat:t.atea are acceptable vhere it ia appareat
tha't the deai&D tlood is strictly 11m1ted by eeODOIIlie conaiderationa aDd
is IIUbetantia.U.y lees the the SPF. Tbe baais ot SPl" estimates shDul.d be
clearly stated in each ease.
4-03. MAJOR DRAIBAGE PROJEX:TS. In accordance with the oa.R cited above,
SPF estimates v1ll not be required tor "Jat..jor dra1Dase" projects unless such
projects sene &lao to provide protection agaillllt floods sreater thaD those
haVi.Dg a-nraae f':requency ot approximately cmce 1l1 25 yean.
18
4-<>5. RESF.:RVOin ~. In aome 1natcmcea SPF eutimatea serve u
the priJD&ry bu1s ror aelectina the storage capacity or nood coutrol naer·
YOin, ud 1D euch cue• the estimate should be prepared With subatanti&l.ly
the eame care ud detailed atudy obserntd ill connection with det.el'III1D&t1ou
tor local protection proJecta or comparable importance. llovewr, 1D 1110.-t
caaea aelection ot storage and outlet capacities tor reservoirs are governed
b7 ccmaideration• other thaD the SPF eatiJDate, in which cue tbe SPF eatiJDAte
1a ot aecondary importuce &lld may be approximated aatist'act.or1ly by aaaua•
~ that tbe SPF equals 50 peroent or tbe spillvay 4eaigz:l 1'1.ood tor the
proJect. (See para 2-o4.).
(l) SPF estimates tor small drainage a.reu (leu than approx•
1.11ately 1000 s~.lli.les) baaed on generalized rainra.ll crt terta and procedures
preaented herein need not be submitted to OCE tor advance approval UDlese
the reporti.Dg officer considers adV&Dce approval &dv1e&ble 1.n apecitic cuea.
(2) SPP' esti.IDates prepared tor indiVidual reservoirs need
DOt be wbmitted to OCE tor advance approval unless the estimate coutitutea
the primary basis tor selection ot tbe reservoir storage and outlet capacities.
19
C1~1 Worke Ea&:l.uer BulJ,etiA )(o. 52-8
GENERALIZED ESTIMATES
MAXIMUM POSSIBLE PRECIPITATION
I
/ \
I
·- ............;,-·-·-·----~.,j._i
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12
STANDARD PROJECT STORM ~ES
(P'i. ol AI[IIAG€ OEPTH 01 RAIWAU. IN
tow«• too M 111. •• •• - •
. GENERALIZED ESTIMATES
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110
0/F IIIOU
OEPART'MENT ~ THE ARMY CORPS OF ENGtNEERS
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30000 I!' I I I J I 1 1 • : , I •
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20,000 ._._.. ~· :~·--·· - "'-+ +
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STANDARD PROJECT STORM STUDIES
so r---: SPS DEPTH-AREA- DURATION RELATIONSHIPS
~.. '
20~
BY 24-HOUR STORM INCREMENTS
•
. ..
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10 ...-·~·~l~t~T~~~~~~~~~~~~~~~~~~~~~~~~I~!~~·~·~~~~~~~~~~L-~~~~~
0 20 60 60 100 120 140 .a
SPS INDEX RAINfALL RATIO (IN PERCENT)
.
INMI
IIAIN"AU. IPS lt&IN,AU. IN
OUIQII&TfD &-.- "l"'DD
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'IG. (D) TYPICAl. ARRANGEMENT ... ....
i
It
f.- ......- - I
OF 1-rtOUR RAINFALL
OUANTITIE9 IN SPS
IJ
14
,,
1'0
,.
co
11'0
101
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.• ...
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TIME DISTRIBUTION
~ Of 24-HOUR SPS RAINFALL
0
L-----------------------------------------------------------------------------------------------------------------~-----------------------------------P
DEPARTMENT OF THE ARMY CORPS OF ENGINEERS
2nd 6z 53 l2
Jrd 21 lS
i
I 4th 38
!'
Sth 14
6th 11
TarAt 100 100 100 100
tor Cinl Woru, Part. CXIV - 97drololic and fb'dra\llic Anaqeee, Qwpt.er S-
.Floocl-HJdrograph Anal:'••• .a Collput.at.ion•). 1'be toUGvin1 nanded-ott
U ;, eaceeda 16, •e ; a 6
u t.P 1e between 12 ancl 16.. •• t. : 3
1
It tp 11 bet.wen 6 and 12 • • • il : 2
U t.P i l bet.nen 4 and 6, •• ; : 1
N~~--------------------------------------~--------------------------------------~
0
<
;= Gclti"t StoiiOft No. I flood Control RtHrvalr
Droiftclte AIIO 440 $cl. Mi Dr~ Ated' 234 s.. MI.
Ien ~StatlaftNt.l
" Drainage ArlO 201 Sq....
"'!!z
z
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::Ill
II'
c
r
r
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LOcal ·ProtectiOft Project
Oroinop Areo 458 $4. MI.
.
UNIT HYOROGRAPH DllTA
'• ,.,.
t
DRAINAGE L
LOCATK*
AREA Leo (L·laf· , tp t, o,
~
Oaln A 236 37 20 '7.3 1.8 13.1 2.4 3.0 13.2 380
· LPP 8 222 3S II 6.1 2.3 15.9 2.9 3.0 15.9 420
NOTES
STANDARD PROJECT STORM STUDIES
1. ProJ•cl IDctJiion: Ltll. .J1~ · Ltlllf. 94• (/nd•• r~~inftlll' /.J !· "}.
2. lsohyets ctNr•spond to tllou of Plot• ND. 12 with fMrC,Itl•l
ILLUSTRATIVE EXAMPLE
multipll•d by ind•x rolnfoll of /.J. $ inch•£ APPLICATION OF ISOHYETAL PATTERN
.J. Ftlr d•linllion and oppllcolion of un/1-hydrogrDplt symbfJfl ,.,
(MAXIMUM 96-HOUR PERIOD OF SPS)
Enginuring MDnutll for Civil Worts, Pori CXIV, Chop ...-., ~.
c
4. 1 oniJ Cp baud on floods obs•rv~d ol 909ing slolicv•s /IJ 2.
I I I I I I
'· 'R bos~d on crll,io on Ptot• No. II. 10 I 0 10
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