Shallow-Water Waves and Fluid-Mud Dynamics, Coast of Surinam, South America.

摘要

Time series measurements of shallow-water waves and fluid-mud density variations, taken simultaneously with tide elevation and suspended sediment data, indicate that wave/fluid-mud interactions in the nearshore may be largely responsible for the present-day accumulation of fine-grained sediment on the open, unprotected coast of northeastern South America. Results of field experiments conducted along the central Surinam coast show that accumulations of fluid mud, which can be found up to 1.5 m thick on western flanks of migrating shore-attached mudbanks, affect incoming swell by changing their form from sinusoidal to solitary-like and by preventing wave breaking except for occasional spilling. As long-period swell (T = 12-16 sec) propagates over shallow banks of fluid mud, the wave height to water depth ratio remains nearly constant at 0.23; the steady decrease in wave height with shoaling water depth indicates that substantial amounts of wave energy are lost to a fluid-mud bottom even though breaking does not occur. Using the concept of wave-associated currents, it has been shown, in taking angle of wave approach, average observed concentration of sediment in suspension, and net drift as given by solitary wave theory, that volume transports can be explained by waves alone. If a hypothesis of mud transport by solitary waves is accepted, then the continuous shoreward transport of suspended fluid mud, combined with the high rate of wave energy dissipation, explains in part the ability of muddy coasts to protect their shorelines.