th May 2017, University of the Sunshine Coast Understanding coastal processes … · 2017-05-25 ·...

Specks of Sand - Coastal science forum 13th May 2017, University of the Sunshine Coast

Specks of Sand - Coastal science forum, University of the Sunshine Coast Griffith Centre for Coastal Management, Griffith University

Specks of Sand - Coastal science forum, University of the Sunshine Coast

Understanding coastal processes through monitoring

Dr Darrell StraussAdvance Qld Research Fellow

Research ManagerGriffith Centre for Coastal Management

d.strauss@griffith.edu.au

Dr Darrell Strauss

Advance Qld Research FellowResearch Manager

Griffith Centre for Coastal ManagementCities Research Institute

Griffith University

d.strauss@griffith.edu.au

GCCM Coastal Research

• Coastal infrastructure and natural asset management

• Catchments and waterways• Water future• Climate Change and adaptation• Extreme events and disaster

management• Community engagement and

education – CoastED and BeachCare• Beach and estuarine ecology• Economic values

Research Interests

• Coastal Geomorphology and Oceanography• Beach and Surf Morphology, Rip Currents • Extreme Events, Beach Erosion & Recovery• Numerical Modelling - Waves, hydrodynamics,

sediment transport

Flash Rip - Coolangatta

Morphodynamic Response to Large Scale Nearshore Beach Nourishment

Dr Darrell Strauss, Dr Tom Murray, Ms Gaelle Faivre

Advance Qld Research Fellowship 2016-2019City of Gold Coast Research ProgramGriffith University

Aims• develop process understanding and numerical

modelling capability of sand transport in shallow water waves and currents

• particular focus on the onshore movement of sand

• high-resolution field-scale measurements of bar responses to a large-scale nearshore nourishment projects on Gold Coast beaches.

-50 50 150 250 350 450

3/02/2016 3/04/2016 21/04/2016 31/05/2016 22/06/2016

• Profile surveys show bar crest change • offshore bar migration, Feb 2016 – June 2016

-50 150 350 550

ETA 79

3/02/2016 3/04/2016

-50 150 350 550

ETA 78

3/02/2016 3/04/2016

-50 150 350 550

ETA 77

3/02/2016 3/04/2016

-50 150 350 550

ETA 76

3/02/2016 3/04/2016

Inconsistent bar response at

400m transects

requires higher resolution surveys

for process understanding and

numerical model validation

Specks of Sand - Coastal science forum, University of the Sunshine Coast3/2/2016 3/4/2016 Difference Plot

ETA 79

ETA 78

ETA 77

ETA 76

ETA 79

ETA 78

ETA 77

ETA 76

Infilling of rip

channels

High resolution survey reveals shoreward migration at ETA76 but also in between profiles ETA78 & ETA 79

Coasts?Land-sea interface

Sediments Fine – mud, sand Coarse – shell, gravel, stony

EnergyWindWavesCurrentsTides

VariabilityStormsSeasonsClimate Change

Beach and Nearshore Zone

Schematic view of nearshore zone with corresponding terminology (not to scale) (Schwartz, 2005)

Trough

Spatial and Temporal Scales of Coastal Processes and Evolution

(Cowell and Thom, 1994)

Sea level change

Dunes/ridges

Back Barriers/Estuaries

Tidal Inlets/Deltas

Beaches/Storms

Tides/beachface

Individual waves

Australian Beaches – Issues - Impacts

• Early development in erosion prone areas (dune removal)

• Coastal Infrastructure – ports, estuaries, training walls, groynes

• Tourist destinations, accessibility

• Storm periods

e.g. 1860s-1890s, 1930s, 1950s-1970s

• Major Cyclones, East Coast Lows (QLD)

1954, 1967, 1972, 1974 2007, 2009, 2013, June 2016, March 2017

Australian Beaches

10,685 beaches (Short, 2006)

15 beach types: 6 wave dominated; 3 tide modified; 4 tide dominated; 2 rock flats

or fringing coral reef beaches.

47% Wave dominated - High wave energy, low tide range (<2m)

e.g. exposed ocean coasts of WA, SA, Tas, Vic, NSW and SE Qld.

Australian Beaches

10,685 beaches (Short, 2006)

11% Tide modified – lower wave energy, medium tide range (~2-6m)

e.g. SA gulfs and bays, NW Tasmania, Central Qld

34% Tide dominated – low wave energy, high tide range (2-11m)

e.g. Northern Australia

Wave Dominated Beaches

e.g. Typical surf beaches of Gold Coast, NSW, VIC, SA, SW WA

• Beach states further categorised into dissipative, intermediate, reflective (Wright & Short, 1984; Short 1999)

• Intermediate states include:LBT - Longshore Bar & TroughRBB - Rhythmic Bar & BeachTBR - Transverse Bar & RipLTT – Low Tide Terrace

• Swimmer hazards, rip currents, erosion hotspots• Beach states change with wave conditions and

affect resilience

Wave Climate

NE swell

E Swell

SE swell

S swell

Cyclones

WSW swell

Swell Season – Summer/Autumn (December – May)

Palm Beach short groynes

• Persistent ESE-SE trade winds & swell in SE QLD

• energetic, consistent surf

• Poor windswelland onshore winds in Sth NSW

• Largest waves out of the ENE-ESE (TC’s and East Coast Lows)

• Afternoon seabreezes

Swell Season – Winter (June – August)• Highs track north, SE trade winds north of SE QLD

• Decreased wave energy from Summer to Autumn in SE QLD

• Increased likelihood of East Coast Low’s affecting East Coast

• Southern Ocean Lows pass from W to E generating south swells that often bypass SE Qld coast

• More offshore winds (SW-NW)

Swell Season – Spring (September – November)

•Typically the smallest wave

heights in SE Qld

• Increase in N winds and N-NE

windswell

• Dominant SE swell persists

(although typically lower energy

than other seasons) – SE QLD

Cross shore Sediment Transport• Storm events, surges, high tides • Dune scarps• Storm bar creation / offshore migration• Beach accretion / onshore migration

Offshore sediment movement

Onshore sediment movement Depth of closure

Offshore sand migration / erosion (12/12/2011 – 31/12/2011)

Onshore sand migration / accretion (29/7/2011 – 02/09/2011)

Cross shore Sediment Transport

Shoreface zone is less active, but equally significant

Surf zone (bar zone) is most dynamic

Depth of closure – very minor change

Longshore Sediment Transport• Littoral drift • Straight or curved beaches• Structures, groynes, headlands, reefs

• Trapping and Bypassing

Headland Bypassing• Oblique wave approach• Longshore current• Littoral drift bypassing and entrance infilling

Coastal Monitoring and Data Collection

http://narrabeen.wrl.unsw.edu.au/

Wave Monitoring

Wave Rider Buoys (DSITI, Qld Govt)

Remote sensing - satellite, video

Pressure gauges

Acoustic Doppler (ADCP)

Wave Statistics

Hs, (H1/3) Significant Wave Height

Tp, Tm Peak, Mean, Period

Dp, Dm Peak, Mean Direction

Coastal Imaging – Fixed Coastal Camera Networks

http://ci.wrl.unsw.edu.au/current-projects/northern-gold-coast-narrowneck-reef/

Coastal and Nearshore Survey• Traditional Survey Methods: Emery method (onshore),

Theodolite & staff (surf zone), Boats (offshore)

• Modern Survey Methods: DGPS, RTK-GPS, PWC (surf

zone), Terrestrial and Marine Lidar, Multibeam, Drones!

Survey methods

Increased resolution in space and time

e.g. 400 m spacing vs 50 m spacing

3/2/2016 3/4/2016 Difference Plot

ETA 79

ETA 78

ETA 77

ETA 76

ETA 79

ETA 78

ETA 77

ETA 76

Infilling of rip

channelHigh spatial frequency survey (jetski and land based RTK)

Drones (UAVs)

Debris line Mackay – Cyclone Debbie March 2017

- Data used to calibrate storm surge models (Qsurge)

Tanna Island – Vanuatu 2017

- Drone imagery to develop Point cloud survey for coastal resilience study

Longshore sediment transport and headland bypassing

Santa Catarina Island, Brazil

• Traditional Surveying

• Current Meters

• Sediment Traps

• Sediment Tracer

• Turbidity Loggers

Sediment Transport and Grain size Characteristics

Fluorescent sediment tracersHelley-Smith Sediment Sampler –sediment transport / headland bypassing

Turbidity Logger – converts turbidity into suspended sediment concentration

Grain size distribution from a particle analyser

Physical process based models

2D/3D process basede.g. DELFT3D, Mike 21, XBeach

Cross-shore (storm cut)e.g. Sbeach, EVO

Longshore (shoreline)

Inform decision making & management strategies

Thank you!

th May 2017, University of the Sunshine Coast Understanding coastal processes … · 2017-05-25 ·...

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