MWRPP Report 15.6: Constructed stormwater wetlands literature review, MUSIC uncertainty assessment and study of Melbourne Water’s guidelines and procedures.

Melbourne Water, tasked with managing constructed wetlands for urban stormwater treatment, faces challenges in translating theory into effective design, construction, and long-term operation. The substantial investment involved necessitates a scientific approach to ensure performance and prioritise maintenance.A comprehensive study was conducted, including a literature review, modelling study, and comparison of Melbourne Water Guidelines with current research. Key findings emphasise the importance of plants, careful hydraulic design, and shallow water regimes. The study also highlighted the need for replicating natural wetland heterogeneity and managing multiple interacting parameters.Modelling suggests that MUSIC software reasonably predicts long-term performance of well-functioning wetlands. However, the performance of poorly conditioned wetlands remains uncertain.Melbourne Water's guidelines, especially the 2014 revision, address many issues raised in the literature. However, further guidance is needed on defining measurable objectives, managing initial filling and substrate, supporting plant establishment, incorporating hydrological variability, and conducting monitoring.The study recommends monitoring various characteristics to assess wetland performance, including water levels, plant cover, health, distribution, and substrate characteristics. However, quantifiable relationships between these parameters and water quality are lacking in the literature.While constructed wetlands may function beyond a nominal 25-year lifespan, data on long-term performance is scarce. The report identifies a need for research on optimal maintenance, prolonging wetland lifespan, and performance assessment using proxy indicators for water quality.Recommended actions include defining measurable objectives for individual wetlands, providing guidance on water level manipulation, developing a comprehensive monitoring program, investigating the benefits of greater heterogeneity in design, studying key processes within constructed wetlands, and conducting field trials to understand performance changes over time.