Sediment Flux and Trapping on the Skagit Tidal Flats and Instrumentation for Quantifying Nearshore Sediment Transport and Turbulence (DURIP)

摘要

The long-term objective is to determine the hydrodynamic processes controlling sediment transport and the associated morphologic response on tidal flats. The objectives of our 2008-2009 research program were: quantify the influence of barotropic (tidal) convergence on the lower Skagit tidal flats as a mechanism of sediment trapping and creation of ephemeral mud and sand deposits; determine the role of density fronts in creating and transporting high-concentration sediment suspensions, and assess the influence of these processes on sediment deposition and short-term morphological change; distinguish the influence of wave-induced sediment transport from tidal/fluvial processes, and determine how variations in tidal, fluvial and wind/wave forcing alter the bedform geometry, transport pathways, surficial sediment characteristics and tide-flat morphology. This was the major field year of the Tidal Flats study. The remainder of this report describes the results of that field effort. We deployed an array of instrument platforms on Skagit Flats during a 1-month observational interval in June, 2009. High-resolution surveys of the currents and suspended sediment distributions were conducted in concert with the deployments. The deployment array (Fig. 1) was designed to distinguish the flow and sediment-transport processes in channels and on the flats as well as in different locations across the flats. The platforms (fig. 2, 3) at the lower channel and flats (stations 1-7) documented the tidal, fluvial and estuarine conditions on the flats. Station 8 provided the fluvial conditions at the Freshwater Slough distributary (the largest freshwater source to the southern flats). All of the stations had accompanying surface moorings with TS/OBS sensors, to quantify baroclinic salinity and sediment gradients.