Author(s): Carlos Ocampo, Carolyn Oldham
Linked Author(s): Carlos Ocampo
Keywords: Stormwater treatment, bioretention basin, hydrologic performance, groundwater interactions, water quality.
Abstract: Bioretention basins, at-source control structural elements for stormflow control and water quality improvement, have become common Best Management Practices in Water Sensitive Urban Design for stormwater management. New urbanization in Perth, Western Australia (WA) occurs in areas prone to perched groundwater capable of intersecting bioretention systems during the rainy season and its impact on the hydrologic performance and nutrient removal capacity of structural elements is unknown. This work presents results of an intensive monitoring program aimed to assess the hydrologic performances of a 0. 35 m depth - 370 m3 capacity bioretention basin affected by high groundwater. Continuous records of hydrometric and passive tracer (electrical conductivity) data at inflow, surface water storage, and outflow stations were collected for a year in 2015 to quantify the water balance and to identify the timing of the groundwater intrusion and its effect on the hydrologic performance of the bioretention basin. Results from hydrometric and the passive tracer data indicated that groundwater interactions impacted the performance for a period of 50 days from mid-August to late-September affecting volume control and to a less extend peak flow reduction. The bioretention basin achieved outflow/inflow volumetric ratio (%) of 17% and 44% for small and minor rain events in absence of groundwater interactions but increased to 73% (27% reduction) when groundwater intercepted the underdrain outflow pipes. Hydrologic performance for peak flow reduction was achieved at 98% for small events and 74% and 79% for minor events with and without groundwater interactions, respectively. A transition stage in the bioretention basin functioning was identified from the interplay of inflow peaks, groundwater dynamics and water losses (exfiltration). The study showed and concluded on the need to properly identify groundwater interactions and their implications on nutrient loading and removal assessment that are often neglected
Year: 2017