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|Title:||A study of sediment sorting by waves shoaling on a plane beach|
|Authors:||United States, Beach Erosion Board|
Ippen, Arthur T.
Eagleson, Peter S.
|Publisher:||United States, Beach Erosion Board|
Engineer Research and Development Center (U.S.)
|Series/Report no.:||Technical memorandum (United States. Beach Erosion Board) ; no. 63.|
This report represents an investigation into the mechanics of the processes by which beach sediments are sorted selectively when acted upon by shoaling waves. The experimental facilities consisted of a 100 foot long, 2 and 1/2 foot wide and 3 foot deep glass-walled wave channel in one end of which an artificially roughened, fixed, plane beach of 1 on 15 slope was installed. Waves were generated at the other end by a horizontally reciprocating piston actuated by a hydraulic servomechanism with continuously variable speed and stroke. Test conditions comprised seven waves in a range of equivalent deep-water steepness of Ho/Lo = 0.02 to 0.06. Still-water depth was kept constant at 1.75 feet. The statistical motion of discrete spherical sediment particles 2 to 6 mm. in diameter and covering a 500 percent variation in fall velocity was studied for two separate uniform beach sand roughnesses, k = 0.79 mm. and k = 1.83 mm. Celerity and profile characteristics of the transforming waves are compared with the theory of Stokes extrapolated to the case of nonuniform depth. Net sediment motion is found to be due essentially to inequality of hydrodynamic drag and particle weight with a position of equality separating zones of net onshore and net offshore motion. Net onshore particle velocities were found proportional to the indicated mass transport velocity and approached it as the fall velocity of the particles became negligible. A theoretical analysis is presented which yields a general functional equation for net particle velocities. Specification of this expression for the cases of zero net motion and of net onshore motion leads directly to correlation of the experimental data for these two cases in terms of the local wave and particle characteristics, the sphere-roughness diameter ratio, D/k, and the approximate boundary layer thickness, ~ . Note: The symbol ~ indicates the presence of a scientific symbol that could not be rendered by the character set available to this system. The missing symbol can be seen in the downloaded file.
Massachusetts Institute of Technology. Hydrodynamics Laboratory
|Appears in Collections:||Technical Memorandum|