The Time-Lapse Delta: Quantifying Landscape Change on a Prograding Delta Top
Résumé
Coastal wetland systems provide a number of ecological and economic benefits to society; however, they are among the most dynamic landscapes on Earth’s surface. In many areas of the world, these systems are disappearing as managers scramble to understand how healthy systems function and change. Using airborne lidar taken at Louisiana’s prograding Wax Lake Delta, we measure vertical landscape change on the subaerial delta top between 2009 and 2013, quantifying volumetric changes to the delta, sub-aerial slope adjustment, and an ‘equilibrium’ elevation. Total volumetric change to the sub-aerial delta over this 4 year period was 46% of volumetric gains made over an overlapping 4-year period to the sub-aqueous delta front. Vertical accretion on the delta was largest on the down-stream regions on the delta, where levees grew by widening through time. The slope of the sub-aerial delta adjusted from -8.2 cm/km to -5.8 cm/km. At the higher up-delta regions, some areas gained elevation while other areas lost it. At the ‘equilibrium’ elevation of 0.683 m NAVD88, change was zero, on average. We calculate an ‘equilibrium timescale’ of 15.7 years to describe how long locations within the delta will take to approach the equilibrium elevation under forcing evident from 2009 to 2013.