Analysis of physical processes leading to extreme sea levels and coastal flooding
Charitha Pattiaratchi1 Oceans Graduate School and The UWA Oceans Institute The University of Western Australia Water levels Water levels Coastal Hazards
Climate Change
Landslides Astronomical Longer term sea level Earthquakes Tides variability (non-tidal) Storm systems
Tsunamis Surface Waves Storm Surges
Sea level changes
Coastal flooding Beach Stability Coastal Amenity Extreme sea levels Extreme Events – storm surge
Broome Tropical Cyclone Rosita TC Alby ‘Energy’ @ 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 Sea Level Fluctuations
Tide(t) + Sea Level (t) = Surge(t) + Mean Sea Level(t)
Highest WL +1.9m CD
Daily Range 0.4 – 0.6m
Lowest WL –0.1m CD Range = 2m Fremantle Tide Spectrum
1950-2010 Water level variability at Fremantle
1.0 yr
0.8 surges tsunami
0.6 tides iurnal
annual
d -
0.4
nter
i
odaltides
annual
seiches
n lobal lobal 100 warming /
0.2 g Water level range (m) range level Water 0.0 Meteorological Effects Water level: June 2012
Highest water level recorded in 115 years Coastal flooding: Riverside Drive Fremantle: mean sea level
0.20 cm
Mean rate of increase: 1.7 mm/year (1897-2018)= 20.7 cm Australian tides Long-period tides: 18.6 yr nodal cycle
±5°
23.5°
The lunar orbital plane is (23.5 + 5o) of the equator
The cycle of variation is from 18.5o (23.5o-5o) to 28.5o (23.5o+5o) and is defined as the nodal cycle Haigh et al., 2011 Fremantle Tides 1948-2008 Measurements: Fremantle
60
40
20
0
-20
-40
50% 20% 10% 5% 2% 1%
-60 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010 Measurements: Fremantle
18.6 years
Ivan Haigh Measurements: Broome
Broome
4.4 years
Ivan Haigh Fremantle High WL Exceedance
Next high water years: Sea Level Rise 2025 2043 2062
Shows bursts of activity, and progressive change Eliot, 2012 Seasonal sea level cycle
January
June
The mean sea levels estimated by satellite altimetry (Source: AVISO, 1994) Seasonal Changes: steric height
Ocean currents Max: 0.20m
Month
Pattiaratchi & Eliot, 2008 Seasonal Changes: steric height Inter-annual Variability
La Niña
25cm El Niño
Post 1966: 1 unit SOI = ~13 mm mean sea level. No relationship prior to 1966 Extreme sea levels: a range of processes
18.6 yr nodal tidal cycle
ENSO
ARI ARI Inter-annual Variability Sea level & beach width: Cottesloe
Lake, 2018 Sea level & beach width: Mosman Extreme Events – storm surge
Extra-tropical Tropical (cyclones)
1,000 ± 500 km 500 ± 200 km Surge - 2-5 days Surge - up to half a day Several hundred km Usually < 200 km Sprawling geometry Compact and nearly symmetrical Apr-Aug Nov-Apr Cyclone Alby April 1978
• Worst extratropical transition event in Australia • 5 lives lost • Extreme winds, dust storms, power outages • $50 million in damage
• Flooding, coastal erosion, fire • Loss of 1000’s of sheep and cattle
Source: BOM Source: Bunbury public library Extreme Events – storm surge TC Alby Cyclone Alby
Category 4 cyclone that interacted with an approaching cold front with devastating results
Source: Bunbury public library Source: BOM Cyclone Alby
Weather forecasters were caught off guard as Alby unpredictably interacted with a cold front and underwent Extratropical transition (ET)
These transitioning storms can extend tropical cyclone-like conditions over a larger area in regions that do not normally experience such events Cyclone Alby
• Alby accelerated to 80 km/hr as it passed the SW of the state.
• Recorded wind gusts of 150 Strong, dry northerly winds km/hr were recorded with little or no rain along the coast Cyclone Alby – flooding & erosion
Perth
Source: Bunbury public library Bunbury
Source: BOM TC Bianca: 30 January 2011 Continental Shelf Waves (TC Bianca)
Tropical low Tropical Cyclone Bianca: Jan 30-31 2011 Flooding around the Swan river typically commences at about 1.6m CD, with flooding of the Freeway around 1.8 m CD. Perth CBD Perth CBD Tropical Cyclone Bianca Impacts @ Yanchep Beach
17 January 31 January
5 m Fremantle Sea Level: Acceleration ? http://sealevelx.ems.uwa.edu.au/ http://sealevelx.ems.uwa.edu.au/ Conclusions
• Mean sea level has many components. It is important to understand local processes contributing to sea level.
• Expect an increase in mean water levels over next 8 years due to tidal effects Low High 1960 1969 • Implications for coastal flooding, beach 1979 1988 stability and coastal infrastructure 1998 2006 2016 2025 2035 2043 Thank You