Residents evacuate after dam wall bursts
Water gushing from the broken Bolzan Quarry Dam - located south of Toowoomba - has spilled over a levy bank and is flowing into a nearby creek system – but the risk to homes remains low. SEE THE DRONE FOOTAGE
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WATER gushing from the broken Bolzan Quarry Dam has spilled over a levy bank and is flowing into a nearby creek system – but the risk to homes remains low.
Engineers are providing hourly updates on the stability of the dam wall after a hole appeared overnight and began gushing water.
Southern Downs Regional Council Cr Cameron Gow said water had now filled an area below the dam wall, a “cofferdam” which held 50 megalitres.
Beyond that he said was a paddock, which engineers had expected to take much of the water if the levy bank failed to hold it.
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“The water flow is consistent and stable,” he said this afternoon.
“We thought the situation was reducing somewhat but they’ve asked to extend the current lockdown period for a little while longer.”
He said the hole had collapsed “a little” and had gone from around 3.5m across to a little under 5m.
But he said the collapse had not increased the water flow.
“The cofferdam is now full and is gradually starting to release water into Yankee Creek system.”
He said talks were ongoing as to when it might be safe for residents to return to their homes.
“My advice is that everyone could be allowed back as early as this evening,” Cr Gow said.
BURST DAM: THE ONE THING SAVING HOMES FROM MASS FLOOD
AN engineer who assessed the Bolzan Quarry Dam early this morning has given some hope that geography could save houses in the path of a major flooding event.
Water is gushing out of a large hole in the 440 megalitre dam wall - located south of Toowoomba - causing an emergency declaration and the evacuation of houses downstream.
But Southern Downs Regional Council Cr Cameron Gow said an engineer has advised a levy bank – or cofferdam - in front of the breached wall is so far containing the water.
“His advice only a few minutes ago is the water running out of the hole has lowered the height of the water inside by half a metre – or between 15 and 20 per cent of its capacity,” Cr Gow said.
“Immediately below is a levy bank or cofferdam with a 50 megalitre capacity and that is actually containing the water so far.
“Immediately downstream from that is a large paddock and that paddock will provide an area for the water to spread across, which should take away the impact of any flooding.”
Cr Gow said the engineer had not so far recommended any repairs to the hole and that evacuation orders remain in place for the safety of residents.
“Evacuees aren’t being allowed back at this stage,” he said.
“We need to be really sure before that occurs and we will continue to reassess the situation over the coming hours.
“People are being really good, really patient.”
It came as residents south of Toowoomba were forced to evacuate after a private 440 megalitre dam burst, sending water ‘gushing out’ of the at-capacity dam and causing fears the entire wall could collapse leading to dangerous downstream flooding.
The dam holds the equivalent of 176 Olympic swimming pools worth of water.
An emergency alert was issued at 11:15pm last night for up to 5000 residents in Talgai, north of Warwick, after the Bolzan Quarry Dam failed.
Dangerous downstream flooding was expected to affect the area bounded by Hendon Victoria Hill Road, Warwick Allora Road, Pratten Road and Yankee Gully Road.
Earlier today, Southern Downs regional council mayor Tracy Dobie told The Courier-Mail Queensland Fire and Emergency had evacuated nine properties and another 250 were at risk if the dam wall collapsed completely.
An evacuation centre at Warwick Christian College on Horsman Rod was established but has since been closed after residents opted to stay with family and friends instead - leaving the centre empty.
Cr Dobie said a 3.5m x 1m hole formed toward the bottom of the dam wall and ‘water is gushing out’.
The dam is full after the recent deluge and holds 440 mega litres of water.
“The wall has not collapsed completely yet, that was the fear through the night,” she said.
“It’s punched a hole through the bottom of the wall and it is gradually increasing in size.
“We don’t know if or when the wall will let go … we’ve prepared for the depth and width of the flooding and police and emergency services have been on site all night preventing anyone from being in the vicinity of the dam or directly downstream.”
Engineers were on site using drone footage to assess the situation and decide how to take pressure off the dam wall.
Earlier, firefighting and SES crews were at the dam to try and patch up the leak.
However the dam burst again, resulting in more crews and senior officers attending the scene to deal with the flow of water.
The two key water storages supplying southeast Queensland remain far from filled despite the deluge, but 26 dams scattered across the region have all taken a big gulp from the February rains and the year ahead looks brighter for our water supply.
While Queenslanders are mopping up from the deluge, Seqwater officials who look after 26 dams are giving a reserved welcome to the rain, warning a whole lot more is needed to secure a healthy water supply.
The key dam, Wivenhoe, was down to 42 per cent when the serious rain began in early February and today is past 50 per cent capacity.
But the dam levels still hover around those low levels it was recording during the drought leading up to the 2010/11 floods.
Our water supply is still low enough for us to pipe up around 80 million litres a day from the Gold Coast Desalination Plant to pour into our water system.
That desalination plant was part of the much maligned water grid devised by the Beattie Government a decade and a half ago.
The problem for Wivenhoe and Somerset Dam is that falls in the catchment area which spreads across 7000 square kilometres have only averaged around 200mm.
On the Gold and Sunshine Coast the falls were nearly double that.
Lake Macdonald Dam is now spilling excess water https://t.co/6b9lv0xsfA pic.twitter.com/FfBVaLAzZP
— Seqwater (@Seqwater) February 14, 2020
Seqwater says the smaller dams such as Borumba Dam near Gympie and the Hinze Dam on the Gold Coast hinterland received bigger inflows and look a lot healthier.
“We have 10 dams currently spilling,” a spokesperson said.
“The majority of Grid dams at or near capacity are our smaller storages on the Sunshine Coast and Gold Coast.”
The array of tributaries and creeks which feed into the southeast’s water systems will continue to provide extra water in all dams in the days ahead.
There are still 162 road closures across Qld due to flooding - take care on the roads tonight and remember if it's #FloodedForgetIt #QldTraffic pic.twitter.com/CCAIR1waix
— RACQ (@RACQOfficial) February 14, 2020
But more rain will be needed in the weeks ahead, which is possible even if forecasts are light.
That rain would increase run off into our dams because sodden ground won’t absorb much more water.
But Seqwater says our catchments dry out quickly, so more rain would have to come within two to three weeks to take advantage of the February falls.
The Water Grid storage volume has increase by approximately 221,800 ML (or 10.1%) since inflows commenced on February 3.
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