The McArthur River is the largest surface water river in the region with a catchment area of approximately 20,000 km2.
MRM is situated adjacent to the McArthur River, in the middle reaches of the river's catchment and nearby to several intermittent streams including Surprise Creek and Barney Creek.
The main ore body at McArthur River Mine once sat directly beneath the McArthur River and Barney Creek. To access the ore, our open pit development required 5.5 km of the McArthur River and 2.5 km of Barney Creek to be rechannelled. The new channels were completed in 2008.
Stream flows throughout the creek and river changes depending on the time of year. During the dry season, the McArthur River is a slow-flowing catchment, but highly variable due to monsoonal rainfall and cyclones in the wet season. Most years it overflows the channel which can be up to 21 m deep, and regularly inundates the flood plain up to 5 m deep. Water level rises of up to 7 m over a 24-hour period are not uncommon.
The new channels were planned to a great level of detail to ensure they:
- remain stable for all flood events and throughout the mine life and beyond
- will not be subject to higher than natural levels of erosion and sedimentation
- enable the river to continue to flood in parts naturally into the plain without affecting the mine facilities
- re-establish the river vegetation so there is no fragmentation of fauna habitats
- allow fish to continue to naturally pass through the channels.
The channel design for both the McArthur River and Barney Creek copies the natural environmental conditions where possible. The main differences are in the use of bedrock and artificial rock riffles in some locations on the river bed to help prevent eroded sediment flowing downstream.
Riffles are 'U' shaped rocky structures which mimic the existing bedrock outcrops, reducing the speed of water flow, and in doing so, help revegetation along the channel banks. These rock riffles are similar to already naturally-occurring rock bars and will not disrupt fish passage.
The planting of trees, shrubs and grasses along the banks of the McArthur River has been accelerated over the past two years with more than 80,000 tubestock planted in 2017 and 100,000 in 2018. We continue to increase our efforts in this regard, with our on-site nursery undergoing further expansion in late 2018 to allow for additional tuibestock to be propogated from local seeds