Principal components time spectra of suspended sediment in random waves

Sediment turbulent length and time scales are essential elements in modeling the fate and transport of contaminated mud. However, the sediment particle turbulent behavior in the water column is one of the least understood phenomena in sediment transport. Based on dimensional arguments, this paper discusses the spectrum shapes of the sediment concentration measured in the SUPERTANK experiment during broad banded and narrow banded random wave forcings. The sediment spectra used in this study are the fast fourier transforms of the temporal eigenfunctions computed by the Empirical Othogonal Function Analysis Method (Wai et al., 1993) in which the eigenfunctions are the time correlation between profiles. With low sediment concentration and small settling velocity, the sediment dynamics in the fluid has little effect on the flow dynamics, and the turbulent cascade of the sediment particles in the water column follows an Eulerian frequency, f, spectrum with a f-5/3 slope (Tennekes, 1975). If the sediment characteristic length and velocity scales are comparable to the Komogorov scales in the flow field, time spectrum variations with f-2 and f-1 are also possible.