OH, THAT SINKING FEELING: OBSERVATIONS OF LANDSCAPE CHANGE IN THE MISSISSIPPI RIVER DELTA

As sea levels rise, many low-lying coastal areas are undergoing profound alteration. In this regard, the Mississippi River delta is emblematic of most of the world’s major coastal deltas, where the combination of sea-level rise and land subsidence – the sum is called relative sea level rise (RSLR) – is causing rapid changes to the landscape through subsidence, inundation and land loss. Natural landscape evolution, in which subsidence is offset by sediment and biomass accretion, no longer holds due to sediment starvation and a host of other anthropogenic activities that challenge land sustainability. Although wetland loss is particularly high, land sustainability issues arise in all settings, be they natural, agricultural, urban, or industrial. In many parts of the delta the rate of elevation change from subsidence outstrips the rate of sea water level change. In fact, subsidence is often highest in developed areas, where groundwater extraction can drive high rates of subsidence that are not offset by natural recharge. In this presentation, we discuss the results of a series of studies of the Mississippi River delta, ongoing since 2009, that make use of NASA’s UAVSAR synthetic aperture radar to determine the status of and changes to wetlands and urbanized and industrial areas of southeastern Louisiana. We investigate subsidence and land loss, and relate the observations to proximate cause given the local land use. Examples include observation of ground movement before and after formation of the Bayou Corne sinkhole; measurement of subsidence in and around the city of New Orleans; and quantifying wetland loss in the years following the Deepwater Horizon oil spill. Besides documenting detrimental impact, radar remote sensing can be used to study land gain and to evaluate remediation methods. The most recent studies with UAVSAR use rapid repeat imaging to investigate, at the time scale of a tidal cycle, the exchange of surface water between the Gulf and coastal wetlands at the Wax Lake Delta. This is one of the few areas where land is being gained naturally along the Louisiana coast. Because sediment, nutrients, and carbon are transported by water, knowledge of redistribution and settling of sediment is important for evaluating whether net soil accretion can occur in a given area.