Study Objectives Key objectives of this study are to:,

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.

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 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:,

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.

Conclusions: The objective of the study was to undertake a detailed flood study of the Main Drain J catchment and establish models as necessary for design flood level prediction. This included the assessment of inputs to the catchment from Mirrool Creek. In completing the flood study, the following activities were undertaken:,

The study objective was to define flood behaviour on Sugarloaf Creek in terms of water levels, flows and velocities for design floods ranging between 5 and 100 year ARI, as well as for the Probable Maximum Flood (PMF). Figure 1.1 shows the Sugarloaf Creek catchment and its stormwater system. The flood study investigation involved the following activities: ? The collection of flood related data. A Community Newsletter/Questionnaire introducing the study objectives and seeking information on historic flood patterns was forwarded to residents in the floodplain. Rainfall data at several daily gauges were also collected. A previous flood study of the Sugarloaf Creek catchment by Lyall and Macoun Consulting Engineers (LMCE, 1988) also provided information on historic flooding. Three significant storms which had occurred over the past 25 years were identified (5 August 1986, 30 April 1988 and 10 April 1998) and their rainfalls used to test the flood models developed for the study. ? The hydrologic modelling of the catchment of Sugarloaf Creek to determine discharge hydrographs. All reaches of the piped drainage system of diameter 450 mm or larger were modelled. ? Application of the discharge hydrographs to a hydraulic model of the main arm of the creek and its overland flow paths. The model extended from the headwaters of the catchment (to the west of Bales Park) to its outfall to Sugarloaf Bay downstream of the Eastern Valley Way. ? Presentation of study results as water surface profiles, as well as diagrams showing indicative extents of inundation, provisional flood hazard and the hydraulic categorisation of the floodplain into floodway and flood fringe areas. ? Sensitivity studies to assess the effects on model results resulting from uncertainties in model parameters such as hydraulic roughness of the floodplain, the effects of partial blockage of the piped drainage system and the effects on flooding patterns resulting from future climate change. The hydrologic modelling approach was based on the DRAINS rainfall-runoff software. DRAINS derived discharge hydrographs resulting from historic storms for each model sub-catchment area, which were then applied to the hydraulic model to demonstrate that the models reproduced observed flood behaviour. The TUFLOW two-dimensional modelling system was adopted for the hydraulic analysis. Appendix A describes the results of testing the models. Both the DRAINS and TUFLOW models included the piped drainage system and routed the flows to the catchment outlet. Hence both models were able to provide independent estimates of the relative magnitudes of piped and overland flows. However, TUFLOW being primarily a hydraulic model (as opposed to DRAINS which is hydrologically based) was used to route flows over the land surface and determine peak flood levels and flow velocities, as well as indicative extents and depths of inundation. After testing the models for the historic floods, design storm rainfalls ranging between 5 and 100 year ARI were derived using procedures set out in Australian Rainfall and Runoff (ARR, 2001) and applied to the DRAINS model to determine discharge hydrographs. The PMF was also modelled. Flooding patterns derived by TUFLOW for the design flood events are described in Chapter 6 of the report, with exhibits presented in Volume 2.

Conclusions The objective of the study was to undertake a preliminary investigation to identify and map sub-catchments and major overland flow paths within urban areas of the Liverpool LGA. This was achieved through the development of a flood model of the study area, underpinned by the detailed representation of catchment topography defined by available LiDAR data acquired in 2013. The key findings and recommendations of the study are summarised hereunder:,

TUFLOW

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