Sediment MitigationRiver sediment is an ongoing challenge from our mining. Our dredging operation is designed to reduce the amount of sediment in the rivers around our mine.
The discharge of mine waste to the local river system results in increased sediment deposition on the bed of the river.
The resultant heightening of the riverbed over many years has caused an increase in the duration of overbank floodplain inundation.
This flooding resulted in the conversion of parts of the forested floodplain to grassed floodplain in the lower Ok Tedi and the upper reaches of the Middle Fly River system.
Vegetation dieback has also been caused by sand build up in the river channels and during high river flows, over bank deposition of sediments and water floods into the forest in the river’s low-lying floodplains, causing vegetation die-back.
In addition, communities along the river bank have lost some gardens due to overbank flooding and access to forest resources (including Sago) due to dieback.
The extent of forest dieback and changes to grassland is monitored annually and reported to the State in the annual report.
To help control flooding and dieback, OTML has dredged approximately 436 Mt of sand from the river at Bige since 1998.
The dredging operation removes approximately 85% of the sand that reaches the Bige site located in the lower Ok Tedi preventing it from travelling further downstream. Approximately 17 Mt of sand is removed from the river each year and placed in engineered stockpiles on the East and West Banks of the Ok Tedi River.
The dredging operation at Bige will continue to the end of mine life, and this will assist in minimising future physical impacts.
The dredging program has been successful with the bed level of the Lower Ok Tedi dropping since the commencement of dredging and forest dieback declining.