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Lecture 10. Estuaries and coasts. GE0-3112 Sedimentary processes and products. Geoff Corner Department of Geology University of Tromsø 2006. Literature: Leeder 1999. Ch. 21 Estuaries. Ch. 23, ’Linear’ clastic coastlines. Contents. Coastal depositional systems Estuaries

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ge0 3112 sedimentary processes and products
Lecture 10. Estuaries and coastsGE0-3112 Sedimentary processes and products

Geoff Corner

Department of Geology

University of Tromsø

2006

Literature:

Leeder 1999.

Ch. 21 Estuaries.

Ch. 23, ’Linear’ clastic coastlines.

contents
Contents
  • Coastal depositional systems
  • Estuaries
  • Barrier-beach coasts
coastal depositional systems
Coastal depositional systems
  • Controlling factors:
    • Sediment supply (rivers, coastal cliffs, alongshore transport).
    • Wave energy
    • Tidal range
  • Deltas vs. other coastal systems
    • Local dominance of point-source sediment supply  deltas.
    • Dominance of basinal processes  linear clastic coasts, estuaries, etc.
    • Estuaries a special case where fresh and saltwater interact.
coastal types
Coastal types
  • Deltas
  • Beaches
  • Barriers
  • Strandplains
  • Tidal flats
  • Estuaries

Galloway & Hobday 1996

estuaries
Estuaries
  • Definition
  • Processes (mud suspension)
  • Circulation types (type A, B, C, D)
  • Facies: tide- and wave-dominated estuaries
  • Estuaries and sequence stratigraphy
  • Ancient estuarine facies
estuary definitions
Estuary definitions

Walker & James, 1992

Various definitions:

  • Hydrologic (oceanographic): stratified water mass with riverine water (fresh - brackish) overlying or mixed with marine water (brackish - salt).
  • Geomorphologic: coastal inlet, usually a drowned river valley.
  • Geologic: semi-enclosed coastal body of water having free access to the sea and containing seawater measurably diluted by water from land drainage.
slide8

Manukau and

Waikato estuaries, NZ (mesotidal)

slide9
NB. Estuary type (circulation) varies in space & time:
    • From inner to outer
    • From neap to spring phase of tidal cycle
    • Seasonally with variation in river discharge

Tidal/fluvial discharge ratio

vs.

fluvial discharge

estuarine processes
Estuarine processes
  • Fluvial and marine sediment flux.
  • Wave- and tidal reworking.
  • Fresh, brackish and marine water.
  • Sand, mud and bioturbation.
mud suspension and resuspension
Mud suspension and resuspension
  • Flocculation enhances settling.
  • High particle concentration reduces settling.
  • Layers of suspended form in response to tidal pumping.
suspended sediment concentration
Suspended sediment concentration
  • Hindered settling and flocculation produce a lutocline at high sediment concentrations.

Dilute

Concentrated

estuarine circulation
Estuarine circulation
  • Four types:
    • Type A: well stratified
    • Type B: partly stratified
    • Type C: well mixed
    • Type D: homogenous (theoretical end member)
type a estuaries
Type A estuaries
  • Well stratified, river dominated.
  • Salt wedge below buoyant plume
  • Low tidal/river discharge ratio (<20)
type a estuaries1
Type A estuaries
  • Cf. e.g. Mississippi, Fraser and Tana rivers.
  • Deposition at tip of salt wedge; sediment flushing as salt wedge migrates.

Fraser River

type b estuaries
Type B estuaries
  • Partially stratified, moderate tidal turbulence.
  • Salt wedge degraded; gradual salinity gradient.
  • Moderate tidal/river discharge ratio (20 – 200).
  • E.g. Tamar, nr. Plymouth.
type b estuaries1
Type B estuaries
  • Coriollis: up-estuary flow shallowest and strongest to the left in N. hemisphere.
  • Turbidity max. (in suspended particulate matter) most prominent in upper estuary on ebb and flood tides (low on slackwater).

Tamar estuary

type c estuaries
Type C estuaries
  • Well-mixed; strong tidal currents.
  • Salinity gradient downstream and laterally (Coriolis) but not vertically.
  • High tide/river discharge ratio (>200).
  • E.g. Severn, UK, Gironde, France, Weser, Germany.
type c estuaries1
Type C estuaries
  • Repeatable hysteresis of suspended matter concentration (C) with tidal velocity (u):

- deposition during slackwater.

- resuspension during

ebb and flood.

  • Clayey silt, sandy mud.
type d estuaries
(Type D estuaries)
  • Fully mixed; transitional to shelf.
  • No vertical or lateral salinity gradients.
  • Sediment movement by tides; no internal sediment trap.
modern estuarine facies
Modern estuarine facies
  • Sedimentological classification of estuaries:
    • Tide-dominated
    • Wave-dominated

Walker & James, 1992

basic model
Basic model

Walker & James, 1992

  • Subenvironments
    • Bayhead delta (A)
    • Central basin (B)
    • Estuary mouth (C)
  • Sediment types
    • Alluvial sands and gravels (A)
    • Bay silts and muds (B)
    • Marine sands (C)
    • NB. Upward-fining here reflects transgression

C

B

A

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

Severn,

Bay of Fundy.

tide dominated estuaries facies
Tide-dominated estuaries - facies
  • Alluvial
  • Tidal-fluvial channel
  • Saltmarsh/mudflats
  • Upper flow regime sand flats
  • Tidal sand bars
slide26

Walker & James, 1992

  • Example from Gironde-type estuary.
    • estuarine point bar sands w. mud A
    • tidal bar sands B
    • estuarine muds C
    • tidal inlet sands D

C

D

B

A

wave dominated estuaries
Wave-dominated estuaries
  • Micro- to mesotidal.
  • Stratified to partially stratified/mixed.
  • Lagoonal to funnel-shaped, semi-enclosed.
  • E.g.E. coast USA
slide28

UK

NZ

wave dominated estuaries facies
Wave-dominated estuaries - facies
  • Alluvial
  • Bay-head delta
  • Central basin
  • Flood-tidal delta
  • Barrier/tidal inlet
  • Shoreface
delaware estuary
Delaware estuary
  • Outer estuary:
    • E.Holocene – tide-dominated outer
    • L. Holocene – wave-dominated
  • Turbidity maximum:
    • Moved up-estuary in Holocene
    • Mud deposition and tidal wetlands at head of estuary
estuaries and sequence stratigraphy
Estuaries and sequence stratigraphy
  • Incised valley during lowstand.
  • Estuarine valley fill during transgression and highstand.
  • Processes and infill are time and space dependent.

Galloway & Hobday 1996

ancient estuarine facies
Ancient estuarine facies
  • Prograding estuarine succession:
    • Fluvial (above)
    • Bay-head delta
    • Estuarine
    • Marine nearshore (below)
  • Complexities due to s.l variation
  • Criteria for recognition:
    • Tidal facies
    • Brackish water biota

Galloway & Hobday 1996

linear clastic incl barrier coasts
Linear clastic (incl. barrier) coasts
  • Depositional coasts away from deltas and estuaries.
  • High wave energy (micro- to mesotidal).
definitions
Definitions

Beach and barrier systems

  • Beach - narrow strip of sand or gravel attached to a coastline.
  • Strandplain - broad, composite beach.
  • Barrier - beach complex enclosing a lagoon.

Walker & James, 1992

shoreline type morphology
Shoreline type (morphology)
  • Attached
  • Detached

Walker & James, 1992

coastline variability tidal range
Coastline variability: tidal range
  • Moderate wave energy, variable tidal range:
shoreline subenvironments
Shoreline subenvironments
  • Attached beaches and intertidal flats.
  • Partly attached spits.
  • Detached barriers, tidal inlets and lagoon complexes.
  • Shoreface slope and shelf transition.

Galloway & Hobday 1996

tides
Tides
  • Lunar influence gives semi-diurnal tides (interval 12.42 hours)
  • Variations in successive semi-diurnal tides give different semi-diurnal to diurnal tide spectrums
  • Solar influence gives spring-neap cycle (period 14.77 days, 28 tidal cycles for semi-diurnal tides).
  • Flood and ebb-tide
  • Slackwater at high and low-tide

Walker & James, 1992

tides1
Tides
  • Tides develop fully in oceans; smaller seas and lakes show smaller tides
  • Open ocean tide has amplitude of <1 m
  • Tidal range increases:
    • on shallow shelves
    • along convergent coasts
    • where resonance amplification occurs (where natural period of water body is close to astronomic period)

Corner , 2005

tides2
Tides

Tidal range

  • Classification of mean tidal range (Davies 1980):
    • Microtidal: 0 - 2 m
    • Mesotidal: 2 - 4 m
    • Macrotidal: > 4 m
    • (Megatidal: > 8 m)
  • High tidal range in several areas, e.g:
    • S and W coast of UK
  • Maximum tidal range at:
    • Bay of Fundy (Maine) (16.3 m)

Walker & James, 1992

wave processes
Wave processes
  • Significant wave height: mean ht of highest 1/3 of waves over a time interval.
breaking waves
Breaking waves
  • Spilling
  • Plunging
  • Surging
rip currents
Rip currents

Backwash/rip-current eddies at Breivikeidet

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

Galloway & Hobday 1996

beach morphpology and facies
Beach morphpology and facies
  • Onshore coarsening - forward obital wave motion powerful compared with seaward return flow.
  • Beachface steeper in gravel than sand - percolation weakens backflow.
  • Summer profile with berm – constructive swell waves transport sediment onshore.
  • Winter profile with offshore bars – destructive steep waves transport sediment offshore.
beach sediment
Beach sediment
  • Onshore coarsening - forward obital wave motion powerful compared with seaward return flow.
beach morphpology
Beach morphpology
  • Beachface steeper in gravel than sand - percolation weakens backflow.
summer winter profiles
Summer-winter profiles
  • Summer profile with berm – constructive swell waves transport sediment onshore.
  • Winter profile with offshore bars – destructive steep waves transport sediment offshore.

Waikiki Beach, Hawaii

beach bedforms and structures
Beach bedforms and structures
  • Planar (low-angle) bedding/cross-bedding
  • Ripples and dunes.

Sandbukt, Breivikeidet

barrier inlet systems
Barrier-inlet systems
  • Barrier, spit
  • Tidal inlet and tidal delta
  • Washover
  • Lagoon
  • Marsh
barrier inlet systems1
Barrier-inlet systems
  • Barrier, spit
  • Tidal inlet, delta
  • Washover
  • Lagoon
  • Marsh
tidal inlet and delta
Elements

main channel (inlet)

tidal delta

ebb delta

flood delta

secondary tidal channels

Tidal inlet and delta
slide59
Barrier dynamics
    • Storm erosion and rebuilding
    • Washovers
    • Inlet migration
tidal flats and chenier ridges
Tidal flats and chenier ridges

Galloway & Hobday 1996

slide62
Onshore-offshore sediment transport
    • a) spring tide
    • b) neap tide