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Photo: Sugar Loaf Wharf, Coromandel. Jan 5 2014, Stuart Crawley, WRC

Coastal Inundation

An Overview for TCDC

Rick Liefting

Team Leader Regional Hazards and Environmental Compliance

Integrated Catchment Management

Waikato Regional Council

What we will be covering……

• Coastal inundation concepts

• Event frequency (how big, how often?)

• Coastal Inundation Tool

• Current and proposed updated MfE guidance

• WRC’s role in coastal inundation

Coastal Inundation

• Inundation along the coast and within estuaries caused by:

• Astronomical Tides

• Climate (sea temperature changes)

• Storm Surge – wind set up and Barometric pressure (1 HPa = 1 cm)

• Storm Tide = Astronomical Tides + Storm Surge

• Wave effects

• Wave Set up (‘static’ water level along the coast)

• Wave Run up (‘Swash’ of wave up the beach/coast)

• Effects of Climate Change

• Sea level rise

• Increased frequency and Intensity of storm and wave events

King Tides November, 2016

Kaiaua (Firth of Thames)


Thames (Firth of Thames)

Astronomical Tides

• Relatively easy to obtain and are district wide• Tide range varies

• Vertical datum is based on Astronomical tides – Mean Sea

Level.

• Moturiki VD 1953 (MVD)

• Auckland VD 1946 (+ 0.9 mm w.r.t MVD)

• Tararu Local VD 1952 (+ 128 mm w,r,t MVD)

• Sea level have been increasing at ~1.7 mm/year

• Therefore, add ~ 0.1m to obtain current MSL.

Assessment of Coastal Inundation Hazard• Currently no regional or district wide assessment of

Coastal inundation hazard or risk

• Some site specific assessments –(Resource

Consents)

• Determination of ‘Storm Tide’ can be under taken

at a ‘district’ level (i.e. East coast Coromandel)

• Wave effects are tricky to predict and are very site

specific

• LiDAR of coastal area up to 20 m elevation

Assessment of Coastal Inundation Hazard

• ‘Static water’ level = Tides + Storm + Climate+ SLR• Affects all coastal areas (i.e. Inland from the coast)

• Relatively easy to assess and map

• ‘Dynamic water level’ = Wave Set up/Run up• Affects the coastal margins only

• Open coast vs inland coast (estuaries/Harbours)

• Landward extent variable depending on topography and

roughness

• Very site specific (compare Tairua vs Pauanui)

Event Frequency

• The size of an event is based on the frequency or

probability of the event occurring over a period of

time.

• Based on measured/historical information.

• Average Return Interval– Frequency that an

event of a certain size will occur (e.g. 100 y ARI)

• Annual Exceedance Probability (AEP) –

probability that an event will be exceeded in any

one year (e.g. 1% AEP)

Event Frequency

Return Period (y)

Annual ExceedanceProbability

(AEP)

Time Period (y) - approx

2 5 10 20 50 100 200

2 50.0% 75% 97% 100% 100% 100% 100% 100%

5 20.0% 36% 67% 89% 99% 100% 100% 100%

10 10.0% 19% 41% 65% 88% 99% 100% 100%

20 5.0% 10% 23% 40% 64% 92% 99% 100%

50 2.0% 4% 10% 18% 33% 64% 87% 98%

100 1.0% 2% 5% 10% 18% 39% 63% 87%

200 0.5% 1% 2% 5% 10% 22% 39% 63%

Wave surge Whitianga – March 2015• https://www.facebook.com/TheInformerMB/videos/

376127242571144/

https://www.facebook.com/TheInformerMB/videos/376127242571144/

Tararu Tide Gauge (Firth of Thames)

AEP

(%)

ARI

(years)

Water

level (m)

Diff

(m)

39 2 2.20

18 5 2.30 0.1

10 10 2.35 0.05

5 20 2.43 0.08

2 50 2.54 0.11

1 100 2.62 0.08

0.5 200 2.71 0.09

• Extreme Storm

Tide analyse

(NIWA 2015)

Tararu Tide Gauge (Firth of Thames)

AEP (%)

ARI

(years)

Water

level (m)

Diff

(m)

39 2 2.20

18 5 2.30

10 10 2.35 20 y 100 y

5 20 2.43

0.19

64% 99%

2 50 2.54 33% 87%

1 100 2.62 18% 63%

0.5 200 2.71

• Extreme Storm

Tide analyse

(NIWA 2015)

Better way to inform about event frequency?• Niwa (Scott Stephens) doing some great work to

determine:

“How many times will this place get affected”

And

“How many more times with Climate Change”

• Provides better context in terms of assessing

Risk as Acceptable/Tolerable/Intolerable

Coastal Inundation Tool

What is it?

Web based tool that allows users to

explore present day and future

susceptibility of coastal inundation

from tides and storm tides along

Waikato coastlines.

Why do we need it?• High demand for information on potential

effects of present day and future coastal

inundation levels.• Public

• Local councils

• Insurance

• Life line utilities

• Difficult to visualise ‘a number’ and explore

scenarios

• Emergency Management

Whitianga Waterways, 24 June 2017

Source: Thomas Everett Source: Thomas Everett


Thames (Firth of Thames)

Low air

pressure

On shore

winds

What does it show?

Wave

Effects

Present Day Coastal Water Level Estimates Tide Model and Tide Gauges

Storm

Effects Lower Storm Tide (semi annual)

Upper Storm Tide (worst case)

Max Tide

MHWS

Datum (Moturiki Vertical Datum 1953)

Tide

Effects

X

What does it show?Future Coastal Water Levels Sea Level Rise added to Present Day Values

Storm



Max Tide

MHWS


Tide

Effects

What does it show?Future Coastal Water Levels Sea Level Rise component added to Present Day

Values

Storm



Max Tide

MHWS


Tide

Effects

Pre-defined Water Level

Scenarios

Firth of Thames

Coro West Coast

Coro East Coast

ThamesCoro

HarbourMercury

Bay

Present Day

Mean High Water Spring (m) 1.79 1.58 1.10

Max High Tide (m) 2.11 1.86 1.29

Storm Tide Range (Estimate)

Lower (m) 2.20 1.88 1.40

Upper (m) 3.22 2.67 2.10

Future Projected

0.5 m projected Sea Level

Rise


Max High Tide (m) 2.61 2.36 1.79


Lower (m) 2.70 2.38 1.90

Upper (m) 3.72 3.17 2.60

1.0 m projected Sea Level

Rise


Max High Tide (m) 3.11 2.86 2.29


Lower (m) 3.20 2.88 2.40

Upper (m) 4.22 3.67 3.10


King Tides

February 2, 2014

Pauanui WaterwaysTairua Harbour

Whitianga - Buffalo Beach (Mercury Bay)

Gangways underwater

Tairua - Paku Boat Ramp

Tairua – Fishing Club,

tide coming up through

stormwater drains

Public road

How does it work?Simple Bath Tub ModelWater levels mapped at 0.2 m increments

Slider bar on tool controls mapped water levels

Connected inundation (blue shaded

areas), areas where water could directly

flow to the sea.

Disconnected inundation (green areas),

areas that are at or below a chosen water

level, but may have no direct flow path to

the sea.

How do you use it?

Match nearest mapped water level with chosen water level scenario

Explore susceptibility – raise and lower water level

Choose Water Level Scenario for area of interest

Choose Pre-defined User defined

Zoom to area of interest

Photo: Sugar Loaf Wharf, Coromandel. Jan 4 2014, Stuart Crawley, WRC

Sugar Loaf Wharf, Coromandel Harbour - Jan 4 2014

What else do you need to know?• Does not define coastal inundation hazard areas

• Does not recommend minimum floor levels

• Does identify areas that are potentially susceptible

to coastal inundation that may require further

assessment

• Also shows Tsunami Maximum Credible Event

inundation where available

• Updated with new information as required

Where do I find it?

http://www.waikatoregion.govt.nz/coastal-inundation-tool/

http://www.waikatoregion.govt.nz/coastal-inundation-tool/

Coastal Hazards and Climate Change Guidance- MfE 2016

‘Heads up’ to TCDC - Section 5.7

Discussion on future projections and guidance

Timeline

• Final DRAFT completed Early 2017

• Further review to be undertaken.

• ***7 Slides removed as MfE document not

Published***

Coastal Policy Statement 2010• Policy 24: Identification of coastal hazards

• Identify areas in the coastal environment that are potentially affected by coastal hazards

(including tsunami), giving priority to the identification of areas at high risk of being

affected. Hazard risks, over at least 100 years, are to be assessed having regard to:

• physical drivers and processes that cause coastal change including sea level rise;

• short-term and long-term natural dynamic fluctuations of erosion and accretion;

• geomorphological character;

• the potential for inundation of the coastal environment, taking into account potential

sources, inundation pathways and overland extent;

• cumulative effects of sea level rise, storm surge and wave height under storm conditions;

• influences that humans have had or are having on the coast;

• the extent and permanence of built development; and

• the effects of climate change on:

• matters (a) to (g) above;

• storm frequency, intensity and surges; and

• coastal sediment dynamics;

• taking into account national guidance and the best available information on the likely

effects of climate change on the region or district.

Policy 25: Subdivision, use, and development in areas of coastal hazard risk

• In areas potentially affected by coastal hazards over at least the next

100 years:

• avoid increasing the risk10 of social, environmental and economic harm from

coastal hazards;

• avoid redevelopment, or change in land use, that would increase the risk of

adverse effects from coastal hazards;

• encourage redevelopment, or change in land use, where that would reduce

the risk of adverse effects from coastal hazards, including managed retreat

by relocation or removal of existing structures or their abandonment in

extreme circumstances, and designing for relocatability or recoverability

from hazard events;

• encourage the location of infrastructure away from areas of hazard risk

where practicable;

• discourage hard protection structures and promote the use of alternatives to

them, including natural defences; and

• consider the potential effects of tsunami and how to avoid or mitigate them.

http://doc.org.nz/publications/conservation/marine-and-coastal/new-zealand-coastal-policy-statement/new-zealand-coastal-policy-statement-2010/policy-25-subdivision-use-and-development-in-areas-of-coastal-hazard-risk/#10

WRC role in coastal hazards

• Supply of information/monitoring• Tide gauges, beach profile and shoreline monitoring

• Technical advice and guidance • Assist Resource Consents

• Public information • Coastal Inundation Tool

• Upcoming ‘Hazards Portal’

• Public Flood information requests (included coastal hazards)

• Conduit to Central Govt. guidance and advice.

• Waikato Regional Hazards Forum

Beach Profile Sites

• Survey up to 6 times per year

• Currently reviewing effectiveness

• Testing drones and LiDAR

(Source: T&T 2014)

Region wide shoreline mapping

• Mapping historical shorelines from aerial imagery

• The purpose of this process is:• To identify longterm trends of shoreline movement and form a

basic region-wide baseline understanding of how our coast

changes.

• To extend our monitoring beyond beaches (i.e. to include

environments such as cliffs and estuaries).

• As a “first pass” to identify any critical areas that need more

detailed monitoring.

• To inform the public about how the regions shoreline has

changed.

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