Client name: BHP

Location: Newman, Western Australia

Services provided:

• HECRAS modelling
• 12D modelling
• Engineering management plan
• Update of existing drawings
• Construction drawings

Orebody 35 Diversion Drain -Phases I & II

To limit the ingress of stormwater into the Orebody 35 pit, our client BHP planned to divert the flow path of the Whaleback Creek tributary (also known as Southern Creek), a roughly 15km long river and has a catchment area of 27km². Works were completed in 2 phases:

• Phase 1 diverts 14m² of the upper catchment south into a tributary of the Fortescue River, which then discharges into Ophthalmia Dam, the same discharge location as the original Southern Creek flow path
• Phase 2 diversion will intercept the lower catchment of approximately 13km² downstream of the Phase 1 works. This involved constructing a diversion drain and flood protection bunds to move water out of the existing Southern Creek channel adjacent to the Orebody 35 pit.

Scope of Works

Tetra Tech undertook the complete modelling and design for the works, including:

• • Creek Diversion designed to produce hydraulic behaviour consistent with ranges provided by previous investigations
  • Construction optimised to NWO blasting and earthmoving capabilities
  • Creek Diversion design accommodating existing ROM material
  • Cut-off levees to redirect flow from the existing creek into the diversion channel and back again
  • Flood protection bunds
  • Closure planning of OB35 Creek Diversion to protect the ongoing integrity of the diversion post-closure.

Tetra Tech Proteus has to overcome a number of project challenges including:

• Design for construction of a land bridge across an exhausted mine put, where uncompacted overburden material had been used to partially backfill the pit
• Control of subsidence and piping failure under the diversion channel across the land bridge with the use of a Geosynthetic Clay Liner (GCL).