L-86/83-- 1/18/83;  AN OBSTRUCTION WAS FOUND IN THE SAVANNAH RIVER SOUTH CHANNEL AT 32/05/19.2N 81/00/43.8W (NAD 27), 120 METERS SOUTHEAST OF DAYBEACON "A5".  THE OBSTRUCTION IS A LARGE PLATFORM, 10 METERS LONG BY 5 METERS WIDE, FIRMLY LODGED AT THE ABOV