Seqwater has a long running investment program across source water catchments in Southeast Queensland. The key objective of the program was to mitigate the highest risks to drinking water quality. Herein, a spatial optimisation model was applied to identify portfolios of actions that would achieve highest risk reductions for a given budget. The program was successful in intervening in many high-risk sites but was structurally limited to targeting symptoms of processes and high threat land-use management practice, i.e. reactive to current state.
A new water quality investment strategy for source water catchments is being implemented which considers the investment for maintaining current catchment performance as the first tier and targeting highest risks to improve catchment performance as the second tier of investment. Third tier of investment considers emerging contaminants of concern. Investment to maintain catchment performance targets current and future processes that may directly or indirectly degrade system function, hence water quality. An approach to quantify future state with respect to catchment performance under ‘do nothing’ is presented. The approach applied to Lockyer Creek catchment suggests fine sediment loads could increase by 30% and pathogens by up to 2 LRV over a 30-year horizon. Modelling of Tier 1 investment is shown to offset these future increases.