Dynamics of Unvegetated Tidal-Flat Muds: ABSTRACT

Abstract

Process-oriented field studies of tidal-flat muds, together with satellite imagery and aerial photography, have provided new data for a synthesis of tidal-flat dynamics in low-, moderate-, and high-tide-range environments where vegetation is lacking in the intertidal zone. In the three areas studied since 1974 (coast of Louisiana, tide range 0.5 m; coast of Surinam, tide range 2.0 m; west coast of South Korea, tide range 5 to 9 m), intertidal exposures of mud measured normal to the shoreline range from less than 150 m (Louisiana) to over 50 km (Korea) width. Each area is blanketed by a layer of gelatinous fluid mud, several centimeters to over 1 m thick, which extends into the subaqueous zone seaward of the low-tide line. Shallow-water waves in the nearshore zone are substantially attenuated when propagating over soft tidal-flat muds. Attenuation of wave height (without breaking) from a water depth of 15 m to 1 m indicates that there is an 87% energy loss (utilizing linear-wave theory) when waves propagate over a 40-cm thick fluid-mud bottom with a bulk density of 1.30 g cm-3, and greater than 99% energy reduction over a 1-m thick layer of fluid mud with bulk density of 1.18 g cm-3. Tidal-flat muds are suspended and redeposited at End_Page 801------------------------------ wave and tidal frequency, provided bulk densities are less than 1.20 g cm-3. Suspended-sediment concentrations in the nearshore region are typically 1 to 10 × 103 mg 1-1. Thickness of brown oxidized mud which overlies steel-gray muds beneath provides an indication of the depth to which suspension and redeposition occur. In addition to serving as a storehouse for littoral sediments and as a buffer to wave attack, tidal-flat muds serve as a source of sediment for longshore transport processes. Because of high suspended-sediment concentrations, sediment transport rates can be enormous, even under relatively weak currents. End_of_Article - Last_Page 802------------