Modeling and monitoring low impact development (LID) practices at Calgary, Alberta

Low Impact Development (LID) that mimics pre-development hydrology and improves stormwater quality captures and treats stormwater runoff at or close to its source to mitigate the negative impacts of discharging stormwater from urban development. The City of Calgary is implementing LID practices as part of its commitment to protect the water quality in its watersheds and provide sustainable stormwater management solutions in cold and arid climate. The practices include bioretention, soil cells, permeable pavement, green roofs, and absorbent landscapes technologies. A program that monitors individual practices has been developed and implemented to better understand how the LID practices function and perform in cold and arid conditions.

A biorentention pilot project was constructed in the summer of 2015 to treat stormwater runoff being generated from 0.2 ha arterial road. The design incorporated a pretreatment sump and a 100 m² lined bioretention area planted with various willows species. It is being continuously monitored for inflow, outflow, ponded water level, growing media moisture levels and rainfall since June 2016.  During the summer season 10 storm events were sampled at the inlet and outlet for a range of water quality parameters.The volume, pollutants load reduction and hydraulic response was quantified for each storm event. The saturated hydraulic conductivity and composition of the growing media was measured. The monitoring results enable evaluation of specific model and design parameters.

A PCSWMM model was used to estimate water balance, water quality and hydraulic response bioretention pilot using a number of different modelling approaches with typical design and calibrated parameters. The model results were compared against the field measured performance and what would normally be applied in a bioretention design approach. The evaluation will help improve modelling and design procedures when using PCSWMM approaches. Monitoring and evaluation of the test area is continuing into the winter and 2017 season to obtain additional information related to nutrients removal and media infiltration.