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St Georges Dam wall re-build at Creswick Regional Park

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Dam wall rebuild: Nearing completion of the excavation 20,000 cubic metres of soil

3 weeks ago from Parks Victoria

Location: St Georges Dam wall re-build at Creswick Regional Park

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Upgrade Project Underway

The St Georges Lake picnic area is closed to protect visitor safety during the dam construction project. Access to St Georges Lake is restricted and the road to St Georges Lake is closed to all but local residents on St Georges Street and their visitors. A map showing the construction area and visitor access restrictions can be found here.

The lake was emptied to allow for the safe re-construction of the dam wall from June 2014. The lake bed will be slippery, uneven and unsafe as a walking surface. Following the decommissioning of an outlet pipe in early October, the lake is now refilling with water. Access to the lake and picnic area remains closed. 

November update

Works to re-build Creswick’s 100 year old dam are progressing well after plans to remove a faulty dam outlet pipe succeeded. The decommissioning of the pipe and installation of a temporary earthen coffer dam as flood risk protection for the dam construction area, now means the lake is refilling. 

Excavations of over 20,000 cubic metres of soil from the old dam wall site is another major milestone towards the project’s completion. 

The initial works programme estimated the project would be complete in early 2015.  Complications in delivering the project now estimate completion into Autumn 2015.  However, additional benefits are being provided through the dam safety upgrade project for the local Creswick community. 

A new wider beached lake access area has been created alongside the barbecue picnic spot.  The old "beach" had been degraded by previous floods and was not ideal for safe water access. The new "beach"area will be a real improvement for visitors once the project is complete. 

Parks Victoria is also creating a new earth groin fishing platform which will extend out into the lake to provide improved access for local angling enthusiasts. 

July update

Parks Victoria’s contractor began draining St Georges lake in late June. Approximately 200 mega litres of water needed to be drained from the lake via a 300mm diameter outlet to make the construction site safe to build the new dam wall. Draining the lake took a little over two weeks to complete with rain received in mid-July partially refilling the lake. St Georges Lake needs to be completely drained to allow for the safe construction of the new dam wall which is required to meet national dam safety guidelines. 

A zoologist was employed to monitor wildlife at the site and tracked a number of water rats evacuating the area during the water drawdown.  The animals have found new temporary homes in surrounding creeks and waterways. No platypuses were found in the lake during the extensive monitoring. 

An abandoned car body was found on the bottom of the lake along with a collection of sunglasses and picnic items.   

Local residents are encouraged to stay away from the lake bed which is uneven, slippery and very boggy.  Warning signs are posted around the lake edge to prevent access to the deep mud which could trap an unwary curious visitor.  

Community drop-in day

Around 30 locals attended a community drop in day on Saturday March 29 in the lakeside picnic area.  The plan for the day was to take interested locals, including lake neighbours, on a guided tour across the crest of the dam wall.  At least twenty people took up the offer of a tour by the Parks Victoria Project Manager and Ranger in Charge and had plenty of questions about the upgrade to the dam wall. 

The most commonly asked questions are listed below with answers. 

Q1) What will the dam look like and will it be part of the walking track after the works?

The new dam wall is designed to hold less water than the current hundred year old structure. This design feature means that even during high rain events less water will flow more slowly through the dam. 

The current dam wall is made of compacted earth this will be replaced with a concrete structure and a series of rock layers. 

The new secondary spillway will be 67 metres long which is 11 metres shorter and 2 metres lower than the current earth embankment. The primary spillway will be 1 metre lower than it is currently and 12 metres wider. The attached plan shows these two water management structures. The third new and upgraded feature of the dam is a saddle dam (shown in the plan below). The saddle dam will manage water past the picnic area to reduce the chance of a repeat of the historic gouging out of the creek bed which occurred in the 2011/12 floods.

Parks Victoria has designed the new dam specifically to retain the popular walking track across the dam wall and over a series of culverts to be placed in the new, larger, primary spillway. During the works the Goldfields Walking Track will be diverted around the construction site to protect contractor and visitor safety.

Plan view (PDF)

Q2) What will happen to the fish in the lake?

Parks Victoria met with a professional fisherman, DEPI Fisheries and the Farmers Arms Hotel Angling Club on this topic in late April. Due to the large population of pest fish, including Carp, currently living in the Lake, Parks Victoria is required to prevent these fish from escaping into downstream waterways. A professional fisherman has been engaged by Parks Victoria to help remove and manage the fish. Parks Victoria and the local angling club are also working with DEPI Fisheries to restock the lake when water returns.

Q3) Will local people still be able to swim, fish, walk and have a picnic at the lake after the works are complete?

Yes, all of these recreational activities will again be available after the works are complete. The works to upgrade the dam wall will secure the lake’s future as a key destination for walking, swimming and enjoying nature in Creswick. Locals will be able to undertake their favourite recreation activities at the lake again once the project is complete. In recognition of the site’s recreational use, we have kept the walk way over the new dam structure so that people can continue to enjoy the loop walk and links to the Creswick township.

Q4) When will the works finish?

The successful contractor was appointed in May and took possession of the area in late May when they commenced works.  The project is due for completion during Autumn 2015. 

Q5) How long will it take for the lake to re-fill after the construction works are complete?

We are not sure how long it will take for the lake to re-fill as it will depend on rain and inflow rates after the works are complete. However, Parks Victoria can draw on experience after the drought broke in 2010 and the lake was able to re-fill quickly over a 4 – 6 week period with consistent rain.

Q6): What will Parks Victoria do to protect platypuses living in the local area?

Parks Victoria engaged Atlas Ecology to undertake a wildlife survey in January 2014. The survey was unable to find evidence of platypuses living in the lake. However, Parks Victoria understands that local people believe that platypuses are living in the area and as a result has engaged a zoologist to inspect the banks of the lake daily during the lake’s draining to rescue any protected animals found in the area. Parks Victoria also sought advice from the Platypus Conservancy about the natural migrating practices of platypuses during low water levels. The anticipated behaviours of any platypuses present during the lake being drained are to seek out local creeks which are better habitat and food foraging locations. 

Why is Parks Victoria re-building the dam wall?

In late 2010 severe storms resulted in water levels creeping dangerously close to the crest of the dam wall. This close call reinforced the need for the 100 year old structure to gain an urgent upgrade.

Water cascading through spillways
Torrents of water cascading through the primary and secondary spillways during the 2010 storm. 

Parks Victoria worked with emergency services to sand bag the crest of the dam wall as a temporary protection against the risk of the water over topping the dam wall.

Sandbagged wall

Water engineers have advised Parks Victoria that the historic dam was only designed to withstand a 1 in 350 year storm risk. This is well below the current national guidelines for large dams which requires a dam wall to withstand a 1 in 100,000 year storm event. 
 
In October 2011, Parks Victoria completed a $250,000 project to raise the height of the dam wall to reduce the risk of water over topping the dam in future heavy storm events.  The interim works provided a water proof gabion rock wall height extension to the dam wall which, when complete, could withstand a 1 in 10,000 year storm event. 

Interim works completed
 
Since the interim works Parks Victoria has been working with expert dam engineers to find a long term solution for the dam at St Georges Lake. The design of the new dam wall and its spillways will reduce the volume of water held by the lake, therefore improving safety during high rainfall and flood events.

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