The objectives of the Flood Study are to: • Identify all the flood-related data by searching all relevant data sources. • Determine the likely extent and nature of flooding and identify potential hydraulic controls by carrying out detailed site visits of the study area. • Define existing catchment condition flood behaviour for mainstream flooding in the catchment with due consideration to the impact of Lake Macquarie levels on flooding characteristics. • Define design flood levels, velocities and flow distributions for the catchment. • Define the extent of flooding for the 200 year, 100 year, 20 year, 10 year and 5 year ARI floods and Probable Maximum Flood (PMF) for the catchment. • Define Provisional Flood Hazard for the flood-affected areas. • Define the Hydraulic Categories for the flood-affected areas. Two numerical modelling tools were developed: • A hydrologic model to convert rainfall on the catchment into runoff. The hydrologic model combines rainfall information with local catchment characteristics to estimate runoff hydrographs. • A hydraulic model to convert runoff hydrographs into water levels and velocities throughout the study area. The model simulates the hydraulic behaviour of the water within the study area by accounting for flow in the major channels as well as all the potential overland flowpaths, which develop when the capacity of the channels is exceeded. It relies on boundary conditions, which include the runoff hydrographs produced by the hydrologic model and the appropriate downstream boundary level from Lake Macquarie.

This Floodplain Risk Management Study investigates what can be done to reduce or manage the effects of flooding in the catchment. The Floodplain Risk Management Plan recommends a mix of strategies to manage the risks of flooding. Using the merits-based approach advocated in the NSW State Government’s Floodplain Development Manual (2005) and in consultation with the community, Council and state agency stakeholders, a number of potential options for the management of flooding were identified. These options included: • flood modification measures; • property modification measures; and • emergency response measures. An extensive list of options was assessed against a range of criteria (technical, economic, environmental and social). Hydraulic modelling of some of the flood modification options was undertaken to provide a comprehensive analysis of those options that would involve significant capital expenditure.

Objective This Floodplain Management Study defines the nature and extent of the flood hazard in the three catchments. It also identifies and assesses strategies and measures aimed at reducing the impact of flooding on both existing and future development, and measures to prevent future development from making flooding worse. The results of this Floodplain Management Study are being used to prepare a Floodplain Management Plan (FPMP). The objective of the FPMP is to establish a cost-effective floodplain management strategy for the area and to recommend a programme for implementation of the Plan. The Study Brief is attached as Appendix A. What is in the Study The Floodplain Management Study and Plan will not totally eliminate flooding. Flooding is a natural phenomenon which cannot be fully controlled by human works. In fact, excessive artificial controls are likely to be very costly and to have adverse environmental effects. Therefore the Floodplain Management Study and Plan aim to provide a package of best management practices which give a balance between reducing flood hazard and flood damages, allowing appropriate development, and protecting and enhancing the environment of the floodplain. This Report has been divided into the following sections: Section 1: Introduction (page 1) Establishes the context and basis for the plan. Section 2: Background (page 5) Describes the study process, including previous studies, and the background technical information which is available. It includes a review of the previous Muddy Creek Flood Studies. Section 3: Existing Flood Behaviour (page 15) Summarises the available data and modelling results concerning flood behaviour. Section 4: Social and Economic Impacts of Flooding (page 23) Examines the potential flood damages and other social and economic effects of flooding for a range of flood events, including an extreme flood. Section 5: Choosing the Designated Flood (page 28) Discusses the issued to be considered by Council in choosing a designated flood for Rockdale, and recommends that the 1% AEP flood be adopted. Section 6: Available Floodplain Management Options (page 35) Describes in broad terms the range of flood mitigation and other management works and other measures available to address the existing, future and residual flooding problems in the study area. Sections 7, 8 and 9: Options for Management Areas (page 48) These three sections describe in detail, for the Muddy Creek, Spring St Drain and Scarborough Ponds catchments respectively, the feasible options and their likely benefits and costs. Section 10: Assessment of Management Options (page 86) Reviews the financial aspects and the justification for the proposed management measures, identifies priorities and possible sources of funding. These issues will be further addressed in the future Floodplain Management Plan. Section 11: References (page 90) Technical detail which supports the main report is provided in the Appendices, in Volume 2.

The overall objective of this study is to develop a Floodplain Risk Management Study where management issues are assessed, management options are investigated and recommendations are made. Thereafter a Floodplain Risk Management Plan detailing how flood prone land within the study area is to be managed can be completed. The objectives of the Flood Risk Management Study are to:,

The Wollombi Flood Study Review and Model Upgrade completed in 2010 represents the initial stage in the floodplain management process and establishes the basis for the current floodplain risk management study. The objectives of the Wollombi Floodplain Risk Management Study are to:  Identify and assess measures for the mitigation of existing flood risk;  Identify and assess planning and development controls to reduce future flood risks; and  Present a recommended floodplain management plan that outlines the best possible measures to reduce flood damages in the Wollombi locality. This report documents the Floodplain Risk Management Study and presents a recommended Floodplain Risk Management Plan for the Wollombi Village.

FLOODPLAIN RISK MANAGEMENT STUDY The specific aims of this study are to:,

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.

This study investigates the hydraulic effectiveness of the current levee, assess the need for future improvements and also attempt to establish the flood overtopping levels of the levee, for the benefit of emergency services.

This report documents the Burrill Lake Floodplain Risk Management Study and Plan which investigates and presents a flood risk management strategy for the catchment. The study identifies the existing flooding characteristics and canvasses various measures to mitigate the effects of flooding. The end product is the Floodplain Management Plan, which describes how flood liable lands within the Burrill Lake catchment are to be managed in the future.

The objectives of this study are: to define the nature and extent of the flood hazard, to identify, assess and optimise strategies and measures aimed at reducing the impact of flooding on both existing and future development, to determine the effects of development on flooding, to determine flood damages.