LEVEL RISE AND CLIMATE CHANGE IMPACTS FOR PLANNING A NEW HOSPITAL

James Carley, Senior Coastal Engineer, Water Research Laboratory, School of Civil and Environmental Engineering, University of New South Wales

Matt Blacka, Coastal Engineer, Water Research Laboratory, School of Civil and Environmental Engineering, University of New South Wales

Ron Cox, Associate Professor, Water Research Laboratory, School of Civil and Environmental Engineering, University of New South Wales

James McIntosh, Project Manager, Pitt&Sherry

Jane McArthur, Engineer, Pitt&Sherry

Abstract A major new hospital is planned for Hobart, Tasmania. The hospital will occupy near-waterfront land which currently operates as a rail yard. Due to the critical nature of the facility and the expected long project life, high values for storm surge, future rise and freeboard were applied as criteria for assessing the suitability of the site and for planning the new hospital. This paper details the methodology used to assess the risk due to for the proposed new hospital. Furthermore it describes the limits of existing data in extrapolating to extremely rare events, and how with future sea level rise, what are presently considered to be extremely rare water level events will become commonplace. Adaptive management options for dealing with sea level rise on the site are presented, which includes a recommended freeboard in excess of normal building code requirements.

Key Words: Sea level rise, climate change, hospital, infrastructure, Hobart, Tasmania undertaken (WRL Technical Report 2007/35, Introduction Carley et al, 2007). The detailed study The Water Research Laboratory (WRL) of the incorporated the following changes over the University of New South Wales was initial feasibility study: commissioned by Pitt & Sherry acting on behalf of the Tasmanian Department of • Results of a peer review by Worley Health and Human Services to investigate Parsons (incorporating Patterson extreme event water levels and the effects of Britton and Partners). climate change for a potential hospital site at • Accurate site topography data. Macquarie Point, Hobart, Tasmania. The site • More detailed . is currently a rail yard (Figure 1). An initial • A better definition of the site extents. feasibility study was undertaken over a short • A finalised version of the analysis of time frame in the early stages of the project Hobart gauge data from Hunter planning using preliminary information. The (2007). most obvious data found to be lacking was • Analysis of groundwater data accurate ground levels. Data gaps were filled collected from the site. and a more comprehensive study was

Figure 1: Site Extents

nuclear power stations (eg Mai et al, 2002). Probability, Planning Period and The summary findings have been developed Foreseeable Events for a planning period to 2100 and for annual Most designs in the coastal zone are exceedance probabilities for extreme events concerned with a 100 year average of 1% (100 year average recurrence interval, recurrence interval (ARI) event, however, this ARI), 0.05% (2000 year ARI) and 0.01% has a 63% chance of being exceeded over a (10000 year ARI). The use of a 10000 year 100 year planning timeframe, so was ARI event for design, together with a considered inadequate for a critical facility. freeboard, would allow for the uncertainty of many of the variables (see below). Guidance was sought from the following sources: Vulnerability of Site • The Delta Committee (1962) from the Recent surveys show typical ground levels on Netherlands the site are 4 to 6 m AHD (Australian Height • AS 4997-2005 Maritime Structures Datum), and vary between approximately 2.8 Standard and 8.5 m AHD for the section shown. The • Building Code of Australia (2007) aerial photos, site survey and a site visit also • NSW Floodplain Development Manual show that substantial port buildings occupy (2005) most of the foreshore surrounding the • Federal Emergency Management potential hospital site (Figure 1). These Agency FEMA USA (2000) buildings would substantially shelter the potential hospital site from direct wave forces.

Much of the literature on extrapolating coastal Levels at the foreshore (mostly concrete hazards to extremely rare events relates to wharf decks) seaward of the hospital site boundaries are typically 3.2 to 3.4 m AHD on • Previous analyses of extreme water the south facing portion, and 2.2 to 2.4 m levels (Hunter, 2007) AHD at the northern end of the eastern • Barometric setup component of storm foreshore. The hospital site is set back at surge least 150 m from the south facing foreshore • Local wind setup and most of the east facing foreshore, but a • waves small portion is close to the foreshore in the • Locally generated wind waves north-east, where it is more sheltered and • Boat waves elevated. • • Quantification of other climate change Levels around the cenotaph behind the variables such as wind climate subject site are much higher at 20.5 to 22.2 change projections and sensitivity m AHD. Chart datum, which is used in bathymetric charts and tidal predictions was • Wave setup and wave runup. changed for Hobart on 1 January 2006. The new Hobart chart datum is approximately - An example of SWAN modelling of ocean 0.83 m AHD. The old Hobart chart datum swell is shown in Figure 2. was approximately -1.20 m AHD.

Climate Change - IPCC Global Sea Level Rise Projections The following simplified scenarios for global sea level rise were developed from the latest IPCC (2007) publication. More extreme postulations exist, including up to 7 m sea level rise for the total ice melt of Greenland (IPCC, 2007) and 70 m if all the world’s ice was to melt (GAGCC, 2006), but even if this did eventuate, the timescale is considered to be millennia. The IPCC publications represent the international consensus position for planning purposes. Uncertainties in future projections are due to both an imperfect understanding of the processes and unknown future global emissions of greenhouse gases.

Table 1: Adopted sea level rise scenarios

Scenario Year and Sea Level Rise relative to 1990 (m) 2050 2100 “Mid” scenario 0.2 0.5 “High” scenario 0.4 0.9

Processes Considered in Assessing Inundation Levels Figure 2: SWAN modelling of ocean swell The following processes were considered in penetration (250 m grid top, 100 m grid assessing the inundation level: bottom) • Sea level rise Climate Change and Extreme Events - Table 3: Conservative estimate of inundation Best Estimate of Inundation Levels levels For the mid range sea level rise scenario (0.5 m) in 2100, at highest astronomical tide the ARI Year and Inundation Level (m (years) AHD) water level would be 1.3 m AHD which is below ground levels on the site. Storm surge 2000 2050 2100 and events would elevate the SLR 0.4 0.9 inundation level above this. The duration of 100 1.4 1.8 2.3 the peak of these extreme inundation events 2000 1.7 2.1 2.6 would be 1 to 2 hours with the peak of the 10000 1.9 2.3 2.8 tide. As the hospital site is generally set back at least 150 m from the exposed south and Climate Change – Other Variables east foreshores, and is protected by Quantification from the IPCC is available for substantial port buildings, the design future sea level rise using a range of inundation level need not consider wave scenarios. Good quantification is also runup. The best estimate of extreme water available for temperature. Within the levels derived in this study, including tide, resolution of current modelling, future storm surge, global sea level rise (mid changes to temperature, radiation and rainfall scenario) but excluding wave runup are are not able to be differentiated between shown in Table 2. different sites in greater Hobart. Limited information is available regarding future Table 2: Best estimate of inundation levels change to extreme wind speeds (CSIRO, 2007) and generally relates to north-west to ARI Year and Inundation Level (m south-west winds, which are the most severe (years) AHD) for Hobart. The site is most exposed to south- 2000 2050 2100 east winds. Limited sensitivity testing of SLR 0.2 0.5 future extreme wind projections was 100 1.4 1.6 1.9 undertaken and found that the effect on 2000 1.7 1.9 2.2 inundation levels was minor and well within 10000 1.9 2.1 2.4 the freeboard suggested below.

Climate Change and Extreme Events - Conservative Estimate of Inundation Extreme Events - Tsunami Levels Detailed modelling is being undertaken by For the high range sea level rise scenario Emergency Services Tasmania and (0.9 m) in 2100, at highest astronomical tide Geoscience Australia. No quantification has the water level would be 1.6 m AHD which is been provided in this paper. Approximately below ground levels on the site. Storm surge 47 tsunami events have been catalogued for and wind wave events would elevate the Australia since 1858. The maximum tsunami inundation level above this. The duration of runup reported in eastern Australia has been the peak of these extreme inundation events approximately 2 m. Evidence exists for past would be 1 to 2 hours with the peak of the mega-tsunami and paleo-tsunami, but there tide. As stated above, the hospital site is is disagreement on the frequency and risk of generally set back at least 150 m from the these among experts in this field. exposed south and east foreshores, and is protected by substantial port buildings, so the design inundation level need not consider Site Preparation Works and Design wave runup. The conservative estimate of Considerations - Adaptation Options extreme water levels derived in this study, Most of the potential hospital site is above the including tide, storm surge, global sea level inundation levels detailed above (Figure 3). It rise (mid scenario) but excluding wave runup is recommended that an appropriate are shown in Table 3. freeboard of at least 0.5 to 1 m be set over the design water level at the detailed design stage of this project to cover uncertainty in climate change and other variables. Should a typical setback to the waterfront of the lower portions of the site be utilised, a approximately 150 m on the exposed south building can be built on ground below the and east shorelines. Protection from wind inundation and/or wave runup level provided and swell wave impacts for the hospital site is it is engineered to withstand the wave and/or premised on this setback being preserved by hydrostatic forces. In the case of the the continued presence of the port proposed hospital, it must also be engineered structures. to remain operational. Potential engineering solutions include designing a suitably strong In addition to the use of freeboard, detailed structure, water resistant materials, elevating design of the hospital should consider design key components, a suitable seawall and options which may provide protection for suitable drainage which may include pumps design of events larger than those considered at low levels. The potential hospital site has in this study.

Figure 3: Likely extents of site inundation for conservative scenario

assessing the suitability of the site and for Conclusion planning the new hospital. A major new hospital is planned for Hobart, Tasmania. The hospital will occupy near- The summary findings have been developed waterfront land which currently operates as a for a planning period to 2100 and for annual rail yard. Due to the critical nature of the exceedance probabilities for extreme events facility and the expected long project life, high of 1% (100 year average recurrence interval, values for storm surge, future sea level rise ARI), 0.05% (2000 year ARI) and 0.01% and freeboard were applied as criteria for (10000 year ARI). The use of a 10000 year ARI event for design, together with a freeboard, would allow for the uncertainty of (FEMA) Federal Emergency Management many of the variables. Agency USA (2000), Coastal Construction Manual FM55 , USA. This paper details the methodology used to assess the risk due to sea level rise for the Flick, Reinhard E; Murray, Joseph F and proposed new hospital. Furthermore it Lesley C Ewing (2003), “Trends in United describes the limits of existing data in States Tidal Datum Statistics and Tide extrapolating to extremely rare events, and Range”, Journal of Waterway, Port, Coastal, how with future sea level rise, what are and Ocean Engineering , Vol. 129, No. 4, 1 presently considered to be extremely rare July, pp. 155-164 water level events will become commonplace. Adaptive management GACGC (2006), German Advisory Council on options for dealing with sea level rise on the Global Change, The Future – site are presented, which includes a Warming up, Rising High, Turning Sour, recommended freeboard in excess of normal Special Report, Berlin 2006, ISBN 3-936191- building code requirements. 14-X.

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