Dynamic behavior of a thermal plume

The thermal front phenomenon was observed during field surveys in June and October, 1978 at the Ginna Power Plant site on Lake Ontario. Thermal fronts are rapid temperature oscillations in the near field of a thermal plume and are generally observed in calm receiving water. The fronts were measured at a number of fixed locations in the Ginna plume from two boats equipped to measure temperature at four depths and from one boat measuring velocity at 2 1/2 feet below the water surface. Infrared overflight measurements were also taken. Temperature oscillations were observed with amplitudes of over 30C measured from the mean with periods ranging from approximately 100 to 600 seconds depending on the longitudinal distance from the discharge, discharge velocity, water depth in the lake, and receiving water current. Oscillations appeared to be highest near the discharge for the June survey and decayed with distance from the discharge with little variation in depth. During the October survey (when the lake elevation was 2.3 feet lower than the June survey and the plume touched lake bottom for the first 200-300 feet) the oscillations started at about 200 feet from the discharge, peaked at about 500 feet and were not discernible at distances greater than 1400 feet from the discharge. The discharge, meteorological and hydraulic site conditions were all relatively constant during each day of the surveys