Floodplain management plans

Floodplain management plans for the City of Sydney local area have been developed and adopted by Council. The plans include flood mitigation measures and what can be done to help affected areas.

Under the NSW Government's flood prone land policy the City is required to manage flooding issues and put plans into place to safeguard flood-prone areas.

The local area has been divided into 8 catchments covering 2,666ha.

• Alexandra Canal catchment
• Blackwattle Bay catchment
• Centennial Park catchment
• Darling Harbour catchment
• Johnstons Creek catchment
• Rushcutters Bay catchment
• Sydney City catchment
• Woolloomooloo catchment.

Due to high urbanisation since the 19th century across the local area there are not many natural creeks or open surface water bodies in the catchment areas to accommodate stormwater.

Generally, stormwater from frequent minor storm events is managed by conventional pits and pipe systems. In less frequent, but major rainfall events, stormwater in excess of the conventional systems travels along low gradients of the catchments, ultimately draining into Sydney Harbour and Botany Bay.

The combination of steep and flat terrain, high density residential, commercial and industrial areas has made areas susceptible to flash flooding. Being aware of the potential for flooding and knowing how to respond will make flood events more manageable.

We are progressively introducing the floodplain management plans, in the final stage of the floodplain risk management process, as outlined in the NSW Government's flood prone land policy.

There are 35 structural and 14 non-structural flood mitigation measures across the local area that were recommended in the relevant floodplain management plans. The priority ranges from low to high for implementing the mitigation measures over the short to long-term period.

In 2016, the total estimated cost to undertake the recommended mitigation works in the local area is $363m. The works will require collaboration between the City and state government agencies such as Sydney Water and NSW State Emergency Services.

We are now undertaking the following works with Sydney Water:

• Green Square stormwater drain
• Joynton Avenue stormwater drain
• Ashmore downstream stormwater drain.

Council endorsed its interim floodplain management policy in May 2014.

The policy is a responsible and forward-thinking approach to manage flooding issues, which will ensure development in the city is not at undue risk of flood and that proposals do not increase flood risk for existing properties.

Since 1910, the City of Sydney's local area has experienced 35 floods classified as serious, severe or minor. In 13 cases, high rainfall resulted in localised flooding. During this period 4 floods were classified extreme in November 1984, March 1975, January 1973 and August 1971.

Floods can occur at any time and in the future could be bigger than any previously recorded event.

Note: Rainfall levels recorded at Centennial Park, Randwick Bowling Club and Randwick Racecourse since 1888, which caused minor flooding throughout the city.