Catchment Description

Cockle Creek has a catchment area of approximately 109 square kilometres and is located at the northern end of Lake Macquarie waterway at Boolaroo, on the Central Coast of NSW. Cockle Creek has six main tributaries: Winding Creek, Brush Creek, Cocked Hat Creek, Slatey Creek, Burkes Creek and Diega Creek. Winding Creek is the tributary that has been the most developed for urban usage with the town of Cardiff straddling its banks. However, in the last 20 years there have been significant new residential sub-divisions in the Cocked Hat Creek catchment accompanying the much older residential developments at Barnsley, Holmesville and West Wallsend.

This flood study includes all the tributaries draining into Cockle Creek downstream of the confluence with Winding Creek. The main Cockle Creek channel and floodplain from Barnsley to Lake Macquarie waterway was modelled in the 2017 Winding Creek and Lower Cockle Flood Study and was not included in the present study.

Cockle Creek drains into Lake Macquarie waterway 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 February 1990, June 2007 and April 2015 the peak lake level reached approximately 1 m AHD.

Flooding History

Flooding in the Cockle Creek catchment has been recorded periodically since the 1930’s but there are many more recorded instances of flooding in the Winding Creek catchment. It is possible that the incidence of flooding has historically been under reported along Cockle Creek as there is 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 more recent times there have been two significant events, in February 1990 and June 2007.

Study Objectives

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.