ge0-3112 sedimentary processes and products lecture 10. estuaries and coasts geoff corner department...

GE0-3112GE0-3112 Sedimentary processes and products Sedimentary processes and products

Lecture 10. Estuaries and coastsLecture 10. Estuaries and coasts

Geoff CornerGeoff CornerDepartment of GeologyDepartment of GeologyUniversity of TromsøUniversity of Tromsø20062006

Literature: Literature: Leeder 1999. Leeder 1999. Ch. 21 Estuaries.Ch. 21 Estuaries. Ch. 23, ’Linear’ clastic coastlines.Ch. 23, ’Linear’ clastic coastlines.

ContentsContents

►Coastal depositional systemsCoastal depositional systems►EstuariesEstuaries►Barrier-beach coastsBarrier-beach coasts

Coastal depositional systemsCoastal depositional systems

► Controlling factors:Controlling factors: Sediment supply (rivers, coastal cliffs, alongshore Sediment supply (rivers, coastal cliffs, alongshore

transport).transport). Wave energyWave energy Tidal rangeTidal range

► Deltas vs. other coastal systemsDeltas vs. other coastal systems Local dominance of point-source sediment supply Local dominance of point-source sediment supply deltas. deltas. Dominance of basinal processes Dominance of basinal processes linear clastic coasts, linear clastic coasts,

estuaries, etc.estuaries, etc. Estuaries a special case where fresh and saltwater interact. Estuaries a special case where fresh and saltwater interact.

Coastal typesCoastal types► DeltasDeltas► BeachesBeaches► BarriersBarriers► StrandplainsStrandplains► Tidal flatsTidal flats► EstuariesEstuaries

Galloway & Hobday 1996

Variation in coastal morphology Variation in coastal morphology as a function of tidal rangeas a function of tidal range

EstuariesEstuaries

►DefinitionDefinition►Processes (mud suspension)Processes (mud suspension)►Circulation types (type A, B, C, D)Circulation types (type A, B, C, D)►Facies: tide- and wave-dominated Facies: tide- and wave-dominated

estuariesestuaries►Estuaries and sequence stratigraphyEstuaries and sequence stratigraphy►Ancient estuarine faciesAncient estuarine facies

Estuary definitionsEstuary definitionsVarious definitions:Various definitions:► HydrologicHydrologic (oceanographic): (oceanographic):

stratified water mass with stratified water mass with riverine water (fresh - brackish) riverine water (fresh - brackish) overlying or mixed with marine overlying or mixed with marine water (brackish - salt).water (brackish - salt).

► GeomorphologicGeomorphologic: coastal inlet, : coastal inlet, usually a drowned river valley.usually a drowned river valley.

► GeologicGeologic: semi-enclosed : semi-enclosed coastal body of water having coastal body of water having free access to the sea and free access to the sea and containing seawater containing seawater measurably diluted by water measurably diluted by water from land drainage.from land drainage.

Walker & James, 1992

Manukau andWaikato estuaries, NZ (mesotidal)

► NB. Estuary type (circulation) varies in space & NB. Estuary type (circulation) varies in space & time:time: From inner to outerFrom inner to outer From neap to spring phase of tidal cycleFrom neap to spring phase of tidal cycle Seasonally with variation in river dischargeSeasonally with variation in river discharge

Tidal/fluvial discharge ratiovs.fluvial discharge

Estuarine processesEstuarine processes► Fluvial and marine sediment flux.Fluvial and marine sediment flux.► Wave- and tidal reworking.Wave- and tidal reworking.► Fresh, brackish and marine water.Fresh, brackish and marine water.► Sand, mud and bioturbation.Sand, mud and bioturbation.

Mud suspension and Mud suspension and resuspensionresuspension

► FlocculationFlocculation enhances settling. enhances settling.► High particle concentration reduces settling.High particle concentration reduces settling.► Layers of suspended form in response to Layers of suspended form in response to

tidal pumping.tidal pumping.

Suspended sediment Suspended sediment concentrationconcentration

► Hindered settling and Hindered settling and flocculation produce a flocculation produce a lutoclinelutocline at high at high sediment concentrations.sediment concentrations.

Dilute

Concentrated

Estuarine circulationEstuarine circulation

► Four types:Four types: Type A: well stratifiedType A: well stratified Type B: partly stratifiedType B: partly stratified Type C: well mixedType C: well mixed Type D: homogenous (theoretical end member)Type D: homogenous (theoretical end member)

Type A estuariesType A estuaries► Well stratified, river dominated.Well stratified, river dominated.► Salt wedge below buoyant plumeSalt wedge below buoyant plume► Low tidal/river discharge ratio (<20)Low tidal/river discharge ratio (<20)

Type A estuariesType A estuaries► Cf. e.g. Mississippi, Fraser and Tana rivers.Cf. e.g. Mississippi, Fraser and Tana rivers.► Deposition at tip of salt wedge; sediment Deposition at tip of salt wedge; sediment

flushing as salt wedge migrates. flushing as salt wedge migrates.

Fraser River

Type B estuariesType B estuaries► Partially stratified, moderate tidal turbulence.Partially stratified, moderate tidal turbulence.► Salt wedge degraded; gradual salinity gradient.Salt wedge degraded; gradual salinity gradient.► Moderate tidal/river discharge ratio (20 – 200).Moderate tidal/river discharge ratio (20 – 200).► E.g. Tamar, nr. E.g. Tamar, nr.

Plymouth.Plymouth.

Type B estuariesType B estuaries► Coriollis: up-estuary flow shallowest and Coriollis: up-estuary flow shallowest and

strongest to the left in N. hemisphere.strongest to the left in N. hemisphere.► Turbidity max. (in suspended particulate Turbidity max. (in suspended particulate

matter) most prominent in upper estuary on matter) most prominent in upper estuary on ebb and flood tides (low on slackwater). ebb and flood tides (low on slackwater).

Tamar estuary

Type C estuariesType C estuaries► Well-mixed; strong tidal currents.Well-mixed; strong tidal currents.► Salinity gradient downstream and laterally Salinity gradient downstream and laterally

(Coriolis) but not vertically.(Coriolis) but not vertically.► High tide/river discharge ratio (>200).High tide/river discharge ratio (>200).► E.g. Severn, UK, E.g. Severn, UK,

Gironde, France, Gironde, France, Weser, Germany. Weser, Germany.

Type C estuariesType C estuaries► Repeatable hysteresis of suspended matter Repeatable hysteresis of suspended matter

concentration (C) with tidal velocity (u):concentration (C) with tidal velocity (u):- deposition during slackwater. - deposition during slackwater. - resuspension during- resuspension during ebb and flood.ebb and flood.

► Clayey silt, sandy mud.Clayey silt, sandy mud.

(Type D estuaries)(Type D estuaries)

► Fully mixed; transitional to shelf.Fully mixed; transitional to shelf.► No vertical or lateral salinity gradients.No vertical or lateral salinity gradients.► Sediment movement by tides; no internal Sediment movement by tides; no internal

sediment trap.sediment trap.

Modern estuarine faciesModern estuarine facies

► Sedimentological classification of estuaries:Sedimentological classification of estuaries: Tide-dominatedTide-dominated Wave-dominatedWave-dominated


Basic modelBasic model► SubenvironmentsSubenvironments

Bayhead delta (A)Bayhead delta (A) Central basin (B)Central basin (B) Estuary mouth (C)Estuary mouth (C)

► Sediment typesSediment types Alluvial sands and Alluvial sands and

gravels (A)gravels (A) Bay silts and muds (B)Bay silts and muds (B) Marine sands (C)Marine sands (C)

NB. Upward-fining NB. Upward-fining here reflects here reflects transgressiontransgression

AB C


Tide-dominated estuariesTide-dominated estuaries► Macrotidal (and megatidal).Macrotidal (and megatidal).► Well-mixed.Well-mixed.► Funnel-shaped, open-ended.Funnel-shaped, open-ended.► E.g.E.g. Gironde,Gironde,

Severn,Severn,Bay of FundyBay of Fundy..

Tidal flats, Banks Peninsula, NZ

Tide-dominated estuaries - Tide-dominated estuaries - faciesfacies

► AlluvialAlluvial► Tidal-fluvial channelTidal-fluvial channel► Saltmarsh/mudflatsSaltmarsh/mudflats► Upper flow regime Upper flow regime

sand flatssand flats► Tidal sand barsTidal sand bars

► Example from Example from Gironde-type estuary.Gironde-type estuary. estuarine point bar estuarine point bar

sands w. mud sands w. mud AA tidal bar sands tidal bar sands B B estuarine muds estuarine muds CC tidal inlet sands tidal inlet sands DD

ABCD


Wave-dominated estuariesWave-dominated estuaries► Micro- to mesotidal.Micro- to mesotidal.► Stratified to partially stratified/mixed.Stratified to partially stratified/mixed.► Lagoonal to funnel-shaped, semi-enclosed.Lagoonal to funnel-shaped, semi-enclosed.► E.g.E.g. E. coast USAE. coast USA

UK

NZ

Wave-dominated estuaries - Wave-dominated estuaries - faciesfacies

► AlluvialAlluvial► Bay-head deltaBay-head delta► Central basinCentral basin► Flood-tidal deltaFlood-tidal delta► Barrier/tidal inletBarrier/tidal inlet► ShorefaceShoreface

Waikato River estuary, NZ

Delaware estuaryDelaware estuary

► Outer estuary:Outer estuary: E.Holocene – tide-dominated E.Holocene – tide-dominated

outerouter L. Holocene – wave-L. Holocene – wave-

dominateddominated

► Turbidity maximum:Turbidity maximum: Moved up-estuary in HoloceneMoved up-estuary in Holocene Mud deposition and tidal Mud deposition and tidal

wetlands at head of estuarywetlands at head of estuary

Estuaries and sequence Estuaries and sequence stratigraphystratigraphy

► Incised valley during lowstand.Incised valley during lowstand.► Estuarine valley fill during transgression and Estuarine valley fill during transgression and

highstand.highstand.► Processes and infill are time and space Processes and infill are time and space

dependent.dependent.


Ancient estuarine faciesAncient estuarine facies► Prograding estuarine succession:Prograding estuarine succession:

Fluvial (above)Fluvial (above) Bay-head deltaBay-head delta EstuarineEstuarine Marine nearshore (below)Marine nearshore (below)

► Complexities due to s.l variationComplexities due to s.l variation► Criteria for recognition:Criteria for recognition:

Tidal faciesTidal facies Brackish water biotaBrackish water biota


Linear clastic (incl. barrier) Linear clastic (incl. barrier) coastscoasts

► Depositional coasts away from deltas and Depositional coasts away from deltas and estuaries.estuaries.

► High wave energy (micro- to mesotidal).High wave energy (micro- to mesotidal).

Shoreline types: wave vs. tidal Shoreline types: wave vs. tidal energyenergy

DefinitionsDefinitions

Beach and barrierBeach and barrier systems systems► Beach - narrow strip of sand Beach - narrow strip of sand

or gravel attached to a or gravel attached to a coastline.coastline.

► Strandplain - broad, Strandplain - broad, composite beach. composite beach.

► Barrier - beach complex Barrier - beach complex enclosing a lagoon.enclosing a lagoon.


Shoreline type (morphology)Shoreline type (morphology)

► AttachedAttached► DetachedDetached


Coastline variability: tidal Coastline variability: tidal rangerange

► Moderate wave energy, variable tidal range:Moderate wave energy, variable tidal range:

Shoreline subenvironmentsShoreline subenvironments► Attached beaches and intertidal flats.Attached beaches and intertidal flats.► Partly attached spits.Partly attached spits.► Detached barriers, tidal inlets and lagoon complexes.Detached barriers, tidal inlets and lagoon complexes.► Shoreface slope and shelf transition.Shoreface slope and shelf transition.


TidesTides► Lunar influence gives Lunar influence gives

semi-diurnal tides semi-diurnal tides (interval 12.42 hours)(interval 12.42 hours)

► Variations in successive Variations in successive semi-diurnal tides give semi-diurnal tides give different semi-diurnal to different semi-diurnal to diurnal tide spectrumsdiurnal tide spectrums

► Solar influence gives Solar influence gives spring-neap cycle (period spring-neap cycle (period 14.77 days, 28 tidal 14.77 days, 28 tidal cycles for semi-diurnal cycles for semi-diurnal tides).tides).

► Flood and ebb-tideFlood and ebb-tide► Slackwater at high and Slackwater at high and

low-tidelow-tide


TidesTides

► Tides develop fully in Tides develop fully in oceans; smaller seas oceans; smaller seas and lakes show smaller and lakes show smaller tidestides

► Open ocean tide has Open ocean tide has amplitude of <1 mamplitude of <1 m

► Tidal range increases:Tidal range increases: on shallow shelveson shallow shelves along convergent coastsalong convergent coasts where resonance where resonance

amplification occurs amplification occurs (where natural period of (where natural period of water body is close to water body is close to astronomic period) astronomic period)

Corner , 2005

TidesTides

Tidal rangeTidal range► Classification of mean Classification of mean

tidal range (Davies tidal range (Davies 1980):1980): Microtidal: 0 - 2 mMicrotidal: 0 - 2 m Mesotidal: 2 - 4 mMesotidal: 2 - 4 m Macrotidal: > 4 mMacrotidal: > 4 m (Megatidal: > 8 m)(Megatidal: > 8 m)

► High tidal range in High tidal range in several areas, e.g:several areas, e.g: S and W coast of UKS and W coast of UK

► Maximum tidal range at:Maximum tidal range at: Bay of Fundy (Maine) Bay of Fundy (Maine)

(16.3 m)(16.3 m)


Wave processesWave processes

►Significant wave height: mean ht of Significant wave height: mean ht of highest 1/3 of waves over a time highest 1/3 of waves over a time interval.interval.

Breaking wavesBreaking waves

►SpillingSpilling►PlungingPlunging►SurgingSurging

Wave refractionWave refraction

Rip currentsRip currents

Backwash/rip-current eddies at Breivikeidet

Beach profileBeach profile► Backshore (>HW)Backshore (>HW)► Foreshore (LW-HW)Foreshore (LW-HW)► Shoreface (<LW...)Shoreface (<LW...)► Offshore (< wave base)Offshore (< wave base)


Beach dynamics and Beach dynamics and sedimentationsedimentation

Beach morphpology and Beach morphpology and faciesfacies

► Onshore coarsening - forward obital wave Onshore coarsening - forward obital wave motion powerful compared with seaward motion powerful compared with seaward return flow.return flow.

► Beachface steeper in gravel than sand - Beachface steeper in gravel than sand - percolation weakens backflow. percolation weakens backflow.

► Summer profile with berm – constructive Summer profile with berm – constructive swell waves transport sediment onshore.swell waves transport sediment onshore.

► Winter profile with offshore bars – destructive Winter profile with offshore bars – destructive steep waves transport sediment offshore. steep waves transport sediment offshore.

Beach sedimentBeach sediment

► Onshore coarsening - forward obital wave Onshore coarsening - forward obital wave motion powerful compared with seaward motion powerful compared with seaward return flow.return flow.

Beach morphpologyBeach morphpology

► Beachface steeper in gravel than sand - Beachface steeper in gravel than sand - percolation weakens backflow.percolation weakens backflow.

Summer-winter profilesSummer-winter profiles

► Summer profile with berm – constructive swell Summer profile with berm – constructive swell waves transport sediment onshore.waves transport sediment onshore.

► Winter profile with offshore bars – destructive Winter profile with offshore bars – destructive steep waves transport sediment offshore. steep waves transport sediment offshore.

Waikiki Beach, Hawaii

Beach bedforms and Beach bedforms and structuresstructures

► Planar (low-angle) Planar (low-angle) bedding/cross-bedding/cross-beddingbedding

► Ripples and dunes.Ripples and dunes.

Sandbukt, Breivikeidet

Offshore barsOffshore bars

Barrier-inlet systemsBarrier-inlet systems

►Barrier, spitBarrier, spit►Tidal inlet and tidal deltaTidal inlet and tidal delta►WashoverWashover►LagoonLagoon►MarshMarsh

Barrier-inlet systemsBarrier-inlet systems

►Barrier, spitBarrier, spit►Tidal inlet, deltaTidal inlet, delta►WashoverWashover►LagoonLagoon►MarshMarsh

Tidal inlet and deltaTidal inlet and delta

ElementsElements main channel (inlet)main channel (inlet) tidal deltatidal delta

► ebb deltaebb delta► flood deltaflood delta

secondary tidal secondary tidal channelschannels

►Tidal deltaTidal delta

►Barrier dynamicsBarrier dynamics Storm erosion and rebuildingStorm erosion and rebuilding WashoversWashovers Inlet migrationInlet migration

►Response to sea-level changeResponse to sea-level change

Tidal flats and chenier ridgesTidal flats and chenier ridges


► Onshore-offshore sediment transportOnshore-offshore sediment transport a) spring tidea) spring tide b) neap tideb) neap tide

► Strandplain and spit at BreivikeidetStrandplain and spit at Breivikeidet

ge0-3112 sedimentary processes and products lecture 10. estuaries and coasts geoff corner department...

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