EMPIRICAL ORTHOGONAL FUNCTION-ANALYSIS OF SEDIMENT CONCENTRATION PROFILES SUBJECTED TO WAVES AND CURRENTS

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