It has been 18 months since floodwaters roared down the Goobarragandra River, tearing 100-year-old gum trees from their undermined foundations and collapsing the road that spanned from Kell’s Lane across to the Little River Road Bridge.
Since the devastation, Tumut Shire Council has undertaken extensive restoration works along the length of the river with the spotlight now focused on the Little River Bridge.
With eight designs considered and community consultation carried out, the $650,000 design chosen for the Little River Bridge restoration is expected to become a reality by the end of January after construction crews commenced work last Monday.
The old bridge, which remains structurally sound despite receiving an almighty battering, once spanned 26m across the normally calm Goobarragandra River.
Now that expanse stretches 56m across, with 30m of river unbridged.
Extensive erosion has scarred the landscape and whilst much of the debris and fallen trees have been removed from the area, the area still reflects the devastation the flood caused.
Tumut Shire Council’s Project Director Flood Recovery, Bede Spannagle has left no stone unturned in terms of planning and is looking forward to delivering a bridge that has been engineered in line with what the public wanted and what will best weather future flood events.
“We have incorporated the old bridge into the design as structurally the bridge was fine and it is worth about $500,000 so we thought it wasteful not to use it,” Mr Spannagle said. “On the Kell’s Lane side, the flood created a channel and the banks were washed out. Now that the river levels are low enough, we can dewater the site and carry out the foundation work for the new bridge extension.”
One of the major day-to-day challenges the restoration crews are facing is the leaking of groundwater into the worksite.
Each day before the workers can carry out more work to create a series of strip footings that will eventually sit under the water’s surface, the area must first be pumped free of the leaked water, and the rock surface cleaned again to allow rock anchors to be drilled and grouted.
“This is the most critical and difficult stage, getting the anchoring system right,” Mr Spannagle explained. “The structural integrity of the new culvert starts underground at bedrock level, so it’s important we get this stage right.”
Apart from the concrete culverts that will help direct the water, in low and high flows periods, the plans also include moving a major sand bar that was left in the wake of the flood waters.
Pushing the gravel from the middle of the river to the Kell’s Lane side will have a two-fold benefit.
“We are restoring the main river channel so where the two flows meet it will be at a softer angle and in turn have less impact on the bank,” Mr Spannagle said. “By also moving the gravel bar across we are reinforcing the bank area around one of the big gum trees so it will also protect the tree and the banks in future.”
Under Office of Water requirements, TSC were required to maintain the two defined waterways.
The design of the new part of the bridge will cater for different levels of flooding and will magnify the flow capacity by four times.
“As the water becomes higher the water will go under the original section of bridge and through the culverts on the opposite side,” Mr Spannagle said. “When the water rises even further and reaches the underside of the original bridge, the water will go over the culvert.
“Rather than putting the bridge and road back how it was, that would create the same flood issues, we are using a design that is more sympathetic to larger floods and possesses the capacity to handle it.”
The plans that will take three months to bring to fruition will join the existing structure to under-over boxed culvert causeways that will drop down slightly with the top of new structure sitting at the same height as the underside of the existing bridge deck.
The designs take into account the level of debris that built up against the bridge in the March 2012 with Mr Spannagle adamant that specific elements including strip footings be used to deal with high velocity flows.
Small adjustments to cater for public requests are also being included like the use of natural rocks in more visible areas where rocking is being used as an environmentally sound method to halt further bank erosion.
The new structure is being funded as part of the Federal Government’s National Disaster Recovery Fund.