Flood recession and salt mobilisation from the Murray floodplains – phase 2 report

Flood recession salt mobilisation has been a significant concern of the Basin Salinity Management Strategy partners for many years. The salinity impact of changes to river operations are simulated using the MDBA's daily flow and salinity model: BigMod. The Basin Plan is expected to affect river flows (and hence salinity) during regulated conditions. It is also expected to have significant impacts on the magnitude and timing of flooding and hence flood related salt mobilisation. BigMod simulates salt loads and salinity from known hydrological and hydrogeological processes. The model calibration process results in a quantity of salt entering the river in each model reach that cannot be explained by known processes, this is termed unassigned ("unaccounted") salt loads. Unaccounted salt loads in the model have been generated by an analysis of historical river salinity data and is re-input to the model as a monthly time-series from 1970 onwards. The unaccounted salt loads are not dependent on flow, that is, they are unable to change with changes to the flow regime. This presents a limitation to the assessment of salinity impacts of actions, including aspects of the Basin Plan that have significant dependence on the magnitude and timing of flooding.

Author: Murrihy, E and Evans, R