Predicting recreational water quality and public health safety in urban estuaries using Bayesian Networks

To support the reactivation of urban rivers and estuaries for bathing while ensuring public safety, it is critical to have access to real-time information on microbial water quality and associated health risks. Predictive modelling can provide this information, though challenges concerning the optimal size of training data, model transferability, and communication of uncertainty still need attention. Further, urban estuaries undergo distinctive hydrological variations requiring tailored modelling approaches. This study assessed the use of Bayesian Networks (BNs) for the prediction of enterococci exceedances and extrapolation of health risks at planned bathing sites in an urban estuary in Sydney, Australia. The transferability of network structures between sites was assessed. Models were validated using a novel application of the k-fold walk-forward validation procedure and further tested using independent compliance and event-based sampling datasets. Learning curves indicated the model's sensitivity reached a minimum performance threshold of 0.8 once training data included ≥ 400 observations. It was demonstrated that Semi-Naïve BN structures can be transferred while maintaining stable predictive performance. In all sites, salinity and solar exposure had the greatest influence on Posterior Probability Distributions (PPDs), when combined with antecedent rainfall. The BNs provided a novel and transparent framework to quantify and visualise enterococci, stormwater impact, health risks, and associated uncertainty under varying environmental conditions. This study has advanced the application of BNs in predicting recreational water quality and providing decision support in urban estuarine settings, proposed for bathing, where uncertainty is high.

The planning and construction of an urban stormwater management scheme

Water Sensitive Urban Design (WSUD) offers a means to integrate stormwater best management practices into urban planning and design to achieve multiple objectives. Some of these objectives relate to stormwater drainage, water quality improvements, aquatic habitat protection, stormwater harvesting and use, and landscape amenity. The Lynbrook Estate, Australia, has incorporated bio-filtration systems and wetlands into the design of major roads, local access streets and parklands that attenuate and treat roof runoff and road runoff from a 32 ha, 270 allotment residential precinct. This paper outlines the process that enabled the concept of a stormwater drainage design to be translated into on-ground works. Details of the construction activities, costs and market acceptance highlight the potential for the adoption of similar practices elsewhere.