GE Sedimentary processes and products Lecture 10. Estuaries and coasts Geoff Corner Department of Geology University of Tromsø 2006 Literature: Leeder Ch. 21 Estuaries. Ch. 21 Estuaries. Ch. 23, ’Linear’ clastic coastlines. Ch. 23, ’Linear’ clastic coastlines.

Contents ► Coastal depositional systems ► Estuaries ► Barrier-beach coasts

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 ► Deltas ► Beaches ► Barriers ► Strandplains ► Tidal flats ► Estuaries Galloway & Hobday 1996

Variation in coastal morphology as a function of tidal range

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 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. Walker & James, 1992

Manukau and Waikato estuaries, NZ (mesotidal)

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

Mud suspension and resuspension ► Flocculation enhances settling. ► High particle concentration reduces settling. ► Layers of suspended form in response to tidal pumping.

Suspended sediment concentration ► Hindered settling and flocculation produce a lutocline at high sediment concentrations. Dilute Concentrated

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

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 ► 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 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 ► 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 estuaries ► Repeatable hysteresis of suspended matter concentration (C) with tidal velocity (u): - deposition during slackwater. - resuspension during ebb and flood. ebb and flood. ► Clayey silt, sandy mud.

(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 ► Sedimentological classification of estuaries:  Tide-dominated  Wave-dominated Walker & James, 1992

Basic model ► 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 A B C Walker & James, 1992

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

Tidal flats, Banks Peninsula, NZ

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

► Example from Gironde- type estuary.  estuarine point bar sands w. mud A  tidal bar sands B  estuarine muds C  tidal inlet sands D A B C D Walker & James, 1992

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

UK NZ

Wave-dominated estuaries - facies ► Alluvial ► Bay-head delta ► Central basin ► Flood-tidal delta ► Barrier/tidal inlet ► Shoreface

Waikato River estuary, NZ

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 ► 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 ► 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 ► Depositional coasts away from deltas and estuaries. ► High wave energy (micro- to mesotidal).

Shoreline types: wave vs. tidal energy

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) ► Attached ► Detached Walker & James, 1992

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

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 ► Lunar influence gives semi-diurnal tides (interval hours) ► Variations in successive semi-diurnal tides give different semi-diurnal to diurnal tide spectrums ► Solar influence gives spring-neap cycle (period days, 28 tidal cycles for semi-diurnal tides). ► Flood and ebb-tide ► Slackwater at high and low-tide Walker & James, 1992

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

Tides Tidal range ► Classification of mean tidal range (Davies 1980):  Microtidal: m  Mesotidal: 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 ► Significant wave height: mean ht of highest 1/3 of waves over a time interval.

Breaking waves ► Spilling ► Plunging ► Surging

Wave refraction

Rip currents Backwash/rip-current eddies at Breivikeidet

Beach profile ► Backshore (>HW) ► Foreshore (LW-HW) ► Shoreface (<LW...) ► Offshore (< wave base) Galloway & Hobday 1996

Beach dynamics and sedimentation

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

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

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 ► Planar (low-angle) bedding/cross-bedding ► Ripples and dunes. Sandbukt, Breivikeidet

Offshore bars

Barrier-inlet systems ► Barrier, spit ► Tidal inlet and tidal delta ► Washover ► Lagoon ► Marsh

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 delta

► Barrier dynamics  Storm erosion and rebuilding  Washovers  Inlet migration

► Response to sea-level change

Tidal flats and chenier ridges Galloway & Hobday 1996

► Onshore-offshore sediment transport  a) spring tide  b) neap tide

► Strandplain and spit at Breivikeidet

Further reading