Near‐bottom currents and sediment transport on the inner Scotian Shelf: Sea‐floor response to winter storms during CASP
Open Access
- 1 March 1989
- journal article
- research article
- Published by Taylor & Francis in Atmosphere-Ocean
- Vol. 27 (1) , 258-278
- https://doi.org/10.1080/07055900.1989.9649336
Abstract
As part of the Canadian Atlantic Storms Program (CASP), near‐bottom current velocity, pressure, light transmission (as a measure of suspended sediment concentration) and water temperature were recorded using a variety of instruments deployed in water depths of 20 to 37 m on the inner Scotian Shelf, during February and March 1986. Detailed mapping of a 12‐km2 area encompassing the instrument mooring sites revealed a variety of bottom types. These include sand and gravel (both forming ripples at various scales), cobble‐boulder lags, and bedrock, resulting in bottom roughness estimates that vary widely (10−4 m < k < 10° m) over short horizontal distances (of the order 102 m). The velocity data provided information on the near‐bottom current response to winter storms anda basis for computations of sediment load and transport rates. The near‐bottom mean flow showed distinct storm‐driven circulation patterns, with velocities roughly parallel to alongshore wind stress but opposed to shore‐normal wind. Wave‐induced oscillatory motions also showed marked increases during storms and frequently dominated the near‐bottom flow. Sediment load (depth‐integrated concentration) and transport were computed using a model in which the load is related to the excess normalized shear stress. The computed mean concentrations were compatible with the optical transmis someter data. These computations yielded estimates ranging up to 0.7 kg m−2 for the mean sediment load and 443 kg m−1 h−1 for the net transport. Hindcast scour rates, of the order of 1 mm h−1 under moderate storm conditions were generally compatible with depths of scour measured by divers.Keywords
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