Landward migration of inner bars

Sunamura, Tsuguo; Takeda, Ichirou

doi:10.1016/0025-3227(84)90144-0

Cited by 52 publications

(6 citation statements)

References 9 publications

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“…However, recent work by Kroon & Masselink (2002) shows that onshore bar‐migration results mainly from surf‐zone processes and that swash processes play a secondary role. The Waterside bars may then be considered intertidal bars that are akin to sub‐tidal, inner surf‐zone bars (Sunamura & Takeda, 1984; Kroon & Masselink, 2002).…”

Section: Resultsmentioning

confidence: 99%

Sedimentology and stratigraphy of a transgressive, muddy gravel beach: Waterside Beach, Bay of Fundy, Canada

2006

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Sediments exposed at low tide on the transgressive, hypertidal (>6 m tidal range) Waterside Beach, New Brunswick, Canada permit the scrutiny of sedimentary structures and textures that develop at water depths equivalent to the upper and lower shoreface. Waterside Beach sediments are grouped into eleven sedimentologically distinct deposits that represent three depositional environments: (1) sandy foreshore and shoreface; (2) tidal-creek braid-plain and delta; and, (3) wave-formed gravel and sand bars, and associated deposits. The sandy foreshore and shoreface depositional environment encompasses the backshore; moderately dipping beachface; and a shallowly seaward-dipping terrace of sandy middle and lower intertidal, and muddy sub-tidal sediments. Intertidal sediments reworked and deposited by tidal creeks comprise the tidal-creek braid plain and delta. Wave-formed sand and gravel bars and associated deposits include: sediment sourced from low-amplitude, unstable sand bars; gravel deposited from large (up to 5AE5 m high, 800 m long), landward-migrating gravel bars; and zones of mud deposition developed on the landward side of the gravel bars. The relationship between the gravel bars and mud deposits, and between mud-laden sea water and beach gravels provides mechanisms for the deposition of mud beds, and muddy clast-and matrix-supported conglomerates in ancient conglomeratic successions. Idealized sections are presented as analogues for ancient conglomerates deposited in transgressive systems. Where tidal creeks do not influence sedimentation on the beach, the preserved sequence consists of a gravel lag overlain by increasingly finer-grained shoreface sediments. Conversely, where tidal creeks debouch onto the beach, erosion of the underlying salt marsh results in deposition of a thicker, more complex beach succession. The thickness of this package is controlled by tidal range, sedimentation rate, and rate of transgression. The tidal-creek influenced succession comprises repeated sequences of: a thin mud bed overlain by muddy conglomerate, sandy conglomerate, a coarse lag, and capped by trough cross-bedded sand and gravel.

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Section: Resultsmentioning

confidence: 99%

Sedimentology and stratigraphy of a transgressive, muddy gravel beach: Waterside Beach, Bay of Fundy, Canada

2006

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“…However, emphasis has been placed upon correlating large-scale morphological behaviour with incident wave character-istics (e.g., Sunamura and Takeda, 1984;Wright and Short, 1984;Wright et al, 1987) and infragravity wave characteristics (especially edge waves --e.g., Chappell and Wright, 1979;Sallenger and Holman, 1987;Bauer and Greenwood, 1990). To date, few studies have examined the near-bed velocity field and the direct response of the local sediment-water interface.…”

Section: Introductionmentioning

confidence: 99%

Equilibrium slopes and cross-shore velocity asymmetries in a storm-dominated, barred nearshore system

Greenwood

Osborne

1991

Marine Geology

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Greenwood, B. and Osborne, P.D., 1991. Equilibrium slopes and cross-shore velocity asymmetries in a storm-dominated, barred nearshore system. Mar. Geol., 96:211-235.The near-bed (0.10 m elevation), horizontal velocities were measured across a two-barred, lacustrine shoreface during a storm and reveal a spatially coherent but temporally variable pattern in the low-order moments of the velocity field. Large cross-shore velocity asymmetries indicated:( 1 ) Spatially extensive and temporally persistent offshore mean flows (up to 0.18 m s-1 across the landward slope of the linear outer bar) reflecting an undertow driven by a wave-induced setup.(2) An onshore directed skewness opposing the mean flow, of wind wave origin and persistent under propagating bores in the inner bar system long after this asymmetry had disappeared from the outer bar.Extensive sediment reactivation with near-zero net sediment flux over the whole of the upper shoreface indicated a sediment prism in a steady state (volumetrically) over the storm cycle. Uniform depths of sediment reactivation with zero bed elevation change over the storm cycle revealed local slopes in a steady state in the outer linear bar. However, time integration of the nearbed velocity field at this location indicated an offshore net flux of water, while sedimentary structures indicated bedform migration (and thus at least bedload) almost uniformly onshore when ripples and megaripples were present. The sediment transport giving rise to the local equilibrium cannot be explained therefore on the basis of the mean properties of the near-bed velocity vector, but requires knowledge of the time-varying, instantaneous sediment transport vector.Onshore migration of the inner bar correlated well with the large and persistent onshore skewness of the velocity distribution in the inner surf zone associated with translatory surf bores throughout the storm decay period. Low-frequency oscillations were only significant close to the shoreline, but may have influenced the development of a sinuous three-dimensional inner bar form as it migrated onshore.

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“…Migration is net offshore directed because offshore migration during storms is faster than onshore migration in between storms (Sunamura & Takeda, 1984). Therefore, bars move a little farther offshore in winter than onshore in summer, which results in net offshore migration (see Van Enckevort & Ruessink, 2003a).…”

Section: Storm Responsementioning

confidence: 99%

The effect of repeated sand nourishments on long-term nearshore evolution: a case study for Noordwijk aan Zee, the Netherlands

Vermeer¹,

Ruessink²,

Price³

2021

Preprint

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Sand nourishments are carried out along numerous sandy coasts worldwide to counteract coastal erosion, with the sand added to the inter- and supratidal beach or to the subtidal nearshore profile. Since the early 1990s beach and shoreface nourishments have been carried out along the Dutch coast, with a total nourished volume of 10 to 15 Mm3/year. Although we have a reasonable understanding of how an individual nourishment temporarily affects the evolution of nearshore morphology, it is not clear how repeated nourishments influence the long-term dynamics of the nearshore zone. This understanding is crucial, not only for the safety of beachgoers or marine life, but especially in view of the expected increase in the number of nourishments and total nourishment volume given expected accelerating sea-level rise in the decades to come.This contribution aims to analyse how repeated nourishments affect the long-term evolution of the shoreline and the two subtidal sandbars at the Dutch beach town Noordwijk aan Zee using Argus video imagery available since 1995. Between 1998 and 2014 four shoreface and three beach nourishments were carried out at the study site. The low-tide time-exposure images of the Argus station were used to determine&#160; sandbar and shoreline position along a 6-km stretch of coast. The results show that prior to the first nourishment the sandbars migrated seaward slowly but persistently. The repeated nourishments permanently decreased this seaward directed migration rate of the sandbars to only a few m/year. The sandbars showed alternating periods of seasonal to multi-year onshore and offshore migration superimposed on this very weak decadal offshore trend. Furthermore, the various sand nourishments gave rise to forked shoreline-sandbar morphology. This large-scale alongshore variability was undone within 1 &#8211; 2 years by switches, in which the landward part of a sandbar or the shoreline on one side of the fork realigned with the seaward part of a bar on the other side. These switches appear to be a direct consequence of the repeated nourishments. For example, the 2013-2014 sequence of a beach and a shoreface nourishment resulted in 4 bar switches within the subsequent 2 years, compared to a total of 12 switches in the total dataset of 24.8 years. Further analysis will focus on the effect of repeated nourishments on the temporal and spatial persistence of rip-channel morphology and on the wave conditions that caused the forked morphology to switch.

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Landward migration of inner bars

Cited by 52 publications

References 9 publications

Sedimentology and stratigraphy of a transgressive, muddy gravel beach: Waterside Beach, Bay of Fundy, Canada

Sedimentology and stratigraphy of a transgressive, muddy gravel beach: Waterside Beach, Bay of Fundy, Canada

Equilibrium slopes and cross-shore velocity asymmetries in a storm-dominated, barred nearshore system

The effect of repeated sand nourishments on long-term nearshore evolution: a case study for Noordwijk aan Zee, the Netherlands

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