Medium‐term bar behavior and associated sediment transport at Hasaki, Japan

Abstract

[1] The medium-term movement of a longshore bar and the associated cross-shore sediment transport were investigated using beach profile data obtained nearly daily for 8 years from the seaward foot of a dune to a water depth of about 5 m at Hazaki Oceanographical Research Station (HORS). Bar crests were found to move seaward repeatedly with a period of a year. The duration time of the seaward bar migration is shorter than those on the other coasts in the United States, the Netherlands, and New Zealand. Although bars migrated in one direction, seaward, the cross-shore sediment transport rate associated with the bar migrations fluctuated seaward and shoreward. Seaward sediment transport occurred on and around bar crests, whereas shoreward sediment transport occurred in trough regions. The cross-shore sediment transport was active when the offshore wave energy was large, from winter to spring and in autumn. However, the direction of the sediment transport in a region where bars were most developed was different during the two periods; it was seaward from winter to spring and shoreward in autumn. A numerical model for beach profile change confirmed that the development and decay of a bar was caused by the spatial and temporal variations of the cross-shore sediment transport rate.INDEX TERMS: 1824 Hydrology: Geomorphology (1625); 3020 Marine Geology and Geophysics: Littoral processes; 4546 Oceanography: Physical: Nearshore processes; 4558 Oceanography: Physical: Sediment transport; KEYWORDS: longshore bar, beach profile response, cross-shore sediment transport, empirical orthogonal eigenfunction analysis, numerical model, morphodynamics Citation: Kuriyama, Y., Medium-term bar behavior and associated sediment transport at Hasaki, Japan,

Dynamics of single-barred embayed beaches

“…For instance, the long sandy beaches with one or two sandbars at Duck, USA, and Hasaki, Japan, have been described by Kuriyama (2002) and Sallenger et al (1985), respectively. Examples of long sandy beaches with multiple bars are Terschelling, the Netherlands (Ruessink and Kroon, 1994), Wanganui, New Zealand (Shand et al, 1999), the Ebro Delta, Spain (Guillén and Palanques, 1993) and the beach barrier of Thau Lagoon, France (Barusseau et al, 1994).…”

“…This interannual behaviour involves: 1) the generation of the bar near the shore (at approximately 1 to 2 m depth); 2) onshore and offshore migration of the bars according to wave conditions but with a net offshore migration through the surf zone; and 3) bar decay at the seaward margin of the nearshore, prompting the formation of a new bar near the shoreline (starting the process at 1). There is a wide inter-site variation in the duration of this cycle, from Marine Geology 280 (2011) 76-90 1 year at Hasaki in Japan (Kuriyama, 2002) to more than 10 years in Poland (Rozynski, 2003) or the Netherlands (Ruessink and Kroon, 1994;Wijnberg and Terwindt, 1995). Ruessink et al (2009) distinguished between interannual NOM (an approximately uniform migration associated to sea-dominated coasts) and episodic NOM (steered by storm events in swell-dominated coasts).…”

Numerical predictability experiments of cross‐shore sandbar migration

“…[6] The cross-shore bed profiles we used to initialize and verify the model predictions are an approximately 1.5 year long data set of daily profiles collected between January 1987 and July 1988 along the pier of the Hazaki Oceanographical Research Station at Hasaki Beach, Kashima Coast, Japan [Kuriyama, 2002] (Figure 1a). We interpolated the available bed profiles to a regular cross-shore grid with 5 m spacing using a scale-controlled linear smoother [Plant et al, 2002] to remove measurement errors and small bathymetric features unresolved by the observations and the model (e.g., bed ripples).…”

“…[4] Here, we employ a coupled hydrodynamic/sediment transport model [Ruessink et al, 2007] in an ensemble prediction scheme [Hoffman and Kalnay, 1983] using a multi-year data set of daily bed profile surveys [Kuriyama, 2002] to examine the time scales on which our model might reflect reality and to address the question as to whether the unpredictability of cross-shore sandbar migration results from model inadequacy or deterministic chaos. First, we discuss the model, data, and ensemble scheme; next we examine the temporal evolution of ensemble spread and model skill; and finally we consider the implications of the results for surf zone research and modeling.…”

Morphological coupling in multiple sandbar systems – a review

“…Evans, 1940;Saylor and Hands, 1970;Greenwood and DavidsonArnott, 1975;Lippmann et al, 1993;Ruessink and Kroon, 1994;Shand et al, 1999;Almar et al, 2010;Kuriyama, 2002;Ruessink et al, 2003;Wijnberg and Terwindt, 1995, and references therein). Sandbars often have multi-annual lifetimes and can occur as a single feature, or as a multiple bar (most often two, sometimes up to five) system.…”