The objectives of the Flood Study are to: • Identify all the flood-related data by searching all relevant data sources. • Determine the likely extent and nature of flooding and identify potential hydraulic controls by carrying out detailed site visits of the study area. • Define existing catchment condition flood behaviour for mainstream flooding in the catchment with due consideration to the impact of Lake Macquarie levels on flooding characteristics. • Define design flood levels, velocities and flow distributions for the catchment. • Define the extent of flooding for the 200 year, 100 year, 20 year, 10 year and 5 year ARI floods and Probable Maximum Flood (PMF) for the catchment. • Define Provisional Flood Hazard for the flood-affected areas. • Define the Hydraulic Categories for the flood-affected areas. Two numerical modelling tools were developed: • A hydrologic model to convert rainfall on the catchment into runoff. The hydrologic model combines rainfall information with local catchment characteristics to estimate runoff hydrographs. • A hydraulic model to convert runoff hydrographs into water levels and velocities throughout the study area. The model simulates the hydraulic behaviour of the water within the study area by accounting for flow in the major channels as well as all the potential overland flowpaths, which develop when the capacity of the channels is exceeded. It relies on boundary conditions, which include the runoff hydrographs produced by the hydrologic model and the appropriate downstream boundary level from Lake Macquarie.

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.

This document constitutes the first and second stages of the management process for the North Creek catchment. It presents a compilation of the data collected and has defined flood behaviour and flood risk for the catchment area. This study was commissioned under the 2005 NSW Floodplain Development Manual (Reference 1), however, it is recognised that the 2023 Flood Risk Management Manual (Reference 2) was gazetted shortly after the project commenced. While the study was undertaken in accordance with the 2005 manual, there are elements that are consistent to both the 2005 and 2023 manuals. Where appropriate, the 2023 manual is referenced where project methodology or outputs are consistent with the new 2023 manual

Study Objectives The key objective of this Flood Study is to develop computational models that can be used as the basis for a Floodplain Risk Management Study and Plan for the study area. The study is also to assist SCC to undertake flood-related planning decisions for existing and future developments. The study covers the Lake Wollumboola catchment and the Culburra Beach village catchment. The components of the study were to: collate available historical flood-related data; analyse of historical rainfall and lake level data; undertake a community consultation program; develop numerical models of flooding in the catchment and calibrate them to historical data; determine the flood behaviour including design flood levels, velocities and flood extents within the catchment; to determine provisional residential flood planning levels and flood planning area; to assess the sensitivity of flood behaviour to potential climate change effects such as Lake Wollumboola Flood Study WMAwater 150917_LakeWollumboola_FloodStudy_Final:24 September 2015 5 increases in rainfall intensities and sea level rise; and to assess the floodplain categories in accordance with Council policy and undertake provisional hazard mapping.

The primary objective of the flood study is to provide Council with design flood levels for Tuggerah Lakes. A second objective, to provide a flood forecasting capability, is described in a separate report (ref 18). A hydraulic model has been developed to assess the nature and extent of the flood hazard in the Tuggerah Lakes floodplain, and the model can be used to determine design flood levels and velocities for the purpose of evaluating floodplain management options.

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:,

This study updates the previous Wrights Creek Flood Study (Patterson Britton & Partners, 2007) and provides Council with a suitable platform for undertaking the next steps in the Floodplain Risk Management Process. The XP-RAFTS hydrologic model developed in the 2007 Flood Study has been adopted for this study. A TUFLOW hydraulic model of the catchment has been established using up to date survey of the ground levels and culvert and bridge structures. The TUFLOW hydraulic model has been used to reproduce the historical flood behaviour from events in 1995 and 2002 and to define flood behaviour for a range of design events. Actions undertaken as part of this flood study include: • collection of additional survey, • development of a TUFLOW hydraulic model, • definition of the design flood behaviour, • assessment of provisional hydraulic hazard, • assessment of hydraulic categorization, • assessment of the model sensitivity to parameter changes, • assessment of climate change impacts on model results, • assessment of sensitivity of model results to the new ARR 2016 design inputs, • community consultation.

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.

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.

Flood Study August 2010