EXECUTIVE SUMMARY

Cockle Creek has a catchment area of approximately 109 square kilometres and is located at the northern end of Lake Macquarie at Boolaroo on the Central Coast. Cockle Creek has five main tributaries: Winding Creek, Brush Creek, Cocked Hat Creek, Flaggy Creek and Burkes Creek. Winding Creek is the tributary that has been the most developed for urban usage with the town of Cardiff straddling its banks.

Cockle Creek drains into Lake Macquarie which ultimately drains to the Pacific Ocean by the narrow and shallow 4 kilometre long Swansea Channel. The lake level is normally at 0.1 m AHD and tidal fluctuations are generally only ± 0.05m. Elevated ocean levels due to high tides and storm surge as well as intense rainfall over the catchment cause the lake level to rise and thus elevate the lower parts of Cockle Creek. In both February 1990 and June 2007 the peak lake level reached approximately 1 m AHD.

Flooding along Winding Creek and to a lesser extent along Cockle Creek has been recorded since the 1930’s. It is possible that the incidence of flooding has historically been under reported along Cockle Creek due to less urban development affected than on Winding Creek. The February 1981 event was a large event on Cockle Creek but not on Winding Creek. In recent times two significant events occurred on Winding Creek, in February 1990 and June 2007. In both these events there was extensive flooding in the Newcastle, Lake Macquarie and Wyong/Gosford regions. Flooding causes significant hardship, including both tangible and intangible damages, to the community and for this reason Lake Macquarie City Council has undertaken a program of studies to address the management of the flood problem.

The present study was initiated by Lake Macquarie City Council to reassess design flood levels in light of updated data and technology, and in addition incorporate sea level rise benchmarks based on predictions by the Intergovernmental Panel on Climate Change (IPCC) and the CSIRO technical review for Australia, and also the potential increase in rainfall intensities due to climate change.