ABSTRACT114 temperature sections, each containing an average of 10 bathythermograms, show that internal waves commonly become altered on crossing the shoaling bottom of the continental shelf in Santa Monica Bay, Calif. The alteration takes the form of internal swash (in which the lower isotherms reach farther landward than would be expected from their depth above the outer shelf or above deeper bottom) and of internal surf (that is, denoted by temperature inversions, isolated boluses of colder water at the bottom, and complex short wave-length variations of isotherms).Evidence of internal swash and surf produced by internal waves crossing the continental shelf was found in the 1950s during studies of water characteristics needed for the evaluation of potential effects of sewage disposal at Santa Monica Bay, Calif. These studies were conducted at the Allan Hancock Foundation, University of Southern California, under the general direction of R. E. Stevenson (1) and at the Bureau of Sanitation, City of Los Angeles, under the direction of Gunnerson (2). The data on internal waves and their effect upon suspended sediment were considered important and useful enough to justify further work perhaps as doctoral dissertations. Unfortunately, local student interest did not occur, perhaps because of changes in the organizations. Accordingly, the writers have prepared this summary from data nearly 20 years old in the renewed hope that others may continue the effort on different continental shelves of the world. MEASUREMENTS AND RESULTSThe best series of data on the internal waves, swash, and surf on the continental shelf during this study was obtained for 114 thermal sections across the shelf between Santa Monica and Redondo submarine canyons (Fig. 1). These measurements were made during a nearly 2-year period, August 1954 to May 1956. Most sections ranged from 10-to 15-km long usually between the shelf-break at about 90 m to the nearshore zone. They required 20-70 min, or an average of 45 min. Along each section were 5-20 bathythermograph lowerings, an average'of 10 per section, or a total of about 1150 lowerings.Plots of isotherms with depth between the position of each bathythermograph recording along the sections revealed the presence of broad undulations in virtually every section (Fig. 2). These undulations are considered evidence of internal waves, as discussed by Summers and Emery (3) and LaFond (4). They have about the same apparent wave length whether the section was made in a seaward or a shoreward direction, indicating that the speed of the internal waves was slow compared with the 14-18 km/hr speed of the ship on which the bathythermograms were made. Probably they are of tidal period, like those described from the same region by Summers and Emery that proceeded from west to east at a speed of 2379 about 13 km/hr over deep water and of less than 2 km/hr across shelf depths. Plots show that the wave length of the internal waves ranged from 3 to 24 km and averaged 9 km. The maximum amplitude of isotherms in each s...
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