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 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:,

INTRODUCTION The Tabourie Lake Flood Study has been prepared for Shoalhaven City Council (Council) to define the existing flood behaviour in the Tabourie Lake catchment and establish the basis for subsequent floodplain management activities. This project has been conducted under the State Assisted Floodplain Management Program and received State financial support.

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.

The key objective of this Flood Study is to develop a suitable hydrologic/hydraulic model that can project flood and permanent inundation water levels in Lake Macquarie from rainfall, sea level rise and storm surge. These results will be used by Lake Macquarie City Council, in consultation with the community of Lake Macquarie City, to manage flood and permanent inundation risks to low lying land around the Lake Macquarie waterway. The key stages in the process are: Undertaken a comprehensive review of the 1998 Lake Macquarie Flood Study (Part 1 – Reference 1) and develop suitable hydrologic/hydraulic models to define flood behaviour over the full range of design events for existing catchment conditions, Use the hydrologic/hydraulic models to assess various climate change scenarios, including application of the NSW Government’s sea level rise benchmarks, Assess the potential increase in storm surge as a result of climate change and its impact on elevated ocean levels, Review the potential impact of climate change on the local wind/wave climate as this affects the extent of wave runup on the foreshore, Assess the hydraulic and hazard categories for existing and climate change conditions. This report details the results and findings of the above investigations. The key elements include: a summary of available historical flood related data, establishment of the hydrologic and hydraulic models, calibration of the hydrologic and hydraulic models, definition of the design flood behaviour for existing catchment conditions, sensitivity analysis of the design flood behaviour, assessment of the impacts of climate change on the still water and wave runup water levels re-definition of the flood extent and hydraulic and hazard categories mapping for existing and climate change conditions. A Flood Study is a technical document and not easily understood by the general public. A glossary of flood related terms is provided in Appendix A to assist. If more explanation of terms or a better understanding of the approach is required, type “NSW Government Floodplain Development Manual” into an internet search engine and you will be directed to the NSW Government web site which provides a copy of this manual and further explanation. Flood levels given in this report relate only to the water level with the lake itself. Design water levels in the creek systems entering the lake (Cockle Creek, Dora Creek etc.) will be higher than those shown for the lake.

Conclusions The objective of the study was to undertake a detailed flood study of the Lake Wyangan catchment and establish models as necessary for design flood level prediction. Through the undertaking of the flood study it has been found that during flood events the majority of the catchment runoff flows to Tharbogang Swamp rather than Lake Wyangan, as had previously been assumed. Historically there has been little response of Lake Wyangan water levels to rainfall events within the catchment, with only the March 1989 event producing a significant response. The limited response in Lake Wyangan is due to a number of factors: It has a relatively small catchment area of around 100km2, including diverted catchment runoff through the Lake View Drain (Lake Wyangan’s natural catchment is around 75km2); The calibration process found the catchment to indicate a high initial rainfall loss for the events considered. A large amount of rainfall (>60mm) is required before any catchment runoff is generated and a response in the lake can be observed; and A proportion of the catchment runoff volume is retained in temporary flood storages in the catchment, rather than further contributing to the flood storage in the lake. Being a volume-driven closed-catchment system with no natural outlet, flood levels in Lake Wyangan and Tharbogang Swamp are directly related to the catchment runoff volume generated by any given flood event. The high rainfall losses generate relatively small effective rainfall depths and the flood levels are therefore highly sensitive to changes in the adopted initial loss value. The calibration process found an initial loss value of around 60mm to be appropriate for the events considered. However, due to the characteristics of the available design rainfall temporal pattern, this loss value was reduced for design purposes. Tharbogang Swamp has a much larger catchment area than Lake Wyangan and therefore shows a much greater flood response. Unfortunately there has been no history of flood level recording in Tharbogang Swamp to compare to the modelled flood response. The study also identified a number of local overland flow paths which impact of the planned development areas of Council’s Growth Strategy 2030. It is important that these flow paths are taken into consideration during the stages of development planning. The flood study will form the basis for the subsequent floodplain risk management activities, being the next stage of the floodplain risk management process. The key locations to consider during this process have been identified as: Locations where there is potential for cross-catchment flow transfer from the Tharbogang Swamp catchment into Lake Wyangan (potential changes to the existing flow distribution may result from future on-ground works in these localities) ; and Locations where the floodways occur within the proposed development areas of the Giffith Growth Strategy 2030.

Study Objectives Key objectives of this study are to:,

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 main objective of this study (in two parts) has been to determine water levels in Brisbane Water for the full range of flood and ocean events that can occur due to the various natural physical processes, taking joint occurrence issues into account to some extent. The flooding behaviour can be influenced, either separately, or by a combination of, catchment rainfall runoff flooding, rainfall directly onto Brisbane Water, elevated ocean levels, local winds and, to a minor extent, the condition of the ocean entrance channel near Ettalong. The outcomes from this study include: -,

Objectives Sutherland Shire Council engaged Webb, McKeown & Associates to prepare the Kurnell Township Flood Study, utilising current technology and data. The information and results obtained from the study will be used in the preparation of the Floodplain Risk Management Study and Plan. The specific objectives of the Kurnell Township Flood Study are to:,