About the Burrill Lake Bridge project
Burrill Lake crossing is located on the Princes Highway approximately four kilometres south of Ulladulla. The Princes Highway crosses Burrill Lake on a causeway and low-level bridge that was built in 1958.
This link on the Princes Highway is used by more than 8,000 vehicles a day. Assessments have found that, while the bridge is currently structurally sound and safe to carry traffic, it would require significant maintenance to ensure longevity.
After considering the costs and benefits of various maintenance options against a replacement bridge, the NSW Government has committed to build a new bridge with major work expected to start in early 2016 and be completed in early 2018.
Community feedback from the display of the Review of Environmental Factors and concept design in March 2014, has resulted in improvements and additions to the design. These include increasing the number of car parking spaces near the shops at Balmoral Road and installing navigation markers on the new bridge to improve boating safety.
The bridge over Burrill Lake was designed in 1956 and built in 1958. It is a composite prestressed unit bridge with six spans of 9.14 metres each and an overall length of 54.86 metres.
The bridge has a carriageway that is 8.5 metres wide with a 1.53 metre footway on the western side of the bridge. There are reinforced concrete safety barriers on each side of the bridge.
The northern approach of the bridge was constructed into the lake as a causeway that is approximately 150 metres long.
Future maintenance needs
Burrill Lake bridge is supported by 35 concrete columns called piles that are driven into the floor of the lake.
The piles are up to 15 metres long. Up to 24 of these columns have deteriorated due to a weakening of the concrete caused by the curing process used when they were manufactured. This concrete deterioration is called delayed ettringite formation (DEF). This problem is experienced by some types of bridges built in the same manner around the same time.
The deterioration currently poses no threat to the structural integrity of the bridge but will require significant maintenance intervention in the short to medium term if the bridge is to remain in use.
The bridge is also one of the most low-lying bridges on the Princes Highway and is flood prone.
Roads and Maritime considered options to maintain the existing bridge or to replace the bridge and causeway to the east or west.
Maintenance options meant the causeway and existing flooding problems on the highway would remain.
Options to the west of the existing highway and bridge were considered to have unacceptably high social impacts and costs, as they would have involved the direct removal of numerous homes and businesses on both sides of the crossing.
The options considered are documented in the Strategic Concept and Options Study Report.
Value management workshop
A value management process was undertaken as part of the considerations into the future of the Burrill Lake crossing. This is part of Roads and Maritime's process to recommend a preferred option, along with considering feedback from consultations during 2012 and other investigations and internal deliberations.
The value management process involves considering potential options from a wide range of perspectives. It includes evaluating the options against agreed and weighted criteria to determine which option is likely to provide a balance across social, economic, environmental and functional issues while also taking cost into consideration.
The value management workshop was held on Thursday 7 December 2012.
The main outcome of the workshop was that participants recommended a new bridge spanning the lake on a new alignment for further consideration. A number of different options for the existing bridge and causeway were also recommended for further investigation.
A new bridge on a new alignment was assessed as the best performing option. The value management workshop recommendations are not a final decision but provide direction for Roads and Maritime to focus its further investigations.
The workshop was attended by an independent facilitator, representatives from Shoalhaven City Council, NSW Department of Primary Industries (fisheries), Maritime Operations, a member of the Milton Ulladulla Lions club, Roads and Maritime representatives and technical advisors.
The Value Management Workshop report is available.
Since June 2012 Roads and Maritime has completed a series of investigations to help inform the decision to either maintain the existing bridge or replace it with a new bridge.
This has included:
- Flood and hydraulic modelling of the bridge, causeway and lake
- Flora, fauna, archaeology, noise, traffic and safety studies in the area around the existing bridge and highway approaches
- Building a picture of the local community that includes business, tourism, social, pedestrian and other community considerations
- Bridge and road engineering investigations
- Surveying the existing bridge, highway approaches and landforms
- Drilling to obtain geotechnical information about ground conditions around the bridge and highway approaches
- Investigative drilling in the causeway.
In 2010 Roads and Maritime undertook a high level review of the various engineering options available for the future of Burrill Lake bridge. This is documented in the Strategic Concept and Options Study Report.
While this report provides valuable background, RMS recognises there are other factors besides engineering, including issues for residents, business operators and motorists, which need to be considered before a plan for the future of the bridge is decided upon.