Monitoring incipient breaching at an artificial inlet: Georgica Pond, New York

Georgica Pond, on Long Island's ocean coast in East Hampton, NY, is normally separated from the ocean by a beach about 100 m wide, but mechanically opened to the Atlantic Ocean. Observations of the breach were made for three days, until it closed naturally. A channel 6 m wide was dug on April 23, 2008. The water level in the Pond was initially 1.46 m higher than the ocean. Upon completion of the channel, pond water rushed seaward through the new inlet at a speed reaching 3.7 m/sec. The flow was supercritical with a hydraulic jump forming at the inlet mouth. The cut widened in an hour by the progressive, sudden collapse of steep sections of bank along its length, growing at a rate of about 0.2 m/min, then slowing to about 0.1 m/min, eventually stabilizing at a width of 43 m. Forty-two hours after opening, the salinity in the pond suddenly jumped from 7 to 19. Pond salinity reached 26 about four days after the inlet opened. Over the course of five days, the water level in the pond fell 0.5 m, draining 530,000 m³ of water into the ocean. About 3,800 m ³ of sand formed an ephemeral ebb shoal that was gradually swept to the west and back into the western beaches by wave-induced longshore transport. The inlet closed by April 28. On May 2, 8.5 days after the opening, salinity dropped to 13 and continued to fall slowly as freshwater drained into the pond.