Ancient Floods, Modern Hazards

381 Pages·2002·13.664 MB·English

Water Science and Application 5
Ancient Floods, Modern Hazards
Principles and Applications of Paleoflood Hydrology
P.K yle House
Robert H. Webb
Victor R. Baker
Daniel R. Levish
Editors
lgS'tahc companyCinDg-R OMc ompileadn dd esignbedyP .K yleH ousaen dL arryM ayer
AmericaGne ophysiUcanli on
Washington,
Publisheudn derth ea egiso f theA GUB ooksB oard
JohnE . CostaC, hairD; avidB ercovicAi,n drewD esslerJ,e ffreyM . ForbesW, .R ockweGlle yerR, ebeccaL ange,
DouglaSs. LutherD, arrelSl trobeal,n dR . EugenTeu rnerm, embers.
AncientF loodsM, odernH azardsP: rincipleasn dA pplicationosf PaleoflooHd ydrology
Water Science and Application5
Library of Congress Cataloging-in-Publication Data
Ancientf loods, modern hazards: principlesa nd applicationso f paleofloodh ydrology/
P. Kyle House ... [et al.], editors; with accompanyingC D-ROM compileda nd designed
by Larry Mayer and P. Kyle House.
p. cm.- (Water science and application; 5)
ISBN 0-87590-354-1
1. Paleohydrology2. . Floods.I . House, P. Kyle. II. Series.
QE39.5.P27 A53 2001
551.48'9-dc21 2OO 1 O53365
ISBN 0-87590-354-1
ISSN 1526-758X
Copyright2 002 by the AmericanG eophysicalU nion
2000 Florida Avenue, N.W.
Washington,D C 20009
Cover: Upper portiono f the Dogleg Bar reach of the Owyhee River Canyon,s outheast-
ern Oregon. The Dogleg bar (lower right) is the lowest of three discrete river terraces,
each composed predominantlyo f volcanic boulders deposited by extreme floods.T he
two highert erraces are discernibleo n the opposites ide of the river in the right and cen-
ter of the photo. Photographb y Kyle House, May 2001.
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Printed in the United States of
CONTENTS
Preface
P. Kyle House,R obertH . Webb,V ictorR . Baker,a ndD aniel R. Levish. ............................... v
Background
The Scientific and Societal Value of Paleofiood Hydrology
VictorR . Baker,R obertH . Webb,a nd P. Kyle House ............................................. 1
Climate Variability and Flood Frequencya t Decadal to Millennial Time Scales
Kelly T. RedmondY, ehoudaE nzel,P . Kyle House,a ndF rancoB iondi ............................... 21
Principles and Methods
PaleofioodR econstructiono n FloodplainsU sing GeophysicalS urvey Data and Hydraulic Modeling
GeoffP ickup,A lan Marks, andM ary Bourke. ................................................. 47
Mapping Flood Inundation in SouthwesternA rizona Using Landsat TM Data:
A Method for Rapid Regional Flood AssessmenFt ollowing Large Storms
Larry Mayer andP hilipA . Pearthree. ....................................................... 61
DendrochronologicE vidence for the Frequency and Magnitude of Paleofioods
ThomasM . Yanoskya nd RobertD . Jarrett .................................................... 77
Reliability of PaleostageI ndicators for PaleofioodS tudies
RobertD . Jarrett andJ ohnE England,J r. .................................................... 91
One-DimensionalE stimation Techniquesf or Dischargeso f Paleofioodsa nd Historical Floods
Robert H. Webb and Robert D. Jarrett ....................................................... 111
Robust Determination of Stagea nd Discharge:A n Example From an Extreme Flood
on the Verde River, Arizona
RogerP . Denlinger,D . R. H. O'Connell,a nd P. Kyle House ...................................... 127
Initial Motion of Boulders in Bedrock Channels
PaulA. Carling, Mark Hoffmann,a ndA ndreaS . Blatter. ........................................ 147
Bias and Information Content of Paleoflood Data in Flood-Frequency Analysis
J. B. Blainey,R . H. WebbM, . E. Moss,a nd V. R. Baker ......................................... 161
PaleohydrologicB ounds(cid:127)Non-ExceedanceI nformation for Flood Hazard Assessment
Daniel R. Levish ....................................................................... 175
Applications
Cosmogenic3 He Ages and GeochemicalD iscrimination of Lava-Dam Outburst-Flood Deposits
in Western Grand Canyon, Arizona
CassandraR . Fenton,R obertH . Webb,T hureE . Cerling,R obertJ . Poreda, and Barbara P. Nash .........
CONTENTS
Evaluation of Glacial Outburst Flood Hypothesisf or the Big Lost River, Idaho
Keith L. Knudsen,J anet M. Sowers,D ean A. Ostenaa, and Daniel R. Levish ......................... 217
Watershed Scale and the Stratigraphic Record of Large Floods
J. C. Knox and J. M. Daniels ............................................................. 237
Slackwater Depositsa s PaleostageI ndicators in Canyon Reacheso f the Central Appalachians:
Reevaluation After the 1996 Cheat River Flood
J. StevenK ite, Terry W. Gebhardt,a nd GregoryS . Springer ...................................... 257
Historical Flood and Paleofiood Chronology of the Lower Verde River, Arizona:
Stratigraphic Evidence and Related Uncertainties
P. Kyle House,P hilip A. Pearthree,a nd JeanneE . Klawon. ...................................... 267
Paleofiood Hydrology of the Paria River, Southern Utah and Northern Arizona, USA
R. H. Webb,J . B. Blainey,a nd D. W. Hyndman. ............................................... 295
Paleofloodsa nd the Estimation of Long Term TransmissionL ossesa nd Recharge
to the Lower Nahal Zin Alluvial Aquifer, Negev Desert, Israel
Noam Greenbaum,U ri Schwartz,A sher P. Schick,a nd YehoudaE nzel .............................. 311
Caves and Their Potential Use in Paleoflood Studies
Gregory S. Springer. ................................................................... 329
Modeled PaleofioodH ydraulics as a Tool for Interpreting Bedrock Channel Morphology
Ellen Wohl ........................................................................... 345
Perspective
The Geology and Geography of Floods
Jim E. O'Connor, Gordon E. Grant, and John E. Costa .........................................
PREFACE
Floodingi s the mostp ervasivea nd costlyn aturalh azard depthp erspectivoen specifica spectso f the field andt heir
regularlyf acedb y societyE. xtremef loodsc onstitutes ignifi- applicationsc,a ns ervea s a frameworkf or futured evelop-
canta gentso f physicacl hangeo n portionso f theE arth'ss ur- mentsa nd applicationsT.h e scopeo f informationp resent-
face and leave diagnosticim printsi n the geologicr ecord, ed here will satisfyb oth the investigatowr ho wishest o
both ancienta nd recent.M ost large floodsr esultf rom the learnb asicm odalitieso f paleofloodr esearcha ndt he expe-
integratede ffectso f complex,m ulti-scaledin teractionisn riencedi nvestigatosr eekingc onceptuaal nd methodologi-
Earth'sa tmospherFe.l oodr ecordsfr om gagings tationsty pi- cal insightsa s guidancea nd inspirationW. ithoutq uestion,
cally havei nsufficienlte ngtht o adequatelyc haracterizteh e the collectiveb ibliographyo f each of the chaptersw ill
actualt emporalc ontexto f hydrologice xtremesli ke large servea s an authoritativea nd comprehensivree ferenceli st
floods.T he foregoings tatemenths ave a commont heme-- for thoses cientistws ishingt o delved eeperin tot he subject.
paleofloodh ydrology--anin terdisciplinasryc ientificm ethod Overall,t he booke mphasizerse cent,s ignificanitm prove-
of reconstructinthge h istoryo f floodingo nr iversa nds treams mentsi n the methodologicaaln dc onceptuabl asisf or pale-
fromt heb asiso f physicael videnceo f floodingF. roma soci- ofloods tudiesp, rovidesq uantitativea nds tatisticatle stso f
etal perspectivep, aleofloodh ydrologyp rovidesa direct thec ommona ssumptionths atu nderliep aleofloodre search,
recordo f thet ypeso f floodst hata rem ostl ikely to causeth e and presentsth e resultso f recenta pplicationasn d varia-
greatesdt amageA. s a resultf, loodp lainm anagerasn dr egu- tions on basicm ethodsa nd concepts.
latorya genciess houldb enefitg reatlyf rom the researcha nd Each contributedc hapterr epresentsa n outgrowtho f
interpretationthsa tp aleofloodh ydrologyo ffers. papers and discussionsa t the Second International
Paleofloodh ydrologyu sesp rincipleso f geologyh, ydrol- Paleoflood Conference held in Prescott, Arizona
ogy, and fluid dynamicst o exploit the fact that floodsc an (Septembe2r 7-29, 1999). This conferenced, edicatedto
leavel ong-livedp hysicale videncein their wake. The pri- presentintgh e state-of-the-airnt paleofloodh ydrologyw, as
mary goal in paleofloodh ydrology is to extend flood organizedw ith sponsorshipfr om the U.S. Bureau of
chronologieosv erp eriodso f time rangingf rom centuriesto Reclamationt, he HydrologicalS ciencesP rogramo f the
millennia.P aleofloodc hronologiesc an form the basisf or National ScienceF oundationt, he USGS WesternR egional
proxy chronologieso f flood producinge vents,p rovide CompetitiveG rantsP rogramin WaterR esourceRse search,
insighti ntoc hangesin river channeml orphologya, nds erve the INQUA Global Commission on Continental
as a standardfo r comparisono f modeledc onceptionso f Paleohydrology (GLOCOPH), the Desert Research
floods and flood hazardso n specificr ivers and streams. Institute,t he Nevada Bureauo f Mines and Geology,a nd
Paleofloodh ydrologyc an makei ts greatesct ontributionto theA rizonaG eologicaSl urveyE. achp aperi n theb ookh as
societyi n the appliedd omaino f flood-riske valuationa nd been subjectedto independenpt eer and editorialr eview
hazardm anagementH. owever,t he explicit and effective and,i n somec aseso, fferso nly a glimpseo f the breadtho f
assimilationo f paleofloodh ydrologyi nto the realm of presentationast t hec onferencAe. poolo f 45 reviewers(2 7
flood-hazardm anagemenrte mainst o be fully realized. of whomw eree ntirelye xternatl o the monographd) onated
This book providesa comprehensivoev erview of the their time and expertiset o enableu s to completet his
presents tate of knowledgei n paleofloodh ydrologya nd processa, nd we gratefullya cknowledgteh eir assistance.
offersn ew perspectiveosn its applicabilityt o a varietyo f The compilatioonf thisb ookw ouldn oth aveb eenp ossible
relateds ubjectsI.t is not intendedt o servea s an explicit withoutt hep ersistencaen dd edicationo f eachc ontributing
"how-to"m anualo n paleofloodh ydrologya s achievedb y author, and we thank them all. We would also like to
the bookF lood Geornorphologbyy Bakere t al. published acknowledgeth e effortse xpendedo n behalfo f this book
in 1988. Instead,t he presentv olume, which offers an in- andt he conferencefr om whichi t was developedi;n
ular, Terri Garside, Jack Hursh, Kris Pizarro, and Susan text, and data tables.I n somei nstancest,h e CD provides
Tingley,a ll of the NevadaB ureauo f Mines and Geology, some color figures that give additionali nformationy et
helpedi n innumerablew ays. weret oo expensiveto reproducew ithint he text. The inclu-
One technical note about this book: siono f the CD is not necessarilye ssentiatlo the contento f
We includea CD-ROM that containsf iguresa nd data the monographb, ut it is an importants upplementth at has
from selectedp apers,l argely to allow the authorst o pro- allowed some authors to share their data and to include
vide ancillaryi nformationfo r theirc hapterss, ucha sd igital color imagesa s a componenot f their chaptera t minimal
imagesf rom the chapters, upplementariym agesn ot in the expense.
P. Kyle House
Universityo f Nevada
Reno, Nevada
Robert H. Webb
U.S. GeologicalS urvey
Tucson,A rizona
Victor R. Baker
Universityo f Arizona
Tucson,A rizona
Daniel R. Levish
U.S. Bureau of Reclamation
Denver, Colorado
CD-ROM INFORMATION
The CD-ROM thata ccompaniethsi sb ookc ontainfsi guresa ndd ataf rom
selectepda persi,n cludingd igitali magesin text,s upplementaimrya gesn ot
in text, datat ables,a ndc olorf igures.P leasen otet hisc onventionfo r CD-
ROM figurest hroughoutth e book:
In chapterws herea uthorsc ontributeadl l figuresa s printedf or
inclusiono n the CD, the first call-out in the text will include the
statement "also on CD."
If the figurei s blacka ndw hitei n text but hasa corresponding
colorv ersiono nt heC D, it will bec alledo uta sa "plate"f ollowed
by thes tatemen"fto rc olorv ersions eeC D" or somethinsgi milar.
Wheret he CD containsfi gurest hata re supplementa(rbyu t not
essentiatl)o thet ext,t heya rec alled-ouat s" CD Figures"o r "CD
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respectively.
The Scientifica nd SocietalV alue of PaleofloodH ydrology
Victor R. Baker
Universityo f Arizona, TucsonA, rizona
Robert H. Webb
U.S. GeologicalS urvey,T ucsonA, rizona
P. Kyle House
NevadaB ureauo f Mines and Geology,R eno,N evada
Floodd amageisn theU nitedS tatesc ontinueto increased espitein creasesdp ending
for flood controla nd mitigation,s uggestintgh at new methodsfo r estimatinga nd
characterizinfglo od hazardsw ould be valuedb y society.P aleofloodh ydrology
was developedin the 1970sa s a way to understandth e magnitudeo f extreme
floodingin centraTl exasa ndh ase volvedc onsiderabilny the last3 0 yearst.o
becomea n importanst cientifice ndeavowr ith broads cientifica nds ocialr elevance.
The interdisciplinarmy ethodso f paleofloodh ydrologyh avee volvedt o overcome
difficultiesr,e ala ndp erceivedi,n volving( 1) inaccuracieisn estimatingth e ageso f
floods, (2) inaccuracieisn reconstructinfglo od discharges(,3 ) lack of robust
statisticaml ethodsfo r incorporatinpga leofloodd ata in flood-frequencayn alysis,
and( 4) the effectso f climatics hiftsa ndn onstationaritOy.f these,o nlyt he fourth
representas real problemt hat is facedb y bothc onventionafllo odh ydrologya nd
paleofloodh ydrologyIt. s resolutionre quiresfu rtherc ollectiono f floodd ata,b oth
from gaging stationso n unregulatedri vers and paleofloods ites. The basic
techniqueosf paleofloodh ydrologyle adt o the use of paleofloodd ata in flood-
hazarda nalysisb, oth in terms of traditionalf lood-frequencayn alysisa nd the
potentialu se of flood historyw ithin the contexto f flood-hazarda ssessment.
Becausep aleofloodd atar educeth e uncertaintiyn estimateos f longr eturn-period
floods,u seo f this techniqueo fferss ubstantiaslo cietabl enefit,p articularlyin the
designo r retrofittingo f damso r others ignificanftl oodplains tructureIsm. proving
the generaul nderstandinogf hydroclimatiecf fectso n flood frequencyre presents
oneo f them osti mportanct ontributionths atp aleofloodh ydrologyc anm akei n the
future. With continuedm ethodologicaaln d conceptuarle finementp, aleoflood
hydrologhya st hep otentiatlo guidei mportancth angeisn thet raditionapl aradigms
of flood-frequencayn alysisa ndf lood-hazarads sessment.
INTRODUCTION
AncientF loods,M odemH azardsP: rinciples
andA pplicationosf PaleofloodH ydrology
WaterS ciencea ndA pplicationV olume5 , pages1 -19 Paleoflood hydrology is the scienceo f reconstructing
Copyrigh2t 002 by theA mericanG eophysicaUln ion the magnitude and frequency of large floods using
2 PALEOFLOODS AND SOCIETY
geological evidence and a variety of interdisciplinary 1993 E1 Nifio and its effects on California, Arizona, and
techniquesW. ithin the last 30 years,p aleofloodh ydrology statesa long the MississippiR iver. The 25-year nmning
has emerged as an important and highly relevant mean of flood damagesh as risen from $0.043 to $3.15
componenot f earth sciencew ith numerousa pplicationsto billion dollars per year (Figure l a). Even adjustedf or
the understandingo f flood occurrenceasn d the evaluation inflation to 1997 dollars, flood damagesh ave increased
of flood hazards.P aleofloodsa re eventsg enerallyr ecorded dramatically(F igure lb).
outsideo f gagingr ecords,o r they are historicalf loodst hat Flood damagesa re increasedb y a numbero f factorsn ot
can be placedw ithin a long-termh istoricalo r geological related to estimationo f the magnitudea nd frequencyo f
context.T hey canb e extremelya ncient;f or example,t here flooding.S omef lood damagesa re by design;f or example,
is plentiful evidencef or catastrophifcl oodsp reservedin farmersm ay lose cropsg rown deliberatelyi n floodways
regions of Earth affected by glaciation in the late that are designedto be inundatedin frequentlyd uringm ajor
Pleistocene,a nd there is clear evidence of catastrophic floods. Pielke and Downton [2000] attributet he increases
floodsf rom billions of yearsa go preservedo n the surface in flood damaget o increasedp recipitationa mountsw, hich
of Mars [Baker, 2001]. Neverthelesst,h e paleofloodso f implies climatic nonstationarity( see later sections).I n
greatestc oncernt o humansa re those associatedw ith many cases,h owever, flood damagesa re high because
climaticc onditionsm ostl ike the present.S uchf loodsh ave zoning to minimize flood damagesi s inadequate[ van der
generallyo ccurredin Holoceneo, r approximateltyh e last Vink et al., 1998].
10,000 years. The basic flaw of flood science is that conventional
The science of extreme floods has been revolutionized methodsf or estimatingf lood hazard, while rigorouss ta-
in recent decadesb y two major advances.F irst, comp- tistically,l ack understandinogf the flood processa ndt ypi-
utationalm ethodsh ave allowedt he modelingo f the diverse cally are basedo n lesst han 100 yearso f gagingd ata. One
rangeo f phenomenean visionedfo r extremef looding,a nd of the largestb enefitso f paleofloodh ydrologyi s the recon-
second,a whole world of data on extremef loodsh as been structiono f flood dischargeso ver thousandso f years,
openedu p by the rapid developmenot f scientifict ech- whiche stablishetsh e long-termc ontexto f shorth ydrologic
niqueso f paleofloodh ydrology. recordsa ndt herebyg reatlyi ncreaseso ur abilityt o estimate
The purposeo f this chapteris to reviewt he evolutiono f flood hazards.
paleofloodh ydrology as a distinct scientificf ield. We
describei ts basic principles( with particularr eferencet o A BRIEF HISTORY OF PALEOFLOOD HYDROLOGY
chapters in this monographi n addition to seminal
contributionsin the field) and discusst he need for paleo- Less than two decadesh ave passed since the intro-
flood techniques and data to become more widely duction of the term "paleofloodh ydrology" [Kochel and
integratedi nto the realm of conventionahl ydrologya nd Baker, 1982].N early all the conventionahl ydrologicaul ses
engineeringIn. thisv ein,w e discustsh e problemo f persis- of paleofloodd ataw ere developedd uringt his period[ e.g.,
tentlyi ncreasingfl oodd amagesin the UnitedS tatesd espite Kochel and Baker, 1982, 1988; Stedinger and Baker,
unprecedentedco mputationaal dvancesi n conventional 1987]. Paleofloodsa re floodst hat occurredi n the pastb ut
flood hydrology, how the techniqueso f paleoflood were not recorded,e itherb y stream-gagingst ationso r by
hydrologyw ere developedt o addresst he estimationo f other indirect means of human observation or measure-
extremef loods,a ndh ow paleofloodd atac anb e efficiently ment. Paleofloods are closely related to, but can be
integratedi nto flood-frequencya nalysis.W e stresst he distinguishedfr om, floods that occurredh istoricallyw ith
value of paleofloodd ata in a societalc ontext,g iven that observeds tages;t hese are termed "historicalf loods." In
this type of data can improvec onfidencein estimateso f general,p aleofloodsa re indicatedb y the effectso f their
flood hazard and potentially reduce damages from passageth at remain preservedl ong enoughf or later inter-
flooding. pretation.A flood occurringi n a remote area, without a
gagingr ecordo r humano bservationc, an be describeda s a
FLOOD DAMAGES IN THE UNITED STATES paleofloode ven thoughi t occurredv ery recentlyb ecause
the magnitudeo f the flood is reconstructedu sing geo-
The greatp aradoxo f flood sciencei s that, despitei m- logicale vidence.
mense expenditureso n flood-hazardp reventiona nd ad- One of the first descriptionos f what we now interpreta s
vancesi n statisticalm ethodsf or evaluatingf lood hazards, slackwater flood deposits (SWD) was made by Tarr
damagesfr om floodsc ontinueto rise at an alarmingr ate in [1892], who worked along the Colorado River in central
the United States [Pielke and Downton, 2000]. In real Texas. In 1922, J.E. Stewartr ecognizedt he importanceo f
dollars( not adjustedfo r inflation),f lood damagesb etween suchs edimentsa s paleostagein dicators( PSI) in a studyo f
1903 and 1999 peakedw ith the floodsa ssociatewd ith the the Skagit River in Washington[ Stewart and Bodhaine,
BAKER ET AL. 3
2O flood record with paleofloodd ata. By the early 1980s, a
new, innovative and considerablyl onger viewpoint was
25-Year Running Mean
possiblein flood hydrology.
In 1976, the newly developings ubdisciplineo f SWD-
PSI paleoflood hydrology was thought to have the
following problems:( 1) it was presumedi mpossiblet o
determinet he ageso f ancientf loodst o a accuracyd esirable
for flood-frequencya nalysis,( 2) it was unlikely that the
dischargeo f an ancient flow event could be estimated
accurately,( 3) there was no appropriates tatisticalp ro-
........................................... fi I1.,, (cid:127)__ cedure that would incorporatep aleoflood data to make
accuratee stimateso f the frequencyo f large floods,a nd (4)
past changesi n climate and(or) land-usep racticesw ould
invalidate any flood-frequencya nalysist hat incorporated
(cid:127) 25-YearR unningM ean
o15 paleofloodd atat o addressfu ture flood hazard.T heset ypes
of criticismsp ersistedin to the mid- to late-1980s [Hosking
and Wallis, 1986a, 1986b; Yevjevicha nd HarmanciogTu,
'-10
o'(cid:127) 1988].
These initial and, to a lesser extent, continuing criti-
'(cid:127)o
cismso f presumedp roblemsw ith paleofioodh ydrologya re
inevitablef or a younga nde volvingd isciplineI.n fact, early
criticismo f paleofloodt echniquesp romptedf urther inno-
, vation and intellectual developmento f its conceptsa nd
0 0 0 0 0 0 0 0 0 0 0
0O (cid:127) (cid:127)O--(cid:127) OO(cid:127)(cid:127) COO(cid:127) 'O(cid:127)'(cid:127) O(cid:127) (cid:127) OCO(cid:127) O(cid:127)'(cid:127)(cid:127) COO(cid:127) OO(cid:127)(cid:127) 00 applicationsT. he intensityo f criticismh asw anedo veralla s
the basic principleso f the disciplineh ave been repeatedly
Figure 1. Flood damagesin the United States,1 903-1999.A . testeda nd proven in a multitude of settingsa nd contexts.
Damagesin billionso f real dollars.B . Damagesin billionso f Nonethelesst,h is brief review of the basicc riticismsh elps
dollarsa djustedto 1997. [Pielkea nd Downton,2 000; datas ource: to frame the context of the development of modem
http: //www-nws-nøaa.gøv/øh/hic/fløød-stats/F1løøsøsd- time-seri paleofioodh ydrology as well as to illuminate some mis-
es.htm] conceptiontsh at persistt o the presentd ay.
Many critics of the techniquesa ppeart o be unfamiliar
1961; Costa, 1987a]. Similar studies of historical flood with basic conceptso f geology as they are applied to
depositsw ere conductedf or the Ohio [Mansfield, 1938] paleofloodh ydrology,a nd they are overconfidenti n the
and Connecticut Rivers [Jahns, 1947]. However, the assumeda ccuracy/validityo f more traditionalm ethodsA. s
cataclysmicl ate PleistoceneM issoula flood depositso f an example,c riticism( 1) reflectsm isconceptionasb outt he
eastern Washington [Bretz, 1929; Bretz et aT., 1956] accuracyo f modemg eochronology.
providedt he greatests timulust o paleofloods tudiesin the Criticism (2) is curiousb ecausei t is the conventional
United States [Costa, 1987a; Patton, 1987]. Research on stream gages that have great difficulty in accurately
Pleistocenefl oodsi n the United Statesc ontinuesto this day recordinge xtreme floods. Streamflowg aging stationsa re
[e.g., Fenton et aT., this volume; Knudsen et aT., this establisheda nd rated mostr eliably for common,r elatively
volume]. small discharges.T he very rare flood usually does not
Working in the samer egions tudiedb y Tarr [ 1892], and occur in a gaging record, and when it does, its direct
applying experience gained by studies of the late measurement is usually compromised by complex
PleistoceneM issoulaf loods [Baker, 1973], the major con- hydraulicsa nd flood damage( e.g., Figure2 ), and the flood
cepts of SWD-PSI paleoflood hydrology were mostly magnitudei s computedu sing indirect methodst hat are
formulatedd uringt he 1970s.B aker [1974, p. 63] observed typically used in paleofiood magnitude determination
that floods in central and west Texas deposits edimenti n [Webba nd darrett, this volume].A lthought he high energy
eddies that form at the mouths of tributaries, and the of large floods may damageo r destroya gaging station,
elevationso f the depositsp rovidem inimum stageso f past their effects on the landscapea nd sedimentationa re such
floods. Patton et aT. [1979] and Kochel et aT. [1982] that the resultingp aleofioodr ecord standst he most chance
improved and added to the techniques.T he 10,000-year of long-termp reservationA. dvancesi n hydraulicm odeling
paleofloodr ecord of the PecosR iver in west Texas was [Webb and Jarrett, this volume;D enlinger et al., this
incorporatedin to a flood-frequencya nalysis[ Patton and volume] make the methods used for paleodischarge
Baker, 1977;B aker et aT.,1 979], the first augmentationo f a estimatione quivalentto thata t gagings tations.
4 PALEOFLOODS AND SOCIETY
stand the complex, often time-variant linkages between
floodsa ndc limate[ e.g.,R edmonde t al., this volume].
In each instance,e ach categoryo f criticism,r egardless
of its basis in fact, has served and continuest o serve the
important purpose of ultimately generatingt houghtful
responsest hat involve ft(cid:127)her testing, ref'mement,a nd
improvemento f techniquesa nd conceptso f palcoflood
hydrology.T he publicationo f this monographi s a testa-
ment to the strength and viability of the conceptso f
palcofloodh ydrologya nd the maturityo f its development
as a distincts cientificf ield. It will also servet he purposeo f
eliminating lingering misconceptionsa bout its techniques
and will, ideally, enable more efficient integration of
palcofloodh ydrologyi nto the realm of conventionafll ood
science.
PALEOFLOOD TECHNIQUES
Many techniquesa re availablef or the inferenceo f past
flood-flow parametersu sing principleso f geomorphology
and related aspects of Quaternary stratigraphy, geo-
chronologya nd sedimentologyT. he most commonlyu sed
procedurecsa nb e dividedi ntot he followingc ategories(:1 )
regime-basedp alcoflow estimates (RBPE), (2) palco-
competences tudies,( 3) floodplain stratigraphy,a nd (4)
palcostagee stimatesa nd bounds.P ortionso f the following
discussioni s generalizedf rom Baker [1987] and Baker
[2000].
Regime-BasePd aleofiowE stimates
Regime-basedp aleoflow estimates use empirically
derivedr elationst o estimatet he valueso f relativelyh igh-
Figure 2. Photographss howing gaging stationsc ompromised probabilityf low events,s ucha s the mean annualf lood or
during large floods. A. The Santa Ynez River, southern bankfull discharge,f rom paleochanneld imensions,s edi-
California, showingt he high-waterl ine of the January2 5, 1969, ment types, paleochannel gradients, and other field
floodo f an estimate2d, 266 m3/s[ seeL evishe t al., 1997].
evidence.T he relationsa pply exclusivelyt o alluvial chan-
Remnantso f the stilling well (arrow) for the Crawford Reach
nels, which adjust their width, depth, sedimentt ransport,
streamg age, 1.6 km downstreamo f BradburyD am, lies in the
-and slopet o somer epresentativvea lue of streamflow
high-waterl ine of the flood (Dan Levish).B . The Verde River,
discharge.T hese variablesa re related to dischargeb y
Arizona, at the Tangle Creek gagings tations howingf lood waters
near the estimatedd ischargeo f 3511 m3/s on February2 0, 1993 regression expressions derived from observations of
(USGS). The gage house is at lower left. The gaging station relations in modem alluvial channels. RBPE studies have
recordedth e staged uringt he flood, which is unusualf or an event been summarizedb y Dury [1976], Ethridge and Schumm
of this size. [1978], and Williams [1984, 1988]. Becausen early all
regime relationsa pply only to relatively frequentf loods,
Criticism( 3) mostlya risesf rom statisticaql uestionsa nd they are of little use for estimatingt he frequencyo f
assumptionthsa te rrorsa ndu ncertaintieisn palcofloodd ata extreme floods, but offer important insights into more
degradet he value of gaging data in flood-frequency moderate( average)f low conditions.
analysisT. his is an easilyr efutedc riticism[ Blaineye t al.,
this volume], and new methods explicitly account for PaleocompetencSe tudies
uncertaintieisn flood magnitudea nd timing [O'Connelle t Paleocompetencset udiesu se empirical regressiono r
al., in press]. theoreticale xpressionsto relate very large sedimentary
Criticism (4) will be discussedla ter in this paper. The particlest o hydraulicc onditionsn ecessaryfo r their entrain-
ramificationso f hydroclimaticallyin ducedn onstationarity ment, transport, or deposition. The hydraulic variables
in flood-frequencyb olstert he need for using palcoflood generallyi nclude shears tress,v elocity, or streamp ower
and relatedp alcoenvironmentdala ta to more fully under- [Jarrett, 1991; O'Connor, 1993; Carling et al., this