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Sediment dynamics in coastal waters has relevance to a broad spectrum of marine science and engineering. Through the processes of accretion, erosion and transport, sediments define our coastlines, marine habitats, and nearshore recreation zones. Seabed sediments critically affect the stability of marine structures, shoreline protection and development, and navigation in coastal waters. Sediments act as reservoirs for nutrients and contaminants and as regulators of light transmission, thereby impacting significantly on water chemistry and primary production. Thus, predicting sediment transport, erosion and deposition is of great practical importance on a global scale, but is also very challenging. The challenge is associated in part with the complex and often non-linear interactions among combined forcing by waves and currents, the dynamic response of the bed, and sediment size and type, as well as the fundamental role of turbulence. Part of the challenge has also been the absence, historically, of suitable technologies for making the comprehensive measurements needed to adequately test or validate the models.

The long-term goal is to quantify ripple and ripple field properties in response to wave and current hydrodynamic forcing and grain size variability. The overall objective of the 2007 experiment at the Martha's Vineyard Coastal Observatory (MVCO) is to investigate the relative adjustment of ripples in the coarse and fine sands to forcing events involving a range of different surface gravity wave and mean current forcing conditions, as a function of cross-shore distance (i.e. water depth). Our primary objective is to determine the temporal and spatial evolution of wave-forced seafloor ripple geometry and as a function of both hydrodynamic forcing (as modulated by water depth) and grain size (fine and coarse sand). The observations will be used to validate existing models and to develop new models for ripple geometry as a function of forcing hydrodynamics and seabed characteristics. The observations will also have a smaller focus on small scale sediment transport processes over ripples and larger scale wave field variability over spatially variable ripples. The small scale sediment transport process observations, which combined with realistic transport - morphodynamic models being developed by other investigators, will lead to physics-based models of ripple evolution. Wave models, initiated with the measured wave directional spectrum offshore, will be used to generate predicted wave fields for comparison to co-located observations of wave and ripple properties across the shoaling region, in both fine and coarse sand. These results will provide the basis for extending ripple property predictions based on the modeled waves to the full experimental domain. These predictions will be tested against the sidescan/multibeam survey data.

The central goal of this research is a deeper understanding of bed state adjustment in mobile sandy sediments on the inner continental shelf, and in particular the adjustment(s) to the combined effects of variable fluid forcing and biological reworking of the sediment surface. The work is motivated by the lack of a suitable observational basis for developing and testing models of the temporal evolution of the seabed roughness spectrum resulting from fluid-sediment-biological interactions in environments subjected to transient wave forcing events. Our primary objective in this first phase of the project is to quantify the rates of ripple degradation and seabed roughness change arising from biological activity on and within the seafloor. The second objective is to compare the measured degradation rates to those predicted by analytic and numerical models of bed roughness change by biological organisms, as a function of spatial frequency spanning the ripple band.

The central goal of this research is a deeper understanding of the dynamic adjustment of mobile sandy sediments to the variable fluid forcing the nearshore zone and inner continental shelf at small (1-cm to 10-m) and intermediate (10-m to 100-m) horizontal scales. The effort is motivated by the dual need to develop more realistic models of fluid-sediment interactions in these environments, and for suitable measurement techniques to make the observations necessary to adequately test the models. The objective of the proposed project is to advance the state-of-the-art of acoustic remote sensing systems for sediment and fluid dynamics studies in the wave-current bottom boundary layer. The particular focus of this project is the remote (and routine) measurement of bottom stress in energetic combined flows above mobile beds., Prepared in cooperation with Memorial University of Newfoundland, St. John's.

The objective of the proposed project is to advance the state-of-the-art of acoustic remote sensing systems for sediment and fluid dynamics studies in the wave-current bottom boundary layer. The particular focus of this project is the remote (and routine) measurement of bottom stress in energetic combined flows above mobile beds., Prepared in collaboration with the Department of Physics and Physical Oceanography at Memorial University of Newfoundland, St. John s, NF. The original document contains color images.

The central goal of this research is a deeper understanding of bed state adjustment in mobile sandy sediments on the inner continental shelf, and in particular the adjustment(s) to the combined effects of variable fluid forcing and biological reworking of the sediment surface. The work is motivated by the lack of a suitable observational basis for developing and testing models of the temporal evolution of the seabed roughness spectrum resulting from fluid-sediment-biological interactions in environments subjected to transient wave forcing events., Prepared in cooperation with Dalhousie Univ, Halifax, Nova Scotia, Canada. The original document contains color images.

The central goal of this research is a deeper understanding of bed state adjustment in mobile sandy sediments on the inner continental shelf, in particular the adjustment due the combined effects of variable fluid forcing and biological reworking of the sediment surface. The work is motivated by the lack of suitable observational basis for developing and testing models of seabed roughness evolution through fluid-sediment-biological interactions in sandy inner shelf environments. Our primary objective in this first phase of the project is to quantify the rates of ripple and seabed roughness degradation arising from biological activity on and within the seafloor. The second objective is to compare the measured degradation rates to those predicted by analytic and numerical models of bed roughness change by biological organisms., Prepared in collaboration with the Department of Oceanography, Dalhousie University, Halifax, N.S., Canada.

The central goal of this research is a deeper understanding of the dynamic adjustment of mobile sandy sediments to the variable fluid forcing the nearshore zone and inner continental shelf at small (1cm to 10m) and intermediate (10m to 100m) horizontal scales. The effort is motivated by the dual need to develop more realistic models of fluid-sediment interactions in the nearshore zone and on the continental shelf, and for suitable measurement techniques to make the observations necessary to adequately test the models. The objective of the proposed project is to advance the state-of-the-art of acoustic remote sensing systems for sediment and fluid dynamics studies in the wave-current bottom boundary layer. The particular focus of this project is the remote (and routine) measurement of bottom stress in energetic combined flows above mobile beds., Prepared in collaboration with the Department of Physics and Physical Oceanography, Memorial University of Newfoundland, St. John s, NF, Canada.

The central goal of this project is a deeper understanding of the dynamic adjustment of mobile sandy sediments to fluid forcing in and near the surf zone at small (1cm to 10m) and intermediate (10m to 100m) horizontal scales. The effort is motivated by the dual need to develop more realistic models of fluid-sediment interactions in the nearshore zone, and for suitable in situ measurement techniques to make the observations necessary to adequately test the models. The primary objectives of this project are: (1) to study the role of bedforms of different characteristic spatial pattern and scale in the local sediment flux and momentum balances, and (2) to investigate bedform genesis, growth, migration, and decay in relation to the fluid forcing conditions and predicted sediment transport rates. Of particular interest are the relationships between sediment fluxes, bedform properties, and asymmetries in the fluid motions. A key initial objective was to obtain a comprehensive set of measurements of bed adjustment through time, as a function of cross-shore position, and over a period of several months. This data set was obtained in SandyDuck, and is providing a basis for determining cross-shore differences in response synoptically, and for differences in the response trajectories through time and between forcing events, over a suitably wide range of conditions.

Our research program focuses on identifying and quantifying sediment erosion, transport, and deposition processes on the continental shelf through state of the art observational techniques in both fine grained and sandy environments. In sandy environments our goal is to understand the detailed interactions and feedbacks between hydrodynamics, bedforms, and the resulting sand transport. In fine grained such as the environments, Eel River shelf we have been investigating the role of gravitationally forced fluid mud flows in the wave boundary layer as a cross-shore transport mechanism. In certain environments bedload or near bottom suspended load can be the dominant mode of sand transport. In particular, these modes of sediment transport can have important impacts in terms of understanding erosion and deposition mechanisms in coarser sand environments with active bedform processes. These bedform processes, which may be forced by bedload transport, have been observed to change the local seafloor elevation tens of centimeters in time scales of hours to days. However, there is a lack of suitable observational techniques to measure bedload and near bottom suspended sand transport and their relationship to the hydrodynamic forcing. Therefore, we are developing and testing acoustic Doppler instrumentation that can quantitatively measure the bedload and near bottom suspended load flux magnitude and direction on a rapid time scale and its relationship to the hydrodynamic forcing. The approach for this project is based on a combination of modeling sensor geometry and response and testing actual systems in laboratory and field environments. The modeling effort will be used to guide development of sensor geometries and signal processing schemes. These will then tested using the components of Coherent Doppler Profiler developed at Dalhousie University., Prepared in collaboration with Dalhousie University, Halifax, NS, Canada.

The central goal of this project is a deeper understanding of the dynamic adjustment of mobile sandy sediments to fluid forcing in the surf zone at small (1cm to 10m) and intermediate (10cm to 100m) horizontal scales. The effort is motivated by the dual need to develop more realistic models of fluid-sediment interactions in the nearshore zone, and for suitable in situ measurement techniques to make the observations necessary to adequately test the models. Of particular interest is the role of bedforms of different characteristic spatial pattern and scale in the local sediment flux and momentum balances. The overall objective of this project is to study bedform genesis, growth, migration, and decay, together with the associated fluid forcing and sediment suspension, in the natural surf zone. A key initial objective was to obtain a comprehensive set of measurements of bed adjustment through time, as a function of cross-shore position, and over a period of several months. This data set will provide a basis for determining cross-shore differences in response synoptically, and for differences in the response trajectories through time and between forcing events, over a suitably wide range of conditions., See also ADM002252.