Flood Mapping Compendium to support main report

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.

Complete report

AIMS OF THE CURRENT STUDY In broad terms, the current Floodplain Risk Management Study has investigated what can be done to minimise the effects of flooding in the Haslams Creek catchment and recommended a strategy in the form of a draft Floodplain Risk Management Plan. Specific objectives of the study include: a review of the results from the 1999 Flood Study; consideration of the potential for culvert blockages and associated flood impacts; the implementation of a community consultation strategy, to ensure community input is obtained at key times throughout the study; a description and quantification of the flood problems in the Haslams Creek catchment including the likely cost of flooding to the local community; the identification and assessment of potential floodplain risk management measures to reduce the risks and hazards of flooding; a detailed review of issues relating to planning and development controls within the floodplain. Don Fox Planning Pty Ltd has prepared a document entitled Report on Planning Issues as part of this study. It is reproduced in Appendix A. Included in this report, is a proposed draft Development Control Plan (DCP) entitled “Managing Our Flood Risks”; the development of a recommended draft Floodplain Risk Management Plan for the Haslams Creek catchment that outlines the best measures to reduce flood damage, based on environmental, social, economic, financial and engineering considerations.

Complete report

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:,

Data contains * Main Report * Mapping * Options Impacts

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.

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: -,

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.