Tweed Valley Flood Study update and expansion

To attend an information session, click the relevant session below. If your suburb is not listed, please select the closest locality.

All face-to-face sessions are in the afternoon, from 4 pm to 6 pm. To register click on the session you would like to attend:

• Tyalgum – Tylagum Community Hall – Monday 19 February 2024
• Uki – Holy Trinity Anglican Church – Wednesday 21 February 2024
• Chillingham – Chillingham Community Hall – Thursday 22 February 2024
• Murwillumbah – Murwillumbah Civic Centre Auditorium – Monday 26 February 2024
• Chinderah – Kingscliff Beach Bowls Club – Tuesday 27 February 2024
• Tweed Heads – South Sea Islander Room, Tweed Heads Civic and Cultural Centre – Wednesday 28 February 2024

If you can't make it in person, you can join our online session at 5 pm on Thursday 7 March 2024.

Locality specific areas

We have prepared information specific to some key locations to give you a better understanding of flooding in your area:

• Chillingham
• Chinderah
• Murwillumbah
• Tweed Heads
• Tumbulgum
• Tyalgum
• Uki

What is the Tweed Valley Flood Study update and expansion?

Tweed Shire Council, with support from the NSW Department of Planning and Environment (DPE), has engaged flood specialists WMAwater to update and expand the Tweed Valley Flood Study. The previous flood study was completed in 2009 and only covered the area from Murwillumbah to Tweed Heads.

A flood study is a comprehensive technical investigation of flood behaviour within a catchment, in this case, the Tweed Valley. It defines the nature of flood hazards across the floodplain by providing information on the extent, level and velocity of floodwaters and the distribution of flood flows.

The flood study uses sophisticated computer models to simulate flooding across the Tweed Valley. These models are calibrated to actual recorded floods (2017, 2022, 2021, 1989) to ensure they accurately represent real-world flooding.

The study simulates a broad range of 'design' flood events from very minor/frequent floods up to extreme/very rare floods and future climate change scenarios. The study outputs include extensive mapping for each of these events such as peak level, depth, velocity, depth x velocity, hazard and hydraulic categories. These maps define flooding characteristics across the floodplain and are used for flood risk planning, development controls and emergency management.

This flood study does not consider measures to alleviate or mitigate flood risk (e.g. levees, bypass floodways, evacuation route upgrades, house raising). Under the NSW Flood Risk Management Manual model, a flood study simply quantifies flooding. It is a Floodplain Risk Management Study that evaluates options to mitigate flood risk. This is a subsequent step in the NSW process. For now, the Tweed Valley Floodplain Risk Management Study and Plan 2014 remains Council's adopted strategy for the management of flood risk in the valley. However, updates to that study and plan are intended to follow from the completion of this flood study.

This project is funded under the NSW and Commonwealth Government's Natural Disaster Resilience Program.

Why do we need a new flood study?

Due to software and computing technology limitations at the time, the 2009 flood study produced mapping for the lower valley only – the area from Murwillumbah to Tweed Heads. This study will produce mapping for the entire Tweed Valley.

The Tweed has experienced the two biggest floods on record (2017 and 2022) since the 2009 flood study. Lessons learned from these events have increased our understanding of flood behaviour in the valley. Additionally, a wealth of data has been collected from these major floods, helping us to calibrate our computer flood models.

Australian Rainfall and Runoff, the guidebook for all things hydrology and surface water hydraulics in Australia, has undergone an extensive update since the 2009 flood study. The 2019 version of the guidebook revolutionises the practice of hydrology in Australia and this contemporary best practice has been fully incorporated into this flood study.

What’s been done so far?

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 have been compiled summarising the work completed and mapping produced.

The study has now progressed to the draft flood study phase. The draft has been reviewed by the Tweed Floodplain Management Committee and presented to the elected Council, which resolved to proceed to public exhibition.

What has changed since the 2009 Study?

A flood study is a highly complex process. The new study follows different industry guidance (Australian Rainfall and Runoff 2019) to the 2009 study and also enjoys the benefit of lessons learned in the 2017 and 2022 major floods. Therefore, the results of this flood study do not match those of the 2009 study precisely.

The report contains an entire chapter on "what has changed" comparing the draft results to those of 2009 study.