Braided River

Fluvial Processes & Sediment Regimes, Methodology

1. Braided River
(Fluvial Processes & Sediment Regimes,
Methodology)
BY: H.MOHAJER SOLTANI
2021

2. Concepts:
Braidedriversarecharacterizedbyanunstablenetworkof
multiplechannelsandveryactivechannelprocesses.
1

3. Concepts:
Theycanbefoundindifferentclimateregions(e.g.fromglacial
areastoaridregions)
Braidedriversareverydifferentphysiographicsettings(e.g.
fromsteepmountainareastolowcoastalplains)
2

4. Concepts:
Braidingprocessesoccurwhentherearenon-cohesive
materials(e.g.gravelandsand),highsedimentsupply,and
absenceorlimitedlateralconfinement.
Sedimentsizeofbraidedriversrangesfromcobblestosilt.
3

5. Morphology:
Braidedmorphologyischaracterizedbyanunstablenetworkof
multiplechannelsseparatedbyephemeralbars.
Understandingofbraidedrivermorphologyandprocesseshas
developedthroughphysicalmodeling,fieldobservations,and,
toalesserextent,numericalmodelingSedimentsizeofbraided.
4

6. Morphology:
Fieldstudiesarenoteasytocarryoutinabraidedsystembut
remotesensingandrecenttechnologies(e.g.LiDAR,TLS)have
improvedourcapabilityofobservationinthefield
Aerialphotographsandsatelliteimageshavebeencommonly
usedtodescribethemainelementsofbraidedriverplanform,
while,morerecently,newtechnologieshaveallowed
constructionofDigitalElevationModelsand,therefore,more
comprehensivedescriptionofbraidedmorphology
5

7. Morphology:
6
Detrended digital elevation model (a) and bathymetric map (b) of the Ahuriri River

8. Morphology:
Thebraidplain,alsocalled“braidbelt”or“braidedchannel
belt”braidplainiscomposedbydifferentbartypes,mainand
secondarychannels,commonlycalledanabranches,and,in
somecases,islands.
Barsarethemaindepositionalfeaturesandareexposedmost
ofthetime.
Anabranches,representingthelowesttopographicfeatures,
cancarrywatermostofthetimeinmorehumidenvironments,
butcanbealsodryformostoftheyearinaridclimatesorin
smallstreams
7

9. 8

10. Morphology:
Braidingintensity,ordegreeofbraiding,isabasic
morphologicalpropertyanalogoustosinuosityinsingle-thread
channels.
Channelbifurcationsandconfluencesareotherbasic
morphologicalfeaturesofbraidedrivers.
HundeyandAshmore(2009)foundthatthereisalinear
relationshipbetweenchannelwidthandthedistancebetween
anabranchconfluencesanddownstreambifurcation.
Inaphysicalmodel,confluencebifurcationlengthsturnedout
tobe4–5timesthewidthofthemainchannel
9

11. 10
Relation between the average width of the main channel and confluence bifurcation length
(from Hundey and Ashmore 2009)

12. Morphology:
Bifurcationscontrolthepartitionofflowandsedimentdischarge
intheanabranchesofabraidednetwork.
Bifurcationsmaybesymmetricorasymmetric.
InthesymmetricBifurcationsbothanabranchesconveyflow
andtransportbedmaterial
inasymmetricbifurcationsonlyoneanabranchtransportsbed
materialandoneorbothanabranchesconveywater
11

13. Morphology:
Ingravel-bedrivers,whereShieldsstressisrelativelylow,
bifurcationsevolvetowardasymmetricalconfigurations.
insand-bedrivers,whereShieldsstressishigher,theymay
evolvetoasymmetricalconfiguration
InasymmetricalBifurcations:
anunbalancedwaterdistributionanddifferentwidthofthedownstreambranches
thelateralshiftofthemainbranch,theonecarryingmorewater,towardsthe
externalbank,wheremostoferosiontakesplace
12

14. Morphology:
confluencerepresentatransferzonebetweenupstreamlateral
erosionsitesanddownstreamsedimentationsites.
SomeconfluencesdisplayasimplesymmetricalYshapebutin
mostcasestheirmorphologyismorecomplicated.
Thistypeofconfluenceischaracterizedbyadeepscouratits
centerandmid-channelbar.
Scoursizeanddepthisprimarilycontrolledbyconfluenceangle
anddischargeoftheconfluentanabranches
13

15. 14
Sedimentary description
Miall(1985)proposedanelaboratedlithofaciescodeto
describeandclassifyfluvialdeposits
Thislithofaciescodewasfurtherdevelopedandextendedby
Keller(1996)andHeinzandAigner(2003).Thiscodeisoftentoo
detailedtodescribeinastraightforwardmannercomplex,
laterally-varyingsedimentheterogeneity.
Furthermore,thenumerouslithofaciesgenerallytranslateintoa
handfulofhydrofaciesasdemonstrated byhydraulic
measurementsofsamplesorempiricallawslinkinggrain-size
distributiontohydraulicconductivity

16. 15
Lithofacies code by Keller (1996) and Heinz and Aigner (2003)

17. 16
Sedimentary description
HuggenbergerandRegli(2006)proposedanovelclassification
schemetodescribethemaincharacteristicheterogeneitiesof
coarse,braidedriverdepositsforhydrogeologicalapplications
Sedimentary textures, structures, and depositional elements proposed by Huggenberger and Regli (2006)

18. 17
Sedimentary Textures
open-frameworkgravel(OW):Awell-sortedgravel,inwhich
porespaceisfreeofsandandsilt,althoughclayandsilt
particlesoccasionallydrapethepebbles.
A fining-upward open-framework gravel

19. 18
Sedimentary Textures
bimodalgravel(BM):Agravelconsistingofamatrixofwell-
sortedmediumsandthatfillsintersticesofaframeworkofwell-
sortedpebblesandoccasionalcobbles.
open-framework–bimodal gravel couplets

20. 19
Sedimentary Textures
poorly-sortedgravel(GP):poorly-sortedgravel,containingcoarse
sand,granules,pebblesand,rarely,cobbles.Thegravelparticles
arewell-rounded.Clayandsiltparticlesnevermakeupmorethan
5%.
Poorly-sorted gravel

21. 20
Sedimentary Textures
Poorly-sorted,sandygravel(GM):poorly-sortedgravelwith
sandandsilt.
horizontal to sub-horizontal layering of 3-m-thick poorly-sorted gravel

22. 21
Sedimentary Textures
Siltygravel(SG):poorly-sortedgravel,oftencontainingupto
30%sandandnearly20%siltandclay.
Silty gravel

23. 22
Sedimentary Textures
Sand (SA): Poorly sorted to well-sorted sand without significant
silt or clay fractions.
Silt (SI): Poorly graded silt.
Sand

24. 23
Sedimentary Structure
Among allthesedimentarystructuresidentifiedby
HuggenbergerandRegli(2006).
Open-framework–bimodalgravel(OW–BM)structureisthemost
singular.Itconsistsoffining-upwards,normalgradedsequences
ofbimodalgravel(BM)atthebaseandOWatthetopwitha
sharpboundarybetweenthesandintheBMandtheopen
poresoftheOW.

25. 24
Other sedimentary description
Andersonetal.(1999)identifiedinanoutcropinWisconsin
(U.S.A.)11lithofaciesthatwerecondensedinto7hydrofacies.
About85%ofthecoarse,braidedriverdepositsconsistedof
only4lithofacies.TheynoticedthesignificantimpactoftheOW
ontheflowsystemeveniftheOWproportionwasverysmall
(about4%ofthedeposits).
Klingbeiletal.(1999)identifiedintheSingenbasin(south
Germany)23(!)lithofaciesthatweremergedinto5hydrofacies
afterhydraulicmeasurements:(i)BM,(ii)OW,(iii)
planar/trough/horizontalgravels,(iv)massivegravels,and(v)
SA.

26. 25
Other sedimentary description
Heinzetal.(2003)distinguished5mainlithofaciesinthe‘former
fluvialdrainagezonesoftheRhineglacier’(southGermany):(i)
SA,(ii)wellsortedgravel(GS-x),(iii)GP(themostfrequently
observedlithofacies),(iv)OW–BMcouplets,and(v)GM.But
theysophisticatedtheirhydrofaciesdescriptionby
Bayeretal.(2011)identified4lithofacies:(i)GP(themost
frequentlyobservedlithofacies),(ii)OW–BMcouplets,(iii)well
sortedgravelandsand(GS-x),and(iv)SA.FollowingHeinzetal.
(2003)theyderived10hydrofaciesbutnoticedthattheir
classificationcouldbesimplifiedbygroupinghydrofacieswith
similarhydraulicproperties.

27. 26
Depositional elements
Depositionalelementsaretheresultsofeitherdepositional
processesorerosionalanddepositional(orcut-and-fill)
processesthatleaveaspecificstructureinthesubsurface.
Inverticaloutcropexposures,depositionalelementscanbe
identifiedby(i)erosionallower-boundingsurfaces,(ii)
sedimentarystructures,and(iii)clastorientation(Siegenthaler
andHuggenberger,1993).
Fourmaindepositionalelementsaregenerallyobservedin
coarse,braidedriverdeposits:

28. 27
Depositional elements
Horizontallybeddedgravelsheet:mainlyconsistofGPwitha
beddedappearancethatextendsuptotensofmeters.
Occasionally,somesingleGMbedsalternatewiththeGP
Thethicknessofthesegravelsheetstypicallyvariesbetween
0.1mand0.3mbutcanreach1m.
Thehorizontallybeddedgravelsheetsmostlikelyoriginatefrom
remnantofgravelsheetsbecausethegravelsheetistheonly
geomorphologicalelementthathasadepositionalcharacter
andisvery

29. 28
Depositional elements
Massivecoarse-grainedgravelsheets:Laterallyextensive,
massiveandcoarse-grainedgravelsheetsarecomposedof
GM.
Theirthicknessrangesbetweenfewdecimetersuptoseveral
meters.
Themassive,coarse-grainedlayersofGMweresurely
depositedbylargemagnitudedischargeswithsolid-solid
momentumtransfer(e.g.,debrisflow,glacialoutburst)

30. 29
Depositional elements
Troughfills:withclear-cuterosionallower-boundingsurfaceand
tangentialcross-bedsarecommonly observedinvertical
exposuresingravelcarries.
Simplified conceptual model of a single trough fill (with alternating open-framework–
bimodal gravel (OW–BM) couplets) embedded into layers of poorly-sorted gravel (GP).

31. 30
Depositional elements
Trough sizes estimated from interpreted three-dimensional ground-penetrating radar datasets

32. 31
Depositional elements
Onsectionsperpendiculartotheformermainflowdirection,the
troughfillsshowcirculararc-likeerosionallower-bounding
surfaceswithstronglycurvedtangentialcrossbedswhileon
parallelsectionstheerosionallower-boundingsurfacesare
spoon-shapedwithstraighterbutstilltangentialcross-beds

33. 32
Depositional elements
Vertical gravel pit exposure perpendicular to the former main flow direction.
(The diameter of the red circle is about 90 cm)

34. 33
Depositional elements
Gravel pit exposure (Huentwangen, northeast Switzerland) perpendicular to the former main flow direction

35. 34
Gravel pit exposure (Marthalen, northeast Switzerland) perpendicular to the former main flow direction

36. 35
Braided river in the reserves exploration
Consideringthepoorapplicabilityofconventionalgeological
modelingtotightsandgasreservoirinbraidedriverfacies,a
modelingmethodof“multi-stageconstraints,hierarchicalfacies
controlandmulti-stepmodeling”wasputforwardtaking
explorationhydrocarbonfield.

37. 36
Braided river in the reserves exploration
ThemethodobtainstheGRfieldbyseismicinversion
constrainedbyloggingdata,andGRmodelisbuiltunderthe
controlofthepriorgeologicalknowledge;therelation
regressionisrealizedbetweentheGRmodelandthesandstone
probability,sandstoneprobabilitymodelisbuilt.
rockfaciesmodelisobtainedbymulti-pointgeostatistics
theory;sedimentarymicrofaciesmodelcontrolledbyrock
faciesandbraidedriver-systemismade;andeventuallyan
effectivesandbodymodelisbuiltbyintegratingsedimentary
microfacies,effectivesandbodyscaleandreservoirproperties
distribution.

38. 37
Geological modeling process

39. 38
Braided river in the reserves exploration
GRmodelwassetupbyusingsequentialGaussianmethod.This
wayreducesthemultiplicityofseismicdata,clarifiesthe
geologicalmeaningofpredictedsands,andguaranteestheGR
valuecontinuitybetweenthewellpointsandinter-wellplaces

40. 39
Comparison of wave impedance inversion and GR inversion

41. 40
Braided river sedimentary system and sedimentary microfacies plan

42. 41
Comparison of sand isopach map based on model and sand isopach based on manual drawing

43. 42
Verification by modeling well pattern coarsening (the data of blue
wells are used and that of red wells are not in the modeling)

44. Thank you for your attention