Coastal Inundation An Overview for TCDC Rick Liefting Team Leader - PowerPoint PPT Presentation

Coastal Inundation An Overview for TCDC Rick Liefting Team Leader Regional Hazards and Environmental Compliance Integrated Catchment Management Waikato Regional Council Photo: Sugar Loaf Wharf, Coromandel. Jan 5 2014, Stuart Crawley, WRC

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)

King Tides November, 2016 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 Time Period (y) - approx Annual Exceedance Return Probability 2 5 10 20 50 100 200 Period (y) (AEP) 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%

Event Frequency Time Period (y) - approx Annual Exceedance Return Probability 2 5 10 20 50 100 200 Period (y) (AEP) 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%

Event Frequency Time Period (y) - approx Annual Exceedance Return Probability 2 5 10 20 50 100 200 Period (y) (AEP) 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%

Event Frequency Time Period (y) - approx Annual Exceedance Return Probability 2 5 10 20 50 100 200 Period (y) (AEP) 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%

Event Frequency Time Period (y) - approx Annual Exceedance Return Probability 2 5 10 20 50 100 200 Period (y) (AEP) 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/

Tararu Tide Gauge (Firth of Thames) AEP ARI Water Diff • Extreme Storm (%) (years) level (m) (m) Tide analyse (NIWA 2015) 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

Tararu Tide Gauge (Firth of Thames) • Extreme Storm ARI Water Diff Tide analyse AEP (%) (years) level (m) (m) (NIWA 2015) 39 2 2.20 18 5 2.30 10 10 2.35 20 y 100 y 64% 99% 5 20 2.43 33% 87% 0.19 2 50 2.54 18% 63% 1 100 2.62 0.5 200 2.71

Tararu Tide Gauge (Firth of Thames) • Extreme Storm ARI Water Diff Tide analyse AEP (%) (years) level (m) (m) (NIWA 2015) 39 2 2.20 18 5 2.30 10 10 2.35 20 y 100 y 64% 99% 5 20 2.43 33% 87% 0.19 2 50 2.54 18% 63% 1 100 2.62 0.5 200 2.71

Tararu Tide Gauge (Firth of Thames) • Extreme Storm ARI Water Diff Tide analyse AEP (%) (years) level (m) (m) (NIWA 2015) 39 2 2.20 18 5 2.30 10 10 2.35 20 y 100 y 64% 99% 5 20 2.43 33% 87% 0.19 2 50 2.54 18% 63% 1 100 2.62 0.5 200 2.71

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

King Tides November, 2016 Thames (Firth of Thames)

What does it show? On shore Present Day Coastal Water Level Estimates winds Tide Model and Tide Gauges Low air pressure X Wave Effects Upper Storm Tide (worst case) Storm Effects Lower Storm Tide (semi annual) Max Tide Tide MHWS Effects Datum (Moturiki Vertical Datum 1953)

What does it show? Future Coastal Water Levels Sea Level Rise added to Present Day Values Upper Storm Tide (worst case) Storm Effects Lower Storm Tide (semi annual) Max Tide Tide MHWS Effects Datum (Moturiki Vertical Datum 1953)

What does it show? Future Coastal Water Levels Sea Level Rise component added to Present Day Values Upper Storm Tide (worst case) Storm Effects Lower Storm Tide (semi annual) Max Tide Tide MHWS Effects Datum (Moturiki Vertical Datum 1953)

Firth of Coro West Coro East Pre-defined Water Level Thames Coast Coast Scenarios Coro Mercury Thames Harbour Bay Mean High Water Spring (m) Mean High Water Spring (m) 1.79 1.79 1.58 1.58 1.10 1.10 Max High Tide (m) 2.11 1.86 1.29 Present Day Storm Tide Range Lower (m) 2.20 1.88 1.40 (Estimate) Upper (m) 3.22 2.67 2.10 Mean High Water Spring (m) 2.29 2.08 1.60 0.5 m Max High Tide (m) 2.61 2.36 1.79 projected Sea Level Lower (m) 2.70 2.38 1.90 Storm Tide Range Rise Future (Estimate) Upper (m) 3.72 3.17 2.60 Projected Mean High Water Spring (m) 2.79 2.58 2.10 1.0 m Max High Tide (m) 3.11 2.86 2.29 projected Sea Level Lower (m) 3.20 2.88 2.40 Storm Tide Range Rise (Estimate) Upper (m) 4.22 3.67 3.10

Pauanui Waterways King Tides Tairua Harbour February 2, 2014 Gangways underwater Whitianga - Buffalo Beach (Mercury Bay)

Public road Tairua - Paku Boat Ramp Tairua – Fishing Club, tide coming up through stormwater drains

How does it work? Simple Bath Tub Model Water levels mapped at 0.2 m increments 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. Slider bar on tool controls mapped water levels

How do you use it? Zoom to area of interest Choose Water Level Scenario for area of interest Choose Pre-defined User defined Match nearest mapped water level with chosen water level scenario Explore susceptibility – raise and lower water level