Modulation of shallow water tides in an inlet‐basin system with a mixed tidal regime

Abstract

During the autumn of 1999 a 56‐day‐long observational study of sea surface elevation and currents was made in Yavaros Bay, a shallow inlet‐basin system with a mixed tidal regime in the Gulf of California. During the late spring of 1998 a similar experiment was performed at the same coastal lagoon as well, although it was shorter. The measurements are used to investigate the modulation of the shallow water tides. The complex demodulation approach revealed that not only the Moon's path cycle modified the generation of shallow water tides but also the lunar declination and the solar declination. The sixth‐diurnal tides showed a spring‐neap modulation. The fifth‐diurnal tides were above the noise level only close to the summer solstice. The fourth‐diurnal tides were modulated by the spring‐neap cycle at the basin, but this modulation was changed by friction at the inlet. At this site the fourth‐diurnal band of the tidal current had a maximum in amplitude during neap tides. The third‐diurnal tides were irregularly modulated. The advection and the nonlinear continuity terms were correlated with the third‐ and fourth‐diurnal bands of the tidal current at the inlet. The quadratic friction terms were correlated with the sixth‐, fourth‐, and third‐diurnal bands of the tidal current. The semidiurnal tides mainly provided the energy of the tidal residual current during the autumnal equinox of 1999. Near the summer solstice of 1998 the semidiurnal band induced a residual current seaward oriented, while the diurnal band induced a residual current landward oriented.