Title

Sediment transport on roberts bank: A sandy intertidal flat on the fraser river delta

Document Type

Article

Publication Date

2010

Publication Title

Journal of Coastal Research

Volume

26

Issue

2

First Page

333

Last Page

341

DOI

10.2112/08-1125.1

Keywords

Fraser River Delta, Sediment transport, Tidal flat, Wind-generated currents

Abstract

Waves and currents were monitored over a range of incident forcing between March 23 and April 24, 2003, on Roberts Bank, the sandy intertidal portion of the Fraser River Delta. A comparison of the dimensionless, current-induced skin friction with the critical skin friction for the initiation of sediment motion suggests that the currents are only capable of entraining sediment briefly with the ebbing tide or when enhanced by the wind. Since these wind-generated currents are associated with storm waves, which typically exceed the critical skin friction, they have a disproportionately large impact on the direction of the sediment transport. An energetics-based model, driven by locally measured near-bottom currents, is used to characterize the rate and direction of bedload and suspended load transport. The largest transport rates were predicted in response to storm waves and were initially directed onshore with weak oscillatory transport and alongshore by wind-generated currents that turned offshore as the ebbing currents strengthened. The integrated transport (over the duration of the study) was predicted to be weakly offshore, but this is ascribed to the coincidental occurrence of storm activity with the ebbing tide. It is argued that if storm waves were equally distributed between the flood and ebb phases of the tide, the wind-generated currents and oscillatory transport would lead to a partly onshore-directed net transport during storms, which may in turn lead to tidal flat accretion. This suggests that sand flats are morphodynamically different than mudflats and open beaches, although further study is required to ascertain the link between the small-scale observations of this study and the larger-scale transport pathways that are ultimately responsible for tidal flat morphology. © 2010 Coastal Education and Research Foundation.