Flood study centres around the opening of Cockrone Lagoon to the ocean when the water level exceeds the let-out-level of RL2.476m AHD. The policy is aimed at minimising the flooding of properties adjacent to the lagoon. The investigation process used in this flood study was: collection of available data assessment of available data overview of lagoon behaviour assessment of coastal processes hydrologic modelling of the catchment to determine flood inflows, and hydraulic modelling of the lagoon to assess flood levels from flood inflows

The investigation process used in this flood study was: - collection of available data; - assessment of available data; - overview of lagoon behaviour; - assessment of coastal processes; - hydrologic modelling of the catchment to determine flood inflows; and - hydraulic modelling of the lagoon to assess flood levels from flood inflows.

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

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.

Separate Flood studies have been undertaken for four coastal lagoons in the Gosford area, that is, Avoca, Cockrone, Terrigal and Wamberal Lagoons. Different analytical approaches have been used for Avoca-Cockrone and Terrigal-Wamberal Lagoons. The physical processes involved in the break-out of the lagoons through the beach are complex. Thus, there is a potential for the different analytical processes to produce significantly different results. For this study, separate MIKE-11 models were established for Terrigal-Wamberal Lagoons. These models were calibrated against the documented openings of August and September 1993. MIKE-11 models have been previously established for Avoca and Cockrone Lagoons as part of the Flood Studies. The Avoca Lagoon hydraulic model established for the flood study was modified to remove the source of numerical noise which resulted in the over-estimation of the volume of water discharged to the ocean during the opening calibration event. The re-calibration did not alter the parameters for initial breakout of the lagoon. The amendment of channel lengths in the Avoca model was also undertaken to remove a minor over-estimation of storage. The revised hydraulic model produced an estimated one percent AEP design flood level 20mm lower than that obtained in the flood study. This variation in estimated flood levels is not considered significant. It is noted that the critical duration storm (that is, the design storm that produces the greatest water level in the lagoon) was the 9 hour storm for each lagoon. The design flood level estimates for the one percent AEP flood in Terrigal Lagoon and Wamberal Lagoon determined by the review hydraulic model were within 30mm of the flood study estimates. This can be considered to provide independent verification of the flood study estimates.

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:,

The Flood Study had three main components:,

Wingecarribee Shire Council engaged Catchment Simulations Solutions to prepare a Flood Study for the Nattai River catchment. The extent of the catchment is shown in Figure 1 in report (refer Flood Study: Volume 2). The objectives of the Nattai River Catchment Flood Study are:,

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 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: -,