Sediment transport in the coastal ocean: a retrospective evaluation of the benthic tripod and its impact, past, present, and future
In-situ observations of near-bed flow and sediment transport have been carried out for approximately 50 years. The observational technique employs a benthic tripod which can remain submerged on the seafloor for an extended period of time upon which are mounted various oceanographic instruments. The instruments transmit their signals to shipboard via connecting cable or more frequently record their output in accompanying data loggers. During the early years of benthic tripod work, measurements emphasized nearbed current velocity and associated suspended sediment profiles over periods of tidal cycles. The objectives of these studies were to evaluate existing boundary-layer flow and sediment transport theories under natural marine conditions. More recently, instrument capabilities and tripod deployment times have increased dramatically. Research objectives have expanded to include documentation of the physical processes active in the coastal ocean and their contribution to along-and across-margin sediment transport. Tripod-based studies continue to be a significant component of many comprehensive field programs. These long-term studies provide a way to document seabed physical processes and sediment transport over the full range of environmental conditions and continue to shape our concepts of sediment transport on continental shelves. Additionally, these boundary-layer studies have provided critical input for boundary-layer-numerical model development. Benthic tripods and self-contained instrumentation also represent a base of expertise that will help with design and implementation of coastal observatories in the future.