ex-severe tropical cyclone debbie - publications · ex-severe tropical cyclone debbie storm surge...

Ex-Severe Tropical Cyclone Debbie Storm surge in south east Queensland and surge bore in the Brisbane River

Coastal Impacts Unit, December 2017

Department of Science, Information Technology and Innovation

Prepared by

Daryl Metters Coastal Impacts Unit Science Delivery Division Department of Science, Information Technology and Innovation PO Box 5078 Brisbane QLD 4001

© The State of Queensland (Department of Science, Information Technology and Innovation) 2017

The Queensland Government supports and encourages the dissemination and exchange of its information. The copyright in this publication is licensed under a Creative Commons Attribution 3.0 Australia (CC BY) licence

Under this licence you are free, without having to seek permission from DSITI, to use this publication in accordance with the licence terms. You must keep intact the copyright notice and attribute the State of Queensland, Department of Science, Information Technology and Innovation as the source of the publication.

For more information on this licence visit http://creativecommons.org/licenses/by/3.0/au/deed.en

Disclaimer

This document has been prepared with all due diligence and care, based on the best available information at the time of publication. The department holds no responsibility for any errors or omissions within this document. Any decisions made by other parties based on this document are solely the responsibility of those parties. Information contained in this document is from a number of sources and, as such, does not necessarily represent government or departmental policy.

If you need to access this document in a language other than English, please call the Translating and Interpreting Service (TIS National) on 131 450 and ask them to telephone Library Services on +61 7 3170 5725

Acknowledgements

This report has been prepared by the Department of Science, Information Technology and Innovation in partnership with Brisbane City Council. Acknowledgement is made of the Brisbane City Council, Seqwater, the City of Ipswich, Maritime Safety Queensland, the Bureau of Meteorology and the DSITI Coastal Impacts Unit for providing Alert gauge, tide gauge, storm tide gauge, weather data and flood reference levels.

Cover image is of modelled winds of ex–Severe Tropical Cyclone Debbie in the South East Queensland region on 30 March 2017. Image from Earth wind map.

December 2017

http://creativecommons.org/licenses/by/3.0/au/deed.en

http://creativecommons.org/licenses/by/3.0/au/

Ex-STC Debbie storm surge in south east Queensland and surge bore in the Brisbane River

i

Executive summary

• Severe Tropical Cyclone (STC) Debbie made landfall as a category 4 severe tropical cyclone around 12:40 pm on 28 March 2017 near Airlie Beach.

• Sustained wind speeds of 195 km/h, wind gusts of up to 260 km/h and a minimum central pressure of 943 hPa generated storm surges south of Airlie Beach. The largest surge of 2.66 m was recorded by the DSITI Laguna Quays storm tide gauge.

• STC Debbie tracked inland back towards the coast until it was downgraded to a tropical low. The low pressure system turned southwards and travelled inland of the coast from Mooloolaba to the Gold Coast on 30 March 2017 where it crossed the coast back to sea.

• Ex-TC Debbie brought severe weather conditions to the south east Queensland coast. Strong north east winds of up to 115 km/h combined with low atmospheric pressure generated storm surges along the south east coastal regions. The surge travelled as a coastally trapped wave southward along the coast from Hervey Bay to the Gold Coast.

• The coastally trapped wave within Moreton Bay peaked at 0.71 m at Shorncliffe Pier with a total surge of 0.88 metres.

• The reported surge was shown to have been generated through the severe wind speeds and falling barometric pressure off-shore and inside of Moreton Bay. The generated surge then travelled without further forcing upstream in the Brisbane River and into the Bremer River as a surge bore.

• The surge bore in the Brisbane River peaked at 0.65 m at the Brisbane CBD with a total surge of 1.23 m above the predicted tide level.

• If the storm surge was to occur at the same time as the next high water the total level would have: - exceeded the moderate flood level at Hawthorn by 0.16 metres - exceeded the minor flood level at the Brisbane CBD by 0.64 metres - exceeded the minor flood level at Oxley Creek mouth by 0.21 metres.

• Heavy rainfall before, during and after the passage of ex-TC Debbie caused flooding in the upper Brisbane and Bremer rivers.


ii


iii

Contents Executive summary ....................................................................................................................... i

1 Background ............................................................................................................................. 1

1.1 Severe Tropical Cyclone Debbie 1

1.2 Ex-Severe Tropical Cyclone Debbie 3

1.3 Tide Gauge and Alert station data 4

1.4 Filtering 6

1.5 Meteorological aspects 6

2 Water surface response .......................................................................................................... 8

2.1 Ex-STC Debbie Storm Surge and Storm Tide levels 8

2.2 Alignment of surge and storm 11

2.3 Meteorological Tsunami 12

3 Conclusions ........................................................................................................................... 14

4 References ............................................................................................................................. 15

4.1 Further information 15

Appendix 1 Raw data .................................................................................................................. 16

Coastal stations 16

Brisbane River Stations 17

Bremer River Stations 20

Appendix 2 Filtered data ............................................................................................................ 21

Coastal Stations 21

Brisbane River Stations 22

Appendix 3 Weather Data ........................................................................................................... 26

Appendix 4 Glossary .................................................................................................................. 29


iv


1

1 Background

1.1 Severe Tropical Cyclone Debbie

On 25 March 2017 a tropical low in the Coral Sea off the coast of north Queensland tracked south before turning south west and developing into Tropical Cyclone (TC) Debbie. TC Debbie took a south-westerly track intensifying over the Whitsunday Islands before making landfall as a category 4 Severe Tropical Cyclone (STC) at Airlie Beach around 12:40 pm (AEST) on 28 March 2017. STC Debbie brought sustained wind speeds of 195 km/h, wind gusts of up to 260 km/h and a minimum central pressure (modelled) of 943 hPa (Bureau of Meteorology, 2017).

Figure 1 Track map of Severe Tropical Cyclone Debbie and of ex-STC Debbie.


2

A storm surge resulted from the extreme wind speeds and very low pressure during the passage, particularly at sites within the zone of maximum winds. The DSITI storm tide gauge network reported the largest storm surge of 2.66 m and a maximum storm tide level of 7.21 m relative to Lowest Astronomical Tide (LAT) at Laguna Quays (Figure 2). The surge reached 0.91 m above the Highest Astronomical Tide (HAT) (see Maritime Safety Queensland, 2017) level.

Figure 2 Laguna Quays storm tide levels relative to LAT during landfall passage of STC Debbie, 27–

29 March 2017.

The storm surge to the south of the landfall point was considerably larger than to the north (e.g. Bowen, see Table 4) due to the wind direction being onshore to the south and offshore to the north (Figure 4).

Table 1 Maximum storm surge and maximum storm tide relative to Lowest Astronomical Tide (LAT) and HAT for STC Debbie.

Site Max surge (m) Max storm tide (m, LAT) Max storm tide (m, HAT)

Bowen 0.52 3.57 −0.16

Laguna Quays 2.66 7.21 0.91

Shute Harbour 1.23 4.54 0.21

Mackay 1.11 6.64 0.06

The atmospheric pressure at Laguna Quays fell to 974 hPa (Figure 3), which contributed around 0.39 m to the surge through the inverse barometer effect (Pugh and Woodworth, 2014). The remaining 2.27 m of the surge resulted from wind forcing alone.

0

1

2

3

4

5

6

7

8

27/03 00:00 27/03 12:00 28/03 00:00 28/03 12:00 29/03 00:00 29/03 12:00 30/03 00:00

Heig

ht (m

, LAT

)

Actual Prediction Residual HAT


3

Figure 3 Laguna Quays Barometric pressure during landfall passage of STC Debbie during landfall

passage of STC Debbie, 27–29 March 2017.

Figure 4 Modelled winds during the passage of Severe Tropical Cyclone Debbie, from left to right starting 26 March 1600 to 29 March 1600, 24 hours apart. Images from Earth wind map.

1.2 Ex-Severe Tropical Cyclone Debbie

After making landfall STC Debbie continued to track inland towards the south west until it was downgraded to a tropical low. The intense low pressure system then followed a southerly arc towards the coast before veering south along the coast and crossing back to sea at the Gold Coast (Figure 1).

The intense tropical low pressure system that remained in the wake of STC-Debbie moved southward inland of the Queensland coast south of Bundaberg. The system brought severe weather conditions to the south east coastal regions in its path. Strong winds from the north east battered the region from around midday up to midnight on 30 March 2017. Heavy rainfall before, during and after the passage of ex-STC Debbie caused flooding in several river systems in the region including the Brisbane and Bremer rivers.

970

975

980

985

990

995

1000

1005

1010

27/03 0:00 27/03 12:00 28/03 0:00 28/03 12:00 29/03 0:00 29/03 12:00 30/03 0:00

Pres

sure

(hPa

)


4

Typically as a tropical cyclone or storm approaches the coast, ocean water levels rise as a result of strong onshore winds and reducing barometric pressure. This rise in water level is collectively known as storm surge (Pugh and Woodworth, 2014) and can cause inundation and flooding in low-lying coastal areas. The level of inundation and destructive capacity of a storm surge depends significantly on the height of the tide at the time that the system passes a site. The higher the tide, the more likely it is that destructive inundation and flooding will occur. The combination of surge, tide and wave setup is referred to as storm tide. The surge is seen to move southward along the coast and as such can be considered a Coastally Trapped Wave (CTW) (Zamudio, et al., 2002).

Figure 5 Tide gauge and alert stations in Moreton Bay, Brisbane River and Bremer River.

1.3 Tide Gauge and Alert station data

Data from five different sources (Table 2) were collected for 27–31 March 2017. Storm tide gauge data from coastal and Moreton Bay stations were provided by DSITI; tide gauge data were provided by Maritime Safety Queensland (Brisbane Bar only). Data from the Alert stations were provided by Brisbane City Council, Seqwater and the City of Ipswich.


5

Table 2 Location and owner of gauges in this study.

Site Owner

Urangan storm tide Dep Science Information Technology and Innovation

Mooloolaba storm tide Dep Science Information Technology and Innovation

Scarborough storm tide Dep Science Information Technology and Innovation

Shorncliffe Pier storm tide Dep Science Information Technology and Innovation

Brisbane Bar tide gauge Maritime Safety Queensland

Brisbane River, Hawthorn Alert Brisbane City Council

Brisbane River, CBD port office Brisbane City Council

Brisbane River, CBD Thornton Street ferry terminal

Seqwater

Brisbane River, St Lucia Alert Brisbane City Council

Brisbane River, Oxley Creek Mouth Alert Brisbane City Council

Brisbane River, Jindalee Alert Seqwater

Brisbane River, Aitcheson Street East Alert Brisbane City Council

Brisbane River, Moggill Ferry Alert Seqwater

Bremer River, Karalee Alert City of Ipswich

Bremer River, Ipswich Alert City of Ipswich

Russell Island West tide gauge Dep Science Information Technology and Innovation

Gold Coast Seaway tide gauge Dep Science Information Technology and Innovation

The storm tide and tide gauge data consisted of one minute interval (time) time series relative to Lowest Astronomical Tide (LAT) datum while the Alert stations record an instantaneous level when the level changes by a predetermined amount (height interval) relative to the Australian Height Datum (AHD). The Brisbane City Council use a 0.02 m change between records while Seqwater and City of Ipswich use a 0.05 m change in level between records.

The height interval data were converted to one minute time interval data by interpolating the levels between each data point by a linear interpolation (Formula 1). The data were then plotted along with tide predictions and the surge (non-tidal residual) relative to LAT in Appendix 1. The tide predictions were generated from tidal constituents where they were available or for the nearest site with suitable tidal constituents. The sites where the tide predictions from a nearby site were used are listed in Table 2.


6

Formula 1 Hn = mtn + Ho

Used to calculate the height at each whole minute between two height interval points, where:

Hn = the height at each whole minute between the two points

m = slope of the line between the two points to be interpolated

tn = the time of each whole minute between the two points to be interpolated

Ho = the height of the first point of the two points to be interpolated

Table 3 Sites where tide predictions were not available and the nearest site used in plotting.

Site Tide Prediction site

Brisbane River, Hawthorn Brisbane River, Brisbane Bar

Brisbane River, St Lucia Brisbane River, Port Office

Brisbane River, Oxley Creek mouth Brisbane River, Indooroopilly reach

Brisbane River, Jindalee Brisbane River, Indooroopilly reach

Brisbane River, Aitcheson Street Brisbane River, Goodna (Woogaroo Creek)

Brisbane River, Moggill Ferry Brisbane River, Goodna (Woogaroo Creek)

Bremer River, Karalee Brisbane River, Goodna (Woogaroo Creek)

Bremer River, Ipswich Brisbane River, Goodna (Woogaroo Creek)

1.4 Filtering

The interval data (both time and height interpolated) were run through a high pass Butterworth filter (Butterworth, 1930) to extract the wave height of the CTW and of the surge bore. The time of the maximum surge, the storm tide and storm surge height were taken from the unfiltered raw data (Tables 5 and 6).The Butterworth filter alters the time stamp of each filter point; hence, more precise timing of the arrival of the surge maximum was achieved from the raw data. The filtered data are plotted in Appendix 2.

1.5 Meteorological aspects

Ex-STC Debbie tracked south over the Sunshine Coast, Brisbane and Gold Coast regions during the afternoon and evening of Thursday 30 March 2017. Damaging wind gusts of up to 115 km/h were recorded by the Bureau of Meteorology weather stations.

Wind and pressure data are presented in Appendix 3. The parameters considered here are wind speed, wind gust and Mean Sea Level Pressure (MSLP). The data, provided by the Bureau of Meteorology, were from sites along the track of ex-STC Debbie with particular focus on sites along the Brisbane and Bremer Rivers (Figure 6).


7

Figure 6 Automatic Weather Stations (AWS) operated by the Bureau of Meteorology.

The weather data are presented in this report to help determine whether the surge originated from north east of and within Moreton Bay and travelled up the Brisbane River, or if the surge was generated along the river by the maximum winds as the system travelled southward. If the surge was generated in Moreton Bay (or seaward of the bay) and travelled upstream independent of the maximum winds then a mismatch between the time of maximum surge and the time of maximum winds should be apparent at upstream sites. One would also expect that the surge may decrease in height as it travels upstream due to friction with the bottom.


8

Table 4 Minimum MSLP, maximum wind speed and direction on 30 March 2017.

Site Time Minimum MSLP (hPa)

Maximum wind gust (km/h)

Wind direction

Cape Moreton 30/03 6:17 pm 996.2

Cape Moreton 30/03 6:53 pm 115 ENE

Brisbane Airport 30/03 8:00 pm 996.1

Brisbane Airport 30/03 7:30 pm 54 ENE

Brisbane CBD 30/03 8:00 pm 996.1

Brisbane CBD 30/03 7:30 pm 54 ENE

Archerfield 30/03 8:30 pm 995.1

Archerfield 30/03 8:00 pm 76 NE

Amberley 30/03 9:00 pm 998.4

Amberley 30/03 8:30 pm 44 ENE

Gold Coast Seaway 31/03 1:00 am 995.2

Gold Coast Seaway 30/03 9:00 pm 70 NE

2 Water surface response

2.1 Ex-STC Debbie Storm Surge and Storm Tide levels

Storm surges were recorded at many sites throughout the passage of ex-STC Debbie. Large storm surge between 0.27 m and 0.9 m are evident along the coast and within Moreton Bay sites with the largest storm surge recorded at Urangan (Table 5). The surge occurred at low water at Urangan and as the CTW passed from north to south the surge progressed into the flood tide into Moreton Bay. The storm tide levels did not exceed HAT at most of the coastal sites until ex-STC Debbie had moved offshore and the winds had swung to the south east (not presented here). The surge did exceed HAT at the Russell Island East site as the surge occurred close to high water (Figure 13).


9

Table 5 Time of maximum surge, height of maximum CTW (from filtered data), storm tide, maximum storm surge, and HAT for coastal and Moreton Bay sites.

Site Time of Max surge

Storm tide (m,LAT)

Max CTW height (m)

Max storm surge (m)

HAT (m,LAT)

Urangan 4:00 pm 1.47 0.27 0.90 4.28

Mooloolaba 5:41 pm 0.83 0.31 0.31 2.17

Tangalooma 6:55 pm 1.14 0.38 0.42 2.51

Scarborough 7:06 pm 1.30 0.55 0.77 2.43

Shorncliffe 7:32 pm 1.77 0.71 0.88 2.62

Brisbane Bar 7:46 pm 1.74 0.49 0.77 2.73

Russell Island 10:01 pm 2.28 0.28 0.74 2.16

Gold Coast Seaway 31/03 12:05 am 1.57 0.08 0.27 1.91

Within the Brisbane River the surge was recorded at the river mouth by the Brisbane Bar tide gauge two hours after low water on the incoming flood tide. The surge maximum followed the flood tide upstream and arrived at the most upstream Alert station in the Bremer River before high water three hours later. The surge at Brisbane Bar of 0.49 m increased to 0.65 m at the Brisbane CBD and then reduced as the surge bore travelled upstream to a minimum of 0.19 m at Karalee. There was considerable flooding in the upper reaches of the Brisbane and Bremer rivers, which may have influenced the surge. Upstream of Jindalee the storm tide level exceeded HAT at time of the surge peak, most likely due to fresh water flooding.

Table 6 Time of maximum storm surge, storm tide, height of maximum bore (from filtered data), maximum storm surge, and HAT for Brisbane River and Bremer River sites. Sites upstream of

Jindalee were influenced by fresh water flooding.

Site Time of Max Surge

Storm tide (m,LAT)

Max Bore height (m)

Max storm surge (m)

HAT (m,LAT)

Brisbane Bar 7:46 pm 1.74 0.49 0.77 2.73

Hawthorn 8:05 pm 2.02 0.64 0.87 2.79

Brisbane CBD Thornton Street

8:11 pm 2.14 0.64 1.23 2.89

Brisbane CBD Port Office

8:12 pm 2.10 0.65 1.20 2.89

St Lucia 8:33 pm 2.27 0.56 1.18 2.98

Oxley Creek mouth 8:38 pm 2.28 0.58 1.54 2.98


10

Jindalee 9:02 pm 2.32 0.53 1.37 2.92

Aitcheson Street East

9:38 pm 2.63 0.42 1.51 2.60

Moggill Ferry 9:46 pm 2.69 0.40 1.37 2.64

Karalee 9:49 pm 2.24 0.19 1.84 2.89

Ipswich 10:55 pm 7.05 0.45 5.28 2.81

The maximum storm tide level was influenced by the surge bore and the stage of the tide, the tide was in flood (incoming) at all of the stations within the river. If the passage of the surge bore were to have coincided with high water then the maximum storm tide would have been higher than reported here. The theoretical height of a maximum storm tide, should the surge bore have coincided with the next high water are presented in Table 7. The theoretical maximum storm tide was calculated by adding the height of the storm surge to the predicted height of the next high water.

Table 7 Theoretical height of maximum storm tide at the next high water relative to AHD, LAT in brackets. AHD – LAT from Maritime Safety Queensland, 2017.

Site Height of next high tide (m,AHD)

Minor flood level

(AHD)

Moderate Flood Level

(AHD)

Major flood level (AHD)

Theoretical Max storm tide

(m,AHD)

Brisbane Bar 1.20 (2.44) na na na 1.97 (3.21)

Hawthorn 1.29 (2.49) 1.7 2.0 2.3 2.16 (3.36)

Brisbane CBD Port Office

1.11 (2.35) 1.7 2.6 3.5 2.31 (3.55)

Brisbane CBD Thornton Street

1.11 (2.35) 1.7 2.6 3.5 2.34 (3.58)

St Lucia 1.17 (2.32) 2.4 3.5 5.5 2.35 (3.50)

Oxley Creek mouth

1.17 (2.32) 2.5 3.5 5.5 2.71 (3.86)

Jindalee 1.27 (2.32) 6.0 8.0 10.0 2.64 (3.69)

Aitcheson Street 1.26 (2.26) na na na 2.77 (3.77)

Moggill 1.31 (2.26) 10.0 13.0 15.5 2.68 (3.63)

Karalee 1.31 (2.26) na na na 3.15 (4.1)

Ipswich 1.31 (2.26) 7.0 9.0 11.7 6.59 (7.54)


11

2.2 Alignment of surge and storm

The time of the maximum surge at each site in the Brisbane and Bremer Rivers and the maximum sustained wind speed at the nearest weather station are presented in a time line in Figure 7 and in Table 8. The time difference between the surge at a site and the maximum wind speed at the nearest weather station (Table 8) show that the maximum surge always arrives later than the maximum wind speed.

Figure 7 The time of arrival of the Maximum surge and the Maximum wind speed on 30 March 2017.

The time difference ranges from 16 minutes at the mouth of Brisbane River where the weather station and tide gauge are very close together up to nearly two hours between the surge in the Bremer River and the maximum wind speed at Amberley weather station. The time taken for the maximum surge to travel from the mouth of the Brisbane River (at the Brisbane Bar tide station) to the most upstream station at Ipswich was three hours and nine minutes. The time for the storm (maximum winds) to pass over from Brisbane Airport to Amberley weather station was only one and a half hours.

18:00 18:28 18:57 19:26 19:55 20:24 20:52 21:21 21:50 22:19 22:48 23:16 23:45

Max Surge

Max wind


12

Table 8 Time of maximum surge and maximum wind speed at the Brisbane and Bremer River sites, nearest weather station in brackets. Time difference and time of maximum surge after Brisbane Bar.

Site Time of Max surge

Time of Max wind speed

Time difference

Time after Brisbane Bar

Brisbane Bar (Brisbane airport) 7:46 pm 7:30 pm 0:16 0:00

Hawthorn (Brisbane airport) 8:05 pm 7:30 pm 0:35 0:19

Brisbane CBD Port Office (Brisbane CBD)

8:12 pm 7:30 pm 0:42 0:26

Brisbane CBD Thornton Street (Brisbane CBD)

8:11 pm 7:30 pm 0:41 0:25

St Lucia (Brisbane CBD) 8:33 pm 7:30 pm 1:03 0:47

Oxley Creek mouth (Archerfield)

8:38 pm 8:00 pm 0:38 0:52

Jindalee (Archerfield) 9:02 pm 8:00 pm 1:02 1:16

Aitcheson Street (Amberley) 9:38 pm 9:00 pm 0:38 1:52

Moggill Ferry (Amberley) 9:46 pm 9:00 pm 0:46 2:00

Karalee (Amberley) 9:49 pm 9:00 pm 0:49 2:03

Ipswich (Amberley) 10:55 pm 9:00 pm 1:55 3:09

2.3 Meteorological Tsunami

A unique and uncommon wave that is very similar to a Tsunami wave hit Queensland coastal regions on the 3 and 4 December 2016 (not reported here but included to generate awareness). The wave occurred during a storm event and passed without being noticed in the stealth of darkness. A Tsunami-like wave train was recorded in many of the Queensland Storm Tide gauges over a 10 hour period. The wave also travelled across Moreton Bay and into the Brisbane River. The Tsunami signal was recorded by the river Alert gauges as far upstream as Karalee at Ipswich. The height of the largest wave in the train at the Brisbane River mouth was 0.32 m (unpublished personal observation). The Meteorological Tsunami is included here as a comparison to the surge bore as it also travelled upstream in the Brisbane River and is yet to be reported on. The driving mechanism behind a Meteorological Tsunami is a sudden change in atmospheric pressure that


13

travels across the coast, from land to sea, and out to the continental shelf. The surge reported in this report was driven by very strong on-shore winds and (slowly) changing atmospheric pressure.


14

3 Conclusions The storm surge that resulted from the passage of ex-STC Debbie along the south east Queensland coast travelled along the coast from north to south and into Moreton Bay, the Brisbane River and into the Bremer River as far upstream as Ipswich. The surge could be considered as a coastally trapped wave (Zamudio, et al., 2002) that travelled along the coast and into Moreton Bay.

The wind direction was consistently north east to east north east during the passage allowing a long fetch from outside of Moreton Bay. The long fetch, very strong winds and falling Barometric pressure contributed to the generation of the surge. The restriction of water movement by the coast meant that water levels could build up at the coastal stations and was essentially funnelled into the Brisbane River mouth as a travelling wave or surge bore.

The storm tide gauge at Urangan Boat Harbor recorded a maximum residual of 0.90 m at 4:00 pm. The storm tide level slowly increased to that maximum starting at around 10:00 am and quickly fell off back to near zero by 6:00 pm. The Urangan site is within Hervey Bay which is open to the north like a funnel, hence, wind forcing from the north east pushed the water into the boat harbor where the water was restricted in horizontal movement. At the Mooloolaba storm side gauge the residual was small in comparison due to the site being in a sheltered position inside the Mooloolah River.

The maximum surge arrived at Tangalooma on the eastern side of Moreton Bay 11 minutes before it arrived at the Scarborough site on the west side of the bay. This would suggest that the surge was generated outside of Moreton bay as the wind direction at the Tangalooma site was off-shore which should force levels down. The surge was however followed by a fall in level (or negative surge) at the three northern Moreton Bay sites.

The surge originated from the long fetch outside of and across Moreton Bay and travelled upstream in the Brisbane River as an unforced surge bore. There is confirmation of this through consideration of the lag between the time of maximum surge at the gauges and the time of maximum winds at the nearest weather stations. Further confirmation comes from the observed decay in wave height as the surge travelled upstream. The surge initially grew from 0.49 m at the Brisbane river mouth, which is considerably wider than the upstream sites (personal observation), to 0.65 m at the Brisbane CBD. Decay in the surge bore height to 0.19 m in the Bremer River followed.

The surge arrived at all of the Brisbane River sites on the incoming flood tide and as such the total storm tide level did not exceed the minor flood level. If the storm surge was to coincide with the next high water, as presented in Table 7 as the theoretical maximum storm tide, the total storm tide level would have exceeded the minor flood level at four sites in the lower reaches of the Brisbane River. At Hawthorn the moderate flood level would have been exceeded by 0.16 metres. Further upstream at the Brisbane CBD port Office the minor flood level would have been exceeded by 0.61 m (0.64 m on the opposite bank at Thornton Street) while at the Oxley Creek mouth site the minor flood level would have been exceeded by 0.21 metres. At St Lucia the theoretical maximum level would not have exceeded the minor flood level. Upstream from Oxley Creek mouth the theoretical maximum level would not have exceeded the minor flood level.

The surge reported on here resulted from the remnants of STC Debbie. The severe low pressure system moved southward at a relatively prompt speed of 15 km/h and with high wind speeds. If the system’s southward speed was slower or the winds more powerful, the storm surge may have also been larger. How much larger the surge had potential to reach is unknown.


15

The wave height of the Meteorological Tsunami on 3 December 2016 was lower than the surge from ex-STC Debbie at the Brisbane River mouth by 0.17 metres. The theoretical storm tide level that the tsunami wave may have reached if it happened at high tide would have reached the moderate flood level at Hawthorn. With these two factors in mind it is recommended that this potential be investigated further through: (1) researching the occurrence of surge/tsunami bore in the Brisbane River and Moreton Bay via historic tide/alert gauge and pressure data and (2) modelling of the capacity of a system to generate surge and tsunami waves. With particular focus on the surge bore and Tsunami bore height growth potential.

4 References Bureau of Meteorology 2017. Severe Tropical Cyclone Debbie regional Queensland office report, accessed 12/09/2017 from http://www.bom.gov.au/announcements/sevwx/qld/qldtc20170325.shtml

Butterworth, S. 1930. On the theory of filter amplifiers. Wireless Engineer, vol. 7, 1930, pp 536-541.

Maritime Safety Queensland, 2017. Semidiurnal Tidal Planes 2017, accessed 12/09/2017 from https://www.msq.qld.gov.au/Tides/Tidal-planes.

Pugh, D. and Woodworth, P., 2014. Sea-Level Science: understanding tides, surges, tsunami and mean sea level changes. Cambridge University Press, pp 156-157.

Zamudio, L., H. E. Hurlburt, E. J. Metzger, and O. M. Smedstad, 2002. On the evolution of coastally trapped waves generated by Hurricane Juliette along the Mexican West Coast, Geophys. Res. Lett., 29(23), 2141, doi:10.1029/2002GL014769.

4.1 Further information

Queensland Government Website Storm Tide Gauge Data:

https://www.qld.gov.au/tides

Wave Buoy Data:

https://www.qld.gov.au/waves

http://www.bom.gov.au/announcements/sevwx/qld/qldtc20170325.shtml

https://www.msq.qld.gov.au/Tides/Tidal-planes

http://dx.doi.org/10.1029/2002GL014769

https://www.qld.gov.au/waves


16

Appendix 1 Raw data

Coastal stations

Figure 8 Urangan Boat Harbor storm tide levels on 30 March 2017

Figure 9 Mooloolaba storm tide levels on 30 March 2017

Figure 10 Tangalooma storm tide levels on 30 March 2017

-0.50

0.51

1.52

2.53

3.54

4.5

30/03 00:00 30/03 06:00 30/03 12:00 30/03 18:00 31/03 00:00

Heig

ht (m

,LAT

)

Actual Prediction Residual

-0.5

0

0.5

1

1.5

2

2.5

3

30/03 00:00 30/03 06:00 30/03 12:00 30/03 18:00 31/03 00:00

Heig

ht (m

,LAT

)


0

0.5

1

1.5

2

2.5

3

30/03/17 00:00 30/03/17 06:00 30/03/17 12:00 30/03/17 18:00 31/03/17 00:00

Heig

ht (m

, LAT

)



17

Figure 11 Scarborough Boat Harbor storm tide levels on 30 March 2017

Figure 12 Shorncliffe Pier storm tide levels on 30 March 2017

Figure 13 Russell Island East storm tide levels on 30 March 2017

Brisbane River Stations

Figure 14 Brisbane Bar MSQ raw data 30 March 2017

-0.5

0

0.5

1

1.5

2

2.5

3

30/03 00:00 30/03 06:00 30/03 12:00 30/03 18:00 31/03 00:00

Heig

ht (m

, LAT

)


0

0.5

1

1.5

2

2.5

3

30/03 00:00 30/03 06:00 30/03 12:00 30/03 18:00 31/03 00:00

Heig

ht (m

, LAT

)


0

0.5

1

1.5

2

2.5

3

30/03/17 00:00 30/03/17 06:00 30/03/17 12:00 30/03/17 18:00 31/03/17 00:00

Heig

ht (m

, LAT

)


0

0.5

1

1.5

2

2.5

3

30/03/17 00:00 30/03/17 06:00 30/03/17 12:00 30/03/17 18:00 31/03/17 00:00

Heig

ht (m

,LAT

)

Prediction Actual Residual


18

Figure 15 Brisbane River, Hawthorn BCC interpolated data 30 March 2017

Figure 16 Brisbane River, CBD Port Office interpolated BCC data on 30 March 2017

Figure 17 Brisbane River, CBD Thornton Street ferry terminal interpolated SEQWater data on 30

March 2017

Figure 18 Brisbane River, St Lucia interpolated BCC data on 30 March 2017

-0.5

0

0.5

1

1.5

2

2.5

3

30/03 00:00 30/03 06:00 30/03 12:00 30/03 18:00 31/03 00:00

Heig

ht (m

, LAT

)


-0.5

0

0.5

1

1.5

2

2.5

3

30/03 00:00 30/03 06:00 30/03 12:00 30/03 18:00 31/03 00:00

Heig

ht (m

,LAT

)


0

0.5

1

1.5

2

2.5

3

30/03 00:00 30/03 06:00 30/03 12:00 30/03 18:00 31/03 00:00

Heig

ht (m

,LAT

)


0

0.5

1

1.5

2

2.5

3

30/03 00:00 30/03 06:00 30/03 12:00 30/03 18:00 31/03 00:00

Heig

ht (m

,LAT

)



19

Figure 19 Brisbane River, Oxley Creek Mouth interpolated BCC data on 30 March 2017

Figure 20 Brisbane River, Jindalee interpolated SEQWater data on 30 March 2017

Figure 21 Brisbane River, Aitcheson Street East interpolated BCC data on 30 March 2017

Figure 22 Brisbane River, Moggill interpolated SEQWater data on 30 March 2017

0

0.5

1

1.5

2

2.5

3

30/03 00:00 30/03 06:00 30/03 12:00 30/03 18:00 31/03 00:00

Heig

ht (m

, LAT

)


-0.5

0

0.5

1

1.5

2

2.5

3

30/03 00:00 30/03 06:00 30/03 12:00 30/03 18:00 31/03 00:00

Heig

ht (m

,LAT

)


-0.5

0

0.5

1

1.5

2

2.5

3

3.5

30/03 00:00 30/03 06:00 30/03 12:00 30/03 18:00 31/03 00:00

Heig

ht (m

, LAT

)


-0.50

0.51

1.52

2.53

3.5

30/03 00:00 30/03 06:00 30/03 12:00 30/03 18:00 31/03 00:00

Heig

ht (m

,LAT

)



20

Bremer River Stations

Figure 23 Bremer River, Karalee interpolated Ipswich Council data on 30 March 2017

Figure 24 Bremer River, Ipswich interpolated Ipswich Council data on 30 March 2017

-0.5

0.5

1.5

2.5

3.5

30/03 00:00 30/03 06:00 30/03 12:00 30/03 18:00 31/03 00:00

Heig

ht (m

,LAT

)


-1

1

3

5

7

9

30/03 00:00 30/03 06:00 30/03 12:00 30/03 18:00 31/03 00:00

Heig

ht (m

,LAT

)



21

Appendix 2 Filtered data

Coastal Stations

Figure 25 Urangan filtered storm tide data on 30 March 2017

Figure 26 Mooloolaba filtered storm tide data on 30 March 2017

Figure 27 Tangalooma filtered storm tide data on 30 March 2017

Figure 28 Scarborough filtered storm tide data for 30 March 2017

-0.4-0.3-0.2-0.1

00.10.20.30.40.5

30/03 00:00 30/03 06:00 30/03 12:00 30/03 18:00 31/03 00:00Heig

ht (m

)

-0.4-0.3-0.2-0.1

00.10.20.30.40.5

30/03 00:00 30/03 06:00 30/03 12:00 30/03 18:00 31/03 00:00Heig

ht (m

)

-0.4-0.3-0.2-0.1

00.10.20.30.40.5

30/03 00:00 30/03 06:00 30/03 12:00 30/03 18:00 31/03 00:00Heig

ht (m

)

-0.4-0.3-0.2-0.1

00.10.20.30.40.5

30/03 00:00 30/03 06:00 30/03 12:00 30/03 18:00 31/03 00:00Heig

ht (m

)


22

Figure 29 Shorncliffe Pier filtered storm tide data on 30 March 2017

Figure 30 Russell Island West filtered storm tide data on 30 March 2017

Brisbane River Stations

Figure 31 Brisbane Bar filtered (MSQ actual) tide data on 30 March 2017

Figure 32 Brisbane River, Hawthorn filtered (BCC Alert actual) data on 30 March 2017

-0.4-0.3-0.2-0.1

00.10.20.30.40.5

30/03 00:00 30/03 06:00 30/03 12:00 30/03 18:00 31/03 00:00Heig

ht (m

)

-0.4-0.3-0.2-0.1

00.10.20.30.40.5

30/03 00:00 30/03 06:00 30/03 12:00 30/03 18:00 31/03 00:00Heig

ht (m

)

-0.4-0.3-0.2-0.1

00.10.20.30.40.5

30/03 00:00 30/03 06:00 30/03 12:00 30/03 18:00 31/03 00:00Heig

ht (m

)

-0.4-0.3-0.2-0.1

00.10.20.30.40.5

30/03 00:00 30/03 06:00 30/03 12:00 30/03 18:00 31/03 00:00Heig

ht (m

)


23

Figure 33 Brisbane River, CBD Port Office filtered (BCC Alert actual) data on 30 March 2017

Figure 34 Brisbane River, CBD Thornton Street filtered (SEQWater Alert actual) data on 30 March

2017

Figure 35 Brisbane River, St Lucia filtered (BCC Alert actual) data on 30 March 2017

Figure 36 Brisbane River, Oxley Creek Mouth filtered (BCC Alert actual) data on 30 March 2017

-0.4-0.3-0.2-0.1

00.10.20.30.40.5

30/03 00:00 30/03 06:00 30/03 12:00 30/03 18:00 31/03 00:00Heig

ht (m

)

-0.4-0.3-0.2-0.1

00.10.20.30.40.5

30/03 00:00 30/03 06:00 30/03 12:00 30/03 18:00 31/03 00:00Heig

ht (m

)

-0.4-0.3-0.2-0.1

00.10.20.30.40.5

30/03 00:00 30/03 06:00 30/03 12:00 30/03 18:00 31/03 00:00Heig

ht (m

)

-0.4-0.3-0.2-0.1

00.10.20.30.40.5

30/03 00:00 30/03 06:00 30/03 12:00 30/03 18:00 31/03 00:00Heig

ht (m

)


24

Figure 37 Brisbane River, Jindalee filtered (SEQWater Alert actual) data on 30 March 2017

Figure 38 Brisbane River, Aitcheson Street East, filtered (BCC Alert actual) data on 30 March 2017

Figure 39 Brisbane River, Moggill filtered (SEQWater Alert actual) data on 30 March 2017

Figure 40 Bremer River, Karalee filtered (City of Ipswich Alert actual) data on 30 March 2017

-0.4-0.3-0.2-0.1

00.10.20.30.40.5

30/03 00:00 30/03 06:00 30/03 12:00 30/03 18:00 31/03 00:00Heig

ht (m

)

-0.4-0.3-0.2-0.1

00.10.20.30.40.5

30/03 00:00 30/03 06:00 30/03 12:00 30/03 18:00 31/03 00:00Heig

ht (m

)

-0.4-0.3-0.2-0.1

00.10.20.30.40.5

30/03 00:00 30/03 06:00 30/03 12:00 30/03 18:00 31/03 00:00Heig

ht (m

)

-0.4-0.3-0.2-0.1

00.10.20.30.40.5

30/03 00:00 30/03 06:00 30/03 12:00 30/03 18:00 31/03 00:00Heig

ht (m

)


25

Figure 41 Bremer River, Ipswich filtered (City of Ipswich Alert actual) data on 30 March 2017

-0.4-0.3-0.2-0.1

00.10.20.30.40.5

30/03 00:00 30/03 06:00 30/03 12:00 30/03 18:00 31/03 00:00Heig

ht (m

)


26

Appendix 3 Weather Data

Figure 42 MSLP at Cape Moreton on 30–31 March 2017

Figure 43 MSLP at Brisbane Airport on 30–31 March 2017

Figure 44 MSLP at Brisbane CBD on 30–31 March 2017

Figure 45 MSLP at Amberley on 30–31 March 2017

995

1000

1005

1010

1015

00:00 06:00 12:00 18:00 00:00 06:00 12:00

Pres

sure

(hPa

)

995

1000

1005

1010

1015

00:00 06:00 12:00 18:00 00:00 06:00 12:00

Pres

sure

(hPa

)

995

1000

1005

1010

1015

00:00 06:00 12:00 18:00 00:00 06:00 12:00

Pres

sure

(hPa

)

995

1000

1005

1010

1015

00:00 06:00 12:00 18:00 00:00 06:00 12:00

Pres

sure

(hPa

)


27

Figure 46 MSLP at Archerfield on 30–31 March 2017

Figure 47 MSLP at the Gold Coast Seaway 30–31 March 2017

Figure 48 Wind speed and gust at Cape Moreton 30–31 March 2017

Figure 49 Wind speed and gust at Brisbane Airport 30–31 March 2017

995

1000

1005

1010

1015

00:00 06:00 12:00 18:00 00:00 06:00 12:00

Pres

sure

(hPa

)

995

1000

1005

1010

1015

00:00 06:00 12:00 18:00 00:00 06:00 12:00

Pres

sure

(hPa

)

0

20

40

60

80

100

120

00:00 06:00 12:00 18:00 00:00 06:00 12:00

Spee

d (k

m/h

)

gust ave speed

0

20

40

60

80

100

120

00:00 06:00 12:00 18:00 00:00 06:00 12:00

Spee

d (k

m/h

)

gust ave speed


28

Figure 50 Wind speed and gust at Brisbane CBD 30–31 March 2017

Figure 51 Wind speed and gust at Amberley 30–31 March 2017

Figure 52 Wind speed and gust at Archerfield 30–31 March 2017

Figure 53 Wind speed and gust at Gold Coast Seaway 30–31 March 2017

0

20

40

60

80

100

120

00:00 06:00 12:00 18:00 00:00 06:00 12:00

Spee

d (k

m/h

)

gust ave speed

0

20

40

60

80

100

120

00:00 06:00 12:00 18:00 00:00 06:00 12:00

Spee

d (k

m/h

)

gust ave speed

0

20

40

60

80

100

120

00:00 06:00 12:00 18:00 00:00 06:00 12:00

Spee

d (k

m/h

)

gust ave speed

0

20

40

60

80

100

120

00:00 06:00 12:00 18:00 00:00 06:00 12:00

Spee

d (k

m/h

)

gust ave speed


29

Appendix 4 Glossary

Parameter Description

Astronomical tide The Astronomical Tide or more simply, the tide, is the periodic rise and fall of water along the coast because of gravitational attraction on the water by the moon and sun. When the moon, sun and earth are in line their combined attraction is strongest and the tide range is greater (spring tides). When the moon and sun are at right angles to each other (in relation to the earth) the effect of the attraction is somewhat reduced and the tide range is smaller (neap tides).

AHD AUSTRALIAN HEIGHT DATUM is the reference level used by the Bureau of Meteorology in Storm Tide Warnings. AHD is very close to the average level of the sea over a long period (preferably 18.6 years), or the level of the sea in the absence of tides.

Coastally Trapped Wave

A wave form that propagates along shore on the Continental shelf.

Flood Tide The incoming or rising tide, occurring between the time when the tide is lowest and the time when the following tide is highest.

HAT HIGHEST ASTRONOMICAL TIDE is the highest water level which can be predicted to occur at a particular site under average weather conditions. This level may not be reached every year.

LAT LOWEST ASTRONOMICAL TIDE is the lowest water level which can be predicted to occur at a particular site under average weather conditions. This level may not be reached every year and is used as chart datum and port datum within Australia.

Meteorological Tsunami

A Meteorological Tsunami or Meteotsunami are tsunami – like waves of meteorological origin. Meteotsunami’s are generated when rapid changes in barometric pressure cause the displacement of a body of water. In contrast to "ordinary" impulse-type tsunami sources, a traveling atmospheric disturbance normally interacts with the ocean over a limited period of time (from several minutes to several hours).

Predicted tide The tide expected to occur under average meteorological conditions. Tide predictions are typically based on previous actual tide readings gathered over a long period (usually one year or more). The sun, moon and earth are not in the same relative position from year to year. Accordingly, the gravitational forces that generate the tides, and the tides themselves, are not the same each year.

https://en.wikipedia.org/wiki/Tsunami

https://en.wikipedia.org/wiki/Wave

https://en.wikipedia.org/wiki/Meteorological

https://en.wikipedia.org/wiki/Barometric_pressure


30

Storm surge An abnormal rise of water generated by a storm, over and above the predicted astronomical tides.

Storm tide A rise in local sea level caused by the combination of regular tides, storm surge (in Queensland wave setup is included in the definition).

Surge Bore Term used in this report (not defined scientifically) to describe the wave like part of the surge that travelled upstream in the Brisbane and Bremer rivers.

Wave setup An increase in water level caused by waves piling up on the beach.

http://tidesandcurrents.noaa.gov/

ex-severe tropical cyclone debbie - publications · ex-severe tropical cyclone debbie storm surge...

Documents