Cross-shore currents in the surf zone: rips or undertow
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Cross-shore currents in the surf zone : rips or undertow. / Aagaard, Troels; Vinther, Niels.
I: Journal of Coastal Research, Bind 24, 2008, s. 561-570.Publikation: Bidrag til tidsskrift › Tidsskriftartikel › Forskning › fagfællebedømt
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TY - JOUR
T1 - Cross-shore currents in the surf zone
T2 - rips or undertow
AU - Aagaard, Troels
AU - Vinther, Niels
PY - 2008
Y1 - 2008
N2 - While the dynamics and kinematics of various types of mean cross-shore current flows in the surf zone (undertow and rip currents) are fairly well understood, the causes for transitions occurring between these two types of mean circulation patterns remain obscure. On longshore barred beaches, such transitions involve the formation and/or degeneration of rip channels. In this paper, field evidence is presented to suggest that transitions between undertow and rip current (cell) circulations may depend upon the magnitude of the wave-induced onshore mass transport across a longshore bar, rip channel spacing and trough cross-sectional area. The results are based on data obtained from four field experiments on the Danish and Dutch North Sea coasts, which encompassed a range of incident wave energy conditions. Two of the data sets demonstrate transitions between cell and undertow circulations. Calculated onshore-directed mass transports in the two circulation types were plotted against At/yr, where At is trough cross-sectional area and yr is longshore distance from the measurement position to a rip channel. The two types of circulation are separated in parameter space by a straight line with a slope of 1 (ms-1). The observations support the model proposed by DEIGAARD et al. (1999), according to which optimum rip spacings exist that depend on the balance between onshore discharge and longshore pressure gradients caused by irregular bar bathymetry. This simple morphodynamic model indicates that both hydrodynamic conditions and existing bathymetry are critical in determining the type of mean current circulation.
AB - While the dynamics and kinematics of various types of mean cross-shore current flows in the surf zone (undertow and rip currents) are fairly well understood, the causes for transitions occurring between these two types of mean circulation patterns remain obscure. On longshore barred beaches, such transitions involve the formation and/or degeneration of rip channels. In this paper, field evidence is presented to suggest that transitions between undertow and rip current (cell) circulations may depend upon the magnitude of the wave-induced onshore mass transport across a longshore bar, rip channel spacing and trough cross-sectional area. The results are based on data obtained from four field experiments on the Danish and Dutch North Sea coasts, which encompassed a range of incident wave energy conditions. Two of the data sets demonstrate transitions between cell and undertow circulations. Calculated onshore-directed mass transports in the two circulation types were plotted against At/yr, where At is trough cross-sectional area and yr is longshore distance from the measurement position to a rip channel. The two types of circulation are separated in parameter space by a straight line with a slope of 1 (ms-1). The observations support the model proposed by DEIGAARD et al. (1999), according to which optimum rip spacings exist that depend on the balance between onshore discharge and longshore pressure gradients caused by irregular bar bathymetry. This simple morphodynamic model indicates that both hydrodynamic conditions and existing bathymetry are critical in determining the type of mean current circulation.
KW - Faculty of Science
KW - Skallingen
KW - Cell circulation
KW - Egmond
KW - Skallingen
KW - beach processes
KW - beach morphodynamics
KW - mean currents
U2 - 10.2112/04-357
DO - 10.2112/04-357
M3 - Journal article
VL - 24
SP - 561
EP - 570
JO - Journal of Coastal Research
JF - Journal of Coastal Research
SN - 0749-0208
ER -
ID: 8804259