Seafloor Ripple Measurements at the Martha's Vineyard Coastal Observatory

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.