Revision I (May 2022).

This study updates the previous Wrights Creek Flood Study (Patterson Britton & Partners, 2007) and provides Council with a suitable platform for undertaking the next steps in the Floodplain Risk Management Process. The XP-RAFTS hydrologic model developed in the 2007 Flood Study has been adopted for this study. A TUFLOW hydraulic model of the catchment has been established using up to date survey of the ground levels and culvert and bridge structures. The TUFLOW hydraulic model has been used to reproduce the historical flood behaviour from events in 1995 and 2002 and to define flood behaviour for a range of design events. Actions undertaken as part of this flood study include: • collection of additional survey, • development of a TUFLOW hydraulic model, • definition of the design flood behaviour, • assessment of provisional hydraulic hazard, • assessment of hydraulic categorization, • assessment of the model sensitivity to parameter changes, • assessment of climate change impacts on model results, • assessment of sensitivity of model results to the new ARR 2016 design inputs, • community consultation.

Tallowa Dam DSEP Inundation Maps SDF and PMF Event Geospatial Data - 2019 Dam Break Assessment

Environmental Impact Statement: The role of cumulative impact assessment in catchment management for the Hawkesbury-Nepean Catchment Area

Hydrologic and hydraulic model input files

The tool should be used in conjunction with the associated guide and with the assistance of the regional DCCEEW flood program representative. This tool has been updated December 2023. Note that the associated guideline has not been updated but is largely still relevant to the current version. Any additional queries may be directed to floodteam@environment.nsw.gov.au

Tuflow input data. Contains data for ARR1987 and ARR2016

The study was commissioned by Bayside Council, with the assistance of the NSW Government Office of Environment and Heritage (OEH). Additional information has been provided by Sydney Water Corporation (SWC). The Flood Study comprises the development of computational hydrologic and hydraulic models that define design flood behaviour for the 20% AEP (0.2 EY), 10% AEP, 5% AEP, 1% AEP and 0.5% Annual Exceedance Probability (AEP) design storms and the Probable Maximum Flood (PMF) in the Bardwell Creek and Wolli Creek catchments.

Summary of Management Plan (1) Most of the flood damage reduction measures considered as part of the 1993 Floodplain Management Study cannot be justified on benefit-cost considerations. They could be reconsidered if new information becomes available that leads to substantially increased benefit-cost ratios. Notwithstanding, Option 1E from the 1993 Floodplain Management Study was shown to have a Benefit-Cost ratio of about 0.4 and therefore should be retained within the Plan. This floodplain management strategy involved the voluntary raising of a 39 houses located in areas of Edgeworth, Barnsley and Boolaroo that are potentially flood affected. It is recommended that these houses be re-assessed and prioritised in terms of their suitability for house raising. Once a prioritised list has been determined, steps should be undertaken to implement the strategy. (2) The Flood and Floodplain Management Studies on which this Plan is based should be revisited. The reason for this and the process that should be followed is outlined in Appendix C. The majority of the floodplain management options considered in the 1993 study are either not viable from a cost/benefit perspective or may not be considered appropriate now. Hence, contemporary floodplain management issues need to be determined through consultation with the Committee and key stakeholders within the community. It is not clear whether any consultation took place as part of earlier studies. However, this is considered to be essential to managing future flooding issues that may arise along creek system and its floodplain. This could be achieved by distribution of a brochure similar to that included in Appendix A. (3) Development within areas defined in Figure 4 as 2A, 2B and 2C, should be able to proceed without extensive independent flood investigations, provided all appropriate requirements specified by the current Local Environment Plan are addressed (eg., those related to filling). (4) Development Restrictions Flooding/Tidal Inundation Certificates should be revised to incorporate the predicted peak level of the Probable Maximum Flood or an ‘extreme’ flood. The format of Development Restrictions Flooding/Tidal Inundation Certificates could be modified to provide more information. (5) Further investigations need to be undertaken to determine whether flood damage reduction measures can be implemented for those problem areas listed in Section 4.3.1 (6) Further hydraulic investigations should be undertaken the determine the amount of time before inundation of key areas along Cockle Creek in a typical major flood. (7) A flood liable lands DCP is to be developed specifically for the Cockle Creek catchment. The DCP would effectively serve as a revised Flood Policy and relate to the specifics of flood behaviour in the catchment (as distinct from the lake inundation flood behaviour that applies in other areas of Lake Macquarie City).

Flood Study Overview, Flood Study Report, 12 technical volumes, 4 map book volumes, Engagement Outcomes Report