Evaluation of Snow Management using Green Infrastructure in Subarctic Climate

<p>In subarctic regions, a significant part of annual precipitation occurs as snow. This creates challenges since (a) the occurrence of rain on snow during melting season might increase runoff peak flow and cause flooding in urban areas and (b) snow needs to be removed from roofs and streets. Current snow management practice includes removal of snow to large deposits outside of cities. Downsides of this approach are the carbon footprint and air pollution caused by transport and the release of untreated polluted melt water to nearby water bodies. One strategy to reduce transport and increase treatment of meltwater could be to integrate snow deposits with existing green infrastructure that manages stormwater within the urban environment, i.e. multifunctional areas.</p><p>When studying the potential performance of multifunctional areas with respect to snow management it is important to consider the flood risk that comes with increased snowmelt and rain on snow. Prior studies have evaluated the combined effect of frozen soils, snowmelt and rainfall during the melting season on runoff from urban catchments, but there are no similar studies on facility scale. Hydrological models can be used to investigate these factors and the snow deposit potential, without risking flooding. It is, however, unclear to what extent current urban hydrological models are suited to this purpose. This study aims to explore how hydrological models can be used to predict snow deposition volumes in multifunctional areas and the effect on runoff.</p><p>This study used EPA SWMM because it is a commonly used urban hydrological model with a relatively advanced snow management module. The modelled facility was a grassed swale in Luleå, Northern Sweden, receiving runoff from a 60 <em>ha</em> catchment with commercial and light industrial land use.  The swale was separated into 6 identical parts to test different scenarios for the amount and distribution of snow deposited in the swale. The long-term performance of the swale with regard to stormwater quantity was investigated with historical rain and temperature data<em>.</em> Runoff from the catchment to the swales was calibrated based on observed data from late spring 2021.</p><p>Hydrological models as a support tool for snow management using green infrastructure shows promising results. Using the model, it was possible to evaluate the effect of snow volume and placement within the swale. Such information can be of great use when designing green infrastructure and snow management strategies. However, SWMM has some limitations in this regard. For example, pollutants such as sediments (gravel, sand and micro plastics) affect the properties and melting behavior of urban snow and the release of pollutants, yet these factors are not represented in SWMM. Differences in the actual melt rate will affect the total volume of snow that can be deposited in the swale, hence this topic requires further research.</p>