Analyzing Suspended Sediment Concentration, Ash Free Dry Weight, and Particle Size Distribution to Understand the Sediment Transport Dynamics in Southeastern Minnesota Streams for the August 19, 2007 Flood Event

As a warm front stalled over the bluffs of southeastern Minnesota, 254 mm to 432 mm of rain fell overnight on August 18th and 19th, 2007. The relief and topography of the blufflands of southeastern Minnesota make the region susceptible to flash flooding with as little as 38 mm of precipitation within a 6 hour period. The August storm system produced rain at rates up to 25 to 50 mm per hour. Several streams rose to all-time record discharges. Water samples for suspended sediment concentration (SSC) was collected from several sites on August 19, 2007, throughout one of the watersheds affected by this event. In addition to the SSC analyses, ash free dry weight was also determined. These data along with particle size distribution analyses using a laser particle counter provides a better understanding of sediment transport dynamics during this flood event. Comparing the data with samples collected during baseflow conditions helps to better characterize how much extra sediment and biological material was transported during this extreme event. This understanding provides insight to watershed management, TMDL development efforts, and land use planning decisions in the region.