An introduction to the Sediment TRansport Events on Shelves and Slopes (STRESS) program

Abstract

TRANSPORT of sediments on continental shelves involves several complex processes, including entrainment and deposition of particles at the sea floor, vertical transport of suspended particles by boundary layer turbulence, water-column evolution of particle size and density by floc aggregation and break-up, and advection of suspended particles by vertically non-uniform, unsteady, horizontal currents (Fig. 1). These processes lead to sediment dispersal and topographical evolution on a side range of spatial scales, which feed back to influence the various transport mechanisms. Shelf sediment transport influences, and is strongly influenced by, the activities of bottom-dwelling organisms, as well as by physical flow-particle and particle-particle interactions. The many processes involved in shelf sediment transport raise an intriguing array of scientific questions with applications related to evolution of bottom roughness and topography, development of stratigraphy, water clarity, and transport of contaminants attached to fine particles. The objective of the Sediment TRansport Events on Shelves and Slopes (STRESS) program (NoWELL et al. , 1987) was to understand the processes controlling sediment transport and microscale topography in the storm-dominated shelf setting, and to develop a tested capability to predict these processes. STRESS was primarily a field measurement program (Fig. 2) designed to provide comprehensive, high-quality measurements sufficient for critical evaluation and improvement of conceptual and mathematical models. The measurement program was a remarkably successful attempt to resolve the vertical distribution of velocity, temperature and salinity throughout the entire continental shelf bottom boundary layer, with corresponding indirect estimates of particle concentration, size and settling velocity, and accompanying observations of small-scale topography. This issue contains 10 articles describing initial results based on STRESS measurements. The first article (SHERWOOD et al . , 1994) provides a description and a classification of sediment transport events during fall and winter storms in the STRESS study area, off the coast of northern California (Fig. 2). A second group of articles addresses the difficult problem of obtaining time-series estimates of particle size and settling velocity, based on a novel laser diffraction device (AG~WAL and PO~SMITH, 1993), a more traditional optical settling tube (Hn~L et al. , 1994), and a combination of acoustical and optical backscatter