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| Titel |
Process-based, long-term morphodynamic modeling to investigate conditions for equilibrium estuarine geometry |
| VerfasserIn |
M. van der Wegen, Z. B. Wang, H. H. G. Savenije, J. A. Roelvink |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250025439
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| Zusammenfassung |
| Literature review suggests that alluvial estuaries all over the world have a shape that
exponentially widens towards the mouth. In strongly tapering estuaries, the tidal
characteristics mimic a standing wave in the sense that the phase difference between
maximum water level and maximum velocity is 1 -2 Ï, whereas the tidal wave still
propagates along the estuary [Friedrichs and Aubrey (1994), Jay (1991), Prandle (2003),
Savenije (2001)]. Furthermore, it has been suggested that, for equilibrium conditions, the
tidal water level amplitude and the velocity amplitude remain fairly constant along the
estuary. This latter condition also implies that sediment transport along the estuary is constant
[Friedrichs (1995)].
The aim of the current research is to investigate the development of these assumed
equilibrium conditions with a morphodynamic, process-based numerical model
(Delft3D).
Model results cover an evolution of a time span of about 6400 years in a 300 km long
tidal embayment under constant tidal forcing conditions. This is an extended version of an 80
km basin described in earlier research [Van der Wegen et al. (2008)]. The model starts
from a highly schematised rectangular cross-section which is uniform along the
embayment. The model allows for bank erosion, bed slope effects and drying and
flooding of intertidal area, whereas short waves are not considered. Grid resolution
is 100 m by 200 m which covers the length scale of the major patterns. Because
of this detailed grid and the long timescale calculations took months on a decent
PC.
Model results show considerable widening at the mouth (roughly along an exponentially
narrowing profile) and a slower development more landward. The 1 -2 Ï time lag
between maximum water level and maximum velocity, the constant water level
amplitude and the constant velocity amplitude develop within centuries and are most
pronounced in the widened part of the embayment. More landward, the tidal wave
characteristics still reflect a (damped) classical progressive wave. After 6400 years the
model shows these two tidal wave characteristics, both present in about 40 % of the
tidal embayment with a 20% transient interval in between. The results suggest that
alluvial estuaries evolve towards an exponentially shaped geometry although the
evolution timescale is long and allows for different tidal wave characteristics more
landward.
Friedrichs, C.T. and D.G. Aubrey (1994), Tidal propagation in strongly convergent
channels, Journal of Geophysical Research, 99(C2), 3321-3336.
Friedrichs, C.T., (1995), Stability Shear Stress and Equilibrium Cross-Sectional
Geometry of Sheltered Tidal Channels, Journal of Coastal Research, 11, 4, 1062-1074.
Jay, D.A., (1991). Green’s law revisited: Tidal long wave propagation in channels with
strong topography, Journal of Geophysical Research, Vol. 96, no C11, 20,585-20,598
Prandle, D., (2003), Relationship between tidal dynamics and bathymetry in strongly
convergent estuaries, Journal of Physical Oceanography, 33, 2738-2750.
Savenije, H.H.G., (2001), A simple analytical expression to describe tidal damping or
amplification, Journal of Hydrology, 243, 205-215.
Van der Wegen, M., Wang, Z.B., Savenije, H.H.G., Roelvink, J.A., 2008. Long-term
morphodynamic evolution and energy dissipation in a coastal plain, tidal embayment, J.
Geophys. Res., Vol. 113, F03001, doi:10.1029/2007JF000898 |
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