Rivers Over Rock: Fluvial Processes in Bedrock Channels

323 Pages·1998·11.501 MB·English

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Geophysical Monograph 107
Rivers Over Rock:
Fluvial Processes in Bedrock Channels
Keith J. Tinkler
Ellen E. Wohl
Editors
AmericanG eophysicaUl nion
Washington,
Published under the aegis of the AGU Books Board
Library of Congress Cataloging-in-Publication Data
Riverso ver rock: fluvial processeisn Bedrockc hannels/ Keith J. Tinkler,
Ellen E. Wohl, editors.
p. cm. -- (Geophysicaml onographs eries;1 07)
Includesb ibliographicarle ferencesa nd index.
ISBN 0-87590-090-9
1. River channels. 2. Sedimenttr ansport. I. Tinkler,K . J., 1942-
II. Wohl, Ellen E., 1962- .III. Series.
GB561 .R595 1998
551.441'2--dc21 98-44136
CIP
ISBN 0-87590-090-9
ISSN 0065-8448
Copyright1 998 by the AmericanG eophysicaUl nion
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CONTENTS
Preface
Keith Tinkler and Ellen Wohl ........................................... vii
A Primer on Bedrock Channels
Keith Tinkler and Ellen Wohl ........................................... 1
HydraulicsS, edimenTt ransporta, nd ErosionaPl rocesses
Conditions for the Entrainment of Cuboid Boulders in Bedrock Streams:
An HistoricalR eviewo f Literaturew ith Respectto RecentI nvestigations
PaulC adinga ndK eithT inkler .......................................... 19
BeyondP ower:B edrockR iverI ncisionP rocesasn d Form
Gregory8 . HancockR, ober8t . Andersona,n dK elinX Whipple ......................... 35
ModelingC onsiderationfosr Simulationo f Flowi n BedrockC hannels
Andrew ]. Miller and Brian L. Cluer ....................................... 61
MorphologicaFl eatureso f BedrockC hannels
DepositionaPl rocesseasn dS edimenSt upplyin Resistant-BoundCarhya nnelsE: xamplefsr om
Two Case Studies
Daniel A. Cenderelli and Brian L. Cluer ..................................... 105
BedrockC hanneMl orphologyin Relationto ErosionaPl rocesses
Ellen E. Wohl ................................................... 133
The Roleo f ExtremeF loodsin ShapingB edrockC hannels
Victor I(cid:127). Baker and Vishwas 8. Kale ....................................... 153
ChanneGl radienta nd LongitudinaPlr ofile
RecenAt djustmenttso the LongP rofileo f CooksvillCe reek,a n UrbanizedB edrockC hannel
in MississaugOa,n tario
Keith ]. Tinkler and John Parish .......................................... 167
InlandP ropagatioonf ErosionaEls carpmenatnsd R iverP rofileE volutioAn crostsh e SoutheasAtu stralian
PassiveC ontinentaMl argin
JeffreyK . Weisseal ndM icheleA . $eidi ..................................... 189
BedrockF luvialIn cisiona ndL ongitudinaPlr ofileD evelopmenOt ver GeologicT imeS calesD etermined
by FluviaTl erraces
Frank]. PazzagliaT, homasW . Gardnera, nd Dorothy]. Merritts ........................ 207
RiverL ongitudinaPlr ofilesa nd BedrockIn cisionM odels:S treamP owera ndt he Influence
of SedimenSt upply
Leonard $klar and William E. Dietrich ..................................... 23
CONTENTS
Methodso f StudyingB edrockC hannels
Field Studies of Bedrock Channels
Ke(cid:127)h Tink(cid:127)er anc(cid:127) œ#en t4/oh! ........................................... 261
FlumeE xperimentatiaonnd S imulatioonf BedrocCk hannePl rocesses
DouglasT hompsoann cœ(cid:127) #enW oh! ...................................... 279
LongP rofileD evelopmenotf BedrocCk hannelsIn: teractiono f WeatheringM, assW asting,
BedE rosiona, nd SedimenTt ransport
,4(cid:127)an [7./-/owarc(cid:127) ................................................. 297
SubjectI ndex ..................................................
PREFACE
Bedrockr iver channelsa res iteso f primarye rosionin the developmenot f regionall andscapesA. s the first state-of-the-
landscapef,i xing the baselevefl or all pointsu pstreamT. his art surveyo f bedrockr iver channelst, his book will interest
volumep rovidesf or the first time an integratedv iew of the hydrologistsg, eomorphologistasn, dc ivil ande nvironmental
characteristicasn do perationo f thisi mportantt,h oughh itherto engineersa,s w ell asa nyonee lsec oncernedw ith high-gradi-
neglected,c lass of channels.E xamplesa re providedf rom ent fluvial channelsw ith part of the boundaryin rock. The
severalc ontinentsa nd cover a wide rangeo f spatials cales volumew as developedfr om a conferenceo n the samet opic
from the larger iver basins( sucha s the ColoradoR iver in the heldi n 1996a t PingreeP ark,a mountainc ampuso f Colorado
United Statesa nd the Indus River in Pakistan)d own to reach StateU niversityI.n ouri ntroductorcyh apterw, e havet riedt o
scalesa nd individuals ites.L ikewiset he geologict imescales summarizeth es tateo f knowledgea sw ell asp ointo uto bvious
considererda ngef rom erosiona ndt ransportatiodnu ringi ndi- lacunae and fruitful lines of attack for future work.
vidual flows to accumulatede ffectso ver periodso f tens of We aree xtremelyg ratefult o all who haveh elpedi n various
millionso f years. waysw ith the manuscriptse,s peciallya ll the reviewersw ho
Bedrockc hannelsa re characteristicallsyt eepa nd generate read and commentedu pon the papers.R eviewers for the
transcritical flow conditions. These are channels where the volumei ncludea uthorso f otherc haptersin the volumea nd
Froude number indicatest hat the fluid flow rangesf rom the followingi ndividualsA: .D. AbrahamsD, . J. Anthony,P .
subcriticalt,h roughc ritical,t o supercriticafll ow botha long BishopJ, .E . CostaL, . L. Ely, A. Gupta,D . J. Harbor,H . Ikeda,
streamlines and in cross-sections. These flow conditions have L. A. James,R . D. Jarrett,A . Kirkbride, S. J. Kite, H. H. Mills,
importanct onsequencefosr thed istributiono f shears tressa nd J. Nott, J. E. O'Connor,S . Ouchi,G . Pickup,J . E. Pizzuto,S .
streamp ower on the streamb ed, and for the ways in which A. Schumm,R . L. Slingerland,a nd M. G. Wolman. The
such conditionsc ontrol erosiono n the boundarya nd the chaptear uthorsh aveb eenm odelso f helpfulnesasn dp atience
transporto f coarsec alibers edimentu p to the size of large duringt he revisions tagesa, nd of coursew e thankt hem for
bouldersF. or theser easonsb, edrockc hannelsb ehavev ery theirm anuscriptws,h ichh avev erya mplyju stifiedt heh opeful
differentlyt han the alluvial river systemsm ore commonly visiont hat we had severaly earsa go in preparingf irst the
describeidn textbooksa ndj ournalp apers. conference and later the volume. We would also like to thank
Previousw ork on bedrockc hannelsh asb eens poradica nd RichardP yrcef or proofreadingth ef inal manuscripts.
frequentlyfo cusedo n small-scalsep ectaculafer atureso f worn
Keith J. Tinkler
rock surfacess ucha sp otholeso r upont he resultso f a single
Brock University
catastrophifclo od,a nciento r modem.I n thisv olumew e have
Ellen E. Wohl
tried to ensurea comprehensivtere atmento f the topic by
ColoradoS tate University
leadinge xpertss o that bedrockc hannelsa re not treateda s
exotic items, but as central and importante lementsi n the Editors
A Primer on Bedrock Channels
Keith Tinkler
Department of Geography,B rock University,S t Catharines, Ontario, Canada
Ellen Wohl
Departmento f Earth ResourcesC, oloradoS tate UniversityF, ort Collins,C olorado
In this introductoryp aper on bedrock channelsw e try to summarizeth e
state of knowledge and point out directions for future work. Fluvial
geomorphology as developed for alluvial and gravel channels does not
readily transfer its results to bedrock channels, for example conventional
hydraulic geometryd oes not seem to apply to these highly variable channels.
Because bedrock channels involve changeso n a resistant boundary that is
usually that of the drainage basin bedrock, baselevel changes effected by
channel erosion are subsequentlyt ransmitted to the rest of the basin, and
therefore have an impact on all aspectso f drainage basin geomorphology
when viewed over geologicalt imescales.W e review existing knowledge of
both morphology and processo ver short and long times scales, and from
reach to basin scales.W e point out that fundamentalt o an understandingo f
bedrock channelsi s the need to appreciatet ranscriticalf low conditionsi n the
channels,a nd the consequencesth at this may have for channel erosion and
sedimentt ransport.T here are opportunitiest o undertakef undamentalw ork in
all aspectso f the subject- from morphologicald escriptiona nd monitoring,
through the mechanicso f channelb ed erosion and sedimentt ransport,t o the
constructiono f flood dischargesc hronologies in relation to environmental
controls, and high-gradient flood hydraulics in the field, the flume and the
computer.
INTRODUCTION boundary( > 50%) is exposedb edrock,o r is coveredb y an
alluvial veneer which is largely mobilised during high
The intention of this chapter is to highlight roughly flows such that underlying bedrock geometry strongly
what is known about the modern observabled ynamicso f influences patterns of flow hydraulics and sediment
bedrockc hannelsa s a meanso f introducingt he subjects movement. This definition thus includes channels formed
discussedin more detail in subsequencth aptersW. e cannot solelyi n bedrock,c hannelsa longw hich bedrocki s exposed
presenta definitive documentb, ut ratherh opet o stimulate onlyi n thbc hannebl ed,a ndc hannelasl ongw hichb edrock
thinking about these little-studied channels. For the may be exposedo nly duringh igh flows.B roadlyc onstrued,
purposeso f this volume,w e define bedrockc hannelsa s bedrockm ay refer to any cohesiver esistants ubstrates, uch
thoser eachesa long which a substantiapl roportiono f the as cementeda lluviumo r gravels,o r Tertiarya ndQ uaternary
clay units,w hich behavei n a mannera nalogousto bedrock.
The subjecto f bedrockc hannelsh asa large but scattered
literature dating back over a century.F igure 1 showst he
Rivers Over Rock: Fluvial Processes in Bedrock Channels world distribution of studies on bedrock channels. An
GeophysicaMl onograph 107 increaseo f interesti n recent years, as exemplifiedb y the
Copyright1 998 by the AmericanG eophysicaUl nion attendance at the Mountain Rivers Symposium at
2 PRIMER ON BEDROCK CHANNELS
Figure 1. World distribution of bedrock channels studies.
ASCE (Hydraulics) meeting in Buffalo, NY (USA), in abundanstu mmevre getatiomn aym askt hisr ealityI.n such
1994, makes it worthwhile to review the various rivers,g ravelb edr eacheasr eu suallys hallows preadosv er
approachesn ow being taken to channelsw hoseb ed and bedrockA. s sucht,h eym ayb ehaved ifferentlyth ans tandard
walls are erodedi n resistantm aterial,t o try to establish gravebl edr iversF. ore xamples,u chs preadms ayr eadilyb e
someo f their salientc haracteristicIsn.c reasedp ressureo n strippedf rom the underlyingr ock when the armour is
uplands and more rugged terrain both for general breacheda, nd as easilyr ebuilt,a nd the hydraulicso f the
recreationalu se and for urban expansionm eanst hat the largef lowsm ay be controlledb y the underlyingb edrock
hydrologic and hydraulic behaviouro f these types of geometry. Bedrock rivers are also more common than
streamsn eedse xamination[ Jarrett, 1984; Carling, 1995]. mightb e assumedfr om the percentagoef papersin the
In additiont herei s the growingr ealisationth ats treamb iota fluviall iteraturew hichd escribessu chs ystems.
ßm usta lsob e allowedf or in designs chemesa,s f or example Flowsi n bedrocks ystemse, ven at quite low stages,
in the Green River, Utah, USA [Harvey, Mussetter, and typically show greater velocities and shears tressesth an
Wick, 1993] whichi ncludesg ravelb edr eachesB. asins cale thosein alluvialr eachesa,n du suallyth eyp osseshsi ghly
landscapee volution models [Howard, 1987; Howard, aerateda nd turbulentf low structuresT.h erei s usuallya
Dietrich, and Seidl, 1994] must directly model bedrock noticeablwe aters urfaceto pographeys, peciallays s tagein -
systemsw hen significanti ncisioni s to take placei nto the creasess:m oothlyd escendinwga ters urfacelse adingto hy-
regionall andscapeM. odes and rateso f incision,a nd their draulicju mps,p rominenst tandingw avet rains( indicating
variability, must be known if thesem odelsa re to address criticalf low), super-elevatioant b endst,o pographricis es
the time variablee ffectively. over kolks burstingo n the surface,a nd travelingw aves
It cannotb e assumedt hat knowledgef rom alluvial and generated in energetic zones which cause miniature
gravelb ed systemsc an be transferredd irectlyt o bedrock shorelinep rocessesto operatea t the streamb anks.I n no
rivers, and indeeda ttemptst o do this have alreadyf allen senaec ano nep retende, vena s a workinga ssumptionth, at
into difficulties, especiallyi n river engineeringw orks the flow is steadya nd uniform. Substantiasl ectionso f the
[Vaughn, 1990] and Cooksville Creek, near Toronto flow are critical (Froude number, F, close to 1) or
[Parish and Tinkler, this volume].I t is probablyt he case supercritica(lF > 1). When mixed regimesa re present
that bedrockr ivers are more commont han is generally alonga streamlinefl,o w is saidt o be transcriticaAl. good
supposed[ Montgomery et al., 1996], even in low relief rule of thumbi s that if flow is audiblei n the channel,t hen
terrain.A lternatingg ravel and bedrockr eachest, ypicali n flow is transcriticailn at leastp art of the channel.T he
some rivers, together with low base flow conditionsa nd substantiveex istenceo f critical or upperr egime
TINKLER AND WOHL 3
matter has been debated for mountain streams [Jarrett, predictt he directiona ndm agnitudeo f channelr esponseto a
1992; Trieste, 1992], but some supportinge vidence has changein the controllingv ariables?"
been produced [Simon and Hardison, 1994]. In our
observation critical flow is extremely common [Grant,
BEDROCK CHANNEL CHARACTERISTICS
1997; Tinkler, 1997a; Tinkler, 1997b], althoughu sually
confinedt o part of the channel,a nds upercriticafll ow is not
In what senses are bedrock channels different from
uncommon, although spatially restricted. As Tinkler
alluvial or gravelb ed systems?
[1997a] suggestst,o understandc hanneld ynamicsi n such
streams the cross-sectional focus for calculation of cross-
sectionaFl rouden umbersm ustb e replacedb y a view along Morphology
the thalweg.
Gradient. The gradient of bedrockc hannelsi s almost
certainly well in excess of those encounteredi n alluvial
REVIEW OF APPROACHES TO STUDYING
channels (see Hydraulics section below)- even though
BEDROCK CHANNELS TO DATE
locally, when the lithology and dip are appropriatet, here
may be substantials ectionso f almost horizontal channel
Approachesto studyingb edrockc hannelsm ay be grouped bed (Miller, 199l a, b). This 'horizontala' ppearancec an be
into at leastt hreec ategoriesb: asins cale,r eachs cale,e xper- misleadingb ecausea s stager ises,g radienti ntegrateso ver
imental.( 1) Basin-scalea pproachegs enerallyf ocuso n the longera nd longerr eachesa nd small stepsr eadilyd rowno ut.
evolutiono f channell ongitudinalp rofile at time scaleso f A relativelys teepm eang radienti s consistenwt ith the typi-
centuries or longer [Weissel and Seidl, this volume]. cal coexistencoef gravelb ed andb edrockr eachesa ndl ateral
Studiesm ay be field-based[ Merritts et al., 1994, Pazzaglia or transverseb arsa long the channel,a nd the needt o trans-
et al., this volume] or orientedt owardsc omputerm odeling port coarsec lastsf rom the bed, walls and adjacentv alley
of basin evolution [Howard, 1987; Howard et al., 1994; slopes.
Seidl et al., 1997; Howard, this volume; Sklar and Change. Morphologicalc hangei s unidirectional- rock
Dietrich, this volume], but the generalf ocus is on long- removed from the bed of a channel lowers the local base
term rateso f profile lowering and the developmenot f an level for all points upstream.I mportantly, local velocity
erosionr ate law. (2) Reach-scales tudiesa re more concerned fields are permanentlym odified. Likewise, rock removed
with the processeso f erosiona ndd epositiona, s thesea ffect from the walls is not replaced.I n alluvial and gravel-bed
channel morphology, at spatial scales of a few square channelst he distinction between channel materials and bed,
metres to several channel widths. Such studiesm ay focus bar and floodplain material may be locally distinct, but
on observablep rocesseso ccurringa t time scaleso f dayst o sedimenti n transportu sually containse noughc lay or silt
decades[e .g., Toda, 1994; Tinklera nd Parish,t hisv olume; to providec oherences o that alluvial channelsc an aggrade,
Tinkler and Wohl, this volume; Hancock et al., this degrade,a nd migrate while channelm orphologyr emains
volume]o r they may take an indirecta pproacho f inferring relativelyc onstant[ Leopolde t al., 1964]. Gravel-bedr ivers,
processefsr om form, with the aid of paleostagein dicators with their tendencyt o braid on shortt ime periods( hours,
and hydraulics imulationp rograms[ O'Connore t al., 1986; dayst o months),s imilarly conservec hannelm orphology-
Baker and Pickup, 1987; Wohl, 1992a,b; Wohl et al., in a statisticals ense- while migrating. Bedrock channels
1993]. Finally, there is reach-scalem athematical flow are not immune to alluviation, but unless siliceous or
modeling,s ome of which is now sophisticateden ought o carbonate precipitates are extremely common in the
capture the transcritical character of flow in bedrock channel,i t is in the nature of temporary "fill" and will in
channels[ Miller and Cluer, this volume]. (3) Experimental time be "cut" out again, speakingi n terms of geological
studies have used a variety of cohesive substratest o timescales.E W observeds uch systemsi n southernU tah,
simulatee ither erosiono f a specificf eature, for example, wherea boriginalp etroglyphsa re partiallyb uriedb y sandy
pothole[sA lexande1r,9 32;(cid:127) ngeby,1 951],o r knickpoints, alluvium in slot gorges.O n a much smaller scale KT has
[Holland and Pickup, 1976; Gardner, 1983], or general seenf ine gravel alluviationd evelopedf rom mining debris
channele rosionu nder varying conditions[ Shepherda nd with remnant 19th-centuryc ookingp ots to lm above the
Schumm, 1974; Wohl and Ikeda, 1997]. presentb ed in the Glen Maye stream( Isle of Man, United
Questionsc ommont o all thesea pproachesin clude: (i) Kingdom), but which has been subsequentlym ostly re-
what are the actualp rocessesa nd rateso f bedrockc hannel moved in bedrockg orgesd ownstreamfr om theses ources.
incision? (ii) how doest he presenceo f a cohesives ubstrate In contrast, in Texas KT has observedi ndurated gravel
causeb edrockc hannelm orphologiesf,l ow hydraulics,a nd terraces( of presumedQ uaternaryt o late Quaternarya ge)
sedimenttr ansportto differ from thoseo f alluvialc hannels? now partly removed which imply incision of rock to
and, (iii)is there a consistenth ydraulic geometry for presentc hannelb ed elevations,i nfill with 4 to 5 metreso f
"steep" channels?B y this we mean, "is it possible to gravel, and subsequentr emoval. On small