Ballina Integrated Flood Modelling Summary of Flood Assessments ...

INTRODUCTION 1-2
The hydraulic model was calibrated and verified using three historical events; 1974, 1976 and 2005.
Following calibration, the model was used to simulate a range of design flood events to assist with the
following aspects of floodplain management:
• Assessment of likely impacts of climate change;
• Establishment of minimum fill levels for future development;
• Estimation of potential flooding impacts of proposed developments and public infrastructure
works; and
• Assessment of potential flood mitigation strategies to mitigate impacts of future development.
The next phase of the floodplain risk management process is the preparation of the Ballina Floodplain
Risk Management Study and Plan (FRMS and FRMP). The hydraulic model will again be used to
assist with the following processes:
• Estimation of the likely damages caused by flooding;
• Evacuation management and planning;
• Update of the assessment of likely impacts of climate change; and
• Further assessment of mitigation strategies.
Preparation of the FRMS commenced in early 2009, and is expected to be completed by mid 2010.
During the interim period between the completion of the Flood Study Update, and commencement of
the FRMS, the hydraulic model has been used for the impact assessment of numerous developments
for Council, the Roads and Traffic Authority (RTA), and private developers.
For this process, Council developed their ‘Base Case’ modelling concept, where each development is
added to the model and the impacts assessed. Hence, the ‘Base Case’ flood model is defined as:
‘the existing catchment conditions including all proposed public infrastructure works, currently zoned
or approved urban development and mitigation measures designed to minimise adverse flooding
impacts to acceptable levels’
The Base Case model is used by Council as a tool for assessing flooding impacts due to future
infrastructure and rezoning across the floodplain. The base case model has been, and will continue
to be, updated and compared with the existing case flood levels to ensure flood impacts of all future
development are assessed on a cumulative basis (i.e. not individually assessed for impacts).
This report has been prepared to summarise these interim assessments, and document the ongoing
development of the hydraulic model. The evolution of the Ballina hydraulic model through each of the
separate assessments is shown schematically as Figure 1-2. Each of the developments are
summarised in the following sections.
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