Estimating Hydrological Connectivity in Coastal Wetlands using UAVSAR
and Numerical Modeling
Abstract
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.