The Narrabeen Lagoon Flood Study has been prepared for Warringah and Pittwater Councils (The Councils) to define the existing flood behaviour in the Narrabeen Lagoon catchment and establish the basis for subsequent floodplain management activities. This study updates previous studies on the Lagoon including the Narrabeen Lagoon Flood Study (PWD, 1990) and studies of the individual tributary streams, providing a holistic assessment of flooding within the catchment. The current Flood Study considers land use changes subsequent to previous modelling investigations, the influence of the Narrabeen Lagoon entrance on flood behaviour and the influence of potential climate change. The primary objective of this Flood Study is to define the flood behaviour under historical, existing and future conditions (incorporating potential impacts of climate change) in the Narrabeen Lagoon catchment for a full range of design flood events. The study provides information on flood levels and depths, velocities, flows, hydraulic categories and provisional hazard categories. The Flood Study has also identified the impact on flood behaviour as a result of future climate change and potential changes in the catchment and lagoon entrance. Specifically, the study incorporates:,

This report details the results and findings of the Flood Study investigations. The key elements include: • a description of the study area; • a summary of available historical flood related data; • establishment and calibration of the hydrologic and hydraulic models; • the estimation of design flood behaviour for existing catchment conditions; • sensitivity analysis of the model results to variation of input parameters; • potential implications of climate change projections; and • identification of the level of flood risk for individual properties in the catchment.

This report comprises an overview of the work that has been undertaken by WMAwater on the Manly Lagoon Floodplain Risk Management Study and Plan. It builds on prior stage reports and, in accordance with the Brief, it additionally includes a discussion of: • hydraulic and hazard categorisation; • future development scenarios; • review of climate change; • flood damages assessment; and • emergency management.

This report documents the Burrill Lake Catchment Flood Study which defines existing flood behaviour and establishes the basis for floodplain management activities in the future.

The Raymond Terrace Flood Study has been prepared for Port Stephens Council (Council) to define the existing flood behaviour in the western Raymond Terrace catchments and establish the basis for subsequent floodplain management activities. The study will also assist Council in considering future upgrades to the drainage network and flood relief pump capacity to the Hunter River. This project has been conducted under the State Assisted Floodplain Management Program and received State financial support.

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.

This Floodplain Risk Management Study and Plan for Mona Vale/Bayview has been undertaken by Cardno Lawson Treloar for Pittwater Council to identify and examine options for the management of flooding within the Mona Vale Main Drain and Cahill Creek floodplain. The study has been undertaken in accordance with the NSW Government Floodplain Development Manual (2005). A locality plan can be found in Figure 1.1. The outline of the study area can be found in Figure 1.2. Study Context This study forms two of the multiple stages of the Floodplain Management process which includes:,

This report has been prepared for Warringah Council to define the nature and extent of flood in the Dee Why South Catchment. Flood modelling was completed to define flood behaviour for a range of storm events from 1 year Average Recurrence Interval (ARI) to Probable Maximum Flood (PMF). The modelling shows that significant flows are conveyed in the piped drainage network and overland through roads and properties. Generally the main overland flowpath starts from several branches at Alfred Street to Beverley Job Park. Flows in the open channel at Victor Road and Redman Road combine with overland flows from Mooramba Road, Fisher Road, and Pittwater Road at the intersection of Redman Road and Pittwater Road. Overland flows are then conveyed along several roads and properties to Dee Why Lagoon as well as in the open channels between Pacific Parade / Oaks Avenue and downstream of Dee Why Parade. In a 1% AEP event, the results show that ponding of runoff occurs at several locations with restricted outlet capacity. High pedestrian areas in Dee Why CBD also experience overland flow inundation, particularly along Redman Road, Pittwater Road, Oaks Avenue and Howard Avenue. In a 1% AEP event floodway and high provisional hazard flow conditions along the open channels, on roads, and some properties including in the Dee Why CBD. A series of climate change scenarios were also modelled to evaluate potential impacts from elevated sea levels and increased rainfall intensity. Results showed that the modelled increases to Lagoon level have an impact to flood inundation of low-lying land near the Lagoon. Most properties within the Dee Why South catchment do not show a significant change in inundation extent for the modelled scenarios. Modelled increases in rainfall intensity showed a rise in peak water levels across the catchment, particularly in trapped low points such as on Sturdee Parade and Alfred Street. Council applies land use planning and development controls to manage development within flood prone areas. The flood result and mapping provided in the document will assist Council with future land use planning, development controls and floodplain risk management. The next stage of the floodplain risk management process following the adoption of the Flood Study is the Floodplain Risk Management Study and Plan. This next stage will investigate various floodplain risk management measures and prioritise these measures for implementation.

Main Report; Appendix A - Flood Mapping; Appendix B - Community Consultation; Appendix C - Design Hydrographs

Complete report