Lunch served for attendees
The seasonal regrowth of vegetation is a primary control on the physical environment in deltaic marshes, driving both the connections with the channel and the transport environment on the marsh. It has often been pointed out that the revegetation event and the spring flood are not synchronized in the same way each year, a fact that lends complexity to our understanding of delta geomorphology, and uncertainty to operation plans for managed marshes.
We used drone-photographed dye injections, hydroacoustic instrumentation, sediment traps, water samples, and monthly vegetation surveys to link the rapidly changing vegetation environment throughout the spring flush with flow and velocity on the marsh, and monthly sediment deposition. Our data was collected in a freshwater marsh in the Mississippi River Delta during the Mississippi River floods of 2018 and 2019. The 2019 flood is notable as a long event that kept water level and incoming flow conditions nearly constant, allowing observations to isolate changes resulting from the vegetation environment.
We use this novel data set to 1) document and explain profound changes in flow conditions and routing during the flood season, and 2) test the hypothesis that stem-generated turbulence is an effective means for predicting sedimentation patterns in field settings. Our initial analysis suggests that velocity thresholds for stem-generated turbulence are exceeded primarily early in the growing season when the vegetation is sparse. During these times the stem-generated turbulence likely increases transport distances, but deposition in the field exceeds theoretical expectations, suggesting that additional sediment-trapping mechanisms are important.
Friday, October 25, 2019 at 11:30am