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Sun Valley Reservoir, snow making dam – Mount Buller

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Sun Valley Reservoir 1,710 mAHD – Mount Buller, Nov-Dec 2014

Case Study: MtBuller Snowmaking Dam leaking approx 1litre per second.

 

Background:

Sun Valley Reservoir was built 20 years ago and the engineered fill side of the dam was lined with 1.5mm HDPE geomembrane. The existing rock face side of the dam was left as is and the liner terminated through the middle of the dam.

Entura- Hydro Tasmania, a specialist power and water engineering firm investigated the reservoir leakage stems from the HDPE liner being only partial and not connected to a watertight foundation.

As the dam is also used for fire fighting season, a completion of the liner could not be realized at that time of year and a watertight trench proposal was accepted.

Sun Valley Reservoir
Sun Valley Reservoir

Mt Buller Dam - Winter

 

Scope of Works:

Entura engaged Geoline to fulfill their resolution of a watertight trench connecting the liner to the rock to stop the leakage. The dams water level was lowered enough to fulfill the scope of works, but still have water for fire fighting.

Geoline mobilized two 20T excavators to the top of MtBuller, 1710m, above sea level that proved to be a mighty feat on its own.

Under the instructions of Entura civil engineers Geoline excavated hundreds of cubic meters of material from the dam wall to the high side of the dam floor.

IMG_1472
Cutting down wall and shaping trench.
Excavating material out.
Excavating material out.

 

 

 

 

 

 

 

 

 

Geoline installed a thick cushion geotextile to the surface of the sub-grade to help protect the HDPE liner. A 1.5mm HDPE liner was then installed over the top of the cushion geotextile and tied into the existing 20-year-old HDPE liner. (Trial weld destructive tests showed no issues with welding 20-year-old plastic exposed to the harshest conditions).

Altitude HDPE Lining
Altitude HDPE Lining

Geoline again installed a cushion geotextile over the HDPE and then placed the excavated fill back into the watertight trench.

Using a pad foot roller we compacted the backfill material in lifts.

Compacting backfill
Compacting backfill

 

 

 

 

Entura and MtBuller happy with project finish.

Finished Project
Finished Project

Project Surprises:

  • Excavator’s diesel fuel filter froze up, even though we were heading into summer. Added alpine fuel additive, worked fine.
  • Prime mover (floating excavator up mountain) started to wheel spin and melt alpine bitumen road at 4pm in the afternoon with a top of 16 degrees.
  • Excavated through two natural springs. Pumps to dewater.
  • One slight batter collapse as batter was 1:1, 7m deep.

 

Project complete Dec 2014.