The systematic contribution of transporting mechanisms to the cross-shore sediment transport in water depths of 3 to 9 m
Ruessink, B.G.; Houwman, K.T.; Hoekstra, P. (1998). The systematic contribution of transporting mechanisms to the cross-shore sediment transport in water depths of 3 to 9 m. Mar. Geol. 152(4): 295-324. http://dx.doi.org/10.1016/S0025-3227(98)00133-9
In: Marine Geology. Elsevier: Amsterdam. ISSN 0025-3227; e-ISSN 1872-6151, more
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nearshore environment; sediment transport; suspended sediments; bars |
| Authors | | Top |
- Ruessink, B.G.
- Houwman, K.T.
- Hoekstra, P.
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| Abstract |
The systematic contributions of short waves, infragravity waves and mean flows to the cross-shore sediment transport were studied with direct measurements of instantaneous near-bed sediment concentrations and velocities as well as with an energetics-based sediment transport model using measured time series of near-bed cross-shore flow as input. The study was conducted at four cross-shore positions in the multiple bar system of Terschelling, Netherlands during three field campaigns, each with a five-week duration. The data were collected in 3- to 9-m water depth during a wide range of conditions, from low-energy non-breaking conditions to almost fully saturated breakers. The height over depth ratio Hs/h was applied at all four measuring stations as a local conditional parameter. All model predictions were grouped into Hs/h classes with a width of 0.02 to highlight the generality of the data. The energetics approach predicted that the suspended load dominated over the bedload at all four stations. Both the sediment flux measurements as well as the model predictions showed that the largest contributors to the gross suspended sediment transport were made by the short waves and the undertow, inducing an onshore and offshore transport, respectively. Their contributions to the gross suspended transport were about 40 to 50% under surf zone conditions. Bound infragravity waves were observed and predicted to result in an offshore directed transport that was of subordinate magnitude compared to the observed and estimated magnitudes by the short waves and the undertow. However, as these transports almost cancelled out because of their about equal magnitude but opposite sign, the suspended transport by bound infragravity waves may not be ignored and may, rather paradoxically, have a relatively large influence on the net suspended sediment transport. Hydrodynamical processes that do not seem to be of importance to the onshore and offshore sediment transport in 3- to 9-m water depth in the long run are mean flows under non-breaking conditions and free infragravity motions. A direct comparison between measured sediment fluxes and the model predictions suggests that simple energetics models are suitable for predicting cross-shore sediment transport in 3- to 9-m water depth. |
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