Tweed's response to flood showcases resilience

Tweed's response to flood

SHOWCASES RESILIENCE

by Anthony Burnham, Manager Water & Wastewater – Business & Assets, Tweed Shire Council

The Tweed’s flood recovery continues to gather momentum as the full extent of the record flood of February-March 2022 becomes clearer.

While the Tweed Shire typically records high rainfall totals each year, the amount that fell in in the Tweed earlier this year blitzed records. According to the Australian Bureau of Meteorology, the Tweed had four of the top 12 rainfall locations in Australia, from 26 February to 4 March 2022.

The village of Uki, near Clarrie Hall Dam, had the unfortunate honour of topping the list with 1,107mm recorded in the period. Kunghur on the Rous River was the fourth highest, with 943mm. Boat Harbour on the Rous was the ninth highest, with 860mm, and North Murwillumbah on the Tweed River was 12th, with 801mm.

Flood levels reached 6.5m at Murwillumbah, 200mm higher than the town’s previous flood record in 2017, and 4.8m at the riverside village of Tumbulgum, to the Shire’s north. The flood at Tumbulgum was 800mm higher than in 2017.

Tweed Shire Council estimates 4.5 times the volume of the Clarrie Dall Dam went over the spillway in just two days. That’s 67.5GL of water.

Following the flooding, the bank of the Tweed River retreated more than 30m in some places.

AFTER THE 2017 FLOOD, COUNCIL RAISED THE UKI PUMP STATION ELECTRICAL SWITCHBOARD TO ABOVE THE PREDICTED FLOOD LEVEL. YET, COUNCIL IS CONCERNED THAT FLOODWATERS IN 2022 CAME WITHIN MILLIMETRES OF THE RAISED CABINET

Tweed's response to flood

SHOWCASES RESILIENCE

HIGH COST OF FLOOD RECOVERY

As the local community marks six months since the devastating deluge, the cost of the recovery is becoming more apparent.

More than 2,100 homes were damaged, with 500 no longer habitable. An estimated 1,600 people required temporary accommodation. Almost 200 businesses reported damages worth $57 million. A total of 90 Tweed Shire Council buildings were inundated.

Council estimates the damage bill to be $100 million for Council infrastructure alone. This includes damage to Council roads, which is now estimated at $80 million – almost four times that of the 2017 flood – with ten significant landslips requiring extensive geotechnical analysis and repair.

WATER AND WASTEWATER RECOVERY

Damage to the Tweed’s water and wastewater network was minimised, thanks in part to some smart resilience works that had already been undertaken.

The initial repair works to 30 June, to make the Tweed’s water and wastewater systems operational following the 2022 flood, cost $642,000. Rectification works will continue for the next 18 months and are estimated to cost an additional $2 million.

The extreme weather of February–March 2022 washed soil and debris into creeks and rivers that flow into water treatment plants and caused power outages at the plants and a number of water pump stations.

In the immediate flood response, Council remained focused on continuing to provide safe drinking water, re-establishing the wastewater network, supporting the community with waste and clean-up options and safely restoring access to local roads.

Crews worked under incredible conditions day and night to repair damages. Their tireless efforts and dedication to the community, combined with existing flood resilience measures and the tankering of water to one key site, ensured drinking water did not run out for the overwhelming majority of residents.

Council also acted fast to introduce temporary Level Four water restrictions, lengthening the water supply left in reservoirs and pipes until all treatment plants and pump stations were operating again.

This was a big ask of the community. As floodwaters receded, most residents wanted to use town water to hose down mud and other flood debris, yet Council asked them to limit their water use to drinking, food preparation and personal hygiene.

While it was difficult to gauge water use, it became clear that restrictions were not uniformly followed, with some areas running out of water in local water reservoirs. Supported with operational network changes, the supply of reticulated water was maintained for a vast majority of areas while the Level Four water restrictions were in place.

The water supply for the village of Uki was of particular concern. Floodwaters had quickly inundated the Uki Water Treatment Plant, causing a loss of pressure in the water supply network. This could have allowed contaminants into the supply system.

Because Council could not guarantee the water quality at Uki, a boil water notice was quickly issued for the village on the first day of the flood. As soon as road access was restored to the village, Council began tankering water, filling the Uki water reservoir with town water from the nearby Bray Park Weir – the source of most of the Tweed’s water supply.

Another area of concern was the heavily inundated South Murwillumbah area, where floodwaters washed out the water main, sewer rising main, main road, a bridge, culvert and footpath.

Immediately, Council issued a boil water notice and worked with the SES to get water supplies to isolated

residents. As soon as floodwaters started receding, repair works began. Safe drinking water started flowing again to residents a few days later. Council is now working on a long-term water supply and sewerage solution to build the area’s flood resilience.

Council’s crews are proud of their response to the flood. By 3 March, they had restored the supply of safe drinking water to 99 per cent of Tweed residents who are connected to the water supply system. By 11 March, all boiled water advisory notices were lifted. The Tweed’s entire water supply network had been restored, with safe drinking water filling all local reservoirs, including Uki.

Getting the Uki Water Treatment Plant operating again was a small feat. The plant was inundated. As soon as floodwaters had receded, crews pulled out the plant’s four motors, dried them, washed out mud and other flood debris from inside the plant, undertook earthworks to stabilise the foundations and then repositioned the motors back into the plant. Their swift actions meant none of the motors were ruined.

By 11 March, crews had also restored wastewater services to all communities in the Tweed, including at Tumbulgum where a vacuum sewer system is in place. Temporary bypass arrangements were put in place in some areas, including at Terranora, where landslips on private and public land impacted the pipes of Tweed’s sewer and water supply network. Work on a more permanent solution continues.

RESILIENCE MEASURES

While councils cannot control the weather, they can plan better to make sure they are ready for any future events given the anticipated impact of climate change.

Tweed Shire Council plans to build back better. A key way it is doing that is by moving essential water and wastewater infrastructure to locations above predicted flood levels.

Council has been undertaking flood resilience works for a number of years, after assessing the consequences of another major flood in 2017.

Today, all but one sewer pump station electrical switchboard in the Tweed are located above select predicted flood levels. This has required Council to raise a number of switchboards, such as the one pictured at Uki.

The accompanying photo shows the Uki pump station switchboard just after this year’s flood. It is clear the electrics remained high and dry despite the flood level.

Moving the switchboards above the flood level means that once water levels recede and power is restored, Council crews can turn the stations on again without major issues and rebuild works.

By raising the switchboards, Council has realised an 84 per cent reduction in its total workload to rebuild switchboards following the 2022 floods, compared to the total workload following the 2017 floods. This is despite the 2022 flood levels being higher.

While the height of the structure at Uki might seem quite ridiculous on a dry sunny day, it saved the day in the recent flood.

Tweed Shire Council thanks the New South Wales and Australian Governments for their support to date and will continue to advocate strongly on behalf of the Tweed community to continue to rebuild in a smarter, more floodresilient way.

A number of projects have been submitted for New South Wales Government funding to determine their feasibility and cost benefits, including: • Further protection of key water supply pump stations from inundation, and the provision of backup electrical generators on high level platforms to these sites • Further protection of electrical items at three wastewater treatment plant sites • Horizontal directional drilling of water and sewer mains under some significant stormwater drainage channels • Rectification of two large land slips where water and sewer mains were lost and need to be reinstated • Improving resilience of SCADA and associated communication networks.

For more information, please visit www.tweed.nsw.gov.au/property-rates/water-wastewater.