Influence of oceanographic processes on coastal erosion, morphology and inundation

Transcription

1 FACULTY OF ENGINEERING, COMPUTING AND MATHEMATICS Influence of oceanographic processes on coastal erosion, morphology and inundation Charitha Pattiaratchi School of Civil, Environmental and Mining Engineering & UWA Oceans Institute,

2 Acknowledgements Ivan Haigh*, Cyprien Bosserelle, Shari Gallop*, Matt Eliot, Sarath Wijeratne School of Civil, Environmental and Mining Engineering, UWA *National Oceanography Centre, Southampton, UK Tony Lamberto, Reena Lowry Department of Transport

3 Coastal impacts From 2001 to 2011, the population of Western Australia increased by 24%, and Greater Perth by 26% concentrated in the coastal zone. 2020, 2050, 2100??

4 Coastal impacts Climate Change Landslides Earthquakes Astronomical Tides Longer term sea level variability (non-tidal) Storm systems Tsunamis Storm Surges Surface Waves Sea level changes Coastal flooding Beach Stability Coastal Amenity

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

6 Coastal Infrastructure

7 Cottesloe

8 Port Beach Fremantle 2003

9 Geordie Bay Rottnest 2003 Matt Eliot

10 Port Geographe 2003

11 Rockingham 2003

12 Beach variability

13 What would this beach look like in 2100?

14 Beach variability Binningup 90m 0.9m 3m 42m

15 Perched Beaches Start Summer N Yanchep Lagoon November

16 Forcing: a range of spatial scales Astronomical Meteorological Oceanic: Indian + Pacific Oceanic: Atlantic + Southern

17 Beach Basin Scale Shelf Scale Beach Scale Wave Climate Storm Surges Mean sea level ENSO (El Nin0/La Nina) Seasonal + Inter-annual Nodal tides Relative MSL

18 Hindcasts 40-year climatology NCEP Re-analysis Ocean Wave model 60-year climatology Tide &Storm surge model Bosserelle et al., 2012

19 Wave climate variability nearshore Nearshore wave climate Offshore wave climate Effect of nearshore wave climate variability on sediment transport on beaches 3

20 Where does the wave energy come from? Instituto de Hidráulica Ambiental Universidad de Cantabria, Spain

21 Mean wave height (40 year)

22 Trends in mean Hs 0.24 over 40 years

23 Max wave heights: 1975

24 Max wave height: 1996

25 Max wave height 2006

26 Annual 90 th percentile time slice Southward shift

27 Evolution of long-term wave climate in WA Increase in number and severity of storms in southern Indian Ocean No trends in extreme wave events off WA but increase in swell height Large wave event tracks shifted southward 7m 8m 9m 10m Bosserelle et al. (2011)

28 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

29 Processes contributing to water level variability at Fremantle Water level range (m) seiches tsunami diurnal tides surges annual inter-annual nodal tides global warming / 100 yr 0.0 Pattiaratchi et al. (2014)

30 Fremantle Tide Spectrum

31 Long-period Tides Fremantle 18.6 years Broome 4.4 years

32 Fremantle High WL Exceedance (cumulative) Sea Level Rise Shows bursts of activity, and progressive change Matt Eliot, 2012

33 Sea level hindcasts NCEP: Tropical Cyclones Global tidal model ~75,ooo simulations equivalent to 10,000 years Total Sea level

34 Storm Surges

35 Storm track categories Storm track Start of storm track Time of max surge 35

36 Decadal changes 36

37 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

38 Tropical storms 10,000 year climatology

39 1:1000ARI: total water level (tropical + extra-tropical) Haigh et al.,, 2013, 2014

40 Study Team: Ivica Janeković and Yasha Hetzel

41 Continental Shelf Wave generation Summer: Tropical cyclones Winter + summer: pressure systems

42 TC Bianca: 30 January 2011

43 Continental Shelf Waves (TC Bianca) Tropical low Mihanovic & Pattiaratchi, 2014

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

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

46 Tropical Cyclone Bianca Perth CBD?

47 Fremantle Sea Level: Mean rate of increase: 1.54 mm/year Mean global rate: 1.88 mm/year ( ) (IPCC R4) Global mean sea level increased throughout the 20th century and in 2012 was 225 mm higher than in 1880: 1.7 mm/year (March : CSIRO & BoM State of the Climate Report)

48 Sea Level Variability (phase) Fremantle (5 yr running means) Mean Sea Level Astronomical Tide Storm Surge Observed Tide

49 Fremantle Sea Level: Acceleration?

50 Global mean sea level rise Acceleration detection timescale 0.5 m 1.0 m 1.5 m 2.0 m It will be several decades before a change in acceleration in individual TG records are detected. This is mainly due to inter-annual to multi-decadal variability Haigh et al., 2014, Nature Communications

51 Coastal Modelling: multiple scales from ocean basins to beaches Basin scale: Meteorological forcing

52 Port Geographe: new marina layout to prevent seaweed accumulations $ 30 million Project

53 Port Geographe 16 October 2014

54 Yanchep lagoon: effect of a severe storm a

55 Yanchep lagoon: effect of a severe storm

56 Yanchep lagoon: how does the sand come over the reef?

57 Yanchep lagoon (1974 to 2008)

58 Yanchep lagoon (1974 to 2008)

59 Rockingham 40 PSM Rockingham Change in Shoreline position with time Position of MSL relative to 1974 (m) Year PSM Rockingham Change in Shoreline position with time (months) Position of MSL relative to 1974 (m) Mar Apr May-0320-May Jun Jul Aug-03 Ailbhe Travers

60 Summary Energy incident at the beach has a range of spatial and temporal scales Wave energy is increasing Sea level has many components and strongly influences beach stability. Expect a decrease in mean water levels over next 10 years due to tidal effects Implications for coastal flooding, beach stability and coastal infrastructure Not a time to be complacent!!!

61 Thank You