Detailed Bathymetry of Selected Areas of the Inner continental Shelf of the Virginian Sea: Southeastern Virginia, Virginia Beach, and Wachapreague, Virginia

The increased need for information involving the physical processes affecting the inner continental shelf has led to these detailed compilations of the nearshore bathymetric data of the Virginian coastline. For example, the growth of population has increased the usage of our beaches for recreation. Contrived short-term and the apparent long-term shortages of fuel, so recently impressed upon the public, have initiated an intensive study of the adjacent continental shelf area for possible future sites of offshore drilling rigs, power plants and port facilities. Among the basic oceanographic information required in all such studies is detailed depth information. To help meet these needs we have prepared these detailed bathymetric maps containing significantly more information than has previously been compiled and made available from this region of the Atlantic shelf

Natural and Human-Induced Variability in Barrier-Island Response to Sea Level Rise

Storm-driven sediment fluxes onto and behind barrier islands help coastal barrier systems keep pace with sea level rise (SLR). Understanding what controls cross-shore sediment flux magnitudes is critical for making accurate forecasts of barrier response to increased SLR rates. Here, using an existing morphodynamic model for barrier island evolution, observations are used to constrain model parameters and explore potential variability in future barrier behavior. Using modeled drowning outcomes as a proxy for vulnerability to SLR, 0%, 28%, and 100% of the barrier is vulnerable to SLR rates of 4, 7, and 10 mm/yr, respectively. When only overwash fluxes are increased in the model, drowning vulnerability increases for the same rates of SLR, suggesting that future increases in storminess may increase island vulnerability particularly where sediment resources are limited. Developed sites are more vulnerable to SLR, indicating that anthropogenic changes to overwash fluxes and estuary depths could profoundly affect future barrier response to SLR

Setup and swash on a natural beach

Wave setup and swash statistics were calculated from 154 runup time series steep beach under incident waves varying from 0.4 to 4.0 m significant wave height. incident wave height, setup, swash height, and total runup (the sum of setup and were found to vary linearly with the surf zone similarity parameter ξ₀ = β(H₀/L₀)¯½ slope appeared the appropriate value for the calculation of ξ₀, although the setup influence of an offshore bar at low tide. For low Irribaren numbers the swash frequency band becomes saturated, while for high Irribaren numbers, no such seen. Thus the infragravity band appears to become dominant in the swash below these data, that value is approximately 1.75, although there is considerable scatter associated with that estimate

Deriving high spatial-resolution coastal topography from sub-meter satellite stereo imagery

High spatial resolution coastal Digital Elevation Models (DEMs) are crucial to assess coastal vulnerability and hazards such as beach erosion, sedimentation, or inundation due to storm surges and sea level rise. This paper explores the possibility to use high spatial-resolution Pleiades (pixel size = 0.7 m) stereoscopic satellite imagery to retrieve a DEM on sandy coastline. A 40-km coastal stretch in the Southwest of France was selected as a pilot-site to compare topographic measurements obtained from Pleiades satellite imagery, Real Time Kinematic GPS (RTK-GPS) and airborne Light Detection and Ranging System (LiDAR). The derived 2-m Pleiades DEM shows an overall good agreement with concurrent methods (RTK-GPS and LiDAR; correlation coefficient of 0.9), with a vertical Root Mean Squared Error (RMS error) that ranges from 0.35 to 0.48 m, after absolute coregistration to the LiDAR dataset. The largest errors (RMS error > 0.5 m) occurred in the steep dune faces, particularly at shadowed areas. This work shows that DEMs derived from sub-meter satellite imagery capture local morphological features (e.g., berm or dune shape) on a sandy beach, over a large spatial domain.French Space Agency (CNES) CNES through the TOSCA program FCT IF/00661/2014/CP1234 FEDER, within the PT2020 Partnership Agreement FEDER, within the Compete 2020 UID/AMB/50017/2019info:eu-repo/semantics/publishedVersio

3-D Morphological Change Analysis of a Beach with Seagrass Berm Using a Terrestrial Laser Scanner

Along many Mediterranean coasts, the detached seagrass material of Posidonia oceanica creates seagrass berms that control the structure and morphodynamics of sandy beaches. Here, we show how Terrestrial Laser Scanner remote sensing data allows analyzing the 3-D morphologic change of beaches where this characteristic geomorphic structure is present. We propose a methodology for estimating accretion/erosion (almost −200 m3 in our study) by considering the sand dominated and seagrass berms as two independent elements. For this purpose, two different sampling dates (named scenarios A and B, before and after an erosive heavy storms period, respectively) recorded in a microtidal pocket-beach (300 m2) with these characteristic geomorphic structures have been modeled in 3-D. The present approach constitutes a cost-efficient, accurate, and quick tool to survey the sand volume in natural and artificial replenished beaches. The innovative approach, which can be considered as a conceptual and methodological starting point, can be useful to examine long-term and high-precision data sets in future studies of the morphodynamic evolution of these characteristic Mediterranean beaches

Wave energy saturation on a natural beach of variable slope

Time series of flow were measured across the inner surf zone during a storm. These data were used to quantify the dependence of wave height (transformed from measured flow) and velocity on local slope and depth. Similar to previous studies, as incident waves broke and propagated into the surf zone, wave energy became saturated, and wave height was strongly dependent on depth. However, the ratio of rms wave height to local depth (Yrms) was found not to be constant but to vary between 0.29 and 0.55; Yrms increased with local slope and was independent of deepwater wave steepness. Thus the surf zone similarity parameter (the ratio of slope to the square root of steepness) did not adequately parameterize Yrms

Infragravity waves over a natural barred profile

Measurements of cross-shore flow were made across the surf zone during a storm as a nearshore bar became better developed and migrated offshore. Measured infragravity band spectra were compared to synthetic spectra calculated numerically over the natural barred profile assuming a white run-up spectrum of leaky mode or high-mode edge waves. As in earlier studies, the spectra compared closely; however, for some frequencies the energy of the measured spectrum exceeded the energy of the synthetic spectrum, suggesting that the run-up spectrum was not white but had dominating frequencies. Utilizing cross-shore flow data and synthetic spectra from a number of cross-shore locations, an equivalent run-up spectrum was calculated for each day. On the first day of the storm, the equivalent run-up spectrum indicated a dominant wave that had a node in velocity reasonably close to the bar crest. Later during the storm, when the bar had migrated farther offshore, there was no evidence for a dominant motion having a velocity node at the bar crest. The structure of the equivalent run-up spectrum compared well with spectra of direct measurements of run-up obtained several hundred meters away. We have no clear evidence in support of the theory that infragravity waves might form or force the offshore migration of a bar. To confirm this finding, longer records obtained synoptically over a developing bar are required. The dominant wave observed early in the storm was consistent with Symond and Bowen’s (1984) theoretical prediction of resonant amplification of discrete frequencies over a barred profile