Evolution of a Surfzone Hole: Part 1. Pilot
Final rept. 1 Jun 2005-16 Aug 2006
WOODS HOLE OCEANOGRAPHIC INSTITUTION MA DEPT OF APPLIED OCEAN PHYSICS AND ENGINEERING
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This project provided funds for initial investigations about the behavior of a large hole in the surfzone. A backhoe was used to create a 10-m diameter, 2-m deep hole that simulated the change to the morphology caused by an explosion near the shoreline. The hole was created near the water line at low tide, and instrumented with many acoustic Doppler current meters. As the tide rose, continuous surveys of the bathymetry within and near the hole were performed, allowing detailed investigation of the evolution of the bathymetry as waves reached and overtopped the hole. Waves and currents were measured from offshore of the hole about 2-m water depth to near the landward extent of the run up above the hole. As water reached the altered beach topography, sediment was transported such that the hole began to fill a combination of collapse of the sides of the hole and sediment transport towards the hole. The hole was filled, and the beach face returned to its initial configuration within one tidal cycle. The experiment was performed 3 times, first to gain experience creating a hole, second to learn how to instrument the hole rapidly, and the third to monitor in detail the waves and currents within the hole. Graduate student Jim Thomson analyzed the current meter data and surveys to show that the water in the hole formed a seich with frequency of oscillation that changed as the hole evolved from circular to semi-circular. The observed frequencies were similar to those predicted for a circular basin and for a semi-circular resonator. Dye patterns showed the path of water and thus of sediment or other tracers in the water as the hole evolved and slowly filled in.
- Physical and Dynamic Oceanography