Flow asymmetry associated with astronomical tides: Implications for the residual transport of sediment

Abstract

[1] Tidal current asymmetry is usually associated to nonlinear tidal interactions in shallow water, generating compound tides and overtides. The present paper demonstrates that tidal asymmetry is not only caused by nonlinear tidal interaction, but is also generated by astronomical tides in absence of shallow-water effects. In particular, the K 1 , O 1 , and M 2 constituents give an asymmetrical periodic flow pattern, with the largest peak velocities persistently in the same direction. A theoretical explanation for this phenomenon is presented, and an inventory is made of other, subordinate constituents that may contribute to repetitive asymmetric flow patterns. Tidal current asymmetry may induce residual transport of sediment. Analytical expressions are derived which quantify the residual transport of sediment due to the K 1 , O 1 , and M 2 tides, as a function of the phases and amplitudes of these constituents, and the time lag between variation in suspended sediment transport and flow velocity. The residual transport induced by the K 1 , O 1 , and M 2 tides is compared to the residual transport due to the asymmetry associated with the M 2 and M 4 tides. The former mechanism is particularly relevant in diurnal, or mixed, mainly diurnal tidal regimes, where the K 1 and O 1 tides are dominant. INDEX TERMS: 4235

Export of materials along a tidal river channel that links a coastal lagoon to the adjacent sea

“…Again, the results demonstrate the nature of the La Mata Channel as a means of export of suspended materials to the river. The values of SM exportation observed for May are small compared with those obtained by Hsieh et al (2010) in 24 h, on two cycles in a semidiurnal tide. Hsieh et al (2010) obtained -16.089 and -13.491 Tons in January and April, respectively, in the channel of a Taiwan coastal lagoon, similar in size to that of the present study but with urban waste water inflow and mangrove-fringed.…”

“…The values of SM exportation observed for May are small compared with those obtained by Hsieh et al (2010) in 24 h, on two cycles in a semidiurnal tide. Hsieh et al (2010) obtained -16.089 and -13.491 Tons in January and April, respectively, in the channel of a Taiwan coastal lagoon, similar in size to that of the present study but with urban waste water inflow and mangrove-fringed. The mean result of La Mata Channel for May was 172 Kg of exported SM, by two cycles of a semi-diurnal tide.…”

“…Net water transport depends on the difference in magnitude and duration between ebb and flood tidal currents; such a difference, known as "tidal current asymmetry", is generally associated with the distortion of the tidal wave entering rivers, estuaries and coastal lagoons (HOITINK et al, 2003). Furthermore, in the La Mata Channel, the freshwater discharge from the microbasin, and likely salty water from the Galindo inlet (Fig.…”

“…The dynamics of nutrients, chlorophylls, suspended materials and salt concentrations, in shallow coastal lagoons directly connected to the sea, have been widely studied and discussed (HSIEH et al, 2010;MOSER et al, 2005;PEREIRA-FILHO et al, 2001). The La Mata Channel presents an untypical morphologic feature; it is connected to the sea by means of the Tuxpan River.…”

“…Tidal currents may be the major source of energy for transporting non-living materials and organisms as they are largely passively driven by these physical forces (LUCAS et al, 1999). Transport depends on differences in current magnitude and duration between ebb and flood tidal currents; such differences, "velocity asymmetry", are produced by the distortion of the tidal wave entering rivers, estuaries and coastal lagoons (HOITINK et al, 2003).…”