Understanding Solids Loading in Minnesota Stormwater

This poster will explore coarse solids loading of urban raingardens in relation to storm events, canopy cover of the watersheds, and street sweeping. The poster will present coarse solids data collected from raingardens in the Twin Cities, MN, from April to December 2021. Figures included in the poster will show mass accumulation over time and organic content of solids samples. A portion of the poster will be dedicated to settling rates of coarse solids as measured in a lab setting and application to stormwater management.

Full Presentation Abstract
This research project aims to understand and represent the role of solid organic components, or gross solids, in stormwater pollutants. These gross solids are often missed by traditional sampling techniques and are likely not well represented when evaluating stormwater quality and stormwater treatment practice design. A relation between canopy cover, watershed area, and loading rate of a raingarden would be useful in planning cleanouts and maintenance.


We have collected gross solids at the inlet of 13 rain gardens in Saint Paul, Shoreview, and Minneapolis, MN from April to December 2021. These measurements will be used to determine annual stormwater loadings of nutrients and organic matter associated with coarse solid fractions in relation to tree canopy cover, complementing the much larger set of information available for the fine fractions of stormwater that are represented in standard stormwater monitoring programs. Sample collection used nylon mesh bags adapted to the specific inlet structure. Street sweeping activity and tree phenology were monitored around each site.


This project also explores settling velocity of solids samples. While the relationship between particles size and settling velocity is well understood, it requires many assumptions to the particle shape which may not always be accurate for stormwater sediments. This lab work is scheduled for December 2021 - January 2022