Paired catchment storm event monitoring: Assessing the performance of a bioretention system (rain garden)

Abstract

Treating urban runoff at its source offers to protect receiving waters by modifying flow characteristics and improving water quality. This paper presents the findings for a paired catchment storm event monitoring program undertaken at a residential development, the Lynbrook Estate, Victoria, Australia. The monitoring program compares catchment runoff characteristics between a landscaped bioretention system and a conventional concrete pipe system located in adjacent urbanised subcatchments. Results indicate that the extent to which bioretention systems function as hydrological buffers depends on their design attributes, in-situ geology, antecedent moisture conditions at inflow and storm magnitude. Reductions in total runoff volume, duration and peak flows discharged from the bioretention system compared to the piped system were observed. Small, frequently-occurring runoff events are completely retained by the system. Pollutant loads are reduced by a combination of catchment runoff retention and physical and/or chemical treatment processes, with the former being the dominant process for nutrients and the latter being dominant for suspended solids. Analysis of pollutant load reduction for the 10 events showed gross pollutant load was reduced by 100%, suspended sediment by 68%, total phosphorus by 60% and total nitrogen by 57%.