Abstract:
An investigation has been made of several physical parameters of the effluent plume of the Columbia River as it enters the Pacific
Ocean. Radioactive material in trace amounts enters the Columbia River from the Hanford nuclear reactors at Richland, Washington. One of these nuclides, chromium -51, has been used to determine the distribution pattern of the plume at sea, the surface velocity of the ocean currents transporting the plume and the lateral eddy diffusion coefficient of the plume as it diffuses into the surrounding
oceanic water. This was achieved by concentrating the 51Cr from the water with a large volume chemistry system and analyzing it aboard a ship. In this system, the 51 Cr in a 580 liter sample of sea water is coprecipitated with ferric hydroxide and analyzed with a sensitive gamma-ray spectrometer. The immediate availability of data permits adjustment of the ship's course to better follow the plume. Results, based on chromium -51 activity, of three plume cruises in different seasons indicated the following: In the summer, the tip of the Columbia River plume extended southward from the river mouth some 380 km and was 240 km offshore. The southward velocity of the surface current which transported the plume was 12-13 cm/ sec. The lateral eddy diffusion coefficient of the plume was (3)107 to (8)107 cm2/ sec. In the winter, the plume extended to the Straits of Juan de Fuca and was generally confined to within 20 km of the Washington coast. The longshore surface velocity of the current transporting the plume averaged 11 cm/ sec northward. The lateral eddy diffusion coefficient for this distribution was (2)106 cm2/ sec, perhaps reflecting the effects of coastal confinement.
