Interactions between the Ebb-Tidal Delta and Landward Shoreline: Price Inlet, South Carolina

Abstract

Patterns of erosion and deposition along the shoreline of Price Inlet, South Carolina, are strongly influenced by ebb-tidal delta processes. The ebb delta goes through cycles of growth and decay (15-20% change in volume) which last from 4 to 7 years. In the growth phase, large intertidal bar complexes are formed on both sides of the main ebb channel by the coalescence of landward-migrating swash bars. During this stage, waves refracting around the southern bar complex produce a reversal in the longshore-transport direction on the downdrifl shoreline. This results in little sediment escaping the inlet and delta system. The sand-trapping mechanism ceases and the delta reduces in volume when the bar complexes migrate onshore and attach to the beach.The inlet shoreline also goes through cycles of 7-to 42-years duration in which its offset configuration changes. The shift in shoreline alignment is controlled by the orientation of the main ebb channel and the resulting ebb-tidal delta morphology. When the inlet has a downdrifl, offset configuration, the ebbtidal delta is skewed along the updrift shoreline. In this position bar complexes preferentially accrete along the ulxlrifl beach causing a progradation of the shoreline. At the same time, the downdrift shoreline erodes due to little sediment bypassing the inlet. This pattern of sedimentation eventually produces an updrift, offset inlet. The erosional-depositional processes are reversed when the ebb flow in the channel thalweg is deflected off the prograding updrift, inlet shoreline. This causes a clockwise rotation of the main ebb channel and a shift in the ebb delta to a position along the downdfift shoreline. In this configuration the updrift shoreline erodes and the downdrift shoreline aecretes. This study documents the close relationship that exists at Price Inlet, South Carolina, between the ebb-tidal delta and landward shoreline. Evidence is presented to show that this relationship may hold for other mixedenergy tidal inlets as well.

Insights into barrier-island stability derived from transgressive/regressive state changes of Parramore Island, Virginia

“…A common, though as yet unproven, hypothesis for the causal mechanism for the rapid erosion/migration of the northern VBI (the "Arc of Erosion": Assawoman, Metompkin, and Cedar islands) is the accumulation of sediment at the recurved spit of Assateague Island ("Fishing Point") (Leatherman et al, 1982;Richardson, 2012;Fenster and McBride, 2015;Fenster et al, 2016). Similar barrier-island shoreline changes are observed in response to variations in sediment supply associated with the tidal-inlet channel and bar dynamics (FitzGerald 1984(FitzGerald , 1988Elias and Van der Spek, 2006;Fallon et al, 2015), sediment trapping at updrift spits (Park and Wells, 2007), and sediment trapping and bypassing of coastal re-entrants and estuaries (Anthony, 1995).…”

“…1, 6). Such inlets often control proximal shoreline behavior (erosion vs. accretion) along barrier islands, largely because of associated wave-and tide-driven inlet-sediment-bypassing and bar-welding processes (FitzGerald, 1984;FitzGerald et al 1984;Fenster and Dolan, 1996). Given the slow long-term growth rate of northern Parramore (1300 m in ~1000 years), it is likely that most sediment delivered to northern-most Parramore through processes associated with Wachapreague Inlet continued to be reworked alongshore to the south, aiding in two major phases of overall island progradation.…”

Sediment Connectivity: A Framework for Analyzing Coastal Sediment Transport Pathways

“…For example, it may bypass the inlet via bar migration on an outer (ebb-tidal) delta (Elias et al, 2019;FitzGerald, 1982;Gaudiano & Kana, 2001;Sexton & Hayes, 1982) or recirculate at the mouth (Herrling & Winter, 2018;Hicks et al, 1999;Smith & FitzGerald, 1994;Son et al, 2011). The net import or export of sediment through the inlet system and changes to the ebb-tidal delta can have a profound influence on the morphological evolution of the adjacent coastline (Elias & Van Der Spek, 2006;FitzGerald, 1984;Hansen et al, 2013;Ranasinghe et al, 2012;Warrick et al, 2019).…”

The formation and morphodynamics of complex multi‐hooked spits and the contribution of swash bars

“…These factors result in a large range of spit sizes (width, length) and tip shapes. Finally, cross‐shore sediment transport associated with swash‐bar welding has been shown to play a significant role in the formation of recurved or hooked spits (FitzGerald, 1984; Gaudiano & Kana, 2001; Kana et al, 1999; Robin & Levoy, 2007; Robin et al, 2009b, 2020). Finally, Hiep et al (2021) showed a significant relationship between a sand spit and a sand terrace in the reconstruction of a recurved sand spit following a tsunami.…”