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Flood studies provide detailed information for policy making, planning and development.

Studies are produced in line with the NSW Government's guidelines and have been publically exhibited and adopted by Council.

Floodplain risk management - studies and plans

South Murwillumbah Floodplain Risk Management Study and Plan (2019)

This study looks at flooding when the Tweed River breaks its banks into the South Murwillumbah residential and industrial areas.

Murwillumbah CBD Levee and Drainage Study (2018)

This study looks at flood behaviour when the Murwillumbah CBD Levee, the East Murwillumbah Levee and the Dorothy/William Streets Levee are overtopped, and drainage behind the levees.

Coastal Creeks Floodplain Risk Management Study and Plan (2015)

The second of four floodplain risk management studies in the Tweed area. This study identifies current and future flood risks, reviews flood mitigation options and considers the best ways to manage flood prone land.

Tweed Valley Floodplain Risk Management Study and Plan (2014)

This plan looks at flood risks in the Tweed Valley and provides a range of floodplain management measures. The study and plan were placed on exhibition for public comment and the Frequently Asked Questions are a response to community questions.

Tweed Valley Flood Study (2009)

A study into the flood behaviour of the Tweed River and its major tributaries, from Boat Harbour and Byangum upstream of Murwillumbah to the river mouth at Tweed Heads.

The study area includes Murwillumbah, Condong, Tumbulgum, Chinderah, Kingscliff, Fingal Head, Banora Point, Tweed Heads, Tweed Heads South and Tweed Heads West.

The addendum provides scenarios for potential impacts of climate change (sea level rise and increased rainfall intensity).

Tweed-Byron Coastal Creeks Flood Study (2009)

A study into the flood behaviour of four coastal creeks: Cudgen, Cudgera, Mooball and Marshalls Creeks.

A joint study between Tweed and Byron Shire Councils (reflecting the cross-boundary flooding between Mooball and Marshall Creek).

The study area includes South Kingscliff, Cabarita - Bogangar, Hastings Point, Pottsville, Burringbar, Mooball, Crabbes Creeks, Wooyung, South Golden Beach, Billinudgel, New Brighton and Ocean Shores.

The study provided model scenarios for possible future changes in land use (e.g. agricultural change from sugar cane production) and potential impacts of climate change (sea level rise and increased rainfall intensity).

Climate change and flooding

In 2008 the NSW Government issued guidelines for councils to include climate change variables into flood studies.

Since then all Tweed Shire Council flood studies have included climate change modelling that considers:

  • a sea level rise of 0.91m
  • an increase in rainfall intensity of 10%

Climate impact maps

Maps of climate change scenarios are available in our flood studies above. In 2010 Council adopted these climate change maps as appendices to our Development Control Plan.

The maps are applied as design flood levels for large scale greenfield residential subdivisions, such as Cobaki, Kings Forest and West Kingscliff.

Flood terms and definitions

Common terms used in relation to flooding:

  • Annual Exceedance Probability (AEP): The probability of a flood event of a given size occurring in any one year, usually expressed as a percentage annual chance.
  • Average Recurrence Interval (ARI) Similar to AEP. The long-term average number of years between the occurrence of a flood as big as (or larger than) the selected event. This is an average (a ‘1 in 100 Year’ ARI event last year does not mean a flood that big will not occur for another 99 years).
  • Design Flood Level: A hypothetical flood representing a specific likelihood of occurrence. For residential property in Tweed Shire, the peak of the modelled 1% AEP (100 Year ARI) flood is the Design Flood Level.
  • Freeboard: A safety factor typically used to set minimum floor levels. In Tweed Shire, the minimum habitable floor level (or Flood Planning Level) is based on the 1% AEP flood event plus 0.5 metres of freeboard.
  • Floodplain: Refers to all flood prone areas in the Tweed catchment.
  • Metres above Australian Height Datum (m AHD): The reference level for defining ground levels in Australia. The level of 0.0m AHD is approximately mean sea level.
  • Minimum Habitable Floor Level: The minimum level in metres AHD at which habitable areas of development (generally including bedrooms, living rooms, kitchen, study, family and rumpus rooms) must be constructed. In Tweed Shire, this is Design Flood Level plus 0.5m of freeboard.
  • Probable Maximum Flood (PMF): An extreme flood, considered the largest flood that could occur at a specific location. Generally it’s not physically or economically possible to provide complete protection against this flood event, but it should be considered for emergency response.
  • The probable maximum flood defines the extent of the Tweed’s flood prone land (floodplain).
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