Tidal and meteorological forcing of suspended sediment flux in a muddy mesotidal estuary

Tidal and meteorological forcing of suspended sediment flux in a muddy mesotidal estuary.
French, J.R.and Burningham, H. and Benson, T.
Estuaries and Coasts, 31 (5). (2008)

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Official URL:http://www.springerlink.com/content/373g023112473v00/
Abstract:Although the supply and fate of suspended sediment is of fundamental importance to the functioning and morphological evolution of muddy estuaries, reliable sediment budgets have been established in only a few cases. Especially for smaller estuaries, inadequate bathymetric surveys and a lack of intertidal sedimentation data often preclude estimation of the sediment budget from orphological change, while instrument-derived residual fluxes typically lie well within the errors associated with measurement of much larger gross tidal transports. Given suitably long-term records of continuously monitored suspended sediment concentration (SSC), however, analysis of the major scales of variation in sediment transport and their relation to hydrodynamic and meteorological forcing permits qualitative testing of hypotheses suggested by directly measured residual fluxes. This paper analyzes data from a 1-year acoustic Doppler profiler deployment in the Blyth estuary, a muddy mesotidal barrier-enclosed system on the UK east coast. Flux calculations indicate a small sediment import equivalent to just 1.5% of the gross flood tide transport. Little confidence can be assigned to either the magnitude or direction of such a small residual when considered in isolation. However, the inference that the sediment regime is finely balanced is qualitatively supported by the close similarity between flood tide and ebb-tide SSC values. Singular spectrum analysis of the SSC time series shows the expectedly large contributions to the variance in SSC at intratidal and subtidal (semi-monthly and monthly) scales but also picks out intermittent variability that is initially attributed to a combination of non-tidal surge and wind stress forcing. Closer examination of the data through cross-correlograms and event-scale analysis indicates that local meteorological forcing is the major factor. Acting through the resuspension of intertidal mudflat sediments at times of strong westerlies, meteorological forcing is directly implicated in episodic sediment export from the estuary. Thresholding of tide-averaged fluxes using a range of critical wind stress values further indicates that ‘tide-dominated’ (i.e.low wind stress) and ‘wave-dominated’ (high wind stress) conditions are associated with sediment import and export. Sediment balance is potentially sensitive to the frequency of high wind stress events, since the associated sediment exports are several times larger than the average import under calm conditions. Intermittent meteorological forcing may thus exert an important control on the sedimentary balance of otherwise tidally dominated muddy estuarine systems, and the role of wind climate should not be overlooked in studies of estuary response to environmental change.
Item Type:Article
Subjects:Maritime > General
Maritime > Estuary management
Coasts > Sediment transport and scour
ID Code:344
Deposited On:12 Aug 2009 08:39
Last Modified:08 Aug 2014 09:00

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