17/03/2015 Coastal‐storm inundation and sea‐ level rise Scott Stephens and Rob Bell Talk outline • Using MHWS to define the Coastal Marine Area boundary • Coastal inundation by storm‐tides and waves • How big and how often? • Mapping coastal‐storm inundation • Sea‐level rise –the elephant in the room • What do we do about it? rtoonStock.com • Tsunami not considered Dave Allen, Ca Dave Allen, © 1 17/03/2015 Coastal Marine Area Boundary • The coastal marine area (CMA) landward boundary delineates a jurisdictional limit for rules under New Zealand’s Resource Management Act (RMA). • It is defined legally by the line of mean high water springs (MHWS). • The CMA boundary defines the landward boundary for activities that require a coastal permit, and the coastal boundary for land‐based planning. • An important component of Auckland Council’s new Unitary Plan will be its graphical representation of the coastal margin (coastline). The mapped coastline in 2012 Okura Estuary 2 17/03/2015 Projecting tide levels onto the land Tide MHWS level Land Defining mean high water spring tide •Discuss MHWS‐10 again, from Rob’s work •Do we want to go into this discussion? (m) Natural land‐sea boundary markers 0 = Perigean spring tide M + S + N • Probably a good idea, just briefly 2 2 2 MSL Nautical spring tide M2 + S2 4000 PPNautical spring tide M + S Kaikoura 2 2 3000 2000 NF NF 1000 Sea level (mm) level Sea 0 -1000 Foxton -2000 05-Sep 12-Sep 19-Sep 26-Sep 03-Oct 10-Oct 17-Oct 24-Oct-96 Date 3 17/03/2015 Updated coastline in Council GIS viewer Okura Estuary Coastal‐storm inundation 4 17/03/2015 A nice place to be Milford Beach 5 17/03/2015 Milford Beach –July 2008 Photo: Rob Waardenburg Tamaki Drive –April 2014 cyclone Ita 6 17/03/2015 Maraetai – cyclone Ita April 2014 NZ Herald Anatomy of a storm tide L Total sea‐level = MSL + sea‐level anomaly + tide + storm‐surge + wave setup and runup Wind Wave setup and runup Storm surge Storm‐tide High Tide Sea‐level anomaly (climate) Mean sea level Local vertical datum 7 17/03/2015 Anatomy of a storm‐tide –neap tide L Total sea‐level = MSL + sea‐level anomaly + tide + storm‐surge + wave setup and runup Wind Wave setup and runup Storm surge Neap Tide Mean sea level Anatomy of a storm‐tide –king tide L Wind Wave setup and runup Storm surge King Tide Mean sea level 8 17/03/2015 Hauraki Plains: May 1938 RNZAF Coastal stopbanks burst Gale‐force winds + rain + very high tide Depth on land = 0.5 to 1.2 m £1000’s damage 1600 ha flooded and houses Whitianga: 23 August 1989 Also sizeable coastal inundation events in 1936, 1968, 1972, 1978 9 17/03/2015 Feb 2014 King Tide –Ohiwa Feb 2014 King Tide –Ohiwa 10 17/03/2015 Feb 2014 King Tide –Ohiwa Auckland awash –23 Jan 2011 –highest storm‐ tide on record at Auckland NZ Herald NZTA: AMA 11 17/03/2015 Storm surge height: EcoConnect forecast Forecast storm surge = 0.33 m in Inner Gulf [Inverted barometer =1015 − 995 hPa= 0.2 m] Actual storm surge = 0.4 m at Port of Auckland Auckland awash –how often in future? 12 17/03/2015 Extreme sea level analysis: Auckland 100‐year ARI 1‐year ARI Climate change and sea‐level rise • Coastal‐storm inundation and erosion is a problem both now, and historically. • What changes will occur in a changing climate that includes sea‐level rise? • NIWA’s Waves and Storm Surge Projections project suggested that the magnitude of the largest waves and storm surges would change by only a few percent by the 2090’s, and would have negligible impact on coastal‐storm inundation over the next 100 years, relative to the effect of SLR. 13 17/03/2015 Storm‐tide & Tsunami wave inundation inundation Groundwater Salinity intrusion table & drainage Coastal/estuarine Ecological effects shoreline erosion MHWS+ tidal flooding Sea‐level Rise Changing state vs past “static” environment paradigm Port of Auckland: Annual MSL (1899‐2014) 2 1.9 (m) Datum 1.60 mm/yr 1.8 Chart MSL: AVD‐46 1.743 m 1.7 Annual 1.6 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010 Linear trend for Auckland is 1.6 cm/decade (NZ average rate is 1.7 cm/decade compared with global average of 1.8 cm/decade) Since 1900, the mean sea level at Auckland has risen by 0.2 m 2014: annual MSL has hit 0.2 m above AVD‐46 14 17/03/2015 Business‐as‐usual (high) emission scenarios: SLR projections for IPCC reports MfE (2008): 0.8 m by 2090s 0.5 m by 2090s Extreme sea level analysis: Auckland 15 17/03/2015 Expected number of exceedances in 100 years 2011 storm tide 1‐year ARI storm tide Effects of sea‐level rise Essentially, only a 0.45 metre SLR is 0.5 m sea‐level rise required for a 23‐ January‐2011 type event to be 2011 storm tide exceeded a few 0.3 m sea‐level rise times per year 16 17/03/2015 Annual number of sea‐level > MHWPS “In Auckland, flooding events became twice as frequent during the 20th century as a result of sea‐level rise” Equiv. Note: MfE SLR values (2115) incl. a further 0.05 m due to SW Pacific difference in projections MfE 2008 above the global mean (2090s) IPCC “likely range” (33% probability may lie outside) 17 17/03/2015 Annual number of sea‐level > 100‐year ARI In 2045 – thirty years from now – flooding, such as that that occurred in Auckland in January 2011, is likely to occur about once every ten years. By 2070 such flooding is likely to be a yearly event if the world takes no action to reduce greenhouse gas emissions This analysis was included in “Changing climate and rising seas: Understanding the science”. Parliamentary Commissioner for the Environment (2014). Climate change and sea‐level rise • Coastal‐storm inundation and erosion is a problem both now, and historically • As sea levels continue to rise, the frequency of coastal storm inundation events that reach damaging elevations will dramatically increase. • The future 1% AEP event will produce deeper overland inundation and have much greater consequences than the 2011 event. 18 17/03/2015 Mapping coastal‐storm inundation for the Auckland region NZCPS policies: 1. Consider climate‐change & hazard effects for at least 100 years (Policies 10, 24‐25, 27) So need to venture beyond the 2100 cut‐off in IPCC projections Need to be looking out to 2115+ 2. Not just SLR –other hazards as well incl. storm tide, erosion, tsunami (Policy 24) 3. Different approach signalled for greenfields (Objective 5, Policies 3, 25) vs existing development (Policy 27) 19 17/03/2015 Extreme sea level analysis: Auckland Hydrodynamic harbour models • Tidal amplification • Wind‐driven storm‐surge • Meteorological record 20 17/03/2015 Extreme storm‐tide elevations ‐ Waitemata Open‐coast –joint probability analysis: storm‐ tide + wave height –WASP WASP: 30‐year hindcast of waves and storm‐surge around New Zealand Pakiri Beach 21 17/03/2015 Open‐coast –joint probability analysis: storm‐ tide + wave height –WASP 22 17/03/2015 23 17/03/2015 Mission Bay 24 17/03/2015 What do we do? • We have coastal‐storm inundation. • The sea is rising. • What can we do about it? 25 17/03/2015 The rising sea‐level challenge: a risky business! Best or most likely estimate (relative to baseline) Selection of sea‐level rise to adapt to, is to be undertaken in the context of a risk management approach (NZCPS and MfE Guidance) The rising sea‐level challenge: a risky business! Risk peaks for higher SLR within a timeframe, hence need for erring on upper range. For infrastructure, also capital & maintenance costs 26 17/03/2015 Adaptation to sea‐level rise • Do nothing • Retreat • Adapt • Protect Policy: Reducing natural‐hazard risk •RMA “Risk‐reduction” not explicitly defined but: . Section 7(i) … "have particular regard to" the effects of climate change . Section 31 … "the control of any actual or potential effects of the use, development, or protection of land, including for the purpose of— (i) the avoidance or mitigation of natural hazards” •NZCPS: reducing risks in relation to managing existing development in areas subject to coastal hazards (Policy 25 (c) and Policy 27). Avoid increasing the risks –avoid redevelopment –locate new development away from areas prone to coastal risks (Policy 25, Objective 5) • Defining risk? Measuring success of “do not increase risk” Direct damage, disruption, clean‐up, loss of utility, indirect impacts Increasing population, house values, infill, infrastructure 27 17/03/2015 Adaptation: adjusting to changes & rising risk •Land‐use planning Zoning e.g., Closed Residential zone in Mapua/Ruby Bay (PC22) Minimum floor and/or ground levels for buildings Restrictions on re‐development Erosion trigger‐points (removable buildings) • Adaptive management approach: Develop master plan for staging based on defined tipping points Adopt current best‐estimate SLR trajectory to initial phasing Monitor & review –amend plan if required (forward or delay) More suitable for infrastructure or urban areas e.g., London, NY, Auckland, Wellington 28 17/03/2015 Local coastal adaptation pathway •Engaging with communities (small is more do‐able) •Determine “lived values” that the community holds to Whitianga and hapu place‐based studies • Issues: External/expert framing for what is a local problem Community differences & local politics ‐ mandates Climate‐change skepticism • Negotiate a decision strategy that provides certainty Manageable steps (e.g. Lakes Entrance‐VIC, Barnett et al.