The NSW Reconnecting River Country Program aims to improve environmental outcomes through raising flow limits so larger environmental flows can be delivered to connect rivers with wetlands and low-lying floodplains in the Murray and Murrumbidgee systems. With increased flow levels there are many predicted ecological benefits, but there is also potential risk of undesirable outcomes.
To assess potential risks, we canvassed the primary issues perceived by various stakeholders and procured assessments of the risk posed by raised flow limits. In some cases, mitigation options for potential hazards were identified and evaluated. Risk assessments were undertaken for the environmental themes of geomorphology, water quality, and invasive species. Largely, the assessments showed that raised flow limits are unlikely to increase the frequency of negative environmental outcomes, and thus the risk of environmental issues is not increased relative to a base case ‘current flow limits’ future.
Acceleration of bank erosion has, so far, been of highest concern to landholders. A geomorphological risk assessment showed low to medium risk in both catchments, with upper reaches of the rivers typically having medium risk. Implementation of identified mitigation measures, however, reduced this risk to low. Changes to the area of suitable habitat for invasive weeds were examined and, to a small degree, suitable habitat for amphibious species decreased and terrestrial species increased under raised flow limits. This yielded small net-decreases in risk. Eight water quality issues were considered, with three mechanistically linked to the proposed flow changes (hypoxic blackwater, blue-green algal blooms, and salinity). The study found no increased risk of adverse water quality events under raised flow limits compared to base case. The potential to bring forward the timing of some high flow events from the warmer months to cooler months with raised flow limits presents a potential net-benefit for water quality issues.