This Flood Study comprised the following principal stages: collection and assessment of available data; investigation of coastal processes to determine design ocean levels for tailwater boundary conditions for the hydraulic model and to determine ocean storm inflows into the lagoon; development and calibration of an hydrologic model to convert design storm rainfalls into design flood hydrographs; and development and calibration of an hydraulic model to determine design flood levels in the lagoon and on the floodplain. Available data comprises: Council records of lagoon openings (the most comprehensive available); Department of Land and Water Conservation (DLWC) Rainfall data at Kincumber Sewage Treatment Plant; and Bureau of Meteorology Daily Rainfall Records. The initial flood studies, outlined in this report, indicated significant sections of the Three Points Avenue area of MacMasters Beach would be flood liable. Ground survey of individual properties showed that the established model was not sufficiently refine to accurately represent the separate flow paths. An individual flood study was undertaken of the drain running parallel to Newell Road and Three Points Avenue. The study report appears as Addendum A to this document, while the results have been included on Figure 10.

Cockrone Lagoon study outlines existing flood behaviour, environmental and planning considerations, flood damages assessment, flood plain management options and their impacts, and preferred strategy.

Storage Volumes: The modelling showed that the approach developed for Terrigal and Wamberal Lagoons could be satisfactorily applied to Avoca Lagoon for the opening of 14 September 1993. In discussions with Paterson Consultants it became apparent that the storage volume of the Lagoon was critical for establishing the peak outflow from the Lagoon. A considerable effort was undertaken in this regard which revealed that a table of height/area of Avoca Lagoon was in error at a level of I.0 m. In addition it was determined that the Mike-II and RUBICON models determine different storage capacities of the lagoon. There was insufficient time to completely resolve this issue, however preliminary work suggested that the Mike- 11 model was over-calculating storage. The differences in storage make no significant difference to the peak flood level. Comparison of Results: For Wamberal, Avoca and Cockrone Lagoons the peak flood levels from both approaches should be very similar. This is because the berm height is the major control and the peak flood level is only just (0.3m) above the berm level. For Terrigal Lagoon the differences in the two approaches are likely to be more significant as the beach berm is much lower (2.5m AHD) and the peak flood level approximately 0.5m higher than the berm. Additional Work: It is recommended that data be collected for future openings. If the data are suitable they should be used in further verification of the hydraulic models.

The Raymond Terrace Flood Study has been prepared for Port Stephens Council (Council) to define the existing flood behaviour in the western Raymond Terrace catchments and establish the basis for subsequent floodplain management activities. The study will also assist Council in considering future upgrades to the drainage network and flood relief pump capacity to the Hunter River. This project has been conducted under the State Assisted Floodplain Management Program and received State financial support.

The main objective of this study (in two parts) has been to determine water levels in Brisbane Water for the full range of flood and ocean events that can occur due to the various natural physical processes, taking joint occurrence issues into account to some extent. The flooding behaviour can be influenced, either separately, or by a combination of, catchment rainfall runoff flooding, rainfall directly onto Brisbane Water, elevated ocean levels, local winds and, to a minor extent, the condition of the ocean entrance channel near Ettalong. The outcomes from this study include: -,

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:,

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:,

The Floodplain Management Plan divides the Cockrone Lagoon area into six precincts: Cockrone Lagoon - Beach Berm High Hazard Floodway/Investigation Cockrone Lagoon - Entrance Area High Hazard – Low Hazard Floodway/Investigation Cockrone Lagoon - Storage Area Low Hazard Flood storage Cockrone Lagoon - Floodway Area High Hazard Floodway Merchants Creek - Floodway Area High Hazard Floodway Newell Road Floodway High Hazard Floodway These precincts have been classified for flood hazard as: High Hazard - Floodways - Cockrone Lagoon beach berm; - Cockrone Gully, from the upstream study boundary to its confluence with Cockrone Lagoon (identified as Cockrone Lagoon floodway); - Merchants Creek floodway from the confluence of Merchants Creek with Cockrone Lagoon to the upstream study extent; and - an existing open drain through the residential areas bounded by Newell Road and Three Points Avenue. High Hazard – Low Hazard Floodway (Floodway Investigation area) - Cockrone Lagoon at its entrance to the ocean (Floodway/Investigation Area); Low Hazard - Flood Storage - Cockrone Lagoon and foreshores excepting high hazard areas above. These precincts are illustrated on Figures 2 and 3, while Figure 4 provides greater detail in the Cockrone Lagoon Entrance Area. Council has adopted a policy of opening the lagoons when water level reaches RL 2.53 m AHD (identified as the let-out-level). Council has, in the past, also adopted a policy that requires new buildings to have floor levels above RL 4.3 m AHD. These two policies effectively constitute Council's current floodplain management practice around Cockrone Lagoon.

Coastal Lagoon Catchments Overland Flood Study Final Report inc. appendices and figures

The study was commissioned by Bayside Council, with the assistance of the NSW Government Office of Environment and Heritage (OEH). Additional information has been provided by Sydney Water Corporation (SWC). The Flood Study comprises the development of computational hydrologic and hydraulic models that define design flood behaviour for the 20% AEP (0.2 EY), 10% AEP, 5% AEP, 1% AEP and 0.5% Annual Exceedance Probability (AEP) design storms and the Probable Maximum Flood (PMF) in the Bardwell Creek and Wolli Creek catchments.