6 june, 2016 · •to close this gap, a new high-resolution wave hindcast and forecast system is...

6th June, 2016

Bilgola Beach, 10th June, 1974

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Timeline of June 2016 storm: “t minus 5 days”

Significant (peak Hsig = 6.3 m)

storm event from unusual ENE

direction coincidentally forecast to

coincide with king tides

Mitch Harley

Storm forecast scaled back to

smaller event (peak Hsig = 3.5 m)


Mitch Harley

Storm forecast scaled back up

to peak Hsig = 5.1 m


Mitch Harley

Storm forecast converging around

peak Hsig ≈ 5 m


Mitch Harley

June, 2016

A handful of researchers knew a week in advance this erosion

event was likely to happen, but very few people who really needed

to know had been informed….

→ and there is currently no existing mechanism to do so

Water Research Laboratory | School of Civil & Environmental Engineering

beach erosion Early Warning System (EWS): a new national research initiativeProf. Ian Turner, WRL Director

Diana Greenslade, Mitch Harley, Jeff Hansen, Ryan Lowe, Mike Kinsela, et al….

Coastal Erosion in the Australian context:

why does it matter?

• Australia is a distinctly coastal-focused nation

- 85% of Australians are presently living within a narrow coastal strip and this is increasing

• Recent attempts to assess our national assets at risk to coastal hazards include1:

- roads ($40 - 60 billion)

- commercial buildings ($58 – 81 billion)

- residential property ($41 – 63 billion)

- enormous cultural and environmental value of beaches to Australians

• It is estimated that the amenity and storm protection provided

by beaches nationally is in the range of2:

$3.8 - $13 million for every kilometre of sandy shoreline.

1 DCCE, 2011 2 Blackwell, 2005


4 decades of coastline monitoring at Narrabeen-Collaroy

Andy Short, circa 1976 Josh Simmons, 2017


4 decades of coastline monitoring at Narrabeen-Collaroy

Historical profile surveys (commenced 1976):

• 3.6 km long embayed beach located on

northern beaches of Sydney (20km north of UNSW)

• microtidal, wave-dominated coastline

(mean Hsig = 1.6 m, Tp = 10 s)

• fortnightly surveys of fourteen profile lines

commenced in April 1976

• after a few years, reduced to monthly

surveys of five representative profile lines

0 50 100 150 200 250-8

-6

-4

-2

0

2

4

6

8

10

Distance (m)

Ele

vatio

n (

m)

Surveys undertaken using the Emery method, a low-cost technique

using two graded poles and a measuring tape

Historical profile surveys (1976-2006):

Video imaging (Argus)

2004 – present

(hourly)

RTK-GPS + Quad bike

2005 – present

(monthly)

Fixed Lidar

2014 – present

(5 Hz)

Unmanned Aerial Vehicle

2014 – present

(pre/post storm)

Airborne Lidar

2011 – present

(pre/post storm)

Evolution of monitoring program (post 2004):

Automated shoreline mapping algorithm has

collected ~100,000 hourly shorelines over

the past 1.5 decades (August 2004 –

present)

31 m

PASHA BULKA

Example - video imaging

4 decades of monitoring: what does the data tell us?

Long-term

Ongoing 40+years of monthly

profile measurements (RTK-GPS)

Unmanned Aerial Vehicle

2014 – present

(pre/post storm)

Airborne Lidar

2011 – present

(pre/post storm)

Continuous + mid-storm

- Coastal Imaging Station (half-hourly)

- Fixed Lidar (5 Hz)

Rapid pre/post deployment

- Airborne Lidar

- UAV (Fixed wing + Quadcopter)

- Jet-ski + Echosounder (NSW OEH)

- Mini waverider buoy (NSW OEH)

June 2016: rapid-response coastal storm

monitoring & modelling project was underway(Australian Research Council – Discovery Project)

Historical perspective – storm erosion demand (1976 – 2016)*

Rank Storm Average (max.) storm demandǂ

(m3/m)

1 June 2016 103 (151)

2 May 1997 76 (137)

3 June 2007 73 (96)

4 April 2015 62 (95)

5 August 1986 58 (68)

* Based on five historical profile lines onlyNarrabeen-Collaroy

Storm June

2007

April

2015

June

2016

Peak Hsig (m) 6.9 8.1 6.5

Average storm direction (° TN) 149 161 107

Duration (h) 65 72 74

Total storm energy (MJh) 1.13 1.37 0.89

Peak water level (m) 0.95 1.22 1.29

Offshore wave measurements

* the dominance of a subtle shift in wave direction

**

* 1 in 5 year event only

‘typical’ storm

wave direction

Vulnerability to wave direction

Mitch Harley

June 2016 storm

direction

‘typical’ storm

wave direction

Vulnerability to wave direction

Mitch Harley

• Operated by UNSW School of Aviation

(<24 hr mobilisation)

• Equipped with Riegl LMS240i Laser Scanner

• Flown pre- and post-storm for regional-scale storm

impact assessments, between Sydney and Coffs

Harbour, NSWNarrabeen

-Collaroy

Narrabeen

-Collaroy

RegionalRegional

400 km400 km

Narrabeen

-Collaroy

Regional

400 km

Regional Response: UNSW rapid-response airborne Lidar

Regional response:

the importance of

local wave direction

• 180 km of sandy coastline

• diverse sediments, orientation,

embayment length, dunes, etc

• Δm3/m every 100m alongshore

• local wave energy & inshore

wave direction (@10 m water depth)

similarly reveals the dominantinfluence of (unusual) wave direction on the observed coastal erosion in SE Australia

Harley et al, 2017. Extreme Coastal Erosion enhancedby anomalous extratropical wave direction.Nature Sci. Rep. 7(1), 6033

Mitch Harley

Lessons learnt for future disaster risk management

• Enhanced erosion not necessarily just a factor of more intense storms and/or sea level

rise – other more subtle changes such as shifting wave direction have the potential to

dominate for the next several decades

• The June 2016 storm also just happened to occur during a King Tide, which further

magnified its impact → foreshadowing the increase in the coastal impact of storms, as

sea levels continue to rise during this Century.

• A few university researchers knew the likely impact of this storm was coming a week in

advance…. but the subtleties of a slightly different wave direction - rather than necessarily

a ‘big’ storm - was understandably missed by the wider coastal management community

and emergency services

• Most importantly, presently in Australia there is no nationally or state-coordinated

COASTAL EROSION EARLY WARNING SYSTEM capability

Lessons learnt for future disaster risk management

The Project:

A new national research initiative to deliver the

knowledge framework and practical guidelines for:

An Australian storm wave damage and beach

erosion Early Warning System

Recognising the significant diversity in coastal landforms around Australia’s

coast, this project is targeted at open ocean sandy shorelines

Two key components:

Tier 2: Localised, high resolution,

hot spot process based model

Tier 1: Regional-scale, first pass

forecasting @100m alongshore

rolling forecasts of approaching (7 → 0 days)

storm waves and water-levels

knowledge of localised pre-storm

coastline conditions

rolling regional forecasts of the

location and type of localise impacts

rolling ensemble site-specific forecasts of

quantitative beach & dune erosion demand

effective and timely delivery of impact/erosion

information, that addresses the needs of specific

emergency services and coastal managers

Conceptual EWS framework:

Two test-case regions and pilot ‘hot-spot’ sites in WA & NSW~300 km of coastline in WA (Mandurah) ~ 300 km of coastline in NSW (Narrabeen)

rolling forecasts of approaching (7 → 0

days) storm waves and water-levels











New variable-resolution wave modelling for coastal applications

• The Bureau of Meteorology's operational wave forecast system (AUSWAVE) is

relatively coarse in spatial resolution (1/10o) and is therefore not able to

accurately represent the transformation of deep-water waves to the nearshore.

• To close this gap, a new high-resolution wave hindcast and forecast system is

being developed and trialled to provide detailed wave information at the coast.

• The pilot system is an implementation of WAVEWATCH III® with variable

resolution of up to 250 m in the coastal zone.

• The model is forced with surface winds from BOM’s operational Numerical

Weather Prediction (NWP) System.

• The coastal wave models are nested within a new global configuration of

AUSWAVE that is initially being evaluated along two ~300km stretches of

metropolitan coastlines in WA and NSW.

Further details: Stefan Zieger et al, Coasts & Ports 2019

Pilot regions and test sites in WA & NSW:

New Argus station, Mandurah

cBathy – ‘real-time’ video-derived bathymetry coastSat – automated assimilation of ‘real-time’ beach width & slope

Airborne lidar

10 20 30 40 50 60 70 80 90 100-1

-0.5

0

0.5

1

1.5

2

2.5

3

3.5Lidar Low Tide Profile Data

Cross-shore Distance (m)

Ele

vati

on

(m

AH

D)

03:16 20/04/2015

05:56 23/04/2015

04:58 20/06/2015

16:34 20/06/2015

17:18 21/06/2015

06:18 22/06/2015

18:06 22/06/2015

07:00 23/06/2015

19:00 23/06/2015

07:45 24/06/2015

20:02 24/06/2015

08:34 25/06/2015

21:12 25/06/2015

09:24 26/06/2015

22:19 26/06/2015

10:12 27/06/2015

23:19 27/06/2015

10:59 28/06/2015

00:10 29/06/2015

11:43 29/06/2015

00:56 30/06/2015

12:26 30/06/2015

Fixed lidar (continuous)

Of course, we are not the first to think about this…

Sources: Sallenger, A. (2000). Storm Impact Scale for Barrier Islands. Journal of Coastal Research, 16(3).

https://marine.usgs.gov/coastalchangehazardsportal/

U.S. East Coast:

• Wide continental shelf generating large storm surge

• Hazards caused by elevated water levels

Large regions of Australia’s sandy open coasts:

• Narrow continental shelf allowing wave energy to reach coast

• Hazards caused by wave energy

Sources: NOAA ETOPO1 Global Relief Model,

UCAR COMET Program

Is the Storm Impact Scale a useful framework in the Australian context?

Storm Impact Scale is only based on the vertical dimension


Is there a better framework?

Storm Impact Scale is only based on the vertical dimension

But around much of Australia’s open sandy coastlines, erosion hazardsshould be primarily defined in the horizontal dimension

Is there a better framework?

Further details: Chris Leaman et el, Coasts & Ports 2019

The development of a new storm impact matrix

Further details: Chris Leaman et el, Coasts & Ports 2019

Quantitative ‘hot-spot’ erosion forecasting:

Storm Demand m3/m But knowledge of pre-storm bathymetry is required as

a boundary condition …..

XBeach is currently the ‘best practice’

storm erosion modelling tool

Evaluating XBeach prediction sensitivity to pre-storm bathy

Preliminary conclusions:

•Use of measured pre-storm bathymetry generally

results in the most accurate predictions of sub-

aerial beach & dune erosion

•Average bathymetry and Dean-type profiles are

the next best choice

•An accurate estimate of the typical surfzone

gradient for a site is crucial – detailed and

regularly updated bathmetry surveys of the

surfzone may be of lesser importance

Further details: Nash Matheen et el, Coasts & Ports 2019









effective and timely delivery of

impact/erosion information, that addresses

the needs of specific emergency services

and coastal managers


Selection of a suitable data assimilation and EWS platform

EWS communication and dissemination

Key next steps:

and now for an advert…..

56

…thanks

6 june, 2016 · •to close this gap, a new high-resolution wave hindcast and forecast system is...

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