Medium-term frequency distributions of cross-shore suspended sediment transport rates in water depths of 3 to 9 m

• Published in: Coastal engineering (Amsterdam) 1999-09, Vol.38 (1), p.25-46
• Main Authors: Ruessink, B.G, Houwman, K.T, Hoekstra, P
• Format: Article
• Language: English
• Subjects: Cross-shore transport; Earth sciences; Earth, ocean, space; Energetics modelling; Exact sciences and technology; Marine and continental quaternary; Medium-term distribution; Nearshore environment; Surficial geology
• ISSN: 0378-3839; 1872-7379
• DOI: 10.1016/S0378-3839(99)00023-X

A data set of several thousands of hours of near-bed flow, obtained at three cross-shore positions in 3- to 9-m water depth in the multiple bar system of Terschelling (Netherlands), was used to estimate the medium-term (≈years) frequency distribution of the cross-shore suspended sediment transport rates induced by short waves, infragravity waves and cross-shore mean flows. Predictions of an energetics-based transport model were categorised into groups of the local height-over-depth ratio with a width of 0.02 and were subsequently coupled to the discrete medium-scale probability distribution of this ratio. At all depths, the estimated medium-scale sediment transport rate by the short waves, q ms,h, and mean flows, q ms,mf, were of approximately equal magnitude and were about three times as large as that of the infragravity waves. In general, the medium-term sediment transport rates were dominated neither by the most extreme conditions nor by day-to-day situations. This was related to the infrequent recurrence of the most energetic events and by the predicted negligible transport rates under daily conditions. In 9-m depth, breaking conditions contributed to about 90% of both q ms,h and q ms,mf. In shallower water (3–5 m), non-breaking conditions became increasingly important for q ms,h, whereas q ms,mf remained fully dominated by surf zone conditions. This observation as well as literature findings for water depths less than about 3 m suggest that the range of small-scale conditions that contribute most to q ms,h and q ms,mf changes in the onshore direction from mainly breaking conditions at depths in excess of 5–7 m towards prolonged non-breaking periods for q ms,h and short breaking events for q ms,mf on the beach.