Why will the 2022 Brisbane floods be different? – Griffith News

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Just 11 years after the devastating floods of 2011, Brisbane is flooded again, but not this time. ]In the new edition,A river with urban problemsDr Margaret Cook, of Griffith University’s Australian River Research Institute, said that fast-moving waters on the south side of the city followed a well-known riverside flooding path, while on the north side, areas untouched since 1974 were inundated. Residents indicated they were left unprepared.

Despite forecasts predicting the weather system to move south, rain continued to fall over Brisbane for several days, bringing a staggering amount of rain. Prime Minister Annastacia Parašchuk expressed the opinion of many:

“I didn’t expect this rain. This rain bomb is relentless. It’s not like a waterfall, it’s like a wave of water. The ‘severe weather’ is like an unpredictable cyclone.” bottom. “

Between 23-28 February, droplets between 400mm and 1,100mm (average 795mm) hit the Brisbane City Council area, most of which fell between Friday 25th and Sunday 27th February.

Dr Margaret Cook, Australian River Research Research Fellow and Environmental Historian

“Brisbane has never experienced so much damage in a month since the 1893 floods,” said Dr Cook. “The three-day record surpassed the 1974 flood, with more than several meters of rain in three days in the northern suburbs of Alderley.”

“In 72 hours Brisbane received about 80 per cent of the city’s average annual rainfall, which London receives almost all of its annual rainfall. In less than a day there was an influx of water equivalent to about three Sydney Harbors.”

Fortunately, at the start of the 2022 flood event, Wivenhoe Dam was only 56% full, allowing it to store 2.2 million megalitres before it needed to be released. The problem is that the rainfall downstream of Mogil was more than triple what it was in 2011.

A moderate flood warning was issued on 26 February, but due to constantly changing weather scenarios, the projected river flood heights will be revised five times over the next 11 hours, and the warning will be issued immediately (or It became outdated before the announcement).

“People may be surprised to hear that the maximum flood height in 2022 at the Brisbane City Gauge on Edward Street was 3.85m, which is significantly lower than the 4.46m recorded in 2011,” Cook said. said Dr.

“The 2011 event was primarily river flooding, with the most severe flooding occurring on the main river itself. This is very different from what we have seen in 2022. Occurred in streams, land currents. Once.”

“Creek floods, particularly on the north side of Brisbane, have surpassed all previous height records, including 1974, which is much closer to the 2022 flood.”

Brisbane flood water levels in 2022

Kedron Brook, north of Brisbane, broke the record with 893mm, compared to 661mm in 1974 and 315mm in 2011. Swollen streams quickly filled the flood plains, flooding roads and homes. After a two-year La Niña of frequent rains, infiltrated ground increased runoff and runoff to land, combined with flooding of creeks, could cause areas left dry in 2011 to become inundated in 2022. Became.

Jamika Santos lived near Enogera Creek on Acacia Drive in Ashgrove for 25 years. In 2011 floodwaters reached her driveway. In 2022, Ogawa rose to less than two meters outside her home.

‘It was crazy,’ she said of home delivery“It kept going up and didn’t stop. I was scared by the sudden rise.”

she wasn’t alone. Pictures of flooded roads, submerged houses and dramatic rescues posted on social media showed residents caught off guard by the rapidly rising flood waters. People and pets were rescued by personal watercraft as 2,770 Brisbane streets were flooded and the Bruce, Warrego and Ipswich highways were all closed to traffic for several days. A total of 13 people died in the 2022 floods, and 23,400 properties were affected in all but 11 of Brisbane’s 188 suburban neighborhoods.

Pontoon debris was also found as far away as Kgalli (Fraser Island) and Noosa, and Moreton Bay was covered in a plume of mud for weeks. Brisbane once again faced massive reconstruction efforts and huge financial debt, while city residents again faced property loss, homelessness and heartache.

Two major floods in quick succession (2011 and 2022), with very different mechanisms and outcomes, brought home to us the region’s subtropical climate and flooding tendencies.

“Even though the region has a complex network of four rivers and 22 streams, we tend to focus only on the Brisbane River when it comes to flooding.” – Dr. Margaret Cook

“But as 2022 has shown, flooding can come from rivers, Brisbane creeks, land currents, or a combination of these. is different and we need to be prepared for every scenario.”

Climate change and rising levels of urban density are projected to increase the risk of extreme floods, and in order to avoid being caught off guard by the inevitable next flood, proactive measures are being taken to mitigate risk. Change is essential. But, as Dr Cook points out, Brisbane’s current reliance on the Wivenho Dam dam to protect it from flooding is highly dependent on where it rains.

Flooding creek near Marist College, Ash Grove, Image Credit: Marist College Ash Grove Seniors Association

“Dams have limited storage capacity and can hold back flooding upstream, but heavy rains downstream will fill Brisbane’s creeks and stormwater systems, as they did in 2022, flooding the city. To avoid this, a flood mitigation strategy could be that Brisbane’s creeks, land-streams and stormwater systems all have the potential to flood independently of rivers when planning and redeveloping cities. , must keep this complex hydrology in mind.”

After the 2011 floods, measures were introduced to raise or refurbish houses to make them more flood resistant, and from 2022 onwards, a buy-back system was implemented to relocate 500 houses off the floodplain. “These are all positive steps in the right direction in developing adaptation strategies to address the region’s complex flood hazards,” Dr. Cook concludes. “But from a zoning perspective, more needs to be done in terms of preventing increased development in flood-prone areas and removing more property from these areas.”

“We go beyond dams for flood mitigation, looking at strategies such as creating vegetation and floodplain submergence, improved stormwater management, new building designs and materials, and finally, subtropical areas like Brisbane. We need to adopt public education to adapt to life in the city, on a flooded river.”

2nd edition ofA river with urban problems By Margaret Cook will be available in bookstores and from Queensland University Press from 23 May 2023.

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