In cold climate, when bioretention that is primarily designed for small storms encounters large storms, how will the bioretention function? This research aims at finding answer to the question. Bioretention in cold climate experiences freeze-and-thaw cycles, affecting its functions with low temperature. Changing climate pattern leads to increased frequency of large storms (e.g., 1-in-100 year storm re-occurs in few years). We need data on the roles bioretention can play in urban flood mitigation in cold climate.

The laboratory bioretention systems we built have capacity to control temperature from plus 22 to minus 20 degree Celsius and to simulate storms at various intensities. The two media, loam and sandy loam, were primarily designed for 1-in-2 year storms and had previously experienced complete freeze-and-thaw cycle, including annual events in summer-autumn-winter and during spring snowmelt runoff. In this study, the bioretention systems were subject to two events of 1-in-5, 1-in-10, 1-in-25, 1-in-50 and 1-in-100 year Edmonton storms, respectively.

The experimental results demonstrate: (1) The bioretention systems can function to certain degree during large storms. The sandy loam medium maintained hydraulic function without overflow up to 1-in-25 year storms. For the 1-in-100 year storms, at least 50% of inflow filtered through both media, with at least 80% peak reduction. (2) With pre-treatment, both media had at least 90% TSS removal. (3) Repeated large storms reduced Ksat value of the media, affecting negatively on lifetime of bioretention; however, the saturated zone (for nitrogen removal) seemed to be a potential counter-measure to this negative impact.

Functions of Bioretention for Cold Climate in Large Storms

The International Low Impact Development Conference highlights interdisciplinary practice, research, and implementation of Low Impact Development (LID), Green Infrastructure (GI), Sustainable Urban Drainage Systems (SUDS) and Water Sensitive Urban Designs (WSUD). The focus of this conference was on using our past and present understanding of LID to tune management programs, design practice, and operation and maintenance into the future.



NOTE: Due to the COVID-19 pandemic, this conference was held virtually. The proceedings have been published to provide readers access to the information that was presented.

[Paper Proceedings](https://doi.org/10.1061/9780784483114)

Conference DOI: https://doi.org/10.26226/m.6317827c362f600015b4eb73