Geologists Quantify, Characterize Sediment Carried by 2011 Mississippi Flood (VIDEO)

The spring 2011 flood of the Mississippi was one of the largest floods in history, with the river swelling over its banks and wreaking destruction in the surrounding areas.

A University of Pennsylvania-led study showed that the floods reaped environmental benefits of transporting and laying down new sediment in portions of the Delta that may actually help maintain the area's wetlands.

The most current study published in Geology examines how much sediment was laid down in the river basins affected by the flood and where the sediments deposited the most.

 "The marshes may be able to maintain their surface area or height above sea level if they receive significant sediment, either from floods or hurricanes or normal fluvial processes," Nicole Khan said, a Ph.D. student of the Department of Earth and Environmental Science. "Ours is the only empirical study to obtain an estimate of how much sediment is deposited by a large-scale flood on the Mississippi."

Comparing measurements from the cores to records of sediment accumulation collected at nearby Coastal Reference Monitoring System sites, the researchers calculated how deposition from the 2011 flood compared to the average yearly sediment deposition. Across the four basins, the flood-carried sediment alone accounted for more than half-a-year's sediment accumulation. In the Atchafalaya Basin, however, the figure was more striking: The flood accounted for 85 percent, or nearly a year's worth of sediment accumulation.

 "The flood sediments had a different color and a looser consistency than the older sediments," Khan said. "The recent sediments also lacked plant roots, because plants hadn't had time to colonize and put roots in the deposits since the flood."

The researchers then further examined the sediment and its biological properties, including sampling for identifiers such as diatoms, or photosynthetic algae, contained in different layers of the sediment. They discovered that the flood sediments had higher ratios of centric or round diatoms. This is a useful indicator if geologists want to further examine deeper sediments for evidence of floods that occur years or even centuries ago.

Researchers are hoping their discoveries concerning the sediment deposition and flood indicator will motivate future research according to Penn University.

Want to see a video of the Missouri River Flood? Check out this video by the U.S. Geological Survey.