Empirical orthogonal functional analysis of sediment concentration profiles subjected to waves and currents

Abstract

Spatial and temporal eigenfunctions for profiles of suspended-sediment concentrations collected during three distinct flow conditions (current-dominated, wave-dominated, and wave- current-dominated) were used to study the non-linear sediment dynamics in the water column. The eigenfunctions were obtained by the method of Empirical Orthogonal Function (EOF) analysis. The variance distribution of the first spatial eigenfunction associated with the largest eigenvalue reflects the characteristic structure of the original profiles, and the second largest spatial eigenfunction indicates the location of possible structural or boundary layer changes in the profiles. The first temporal eigenfunctions for the current- and wave-driven profiles correlate with the turbulence-wave kinetic energy. Because of the complexity of the wave-current flow field, the first two temporal eigenfunctions for the wave-current-driven profiles have a weak relation with the major driving forces. Orthogonal functions can be used to reconstruct sediment concentration profiles efficiently and accurately. To reconstruct 97% of the variation of 10-min averaged profiles in a 2-h data record, only two eigenvalues, and their corresponding orthogonal functions are required, even in the complex wave-current flow field.