SA – Intrusive Dam Safety Investigations at Mount Bold Dam

Author:  Kurt Wiebe of Water Plan Consulting, for SA Water.

Before dewatering

Before dewatering

Mount Bold Dam on the Onkaparinga River creates Adelaide’s main water supply reservoir.  Assessment of the dam’s compliance with ANCOLD safety guidelines required the drilling and geotechnical assessment of multiple rock and concrete cores.   Three key drilling locations were located at the toe of the dam, in a 15 megalitre stilling basin, at positions normally submerged under about 5 m of water.  A plan to stop flow from the reservoir was developed and implemented, the spillway basin was dewatered, an access road and drill rig pads were installed, and continuous diamond-core rock samples were collected to depths up to 60 m below the dam foundation.  Plans were developed with the dam owner’s operations control and production planning staff to fill a downstream storage reservoir so that the flow stoppage did not impact capacity to supply water to the city.  The project required coordination with dam operators, environmental approvals, public access closures, and engagement of consultants and contractors.   The works were completed three days ahead of schedule, allowing SA Water (the dam owner) to restore normal supply procedures and minimise risk of water quality impacts from suspended sediment from the construction areas.

After dewatering

After dewatering

Inclined drill rig in dew

Inclined drill rig in dewatered basin