Tsutomu Komine

FIELD MEASUREMENTS OF CRITICAL RIP CURRENTS UNDER CALM SEA CONDITION

An investigation team comprised of coastal researchers and engineers carried out field measurements of rip currents and experienced drift by the current on Sagara Sun Beach during August 23-24, 2007 with help of lifesavers and surfers. The waves and rip currents were observed near the breakwaters and the data were analyzed from the viewpoint of the safety of the beach users such as sea bathers and surfers. Various water safety problems related to the rip currents were discussed based on the field data, real experience of the drift and information of the lifesavers. A steady rip current around 0.25 m/s generated along a breakwater under calm sea condition yields dangerous situation to sea bathers and the degree of the dangerousness depends on the water depth as well as current velocity.