16
K. Black· M. Green· T. Healy· R. Bell· J. Oldman· T. Hume
ity. The results lead us to suggest that the models appear to be operating effectively. Most of the deviations between models and measurements have related to
difficulties with the collection of comprehensive datasets at a broad spatial scale
as well as at the local site. Of the errors encountered, the water depth throughout
the estuary appears to be the most significant. Because of the short wave periods,
depth strongly influences wave generation and bed orbital motion. The biggest
deviation however stemmed from the low measured wind speeds at a time when
measured orbital motion was significant.
Additional processes where more information would have been useful include wave breaking frequency at the site which could cause average turbulence
levels to vary and fall velocity and grain size spatial variability. Unsteady sea surface gradients in tidal estuaries need to be accounted for but this can be treated
by coupling the wave generation and tidal circulation models (the latter providing accurate water levels), as undertaken here.
In summary, wave breaking under following winds in shallow water, subtle
changes to skin friction at intra-tidal time scales and preferential entrainment
of sediment fractions within a population will need to be studied further before
numerical simulations are able to model all aspects of SSC time series in estuaries. However, the comparison here, using only numerical models to simulate all
of the processes, has shown that good progress is being made.
Acknowledgements
The study was funded by the Foundation for Research, Science and Technology in
the project "Wave and Sediment Dynamics in Coastal and Estuarine Systems". The
first author thanks Dr Jan Harff for his kind invitation to attend the conference.
References
Bell, R.G., Hume, T.M., Dolphin, T.J., Green, M.O. and Walters, R.A. (1998). Characterisation
of physical environmental factors on an intertidal sandflat, Manukau Harbour, New Zealand. Journal of Experimental Marine Biology and Ecology. 216: 11-31.
Black, K.P. (1987). A numerical sediment transport model for application to natural estuaries, harbours and rivers. In: 'Numerical modelling applications to marine systems'. ed: J.
Noye. North Holland/Elsevier. Mathematics Studies No. 145, p. 77-105.
Black, K.P. (1994). Suspended sediment load during an asymmetric wave cycle over a plane
bed. Coastal Engineering. 23: 95-114.
Black, K.P. (1995). The numerical hydrodynamic model 3DD and support software. Occasional Report No. 19. Department of Earth Sciences, University of Waikato, New Zealand. 53 pp.
Black, K.P. (1996). Lagrangian dispersal and sediment transport model POL3DD. Occasional Report No. 21. Department of Earth Sciences, University of Waikato, New Zealand. 69
pp.
Black, K.P. (1997). The numerical wave generation model WGEN3DD. Occasional Report
Department of Earth Sciences, University of Waikato, in press.
Black, K. P. and Gay, S. 1. (1990). A numerical scheme for determining trajectories in particle models. In 'Acanthaster and the Coral Reef: A Theoretical Perspective'. (Ed. R. Bradbury.) Lecture notes in Biomathematics, Springer-Verlag. p. 151-156.
K. Black· M. Green· T. Healy· R. Bell· J. Oldman· T. Hume
ity. The results lead us to suggest that the models appear to be operating effectively. Most of the deviations between models and measurements have related to
difficulties with the collection of comprehensive datasets at a broad spatial scale
as well as at the local site. Of the errors encountered, the water depth throughout
the estuary appears to be the most significant. Because of the short wave periods,
depth strongly influences wave generation and bed orbital motion. The biggest
deviation however stemmed from the low measured wind speeds at a time when
measured orbital motion was significant.
Additional processes where more information would have been useful include wave breaking frequency at the site which could cause average turbulence
levels to vary and fall velocity and grain size spatial variability. Unsteady sea surface gradients in tidal estuaries need to be accounted for but this can be treated
by coupling the wave generation and tidal circulation models (the latter providing accurate water levels), as undertaken here.
In summary, wave breaking under following winds in shallow water, subtle
changes to skin friction at intra-tidal time scales and preferential entrainment
of sediment fractions within a population will need to be studied further before
numerical simulations are able to model all aspects of SSC time series in estuaries. However, the comparison here, using only numerical models to simulate all
of the processes, has shown that good progress is being made.
Acknowledgements
The study was funded by the Foundation for Research, Science and Technology in
the project "Wave and Sediment Dynamics in Coastal and Estuarine Systems". The
first author thanks Dr Jan Harff for his kind invitation to attend the conference.
References
Bell, R.G., Hume, T.M., Dolphin, T.J., Green, M.O. and Walters, R.A. (1998). Characterisation
of physical environmental factors on an intertidal sandflat, Manukau Harbour, New Zealand. Journal of Experimental Marine Biology and Ecology. 216: 11-31.
Black, K.P. (1987). A numerical sediment transport model for application to natural estuaries, harbours and rivers. In: 'Numerical modelling applications to marine systems'. ed: J.
Noye. North Holland/Elsevier. Mathematics Studies No. 145, p. 77-105.
Black, K.P. (1994). Suspended sediment load during an asymmetric wave cycle over a plane
bed. Coastal Engineering. 23: 95-114.
Black, K.P. (1995). The numerical hydrodynamic model 3DD and support software. Occasional Report No. 19. Department of Earth Sciences, University of Waikato, New Zealand. 53 pp.
Black, K.P. (1996). Lagrangian dispersal and sediment transport model POL3DD. Occasional Report No. 21. Department of Earth Sciences, University of Waikato, New Zealand. 69
pp.
Black, K.P. (1997). The numerical wave generation model WGEN3DD. Occasional Report
Department of Earth Sciences, University of Waikato, in press.
Black, K. P. and Gay, S. 1. (1990). A numerical scheme for determining trajectories in particle models. In 'Acanthaster and the Coral Reef: A Theoretical Perspective'. (Ed. R. Bradbury.) Lecture notes in Biomathematics, Springer-Verlag. p. 151-156.