Particle size distribution (PSD) significantly affects stormwater controls that rely on settling to remove sediment. A new study by researchers with the U.S. Geological Survey Wisconsin Water Science Center demonstrates the importance of knowing PSD for properly sizing these stormwater controls. Published Jan. 6 in the open-access journal Water, “The effect of particle size distribution on the design of urban stormwater control measures,” shows that using a single PSD to represent all hydraulic conditions can result in controls that are ineffective or unnecessarily costly.

Researchers concluded that stormwater controls designed using the Nationwide Urban Runoff Program (NURP) particle size distribution could be unnecessarily oversized. According to the researchers, particle size distribution measured in the field typically is coarser than the NURP standard. Using an urban pollutant loading model, PSD can be predicted based on environmental surrogate data. However, even using a median of measured PSD, does not fully capture the variability of individual storm events.