MARSH COLLAPSE BY POND EXPANSION ON THE MISSISSIPPI RIVER DELTA PLAIN (Invited Presentation)

The Mississippi River Delta is losing land at an astonishing rate of 43 km² per year, and if left unmanaged the delta could collapse and revert to open water. Saving this landscape requires restoration strategies, but success depends on defining and reversing the processes leading to collapse. Here we show that portions of the delta are undergoing collapse by pond expansion from edge erosion. Using Landsat images to examine how ponds on the marsh surface change shape over the last 34 years, we show a striking consistency between pond expansion direction and the dominant wind direction. Wider ponds expand faster because winds create larger waves that erode the edges. For ponds wider than 300 m expansion rate increases rapidly, which is indicative of marsh collapse. Our analysis suggests that two basins on the delta, Terrebonne and Barataria, are undergoing marsh collapse, while the Atchafalaya-Vermillion basin is stable. Future restoration schemes should consider restoring sediment supply to these ponds to halt expansion.