Derivation Of Settling Velocity, Eddy Diffusivity And Pick-Up Rate From Field-Measured Suspended Sediment Concentration Profiles In The Horizontally Uniform But Vertically Unsteady Scenario

Accurate determinations of sediment settling velocity (w(s)), eddy diffusivity (D-s), and pick-up rate p(t) from available field data are vital for engineering calculations or numerical simulations of coastal processes. Existing methods to determine these parameters are normally based on the assumption of a steady equilibrium that ignores the "phase lag" and "amplitude damping" effects of a diffusing concentration in unsteady scenarios that are typical of many field settings. The present paper gives an analytical solution for a time-varying suspended sediment concentration profile C(z,t) in the horizontally uniform but one-dimensional vertical (1DV) unsteady scenario with a vertically constant D-s distribution. The model is used to estimate w(s), D-s, and p(t) by determining best fits between the modelled and C(z,t) profiles measured with an instrumented quadripod in the subaqueous Yellow River Delta (YRD) during a local sediment resuspension event. Values of field-derived w(s) range from 0.01 to 0.073 mm/s, while D-s range from 2 x 10(-5) to 1.46 x 10(-4) m(2)/s, and p(t) range from 8.3 x 10(-5) to 3.14 x 10(-4) kg m(2) s(-1) under mild and energetic wave conditions, respectively, which are consistent with our laboratory measurements and with the results reported in the literature; time variations of the derived parameters are also reasonable in response to the synchronous hydrodynamics, both confirm that the parameter optimizations are successful. The proposed analytical model is shown to be a practical tool for inferring w(s), D-sy, and p(t) from available measured C(z,t) profiles free of secondary prediction equations or unknown empirical parameters.