Building a bioretention area in a cold climate

This paper describes an experimental field work setup for testing the performance of bioretention areas in a cold climate setting at Risvollan urban hydrological station in Trondheim, Norway. Bioretention focuses on water retention, peak flow reduction, and water quality improvement with respect to heavy metals and sediments. However, in colder climates the performance of bioretention areas are to a large extent unknown. The most problematic with winter conditions are the many interchanged snow and rainfall events, creating rain-on-snow events, resulting in ice formation, then melting and often refreezing. This causes blockage of stormwater inlets and elevated risk of flooding. The focus of this paper will be on the hydraulic retention properties of the system. The performance of the bioretention area will be evaluated based on peak runoff reduction and detention capabilities. The results so far indicate promising results with respect to detention capabilities also during typical coastal winter conditions. The outflow from the bioretention area was compared to runoff from an equal size impervious area. The average reduction in peak flow rates compared with impervious surface runoff was 49 %. The actual reduction will vary dependent on pre event