Natural resource managers are constantly trying to achieve the greatest environmental and social benefit with a limited budget. Seqwater, the bulk drinking water supply authority for southeast QLD, makes significant and ongoing investment in catchments to protect drinking water quality. However, combining qualitative and quantitative data, research outcomes and on-ground knowledge to support planning decisions is a challenge. The aim of this work was to create a Decision Support System that provides a standard quantitative method to identify and prioritise catchment-based risks to water quality, and prioritise interventions to reduce these risks.
The Catchment Investment Decision Support System (CIDSS) is a spatial optimisation tool that combines numerical and spatial catchment data across 40+ catchments to derive risks to raw water quality received at 39 water treatment plants (WTP). Water quality risk is determined from sediment and microbial hazards, generated by nine catchment processes and landuse activities, and scaled relative to distance and the WTP treatment capability. The CIDSS then considers 50+ potential on-ground interventions and uses simulated annealing to optimise their implementation, based on most efficient reduction in risk for a given investment amount. As an example, in the Pine Valley catchment, running $1.1M, $3.3M, $6M and $10M investment scenarios focused on sediment reduction shows a 13%, 34%, 54% and 74% reduction in sediment loads transported to the WTP. The CIDSS outputs show how cost and volume of interventions vary across different investment scenarios. In the $6M and $10M investment scenarios, extensive basic riparian and landslide fencing and revegetation were the optimal interventions, while short lengths of complex engineering riparian work and revegetation were more beneficial in the $1.1M and $3.3M scenarios. Therefore, the CIDSS can create abatement curves and identify intervention location and type, that ultimately provides a standard quantitative process for catchment investment.