Project Summary

The condition of the Lake Illawarra entrance controls the tidal range within the lake and as a result, the degree of tidal flushing. Conditions at the lake’s entrance can vary from substantially open after floods to completely closed. As a result of previous drought conditions the entrance was closed off to tidal flows leading to poor estuarine health.

The Lake Illawarra Authority engaged NSW Public Works as the construction manager for both stages of the project.  We were responsible for tender management, contract administration and construction management for two separate but concurrent contracts.

The extension of the southern training wall, construction of the northern breakwater and major channel dredging has resulted in increased tidal flushing and a more environmentally sustainable estuarine system.

Project Background

Lake Illawarra is a coastal lagoon situated between Wollongong and Shellharbour, 90km south of Sydney. The lake is a popular natural resource for both locals and visitors for fishing, prawning, boating and swimming. The condition of the lake entrance can vary substantially between open and blocked, controlling the tidal range within the lake and, as a result, the degree of tidal flushing. Estuarine functions are dependent upon tidal processes and an open entrance. As a result of drought conditions the entrance was closed off to tidal flows leading to poor estuarine health.

Project Scope

In 2000, the Lake Illawarra Authority constructed a training wall on the southern side of the entrance channel to help keep it open more often. These initial works aimed to increase tidal penetration and reduce retention time of nutrients and pollutants in the lake body. However, with ongoing drought conditions the lake entrance closed, requiring further construction works.

Construction of the Stage 2 improvement works at Lake Illawarra began in May 2006 and involved:

Phase 1 - Building rock structures

• Construction of a 355m northern breakwater projecting about 175m into the sea
• Extension of the existing 240m southern training wall projecting about 200m into the sea.

The two breakwaters are intended to trap sand that is currently washed into the entrance channel from the adjoining beaches and prevent the entrance being blocked. In addition, the restriction in  the waterway area caused by the twin breakwaters Completion of Southern and Northern Training Walls results in increased velocities during ebb tides. This carries back out to sea any sand that does make its way into the channel and ensures a more permanently opened entrance.

Phase 2 – Dredging and beach nourishment

• Removal of 215,000 cubic metres of sand from the entrance area and disposing of it to Warilla Beach
• Creation of a channel 80m wide and 2m deep from the mouth of the lake 1150m towards Berageree Island to connect the entrance to the body of the lake
• Creation of a bird roosting sand island measuring 220m x 50m with a crest level of 1-1.5m above mean sea level.

The 2m deep channel allows increased tidal exchanges and provides an entrance compartment that can convey major flood flows from the lake, reducing the impact of flooding on adjoining urban areas.

Our Role

The Lake Illawarra Authority engaged NSW Public Works as the construction manager for both stages of the project. In Stage 2 NSW Public Works was responsible for tender management, contract administration and construction management for two separate but concurrent contracts.

NSW Public Works also participated in the monthly Community Liaison Group meetings providing construction status reports to key community, local and state government stakeholders.