The Flood Study had three main components:,

Objectives The objective of this Study is to define the nature of the existing flood behaviour in the Burradoo BU2 catchment. To achieve the objective, the following tasks were undertaken:,

Volume 1 Report This flood study has been undertaken to determine the flood behaviour in the catchment due to local storm runoff for the 0.5% Annual Exceedance Probability (AEP), 1% AEP, 2% AEP, 5% AEP, 10% AEP, 20% AEP, 50% AEP and 100% AEP flood events and the Probable Maximum Flood (PMF). In accordance with its objectives, the study has determined the nature and extent of flooding through the estimation of design flood flows, levels and velocities. Flood impacts due to storm events in the Brisbane Water estuary are detailed in the Brisbane Water Foreshore Flood Study (2009). In undertaking the flood study, a hydrologic-hydraulic computer model of the major channels and floodplain within the catchment was established and verified against historical flood event observations. The hydraulic model was then used with design rainfall conditions to simulate design flood behaviour in the catchment. The study has defined Provisional Flood Hazard and Hydraulic Categories for the flood affected areas. The objective of this Study is to define the nature of the existing flood behaviour due to local runoff only in the Davistown catchment. To achieve the objectives, the following tasks were undertaken:,

This report presents the results of a detailed technical investigation of flooding in the Scotts Creek catchment and has been sponsored by Willoughby City Council (WCC) and Department of Environment and Climate Change. Figure 1.1 shows the location of the catchment which drains the suburbs of Chatswood and Castle Cove before discharging to Sugarloaf Bay in Middle Harbour. The investigation defined flooding as far downstream as the Eastern Valley Way. Mathematical models of the catchment and the floodplain were developed using detailed field surveys and interpreted to present a comprehensive picture of flooding under present day conditions. The study objective was to define flood behaviour in the stream in terms of flows, levels and flooding behaviour for floods ranging between 5 and 200 years average recurrence interval (ARI), as well as the PMF. The investigation involved hydrologic modelling to assess flows in Scotts Creek between its headwaters in the Chatswood CBD area and the Eastern Valley Way. These flows were applied to a hydraulic model of the main arm of Scotts Creek to assess peak water levels and flow patterns. The hydraulic modelling extended from Havilah Street on the eastern side of Chatswood Chase to the Eastern Valley Way. The trunk drainage system of Scotts Creek to Penshurst Street is denoted Stormwater Catchment 26 and is owned by Sydney Water. It comprises sections of piped drains, as well as covered and open concrete lined stormwater channels. The piped drainage system extends through the Chatswood CBD to the eastern side of Chatswood Chase in Havilah Street (Figure 1.2). Between Havilah Street and Baldry Street, flows on the main arm of Scotts Creek are conveyed in Sydney Water’s covered stormwater channel which follows the route of the original creek and extends as far as the Temple Emanuel School near Chatswood Avenue. An open concrete lined stormwater channel also owned by Sydney Water continues downstream and conveys flows to Penshurst Street. Willoughby City Council’s channel continues downstream of Penshurst Street to the Eastern Valley Way, and comprises sections of rock lined and “pillow concrete” lined trapezoidal channel. The total catchment area at the Eastern Valley Way is 3 km2. The headwaters of the catchment are drained by separate piped trunk drainage systems which drain the northern and southern portions of the catchment. Overland flows from the southern trunk drain are diverted into Chatswood Oval, which functions as an off-line detention basin during periods of heavy rainfall. Peak flows from the northern portion of the catchment will be influenced by a flood storage/ water harvesting basin which will be excavated adjacent to Ferguson Lane as part of the Chatswood Civic Place project, due for construction in 2009 and situated just upstream of the intersection of that street with Archer Street. The storage characteristics of both Chatswood Oval and the flood storage basin in Ferguson Lane have been included in the hydrologic model of Scotts Creek developed in this study for the estimation of design flows. The trunk drainage systems meet at the intersection of Archer Street and Victoria Avenue and continue eastwards as separate piped systems along both the northern and southern sides of Victoria Avenue to Havilah Street. The drainage system is of limited hydraulic capacity and has been surcharged, most recently in April 1998, when flooding was experienced in several commercial properties bordering Victoria Avenue. It was reported that overland flows heading eastwards along Victoria Avenue in the April 1998 flood were captured by the prevailing natural surface grade and flowed into the basement car park of Chatswood Chase via the driveway entrance near the intersection with Havilah Street. Overland flows heading eastwards down Mills Lane also entered Chatswood Chase. The car park then acted as a detention basin and had a local influence on downstream flows in the creek. To include the

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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 objective of the study was to undertake a detailed flood study of the Clarence Town catchment and establish models as necessary for accurate flood level prediction. Central to this was the development of a two-dimensional hydraulic model of the floodplain. In completing the flood study, the following activities were undertaken: • Collation of database of historical flood information for the Clarence Town catchment; • Acquisition of topographical data for the catchment including cross section and hydraulic structure survey; • Consultation with the community to acquire historical flood information and liaison in regard to flooding concerns/perceptions and future floodplain management activities; • Development of a hydraulic model (using TUFLOW software) to simulate flood behaviour in the catchment; • Calibration of the developed models using the June 2007, February 2009 and February 2011 flood events; • Prediction of design flood conditions in the catchment using the calibrated models; and • Production of design flood mapping series. A good model calibration and validation was achieved with the available data, confirming the appropriateness of the model for design flood simulation. The local catchment flooding is typically characterised by a series of well-defined overland flow paths that feed the main Town Creek channel prior to discharge to the Williams River. Given the relatively small size of the contributing catchments, extensive flood inundation of property is somewhat limited. Only three existing properties (all commercial premises) have been identified as at potential risk of above floor flooding for events up to the 1% AEP flood magnitude. The majority of the natural flood flow paths are through private land. In most part, development on these lots has been located a sufficient distance from the natural drainage lines to limit potential for building inundation. The lower reaches of the Town Creek catchment are dominated by Williams River flooding. Typically downstream of approximately the IGA culvert, the Williams River 1% AEP design flood results in higher flood conditions than corresponding 1% AEP local catchment event. Accordingly, the Williams River design flood conditions established by BMT WBM (2009) should be applied for future flood planning and development control in these lower reaches.

The objective of the study was to assess the impacts of climate change on the baseline 1% AEP flood condition within the Williamtown / Salt Ash Flood Study area. Central to this was the development of a new two-dimensional hydraulic model of the study area, in order that the impacts could be properly assessed. In completing the flood study review, the following activities were undertaken: • Review of relevant studies regarding flood conditions and climate change impacts within Port Stephens; • Site inspection to confirm the presence and configuration of key hydraulic structures; • Merging of the existing Williamtown / Salt Ash Flood Study and Williams River Flood Study modelled to produce a composite model capable of properly assessing the impact of climate change in the study area; • Updating of model topography with available LiDAR survey data; • Calibration of 1% AEP design event flood levels with the 4.84m AHD level from the Flood Frequency Analysis at Raymond Terrace; • Prediction of design flood conditions in the catchment using the developed model; and • Production of design flood mapping series. The climate change scenarios that were considered were combinations of 2050 and 2100 sea level rise conditions with baseline, +10% and +30% flood flows. A sea level rise of 0.4m by 2050, results in around a 0.2m increase to the 1% AEP flood level in Fullerton Cove. A sea level rise of 0.9m by 2100, results in around a 0.6m increase to the 1% AEP flood level in Fullerton Cove. For the 1% AEP event peak flood levels in Fullerton Cove increase by around 0.1m and 0.3m for the 10% and 30% flow increases respectively. The dominant flooding mechanism (in terms of peak design water levels) for the Williamtown / Salt Ash locality is mainstream Hunter River flooding. Under these conditions, Hunter River flooding results in Fullerton Cove filling and discharging into the Tilligerry Creek floodplain, under crossdrainage structures and through overtopping of Nelson Bay Road. The baseline flood level within the Tilligerry Creek floodplain is increased from 1.2m AHD to 2.6m AHD, under the worst case climate change scenario. The flood levels along Windeyers Creek are driven by flow conditions in the Hunter River. Hunter River flood water provides a backwater influence in Windeyers Creek, which fills the storage area to the east of the Pacific Highway. The total volume of water flowing from the Hunter River along Windeyers Creek determines the flood level reached in the storage area. A higher flood level in the Hunter River will result in a higher flood level in the storage area. At this location, the sea level rise scenarios have little impact on peak flood levels. There is only a small difference between flood levels for the baseline condition and the 2100 scenario. However, the increased flood flow scenarios do have a significant impact, with peak flood levels increasing by around 0.2m and 0.6m for the 10% and 30% flow increases respectively. The baseline flood level at this location is increased from 4.4m AHD to 5.2m AHD, under the worst case climate change scenario. The flood study review will form the basis for the subsequent floodplain risk management activities, being the next stage of the floodplain management process.

Study Objectives Key objectives of this study are to:,

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.