Waves moving over the underwater chasms are focused in some places, generating big waves for surfers, and defocused in others just a short distance away, where toddlers play in gentle waves.
Fierce rip currents can sweep unwary swimmers offshore, and swirling eddies transport sand and drifting sealife, as well as any pollutants that enter the coastal waters during storms. Exactly how the canyons affect water movement is poorly understood, and present predictions of waves and currents can be dangerously misleading.
From September through December 2003, the Office of Naval Research is sponsoring the Nearshore Canyon Experiment (NCEX) to examine this mystery from air, land, sea, and "swash."
NCEX is bringing together a multidisciplinary team of researchers to study how the La Jolla and Scripps Canyons near San Diego affect waves, currents, and beaches. On cliffs overlooking the beach, scientists will install several "beachcams" and radars to monitor the building and breaking of waves.
Underwater, sensitive pressure sensors measure the weight of water in waves passing over them, current meters track the water's speed and direction, and jellyfish-like drifters with GPS will follow the water whither it leads.
During parts of the experiment, a specialized aircraft will take video from overhead and autonomous underwater vehicles will map changes in the seafloor. In the swash, the area of alternatingly wet and dry beach, other sensors will monitor the water's speed, direction, and pressure as it moves up, down, and across the shore.
The data collected will test and improve models of the dynamic nearshore environment so that the Navy and Marine Corps can more confidently predict the safest routes from sea to land. "Our present theories for how waves move over an irregular seafloor are best suited to smooth or gently rolling underwater hills," explains Tom Drake, program manager for the Coastal Geosciences Program at the Office of Naval Research in Arlington, Va.
But submarine canyons and other treacherous underwater landscapes can be found all over the world, and the Navy must be prepared for anything.
According to Drake "these studies will directly benefit beachside communities concerned with erosion and beach nourishment, will give coastal planners improved ability to predict how pollution from storm runoff moves through nearshore waters, and will aid biologists attempting to trace the complex paths of larvae and other marine organisms in the surfzone."
ONR is sponsoring researchers from a number of academic, government, and private institutions. Scripps Institution of Oceanography will be hosting a media day at the NCEX site in October 2003.