This project was part of the Gawler Water Re-use Scheme (GWRS), a key step in a program to unlock new sources of water in the Barossa Valley. McMahon Services worked closely with Bunyip Water and HydroPlan to facilitate and complete the works.
The GWRS has emanated from the creation of a large borrow pit adjacent the Gawler River, excavated to source fill material for the construction of the Northern Expressway. The pit provided a significant opportunity to harvest urban stormwater runoff from the Gawler River catchment when flows are above the environmental threshold (616L/s), and store it in the new and existing dams in the Barossa region, and the nearby Kangaroo Flatt underground aquifer for subsequent reuse in Summer.
It will be piped to a holding dam from where it will be the foundation customers use for urban irrigation in Hewett and vineyards in Western Barossa. Infrastructure to be constructed as part of this scheme included:
- Gawler River flow gauging station;
- Gawler River harvesting pump station;
- 430ML Wingate storage basin and supply pump station;
- Piped supply network, including three booster pump stations;
- Managed aquifer recharge trial site with one bore;
- Treatment plant for urban water re-use;
- Control storage tanks.
McMahon Services were engaged by Bunyip Water Pty Ltd to undertake the civil works for two pump stations and associated pipework, roads, fences, culverts and conduits.
The project scope included:
- Site establishment, dilapidation survey and preliminaries;
- Clearing of trees and vegetation, stripping and stockpiling topsoil;
- Demolishing and disposing of existing stormwater infrastructure;
- Cutting and filling 600mm clay layer and overburden to channel fill location behind pump station number one;
- Laying and compacting 300mm topsoil;
- Swales and drains;
- Rubble Roadways;
- Pump Station number one civil works;
- Pump Station number two civil works and connecting below ground pipework and valves;
- Stormwater pipework and headwalls;
- Underground high-voltage and low voltage electrical conduits and pits;
- Underground communications conduits and pits;
- Rubber liner;
- Gabion Wall;
- Reno mattresses and rock lining;
- Irrigation system;
- Perimeter fence and gates, signage;
- G4 W-Beam Barrier;
- Trenching in an existing 32mm polly water service;
- Winning clay material from messenger land, hauling and placing in the basin.
Due to the depth of the pipe risers, the valve assembly was fabricated prior to installation within the chamber. A complex steel frame was fabricated to ensure verticality upon lifting and placement. Furthermore, potential displacement during filling was checked upon completion and compaction of each layer of fill.
The inlet pit cover design was also changed to allow for a single sheet of fiber-reinforced plastic to be slid on and off the top of the lid and held down with four bolts. This option ended up being much lighter and easier to remove than the original heavier design that called for an aluminium cover raised in 4 x 4m sections.
A significant sustainability initiative for the region, the dam will substitute at least 800ML/annum of River Murray water used in the Barossa, with stormwater harvested on the vineyards. HydroPlan irrigation design engineers have enhanced the water security by connecting to treated wastewater from Bolivar, and providing for managed aquifer recharge expansion to include stormwater anticipated from the Roseworthy Township Expansion.