Flood mitigation for the at-risk Hawkesbury-Nepean region of western Sydney is finally at the top of the political agenda, with the NSW Government and the Federal Opposition vowing to take action.

Following an announcement that NSW will hold a strategic review of flood management for the region, the Federal Coalition’s leaked dams strategy has been shown to feature a $500 million plan to raise the wall of the nearby Warragamba Dam.

As reported in Insurance News (the magazine) in August 2011, the Hawkesbury-Nepean Valley is one of the most heavily developed floodplains in Australia and the country’s biggest flood risk.

NSW Primary Industries Minister Katrina Hodgkinson says the NSW Office of Water will chair a multi-agency review with input from the Sydney Catchment Authority, the State Emergency Service, the Bureau of Meteorology and Infrastructure NSW.

The review, which will report to the State Government later this year, will consider flood planning, mitigation and response, including current arrangements. 

It will also consider whether alternative operating procedures at Warragamba Dam – which supplies 80% of Sydney’s drinking water – can help mitigate flood impacts downstream, Ms Hodgkinson says.

The State Government announcement follows the release last October of Infrastructure NSW’s State Infrastructure Strategy 2012-2032, which featured a $500 million flood mitigation plan for the area – to be completed by 2017 – as a key recommendation.

A flood study conducted for the strategy report found 21,000 homes exist on the floodplain, more than 5000 more than was previously thought. Some 143 hectares of commercial and industrial property has also been built on the plain since 1990.

A one-in-1000-year flood – similar to that in Queensland in early 2011 – would destroy 6500 homes and flood 14,000 houses above floor level, causing $8 billion of damage, the study says. The flood would severely affect towns such as Windsor, Pitt Town, McGraths Hill, Vineyard and Wilberforce.

Such an event would put 43,000 residents and 9000 workers at risk and cause up to six months’ disruption to the main western rail line, affecting Blue Mountains passengers and NSW coal exports.

A repeat of the one-in-200-year flood that hit the region in 1867 would cause up to $3 billion damage.

Infrastructure NSW CEO Paul Broad says if flood mitigation is not undertaken the state “will need to spend an estimated $400-$600 million removing capacity constraints from major flood evacuation routes, including the M4 and Great Western Highway, although this will not stop a flood from affecting the area”.

The Western Sydney Regional Organisation of Councils (WSROC), which counts the Liverpool, Penrith, Blacktown and Hawkesbury councils among its 10 members, has welcomed the focus on flood mitigation.

It wants the wall of Warragamba Dam raised by 23 metres, which would cost about $346 million, with associated costs pushing the bill to $500 million.

It is the “only option if you’re going to prevent any major flood event”, WSROC VP and Hawkesbury Council Deputy Mayor Tiffany Tree told insuranceNEWS.com.au.

Raising the dam wall was first suggested in 1995, but the decision was taken to manage flood risk through road upgrades and building a dam spillway to release excess water.

A spokesman for the Insurance Council of Australia says the organisation and its members look forward to contributing to the NSW review.

“Determining where and how to mitigate existing flood risk is a complex process involving a range of stakeholders,” he said. “The collective experience of the general insurance industry will be an important element in mitigation decision-making processes.”