Mapping Wetland Hydrological Connectivity in the Wax Lake Delta Using Rapid Repeat SAR Images

Abstract:

Coastal deltas are young geomorphic landforms that build and retain or lose land through a fragile balance of organic and inorganic sediment deposition, accretion and erosion, all mediated by the local hydrology. Today most deltas are highly engineered, affecting the natural balance and threatening their sustainability. Understanding the processes controlling sediment transport is key to re-establishing land building in these areas. Maps of the hydrological connectivity and channel networks, including the smaller channels that are often only visible in high water conditions or at high tide, are needed to support realistic hydrodynamic models. However, it can be difficult to access wetland environments, and challenging to survey and install instrumentation that enable the study of the hydrological connectivity in detail. In this work, we present a remote sensing alternative to study these systems based on interferometric SAR. We take advantage of the high-resolution and rapid repeat pass of the images acquired by the Uninhabited Aerial Vehicle Synthetic Aperture Radar (UAVSAR) to map the hydrological connectivity within islands of the Wax Lake Delta, Louisiana, and nearby coastal wetlands, and to see how the network changes during the tidal cycle. The data used consist of 12 L-band SAR images acquired on October 16-17, 2016. The images were taken approximately 30 minutes apart on each day, with one day corresponding to a 3-hour period around low-tide and the other to a 3-hour period during rising-to-high tide. Two time series were generated using the SAR acquisitions: 1) the amplitude information, and 2) a consecutive stack of interferometric coherence formed from the temporal nearest neighbor pairs (30-minute separation). For the latter, statistical measures were calculated. The two stacks and the statistical measures were combined to separate out areas with no water-level change, the channel networks and open water or submerged areas. Results from the analysis reveal the network of channels within the wetlands and their changes as the tide propagates through them. The methodology used and the results will be presented.

This work was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.