Morphological and sedimentological response of a mixed-energy barrier island tidal inlet to storm and fair-weather conditions

Abstract

Abstract. The environment of ebb-tidal deltas between barrier island systems is characterized by a complex morphology with ebb-and flood-dominated channels, shoals and swash bars connecting the ebb-tidal delta platform to the adjacent island. These morphological features reveal characteristic surface sediment grain-size distributions and are subject to a continuous adaptation to the prevailing hydrodynamic forces. The mixed-energy tidal inlet Otzumer Balje between the East Frisian barrier islands of Langeoog and Spiekeroog in the southern North Sea has been chosen here as a model study area for the identification of relevant hydrodynamic drivers of morphology and sedimentology. We compare the effect of high-energy, wave-dominated storm conditions to mid-term, tide-dominated fair-weather conditions on tidal inlet morphology and sedimentology with a processbased numerical model. A multi-fractional approach with five grain-size fractions between 150 and 450 µm allows for the simulation of corresponding surface sediment grain-size distributions. Net sediment fluxes for distinct conditions are identified: during storm conditions, bed load sediment transport is generally onshore directed on the shallower ebb-tidal delta shoals, whereas fine-grained suspended sediment bypasses the tidal inlet by wave-driven currents. During fair weather the sediment transport mainly focuses on the inlet throat and the marginal flood channels. We show how the observed sediment grain-size distribution and the morphological response at mixed-energy tidal inlets are the result of both wave-dominated less frequent storm conditions and mid-term, tide-dominant fair-weather conditions.

Storm Impact on Morphological Evolution of a Sandy Inlet

“…Journal of Geophysical Research: Oceans energy-dominated nearshore environments (Herrling & Winter, 2014;Kaji et al, 2014;Walstra et al, 2013; and many others). The effect of episodic events on mixed wave-and-current energy systems is less well known, although recent studies at the Sand Engine in the Netherlands suggest that storm energy has a similar relationship to sediment transport in the presence of relatively weak tidal currents (<1 m/s) (Luijendijk et al, 2017) when wave-driven currents in the nearshore approach 1 m/s (Radermacher et al, 2017).…”

“…Changes in nearshore bathymetry are pronounced during storms, when high-energy waves, wave-driven flows, and storm surge can alter the shoreface of a beach in just days or even hours (Herrling & Winter, 2014;Lindemer et al, 2010;Miller, 1999;and many others). On decadal time scales, long-term observations of changes in shallow bathymetry along barrier islands in the Gulf of Mexico (Morton et al, 1995;Wahl & Plant, 2015) and the East Coast of the United States (Hapke et al, 2016;Moore et al, 2013) suggest that storm events correlate with the evolution of the coastline, with sea level rise becoming more important on time scales of centuries (Ruggiero et al, 2010).…”

Tidally- and wind-driven residual circulation at the multiple-inlet system East Frisian Wadden Sea

“…The natural evolution of tidal basin systems is driven by the interaction of tidal, wind and wave forcing and the morphological Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/csr development of different units in the system: the ebb-tidal delta, the tidal inlet throat and the channel networks and tidal flats in the basin (Herrling and Winter, 2014;Kösters and Winter, 2014;De Swart and Zimmerman, 2009;Winter, 2011). On the other hand, human interferences to the morphological system, e.g.…”

Field observations and numerical model simulations of a migrating inlet system

“…Alongshore sediment transport can be scaled roughly with the wave energy incident on a shoreline, and thus episodic, high-wave events such as hurricanes shape the morphological evolution of wave-energy dominated nearshore environments [Walstra et al, 2013;Herrling and Winter, 2014;Kaji et al, 2014]. The effect of episodic events on mixed wave-and-current energy systems is less well known, although recent studies at the Sand Engine in the Netherlands suggest storm energy has a similar relationship to sediment transport in the presence of tidal currents < 1 m/s when wave-driven currents in the nearshore approach 1 m/s [Radermacher et al, 2017].…”

“…Changes in shoreline position are especially pronounced during storms, when high energy waves and storm surge can alter the shoreface of a beach in just days or even hours ( [Miller, 1999;Lindemer et al, 2010;Herrling and Winter, 2014]; and many others). On decadal timescales, long term observations of shoreline changes along barrier islands in the Gulf of Mexico [Morton et al, 1995;Wahl and Plant, 2015] and the Outer Banks of the Carolinas [Moore et al, 2013] suggest that storm events (both waves and storm surge) correlate with the evolution of the coastline, with sea-level rise becoming more important on timescales of centuries.…”