A document by Karen An. Click on the document to view its contents.

In response to a growing number of natural and anthropogenic threats, the long-term sustainability of coastal river deltas and wetlands has come into question worldwide. Tools such as remote sensing and numerical modeling have been implemented in an effort to monitor and predict the hydro-geomorphological evolution of our coasts. Hydrological connectivity is known to play an important role in deltaic evolution by delivering flow, sediment, and nutrients to the interior of deltaic islands/wetlands. However, estimating connectivity typically requires detailed field work or numerical modeling, which is difficult to implement over broad spatial and temporal scales. In the present work, we investigate the potential of using remote sensing to estimate hydrological connectivity in the Wax Lake Delta (WLD) and Atchafalaya Delta region of the Louisiana coast. During a three-hour window, five difference maps of water level in the WLD and surrounding wetlands were collected using UAVSAR L-band radar in repeat-pass interferometric mode. We then modeled the WLD subsection of the domain using a 2D shallow-water hydrodynamic model configured to run on the same discharge, tide, and wind conditions as recorded at nearby monitoring stations during the observational window, with vegetation parameterized as a source of additional drag in the deltaic islands. Modeling allowed us to determine the relative influence of tides, vegetation, and wind on WLD water levels, which could then be extrapolated to infer the behavior throughout the rest of the domain. Over the observational window, UAVSAR measured a cumulative loss of over 22 megatons of water from non-channelized wetlands as tides fell. We find that the model tends to under-predict the observed water level draw-down, as well as the degree of hydrological activity in proximal islands that we observe in the UAVSAR data. Models that neglect the influence of wind underestimate the volume of water leaving the islands by up to two-thirds, suggesting the importance of wind on deltaic hydrodynamics during the observational window. With the information gained from the numerical modeling, as well as the computation of information theory statistics, we extend the WLD results to analyze and quantify the water level behavior in the surrounding wetlands and Atchafalaya delta.

Aging flood infrastructure systems will need to be closely monitored as metropolitan areas globally face increasing inundation risk from sea level rise. To augment traditional ground survey, synthetic aperture radar (SAR) is shown to efficiently quantify elevation change along earthen levees with continuous spatial coverage. The study area, California’s Sacramento-San Joaquin Delta, has an exemplar earthen levee system that protects the region from flooding. We investigate evidence of settling from historic levee breaks and small-scale subsidence features with a vertical velocity map and time-series of cumulative displacement derived from data acquired by the UAVSAR (Uninhabited Aerial Vehicle Synthetic Aperture Radar) L-band SAR, during 2009-2015. Comparison between radar and lidar maps (2007 and 2017) show that typical laser elevation surveys can miss subsidence features in the presence of normal maintenance activities. Historic levee break sites show more stable conditions due to the nature of repairs, and can be monitored using the SAR time series product. SAR information helps monitor the efficacy of repairs and targeted improvements to decrease the risk of levee breaks. In light of the upcoming NASA-ISRO SAR satellite mission, for which UAVSAR is the prototype, detailed monitoring will be attainable for levees worldwide.