Physical response of a back‐barrier estuary to a post‐tropical cyclone

Abstract

This paper presents a modeling investigation of the hydrodynamic and sediment transport response of Chincoteague Bay (VA/MD, USA) to Hurricane Sandy using the Coupled Ocean‐Atmosphere‐Wave‐Sediment‐Transport (COAWST) modeling system. Several simulation scenarios with different combinations of remote and local forces were conducted to identify the dominant physical processes. While 80% of the water level increase in the bay was due to coastal sea level at the peak of the storm, a rich spatial and temporal variability in water surface slope was induced by local winds and waves. Local wind increased vertical mixing, horizontal exchanges, and flushing through the inlets. Remote waves (swell) enhanced southward flow through wave setup gradients between the inlets, and increased locally generated wave heights. Locally generated waves had a negligible effect on water level but reduced the residual flow up to 70% due to enhanced apparent roughness and breaking‐induced forces. Locally generated waves dominated bed shear stress and sediment resuspension in the bay. Sediment transport patterns mirrored the interior coastline shape and generated deposition on inundated areas. The bay served as a source of fine sediment to the inner shelf, and the ocean‐facing barrier island accumulated sand from landward‐directed overwash. Despite the intensity of the storm forcing, the bathymetric changes in the bay were on the order of centimeters. This work demonstrates the spectrum of responses to storm forcing, and highlights the importance of local and remote processes on back‐barrier estuarine function.

Effects of Locally Generated Wind Waves on the Momentum Budget and Subtidal Exchange in a Coastal Plain Estuary

“…The role of waves on drag can be important in systems such as Delaware Bay because of the broad spatial distribution of the wave height and age. The Delaware differs from other coastal systems such as back‐barrier estuaries, tidal inlets, and coral reefs (see, e.g., Beudin et al, ; Olabarrieta et al, , ; Rogers et al, ; Uchiyama et al, ) in that that waves are mainly local and wind‐generated instead of remote (Chen et al, ) and in that the bathymetric distribution is the result of both natural and anthropogenic processes. The latter leads to distinct patterns in the wave‐driven momentum budget.…”

“…The energy transfer from the wind to the wave field is calculated following Cavaleri and Malanotte-Rizzoli (1981) and Komen et al (1984). Energy dissipation by whitecapping, bottom friction, and depth-limited breaking is computed with the parameterizations by Komen et al (1984), Madsen et al (1988), and Battjes and Janssen (1978), respectively. Within the COAWST framework, ROMS incorporates output data from SWAN and employs a vortex force formalism to compute the wave effects on currents as implemented by Kumar et al (2012).…”

“…According to the bore model by Battjes and Janssen (1978) used in this study, the fraction of depth-limited breaking waves is set to zero on grid points where β ≤ 0.2. Values of β in Delaware Bay during the simulated storms range from 0.05 in the channel and 0.15 on shallow flats, which explains the highly localized spatial distribution of the breaking term.…”

A Numerical Study of Tropical Cyclone‐Induced Sediment Dynamics on the Australian North West Shelf

“…To our knowledge, this is the first study applying a process‐based numerical model (the ROMS‐based COAWST model here) to simulate in detail the long‐term (decadal) influence of TCs on sediment dynamics of a shelf. Process‐based hydrodynamic‐sediment transport models are usually deployed and validated over short time periods focusing on the responses to particular TC activity (Beudin et al, ; Miles et al, ; Palinkas et al, ; Warner et al, ; Xu et al, ). In this study we used an extensive 2‐year‐long in situ data set that captured two TCs with large impact and two TCs with lower impact in order to support our model deployment.…”

“…In general, for TC regions worldwide, in situ observations of the spatial variability of sediment dynamics in response to extreme TCs at the regional scale remain challenging to capture. Therefore, numerical modeling studies have been carried out in recent years to provide deeper insight (Beudin et al, ; Miles et al, ; Palinkas et al, ; Warner et al, ; Xu et al, ). Nevertheless, these modeling efforts have primarily focused on the short‐term response of marine systems to specific TCs and not thus the integrated effect of a number of TCs on the cumulative shelf sediment dynamics.…”