Measurements of Currents, Bottom Sediments and Seafloor Disturbance CASP

During the Canadian Atlantic Storms Program (CASP), four measurement sites were established along the CASP transect line off Martinique Beach, N.S. The sites were located in 20 m, 30 m, and 37 m depth on sand and in 30 m on gravel on the inner Scotian Shelf.Observations included nearbottom currents, bottom sediment types (using sidescan sonar and grab samples), bedforms (using time-lapse photography, ROV video, and diver reports), and depths of seabed disturbance (using washer assemblies mounted on rods driven into the seafloor). Ripple bedforms at the sand sites ranged from 0.02 to 0.10 m in height and from 0.1 to 0.5 m in wavelength.Larger ripples with heights of 0.3 to 0.4 m and wavelengths of 1.2 to 1.9 m were observed at the gravel site. The maximum observed values of scour and fill were 97 mm and 91 mm, respectively in sand, and 97 mm and 151 mm respectively in gravel.These should be assessed in the context of the wave energy levels encountered during the 1986 winter.The largest characteristic wave height recorded was 5.2 m, less than the extreme value of approximately 8.0 m which was measured at a nearby long term (11-year) wave recording site, and mush less than typical values of 10 to 15 m used for the design of offshore structures and pipelines for the outer shelf region.Large anomalous depressions were encountered in the seafloor near the 30 m sand site.These had widths of 10 to 30 m, depths of 0.8 to 2.4 m, and near-vertical walls developed in muds. The origin of these features remains unclear.