Estimating the Size Distribution of Suspended Sediments in Minnesota Stormwater

Project summary:

The objectives of this research were to improve the technology used in collecting representative samples of the suspended sediment in stormwater runoff and to develop a methodology to determine the suspended sediment size distribution in stormwater runoff across the state of Minnesota.

Portable automatic field samplers have been found to overestimate concentrations of suspended sediment larger than 88 micrometers (coarse silts and sands) using existing methods. Samplers configured with intake manifolds were also found to substantially oversample coarse silts and sands.

This research improves the performance of automatic water samplers for sampling coarse silts and sands. A sampling intake was developed that extracts samples from multiple locations in the cross-section. The new sampling intake increases the range of sediment size where sampling accuracy is within +/- 10% to sand particles less than an equivalent diameter of 250 micrometers. The sampling intake also performs with a predicted bias at larger sediment sizes. The new intake thus demonstrates improved sampling accuracy and precision.

The results of this study will be incorporated into the Stormwater BMP Assessment Protocol.