Lake Hume is a large water storage, located at the junction of the Murray and Mitta Mitta Rivers, upstream of Albury-Wodonga. During the Black Summer Bushfires of 2019-20 over 500,000 ha of land was burnt in the upper Murray River Catchment. We monitored the loads of key constituents from the cessation of the fires in January 2020 until now. In this presentation we compare the loads of total suspended sediments, total dissolved salts, total phosphorus, filterable reactive phosphorus, total nitrogen, NOx, and dissolved organic carbon post-fires with the loads in the two years prior to the fires as well as the historical long-term loads (1978 to 2012).
There have been demonstrable impacts of run-off from the fire fields on water quality in the Murray River (including its tributaries) and Lake Hume. This impacted the operations of Hume Dam and the communities immediately downstream of the dam. A collaborative management approach was coordinated to mitigate these impacts as they manifested.
Approximately 1.35 million tonnes of sediment entered Lake Hume from the upper Murray River catchment since the fires, which is about 15 times higher than the long-term average. The sediment delivery to Lake Hume, especially between 2020 and 2022 (inclusive) is amongst the highest measured in Australia.
There were above average loads of nutrients entering Lake Hume from the Murray River, and this is a possible cause of phytoplankton blooms in the Murray River arm of the Lake in February and March 2020 and, late December 2021 through until mid-2023.
There is evidence that the increased loads of key constituents entering Lake Hume from the Murray River has now abated following the floods in the upper catchment in the second half of 2022.