This report details the results and findings of the Flood Study investigations. The key elements include: • a description of the study area; • a summary of available historical flood related data; • establishment and calibration of the hydrologic and hydraulic models; • the estimation of design flood behaviour for existing catchment conditions; • sensitivity analysis of the model results to variation of input parameters; • potential implications of climate change projections; and • identification of the level of flood risk for individual properties in the catchment.

This report comprises an overview of the work that has been undertaken by WMAwater on the Manly Lagoon Floodplain Risk Management Study and Plan. It builds on prior stage reports and, in accordance with the Brief, it additionally includes a discussion of: • hydraulic and hazard categorisation; • future development scenarios; • review of climate change; • flood damages assessment; and • emergency management.

Narrabeen Lagoon Floodplain Risk Management Study and Plan 2019 - Reports

This Floodplain Risk Management Study and Plan for Mona Vale/Bayview has been undertaken by Cardno Lawson Treloar for Pittwater Council to identify and examine options for the management of flooding within the Mona Vale Main Drain and Cahill Creek floodplain. The study has been undertaken in accordance with the NSW Government Floodplain Development Manual (2005). A locality plan can be found in Figure 1.1. The outline of the study area can be found in Figure 1.2. Study Context This study forms two of the multiple stages of the Floodplain Management process which includes:,

Study Context The preparation of this plan follows on from the Flood Study (WMA, 2006) and Floodplain Risk Management Study (Cardno Lawson Treloar, 2007a) and forms the fifth stage of the Floodplain Risk Management Process which includes:,

Conclusions Provided below is a summary of the key findings of the Flood Study, in particular some of the important considerations for future floodplain risk management in the catchment:,

Background Narromine Shire Council, through its Floodplain Management Committee is undertaking a Floodplain Risk Management Study and Plan for the town in accordance with the New South Wales Government's flood prone lands policy and using procedures set out in the Floodplain Development Manual, 2005. The results of the Study and the draft Plan are presented in this report. The Floodplain Risk Management Study used the data from the recent Narromine Flood Study (LACE, 2006) to undertake a review of the physical, social and economic aspects of flooding on the Macquarie River floodplain at Narromine in order to prepare the draft Floodplain Risk Management Plan. The Floodplain Risk Management Study summarised present day flooding conditions as determined by the LACE, 2006 investigation and identified and assessed potential measures aimed at reducing the impact of flooding on both existing and future development. This process allowed the formulation of a draft Floodplain Risk Management Plan for Narromine having regard to both existing flooding problems and to potential future development. Overview of Report The Floodplain Risk Management Study and draft Plan are set out in this report. Contents of each section of the report are briefly described below:,

The Gloucester and Avon Rivers Flood Study has been prepared for Gloucester Shire Council (Council) to define the existing flood behaviour in the catchment and establish the basis for subsequent floodplain management activities. This project has been implemented through the Gloucester Water Study Project. The primary objective of the Flood Study is to define the flood behaviour within the Gloucester and Avon Rivers catchment through the establishment of appropriate numerical models. The study has produced information on flood flows, velocities, levels and extents for a range of flood event magnitudes under existing catchment and floodplain conditions. Specifically, the study incorporates: Compilation and review of existing information pertinent to the study and acquisition of additional data including survey as required; Development and calibration of appropriate hydrologic and hydraulic models; Determination of design flood conditions for a range of design event including the 50% AEP, 20% AEP, 10% AEP, 5% AEP, 2% AEP, 1% AEP, 0.5% AEP, 0.2% AEP and PMF event; and Presentation of study methodology, results and findings in a comprehensive report incorporating appropriate flood mapping.

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

This report has been prepared for Warringah Council to define the nature and extent of flood in the Dee Why South Catchment. Flood modelling was completed to define flood behaviour for a range of storm events from 1 year Average Recurrence Interval (ARI) to Probable Maximum Flood (PMF). The modelling shows that significant flows are conveyed in the piped drainage network and overland through roads and properties. Generally the main overland flowpath starts from several branches at Alfred Street to Beverley Job Park. Flows in the open channel at Victor Road and Redman Road combine with overland flows from Mooramba Road, Fisher Road, and Pittwater Road at the intersection of Redman Road and Pittwater Road. Overland flows are then conveyed along several roads and properties to Dee Why Lagoon as well as in the open channels between Pacific Parade / Oaks Avenue and downstream of Dee Why Parade. In a 1% AEP event, the results show that ponding of runoff occurs at several locations with restricted outlet capacity. High pedestrian areas in Dee Why CBD also experience overland flow inundation, particularly along Redman Road, Pittwater Road, Oaks Avenue and Howard Avenue. In a 1% AEP event floodway and high provisional hazard flow conditions along the open channels, on roads, and some properties including in the Dee Why CBD. A series of climate change scenarios were also modelled to evaluate potential impacts from elevated sea levels and increased rainfall intensity. Results showed that the modelled increases to Lagoon level have an impact to flood inundation of low-lying land near the Lagoon. Most properties within the Dee Why South catchment do not show a significant change in inundation extent for the modelled scenarios. Modelled increases in rainfall intensity showed a rise in peak water levels across the catchment, particularly in trapped low points such as on Sturdee Parade and Alfred Street. Council applies land use planning and development controls to manage development within flood prone areas. The flood result and mapping provided in the document will assist Council with future land use planning, development controls and floodplain risk management. The next stage of the floodplain risk management process following the adoption of the Flood Study is the Floodplain Risk Management Study and Plan. This next stage will investigate various floodplain risk management measures and prioritise these measures for implementation.