Ocean
Waves LaboratoryOcean
Waves Laboratory
During September-December 2003 we participated in the Nearshore Canyon Experiment (NCEX) funded jointly by the Office of Naval Research and the National Science Foundation.
The field site near La Jolla, California is characterized by two submarine canyons, the larger and deeper La Jolla Canyon branches out to the north-east into a narrow trench, called Scripps Canyon. The heads of both canyons are within a few hundred meters of the shoreline resulting in extreme topographic effects on the relatively long wavelength Pacific swells observed on nearby beaches. For more information about the field site and science objectives please visit the NCEX web site.
In collaboration with Dr. William O'Reilly of the Scripps Institution of Oceanography (SIO) and Dr. Steve Lentz of the Woods Hole Oceanographic Institution (WHOI) we deployed an array of wave and current sensors in depths ranging from about 10-100m. This array includes 7 Datawell Directional Waverider Buoys (yellow triangles), 17 bottom pressure recorders (red squares), 12 Nortek pressure-velocity (white circles) sensors and 2 current profilers (brown diamonds).
Five directional wave buoys and four bottom pressure recorders were concentrated around the head of the canyon where the most severe topographic effects are expected. These instruments were placed as close as possible to the canyon walls while one buoy was moored directly over the canyon axis to obtain detailed measurements of the near field effects of the steep topography on the incident swell. A coherent linear array of 5 pressure guages was positioned on the south side of the Scripps canyon head in a region that is almost completely sheltered by the submarine topography from direct swell arrivals. The purpose of this array is to detect "indirect" swell arrivals resulting from topographic scattering effects as well as possible infragravity edge wave arrivals from more energetic surf zones to the north and south of the canyon head. An alongshore array of 12 Nortek Vector pressure-velocity (PUV) sensors was depoyed along the 10 m depth contour inshore of Scripps Canyon. Several of these instrument sites also included a Nortek Aquadopp velocity profiler. This array forms the offshore extension of an extensive surz zone array with similar instruments (not shown) deployed by Drs. Steve Elgar, Britt Raubenheimer (both at WHOI) and Rober Guza (SIO). This region is of particular interest because the steep and shallow canyon head causes extreme alongshore variations in wave heights. The combined arrays will be used to test models for the shoaling transformation of waves and the associated nearshore circulation.
At the northern end of the NCEX site where the shelf is approximately alongshore uniform, a directional wave buoy, two RDI acoustic Doppler current profilers, and a bottom pressure recorder were deployed along a cross-shore transect (Figure 1). Additional instruments along the same transect in shallow water (not shown) were deployed by Drs. Raubenheimer, Elgar, and Guza. The primary purpose of this transect is to extend our earlier studies of wave shoaling and inner shelf currents on the North Carolina shelf to a narrower west coast shelf. Finally, 7 bottom pressure sensors were deployed in the region between Scripps and La Jolla canyons. The primary purpose of these sensors is to resolve possible seiches between the canyons as well the refraction and focusing of swell by the two canyons.
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Last updated: 1 March, 2006