Tweed Valley Flood Study update and expansion

Tweed Valley Flood Study

Thanks to the Tweed community for participating in the various community consultations. Your valuable feedback has helped shape the final Tweed Valley Flood Study Update and Expansion.

Advances in the hydrology field and new flood records from March 2017 provided a good opportunity to improve our understanding of flood behaviour in the valley.

The updated flood study helps define flooding behaviour under current and future climate conditions and become the basis of flood planning in the Tweed.

The updated flood study includes the upper parts of the valley, including villages of Tyalgum, Chillingham, Uki and the surrounding rural areas for the first time.

The update and expansion include:

  • model calibration and validation – review flood model based on historic events gathered from the community consultation, model flooding events by applying a range of probability based on flood magnitude in models, reporting and data provision
  • hydrologic analysis – review and extend existing model, flood frequency analysis, review rating curve, develop design hydrographs
  • modelling of existing scenarios – model design events, coastal interaction, blockage assessment
  • post processing of model outputs – flood hazard, flood function, high/low flow categorisation, flood emergency response classifications, mapping.

The flood model build and calibration were initially completed in early 2022, shortly before the February/March flood. A project variation was undertaken to incorporate lessons learned from the February/March 2022 floods.

Tweed community helped shaped the flood study

In 2020 and early 2021, Council obtained LiDAR and survey data to facilitate this study. An initial community survey seeking residents' flood experiences was conducted in April/May 2021. The information we received was used in the study to inform known flooding issues and assist in the calibration of the flood model.

 WMAwater has built detailed computer flood models for the valley and calibrated them to known flood events to ensure the models accurately represent real-world flooding. Subsequently, the models were used to simulate flooding for a range of 'design' flood events, with mapping outputs produced for each scenario. Draft reports were compiled summarising the work completed and mapping produced.

Once the draft study was completed, it was reviewed by the Tweed Floodplain Management Committee and presented to the elected Council. The draft study was on public exhibition from Tuesday 30 January 2024 to Sunday 17 March 2024.

The final study was again reviewed by the Tweed Floodplain Management Committee and presented to the elected Council. In July 2024 Council resolved to adopt the study.

This project is funded under the NSW Government Floodplain Management Program. 

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