Flood Risk Management Study & Plan - Main report (Part 1 of 4) This Lake Macquarie Waterway Flood Risk Management Study and Plan constitutes a review of the second and third stage of the management process, namely the August 2000 Lake Macquarie Floodplain Management Study and the July 2001 Lake Macquarie Floodplain Management Plan. This review has been prepared by consultant WMAwater for Lake Macquarie City Council and was undertaken following a review of the 1998 Lake Macquarie Flood Study, to include the June 2007 long weekend storm/flood event and incorporation of the implications of climate change. The results of this Waterway Flood Risk Management Study and Plan Review will provide the basis for the future management of flood liable foreshores areas surrounding the Lake Macquarie waterway. The study concentrates on those areas of the foreshore within the boundaries of Lake Macquarie City Council, with no investigation of land within the Wyong local government area.

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.

Introduction The Dora Creek Flood Risk Management Plan has been prepared for Lake Macquarie City Council (Council) in accordance with the NSW Floodplain Development Manual (April 2005 - Reference 1) and the August 2010 Flood Risk Management Guide – Incorporating sea level rise benchmarks in flood risk assessment (Reference 4) and: Is based on a comprehensive and detailed evaluation of factors that affect and are affected by the use of flood prone land; Represents the considered opinion of the local community on how to best manage its flood risk and its flood prone land; and Provides a long-term path for the future development of the community. The Dora Creek catchment is located on the western side of Lake Macquarie waterway, 30 km south-west of Newcastle and 120 km north of Sydney. Dora Creek has a catchment area of approximately 238 km2 and is the largest catchment flowing into the Lake Macquarie waterway which has a total catchment of 648 km2 (Figure 1). The study area focuses on the existing township of Dora Creek and includes the townships of Cooranbong and Avondale, where new and planned rural and urban developments are proposed within the floodplain. The upper limit of the study area extends above Freemans Drive to Cooranbong and downstream to the confluence of Dora Creek with the Lake Macquarie waterway. There are three main tributaries within the catchment with Dora Creek being joined by Jigadee Creek at Cooranbong and then Stockton Creek before draining into Lake Macquarie waterway at Bonnells Bay and Lake Eraring. Watercourses within the catchment area and above the tidal limit are narrow; Dora Creek is typically less than 15 m wide upstream of Freemans Drive. Below the tidal limit, the creeks become broader with Dora Creek varying from a width of 50m at the Sydney to Newcastle Freeway to 100m where it forms a delta into Lake Macquarie waterway. Upstream of the delta the Eraring Power station draws cooling water for steam condensation from Bonnells Bay, which passes under Dora Creek through a concrete tunnel and open canal.

Main report

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.

Final Report - PDF

Spatial data only- creekline, culvert locations, RAFTS layout, sub catchments, SOBEK x-sections, catchment boundary.

Report (Executive Summary)

The Green Square Floodplain Risk Management Plan has been prepared in accordance with the NSW Floodplain Development Manual (April 2005) and: Is based on a comprehensive and detailed evaluation of all factors that affect and are affected by the use of flood prone land; Represents the considered opinion of the local community on how to best manage its flood risk and its flood prone land; Provides a long-term path for the future development of the community. All possible management measures were evaluated in the Floodplain Risk Management Study (Reference 5) taking into account a range of parameters. This process eliminated a number of measures including:,

Under the NSW Government's flood prone land policy the City is required to manage flooding issues and put plans into place to safeguard flood-prone areas. The local area has been divided into 9 catchments covering 2,666ha. More information on floodplain management catchments