Sea level variability: from surface gravity waves to mean sea level.

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Civil, Environmental and Mining Engineering The UWA Oceans Institute The

1 Sea level variability: from surface gravity waves to mean sea level. Charitha Pattiaratchi, Sarath Wijeratne, Ivan Haigh +, Matt Eliot School of Civil, Environmental and Mining Engineering The UWA Oceans Institute The University of Western Australia Bushfire Natural Hazards Cooperative Research Center University of Southampton

2 Acknowledgements Reena Lowry and Tony Lamberto Department of Transport, Western Australia

3 Extreme Sea levels

4 Extreme Events storm surge Broome Tropical Cyclone Rosita

5 Extreme Events storm surge TC Alby

6 Forcing: a range of spatial scales Astronomical Meteorological Oceanic: Indian + Pacific

7 Tide recording Stations Fremantle

8 Thotagamuwage and Pattiaratchi (2014) Infra-gravity waves ~10 events per month; energy 50% of time s

9 Hillarys m 2.7h 12h 24h

10 Sea Level Fluctuations: Fremantle Sea Level (t) = Tide(t) + Surge(t) + Mean Sea Level(t) Range = 2.22m Highest WL +2.12m CD Daily Range m Lowest WL 0.1m CD

11 Coastal flooding/inundation Flooding around the Swan River typically commences at ~ 1.6m CD Flooding of the Kwinana Freeway and major roads ~1.8 m CD.

12 Sea level components Observed Tide = Mean Sea Level + Astronomical Tide + Surge

13 Processes contributing to water level variability at Fremantle Inter-Annual Tides Continental shelf seiches:~0.2m Tsunamis (seismic & meteo) Storm fronts Diurnal: ~0.5 m Small range Nodal tides important Annual Weather Band Seiches Weather Band: ~0.6 m Storm surges Continental shelf waves Annual & Inter-annual:~0.2m Leeuwin Current ENSO (El Nino/La Nina) Mean sea level :~0.15m /century Global warning

14 Water level range (m) seiches annual tsunami diurnal tides inter-annual nodal tides surges global warming / 100 yr Processes contributing to water level variability at Fremantle

15 Continental Shelf Seiches L Tomczak L = 20 km; h = 50m L = 50 km; h = 50m L = 80 km; h = 50m T ~ 1 hour T ~ 2.5 hours T ~ 4 hours

16 Tsunamis: Seismic and Meteorological Max: 0.60m Max: 0.72m

17 Tsunamis: Seismic and Meteorological 0.62 m

18 Fremantle Tide Spectrum

19 Month Seasonal Changes: tides Broome Fremantle

20 Long-period tides 18.6 yr nodal cycle ± The lunar orbital plane is ( o ) of the equator The cycle of variation is from 18.5 o (23.5 o -5 o ) to 28.5 o (23.5 o +5 o ) is defined as the nodal cycle Haigh et al., 2011

21 Fremantle Tides Max: 0.20m

22 Long-period Tides Fremantle 18.6 years Broome 4.4 years

23 18.6 year tidal cycle % 20% 10% 5% 2% 1% Eliot, 2012

24 Mean Wind Fields - Australia January (mean ) June (mean )

25 The mean sea levels estimated by satellite altimetry (Source: AVISO, 1994) Seasonal sea level cycle January June

26 Seasonal Changes: steric height Ocean currents Max: 0.20m Month

km Sprawling geometry Apr-Aug 500 ± 200 km Surge - up to

27 Extreme Events storm surge Extra-tropical Tropical (cyclones) 1,000 ± 500 km Surge days Several hundred km Sprawling geometry Apr-Aug 500 ± 200 km Surge - up to half a day Usually < 200 km Compact and nearly symmetrical Nov-Apr

28 Storm Surges (& Shelf Waves) Tropical cyclones occur during summer months Extra-tropical storms occur all year, with more during winter

29 Storm Surges

30 Continental Shelf Wave generation Summer: Tropical cyclones Winter + summer: Cold fronts

31 Water Levels: TC Isobel and TC Jacob Eliot & Pattiaratchi, 2010

32 Inter-annual variability Max: 0.25m La Niña El Niño 25cm

33 Meteotsunamis

34 Event of 17 August 2014

35 Event of 17 August: ship accident

36 Event of 17 August 2014

37 Event of 17 August 2014

38 Event of 17 August: air pressure 2hPa

39 Event of 17 August

40 Extreme events 16 May 2003: Winter extra-tropical storm Local storm surge High water level - nodal tide El Nino year 30 Jan 2011: Summer tropical storm (remote) Remote storm surge Mid water level - nodal tide La Nina year 10 Jun 2012: Winter extra-tropical storm Local storm surge Meteo-tsunami Mid water level - nodal tide La Nina year All events coincided with time of local high water

41 Storm Tracks: May

42 Water level: May 2003

43 TC Bianca: 30 January 2011

44 Continental Shelf Waves (TC Bianca) Tropical low

Tropical Cyclone Bianca: Jan 30-31 2011 Flooding around the Swan river

45 Tropical Cyclone Bianca: Jan Flooding around the Swan river typically commences at about 1.6m CD, with flooding of the Freeway around 1.8 m CD.

46 Tropical Cyclone Bianca Yanchep Beach 17 January 31 January 5 m

47 Storm tracks: June 2012

48 Water level: June 2012 Highest water level recorded in 115 years

49 Water level: June 2012

50 Water level range (m) annual tides inter-annual nodal tide meteo-tsunami storm surge CSW Water level components

51 Percentage of water level range tides mean residual Water level components Sea Level (t) = tide(t) + residual (t) + mean sea level (t) ~25% ~50% ~25%

It is important to understand local processes contributing

52 Summary Sea level has many components acting on different spatial and temporal scales. It is important to understand local processes contributing to sea level. Implications for coastal flooding, beach stability and coastal infrastructure

53 Thank You

Sea Level Variability in the East Coast of Male, Maldives

Sea Level Variability in the East Coast of Male, Maldives K.W. Indika 1 *, E.M.S. Wijerathne 2, G. W. A. R. Fernando 3, S.S.L.Hettiarachchi 4 1 National Aquatics Resources Research and Development Agency,