| dc.description.abstract | Tidal systems are found in many locations in the world. Many of these systems contain tidal flats,
i.e. features that fall dry during part of a tidal cycle. The hydrodynamical equations describing tidal systems are
nonlinear and, as a consequence, higher harmonics of the primary tidal frequency are produced. Several processes
have been identified to produce higher harmonics, such as advection of momentum and depth-dependent bottom
friction. The incorporation of tidal flats in the hydrodynamical equations has identified two more processes,
mass storage and momentum loss over the tidal flat, as sources of higher harmonics. On some occasions water
traverses the tidal flat and flows into a channel on the other side of the tidal flat. This process, called cross-tidal
flat mass transport, may be a source of higher harmonics as well. A numerical model, the Network Model
with Parameterisation of tidal flat hydrodynamics (NM-P), has been developed to simulate cross-tidal flat mass
transport. In a simplified geometry, the NM-P is used to quantify cross-tidal flat mass transport and the effect
of cross-tidal flat mass transport on the production of higher harmonics in the channels. A different numerical
model, the Network Model with explicit Flat dynamics (NM-F), has been developed to simulate of flow over tidal
flats more accurately.
Results obtained with the NM-P model indicate that cross-tidal flat mass transport can be a significant flux in the
mass budget of a channel, up to 25% of the total mass flux. A much smaller net cross-tidal flat mass transport
exists as well, always directed from the lagging to the leading channel. The effect of cross-tidal flat mass transport
in the channels is predominantly present in the seaward part of the tidal channel. Higher (lower) velocities are
found in the leading (lagging) channel, while lower (higher) sea level is found in the leading (lagging) channel.
The M4 tidal constituent increases in amplitude with increasing cross-tidal flat mass transport. Results obtained
with the NM-F model indicate that mass flow over tidal flat is slow, with the wave front moving at 17cms-1 over
a dry tidal flat | |
