Report for the Burrill Lake Catchment Flood Study covering the development and calibration of computer models, establishment of design flood behaviour and flood mapping.

1 INTRODUCTION

1.1 Study Location

Burrill Lake is located on the New South Wales south coast, about 180 km south of Sydney (see Figure 1-1). The Lake entrance is around 5 kilometres south-south-west of Ulladulla. The Lake is located within the Local Government Area (LGA) of the City of Shoalhaven. An oblique view of the Burrill Lake catchment is presented in Figure 1-2, showing key locations and areas of interest.

1.2 Waterway Characteristics

Burrill Lake (refer Figure 1-3) has a surface area of 4km2 (WBM, 2001) and is connected to the Tasman Sea by Burrill Inlet, a 3km long, shallow and sinuous channel with a typical depth of around 1m at low tide. The Inlet is crossed by a causeway and bridge. The level of the causeway, which was originally built in the 1880’s, was raised in the 1960's to reduce the frequency of inundation of the highway (SCC, 2003). The span of the bridge over the Inlet is approximately 45 metres. Upstream of the bridge, gross channel positions and the extent of the intertidal shoal have effectively remained unchanged. The entrance to Burrill Lake has intermittently closed in the past, however, it is generally open albeit heavily shoaled. The entrance closed most recently in early 2005 (pers comm. D.Heubusch SCC, 2005), but prior to this remained continuously open from 1987 (Shoalhaven City Council, 2002) since at least the 1940's (PWD, 1992). The entrance shoals are the most active along the Inlet. The main body of the Lake comprises two basins, one to the north and one to the south of the marine dropover, where Burrill Inlet meets the Lake. The northern basin extends for around two kilometres northwards from the dropover, with a typical width of around one kilometre and depths of up to 9 metres (below AHD). The Lake’s main tributary, Stony Creek, flows into the northern end of the northern basin. The southern basin extends for around two kilometres in a south-westerly direction from the dropover, with a typical width of around 500 metres and depths of up to 9 metres (below AHD). A small, unnamed tributary flows into the bottom end of the southern basin.

1.3 Catchment Characteristics

The Burrill Lake catchment covers an area of 78 km2 and is largely covered by agricultural grazing lands to the north and eucalypt forest in the south and west. The main land uses in the Burrill Lake catchment are rural (56%) and forest (37%). The majority of the Stony Creek catchment, particularly towards the northern part of the catchment, has been cleared for agriculture. Most of the foreshore of Burrill Lake remains naturally vegetated. In total there are six urban areas in the catchment: Dolphin Point, Burrill Lake, Bungalow Park, Kings Point, Milton and west Ulladulla.