HR: 1400h
AN: OS53A-05    [Abstracts]
TI: Sediment Re-suspension in a Shallow Tidal Sea: The Upper Gulf of California.
AU: * Alvarez, L G
EM: lalvarez@cicese.mx
AF: CICESE, Km 107 Carr. Tijuana-Ensenada, Ensenada, BC 22860, Mexico
AB: Current velocity and concentration of suspended particulate matter (SPM) were measured near the sea bed at two stations on opposite sides of the Upper Gulf of California, during a fortnightly cycle. This shallow, macro tidal inverse estuary is very turbid due to high concentration of re-suspended sediments. During spring tides SPM concentration revealed a strong quarter-diurnal signal and "twin-peak" structure, both typical of the semi-diurnal tidal forcing. During neap tides, remarkable high concentration peaks exceeded those observed in spring tides. Values of the erosion threshold and the concentration rate of change were obtained from the time series of bed shear stress and SPM concentration. A simple expression in terms of the concentration rate or change and the normalized excess bed shear stress was used to calculate single-level, near-bed SPM concentration during the fortnightly cycle. A variable erosion threshold ( 0.05 to 0.5 Pa ) extracted from the 15-day time series allowed calculation of high concentration events under neap tide conditions. Such outstanding events are proposed to be caused by the re-suspension of bottom fluff layers under low bed shear stress, combined with near-bed horizontal advection.
DE: 0442 Estuarine and nearshore processes (4235)
DE: 3022 Marine sediments: processes and transport
DE: 4235 Estuarine processes (0442)
DE: 4558 Sediment transport (1862)
SC: Ocean Sciences [OS]
MN: 2007 Joint Assembly