There are many reasons why Bunyip Water and the Gawler Water Reuse Scheme has attracted a lot of positive attention. This $22m project harvests stormwater from the Gawler River north of Adelaide and delivers it to urban users in Hewett near Gawler, and rural water users in the western Barossa Valley. HydroPlan were engaged by Bunyip Water as the design engineers and construction managers in March 2015 to help meet stringent Federal Government funding milestones and complete the project by the end of August 2016. HydroPlan will also provide contract Superintendency for 12 months defects liability periods.
In an innovative public-private partnership, a $10.7m grant from the Australian Government, and an $11.3m loan from the Light Regional Council for the capital investment for the infrastructure, with the foundation customer Seppeltsfield Wines providing the bulk of revenue security by entering into long term water supply agreements. They also have options of control over the infrastructure assets after 6 or 10 years by repaying the invested capital. So when the scheme delivers the water it promises everyone wins.
The Barossa is the fifth most renowned wine region in the world but is restricted by limited stormwater, groundwater, recycled wastewater and water imported from the River Murray. This project substitutes 800 ML of Murray water by harvesting up to 1600 ML/a from the Gawler River.
HydroPlan has been fortunate to witness extraordinary leadership by the people involved in creating and steering this project, and copious competence and dedication from the people these leaders choose to work with.
Value for Money
If Seppeltsfield received 1600 ML a year by the time they repay the $22m of capital invested, the "once-off" capital cost of the water would be $13,750 per ML. This is similar to the cost of water from Barossa Infrastructure Limited
(BIL). BIL is currently reliant on the Murray where the equivalent "once-off" market price for water is around $2,000 per ML (the difference is the cost of piping water).
Historically, the lower Gawler River has been dry an average of 3 in 10 years, so an average of only around 1100 ML/a could be practically harvested. Without the flexibility of a water banking license, this made the value for money ($/ML) for the scheme less attractive at 50% more than BIL water. The value for money of an earlier scheme design which was being considered for construction in early in 2015 was largely dependent on aquifer storage to provide water banking in wet years. However, limited water quality data from the Gawler River created risk in investing in the aquifer storage location where approval (if achieved) would be limited to only the freshest flows harvested. The proposed single source "D&C" procurement methodology, deemed required to meet the Federal Government funding program timeframes and foundation customer supply requirements, was well over the project budget and may not have delivered the water to where it was desired.
HydroPlan's alternative scheme design identified the supply risks and led to drastic changes in both the design and delivery process. HydroPlan uses a traditional "Design Then Construct" approach and has proven many times this provides much better overall value for money than D&C (Design And Construct). The work was split into 6 large contracts and almost 100 smaller ones. The Commonwealth and Local government officers required due processes be followed, and that's where good leadership/governance/support made this bearable and possible.
Good design reduces risks and takes time, so it was 6 months before the first and largest contract was awarded for pipelaying. The value for money was excellent so additional pipes were included for Managed Aquifer Recharge (MAR), an "enhancement" that would be completed later if the core project was completed and funds were still available. The contractor (Leed) did a great job to lay 35km
of pipes up to 500mm diameter before Christmas, but there was no water or time to pressure test it.
The dry 2015 winter was followed by an unusually hot summer, and this caused the Foundation Customer to be completely out of its existing water sources by January 6th 2016. Under HydroPlan's direction "Early Water" involved months of planning to bring forward other works and to take over the pipe from the contractor for preliminary operations prior to Practical Completion. This was an emergency response to a dire threat to one of the largest vineyard in the Barossa Valley. Despite bursts, hire pumps and Murphy's extended family, "early" water flowed from the new scheme on January 7th 2016. Then it ran 24x7 (almost) for 2.5 months and saved the bumper crop. This feat involved transferring 8 ML/d from variable water supplies scattered over 8 km feeding into a small 0.25 ML tank, and three diesel pumps in series to lift water 200m uphill through 27 km of DN375 pipe.
Uni students and their Facebook friends were hired by HydroPlan to run the pumps 24x7. An operator was needed at each pump to get them synchronised when starting, and then two operators constantly monitored supplies and manually adjusted rpm to keep them going.
Following approval, HydroPlan added a 2.5 km pipe and connections to the treated wastewater Virginia Pipeline Scheme (VPS) and progressed negotiations to access spare capacity without impacting existing users (a manatory condition of the VPS operator). The recycled water is mostly available in winter but when river water is not available the VPS adds security. VPS water is highly treated and used in glasshouses and broad acre farming in the Virginia triangle for fresh produce, but salinity is on the high side. It has been extensively used and analysed for MAR by CSIRO and SA Water.
Two dams formed critical components of HydroPlan's alternative scheme design. Each dam is very different and fit-for-purpose. Dams are more expensive than MAR but they can take "any water" and they can yield it quickly.
The embankment between the Gawler River and the Northern Expressway (NEXY) borrow pit called Wingate Basin was replaced to create a 430 ML storage below the surrounding flood plain. Additional floodplain modelling took time and money but the results were worthwhile to ensure the project would not increase flood risk. An existing 900mm culvert was converted to the pump intake so water from the River is lifted at 52 ML/d into Wingate Basin. Water can only be pumped out of Wingate Basin to the larger dam storage at 13 ML/d currently, but provisions are made for increasing that three-fold including sending 13 ML/d to MAR.
Wingate Basin will usually be dry so a 5 ML "rubber puddle" at the bottom allows MAR and VPS water to be accumulated and pumped. The 600mm constructed clay liner is covered with 300mm of topsoil, and planted with hardy native varieties that can withstand periods of inundation and drought.
Hill Dam was constructed on Seppeltsfield land, sacrificing 16 ha of partially constructed vineyard. It holds 680 ML where it can feed vineyards by gravity 5km north and 8 km south. Hill Dam has a white HDPE liner over clay.
Both dams were full by 30/10/2016 when the river ceased to flow. Wingate withstood a significant flood event well. Water cascaded over the walls, reversed through the overflow and caused the pumps to flow without electricity.
Managed Aquifer Recharge
As part of water security, HydroPlan arranged equipping one MAR well (constructed prior to HydroPlan's involvement) with a pump and a groundwater license. HydroPlan changed the MAR design to target an aquifer further north where conditions for MAR have since been described by regulators as ideal.
MAR is an enhancement that is essential for water security of the GWRS. Watch this space...