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A cautionary tale of infrastructure and fish

Cheap and nasty bad investment

Having lived in the Braidwood area for 25 years I have been aware of the successes gained by and the failures besetting the local council during the reigns of both Tallaganda and Palerang. Perhaps no failure has been as obvious as the cheap, nasty and poorly engineered Bobs Creek culvert.

Bobs Creek is a crystal clear spring-fed stream rising in the western reaches of the Budawang Mountains, the rugged range that divides the southern tablelands from the lush narrow coastal strip of magnificent southeast NSW beaches and South Pacific Ocean.

Up to the past decade motorists using Charleys Forest Road and needing to cross Bobs Creek were serviced by a cement causeway that was usually only inches under water. Following heavy rains Bobs Creek flooded and became risky to cross or became too dangerous and was closed to traffic.

Due to increasing interest in country lifestyle and agricultural diversification in the area north-east of Braidwood, the population grew to a point where demand for more reliable access to the closest town and beyond became paramount. The solution was to construct a culvert to a height that would guarantee all weather access.

A culvert designed to raise the crossing to the height of approximately 3.5 metres above the creek was considered a satisfactory answer. Large corrugated iron round tunnels formed the basis and packed earth completed the construction of what was believed to be a worthy solution.

First signs of trouble

The first sign of trouble occurred in 2014 when part of the culvert fell away on the southern side. This led to a half road closure while repairs were carried out and warning bollards remained in place until further corrosion and heavy rainfall caused complete failure. The culvert was closed to traffic on the evening of Wednesday, April 22 2015.

The solution to enable traffic flow to resume was the temporary re-establishment of the old Bobs Creek causeway immediately downstream of the work site. At the time of writing, a narrow side road and the old Bobs Creek causeway is still in use.

In relation to environmental issues I was fortunate to be in the presence of a civil engineer working on the Kings Highway project at Warri and visiting Braidwood to attend a dinner meeting. I questioned the necessity to install tunnels as large as those used in the failed culvert construction. An interesting conversation resulted with my gaining information relating to culverts and fish passage.

The migration of fish species both upstream and downstream can be restricted by many factors including culvert length and grade, impediments at inlet and outlets, water levels, turbulence and water velocities. Culverts that are too restricted may reduce habitat connectivity to mainstreams, tributaries, ponds and wetlands.

The three corroded corrugated iron conduits are currently being replaced by reinforced concrete box culverts. The poor failed (and cheap?) original construction has given way to what now  can only be described as a very serious attempt to ensure continuous traffic flow over Bobs Creek and fish under it into the future.

With Jill Mcleod







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