Tsunami protection, Kelian pit, Indonesia

The tsunami (wave) protection bund at the Kelian Equatorial Mining gold mine, in East Kalimantan, Indonesia was constructed to protect river communities. The project comprised a 1 km long and 15 m high earth and rockfill embankment, along the open-pit crest. The pit was flooded post closure. The bund design was intended to prevent an overtopping tsunami (wave), generated from a pit wall failure, from entering the Kelian River and flooding downstream villages.

PSM was engaged to provide geotechnical studies to assess probability and risk associated with in-pit failures generating over-topping waves in the post-closure flooded pit lake. PSM was also responsible for developing hydrology (flood) studies to assess required embankment heights and providing geotechnical engineering design and development of for-construction drawings of all required works.

The Kelian gold mine is located in a remote region of Borneo, approximately 2 km south of the equator. The area experiences high annual rainfalls of between 3-4 m and challenging terrain. An over-topping tsunami would threaten Kelian River communities. Floodwaters pose a risk to mine closure works to reduce contamination level in onsite and discharged effluent waters.

Engineering and technical opportunities included:

• Post-closure pit flooding to reduce the potential for acid mine generation from exposed pit slopes
• Assessment of the probability and consequences of pit slope failures generating a tsunami in the pit lake
• High equatorial rainfall resulting in an estimated PMF of 3,300 cumecs at velocities > 5 m/s in the steeply incised Kelian River valley.

Following rigorous assessment and modelling, PSM’s tailored approach included:

Conceptualisation of the tsunami problem, assessment of risk and development of proposed strategies
Flood studies to establish required embankment heights and freeboard requirements
Installation of a conduit to drain flood waters from low-lying ground between the embankment and the Kelian River back into the pit using engineered sodium bentonite and gravel material to prevent seepage and possible piping failure around the conduit.

The project fulfilled the dual function of protecting the Kelian River from pit tsunamis and preventing floodwaters from entering the pit and damaging mine closure engineering works. The combination of geotechnical engineering design of an earth and rockfill embankment with hydrological assessments of flood height enabled the mine to continue operating.

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