Coastal Inundation. An Overview for TCDC

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 Return Period (y) Annual Exceedance Probability (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/

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

King Tides November, 2016 Thames (Firth of Thames)

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

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

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

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

Pauanui Waterways Tairua Harbour King Tides 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

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

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/

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 risk 10 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.

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

(Source: T&T 2014) Beach Profile Sites Survey up to 6 times per year Currently reviewing effectiveness Testing drones and LiDAR

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.