The 32km2 Erina Creek catchment is one of the major tributaries entering Brisbane Water at East Gosford (Figure 1). Figure 2 shows a digital terrain image of the study area and Figures 3 to 5 show further detail of the study area. Figure 6 indicates the current land use zones.

The Erina Creek Flood Study Review 1990 was completed in 1991 (Reference 1), which utilised information available and current at the time hydrologic and hydraulic models to produce design flood profiles along the lower parts of Erina Creek. The aim of the present study is to update the Erina Creek Flood Study Review 1990 with currently available data, notably the use of airborne laser scanning (ALS) data and more sophisticated hydraulic modelling techniques as well as verification to the June 2007 event.

All earlier flood studies of Erina Creek were superseded with completion of the Erina Creek Flood Study Review 1990.

WMAwater was engaged by Gosford City Council to undertake the Erina Creek Flood Study Review utilising current technology and data. The information and results obtained from the study will provide a basis for development of targeted stormwater management strategies and a subsequent Floodplain Risk Management Study and Plan.

The study was developed in order to meet the primary objective of defining the flood behaviour (50%, 20%, 10%, 5%, 2%, 1%, 0.5%, 0.2% AEP and the Probable Maximum Flood (PMF) design events) along the major tributaries in the Erina Creek catchment. The study area was significantly greater than for the previous 1991 Flood Study.

This report details the results and findings of the Flood Study investigations. The key elements include:

• a summary of available historical flood related data,
• discussion on the calibration of the hydrologic and hydraulic models,
• definition of the design flood behaviour for existing conditions through the analysis and interpretation of model results,
• sensitivity and climate change analysis.