Development of a Continuous Bathymetric/Topographic Unstructured Coastal Flooding Model to Study Sea Level Rise in North Carolina

Abstract

A model to examine the impacts of long term sea level rise (SLR) is being implemented in the coastal North Carolina ecosystem. This area is particularly vulnerable to SLR, as a fragile system of barrier islands protects an extensive but sensitive estuarine system. The primary impact of SLR is to the hydrodynamic response of the system: circulation, tidal amplitude, and inundation patterns due to tides, winds, and storms can all change in response to rising sea level. Rates of SLR in the region are just under 3 mm/year and are increasing, and inundation is tied to inlet conveyance which can be modified by SLR. A Coastal Flooding Model (CFM) has been developed for the region by combining a finite element hydrodynamic model with a continuous bathymetric and topographic elevation dataset. The CFM domain extends from 90 km offshore of the Outer Banks to the 15 m topographic contour and from northern Currituck Sound south to the New River. The CFM provides high resolution of coastal features down to 20 m. High resolution topographic elevation data relative to the North American Vertical Datum of 1988 (NAVD 88) was combined with bathymetric sounding data relative to local tidal datums by transforming the tidal datums to NAVD 88 with the VDatum vertical transformation tool developed by the National Oceanic and Atmospheric Administration’s (NOAA) National Ocean Service (NOS). The VDatum tool allows for transformation among nearly 30 different tidal, orthometric, and ellipsoidal vertical datums. A 6 m horizontal resolution continuous bathymetric/topographic (bathy/topo) Digital Elevation Model (DEM) was constructed for accurate modeling of inundation. The CFM is relative to the NAVD 88 vertical datum and was populated with DEM elevations where available and other topographic and bathymetric data relative to NAVD 88 elsewhere to create a continuous bathy/topo elevation field. A two-dimensional barotropic model is used to simulate the tidal response in the CFM to study changes due to SLR and will also be used to model regional synoptic wind events and hurricane storm surge propagation with SLR. Accurate National Oceanic and Atmospheric Administration, National Ocean Service, Coast Survey Development Laboratory, Marine Modeling and Analysis Programs, N/CS13, 1315 EastWest Highway, Silver Spring, Maryland 20910; phone (301)-713-2809 2 NOAA/NOS/Coast Survey Development Laboratory 3 NOAA/NOS/National Geodetic Survey, Remote Sensing Division 4 NOAA/NOS/Center for Operational Oceanographic Products and Services