Resuspension of Clays Under Waves

Abstract

Owing to their complex form, very small size and relatively low density, clays freshly deposited in a bay are vulnerable to resuspension when agitated by waves. The model of resuspension of clays under wave motion is presented from the point of view of (a) entrainment of the bottom clay at rest into the active semi-fluid layer; (b) diffusion of the near-bottom high-concentration mixture into the lower-concentration field in the upper layer. The near-bottom concentration at the initiation of the wave is estimated from the rate of entrainment. The diffusion equation containing the vertical convection term including the terminal fall velocity of clay is derived to obtain the transient concentration profile. The value of the vertical diffusion coefficient is derived from the energy equation of turbulence where energy production is balanced by dissipation. Then the diffusion coefficient is approximated directly from wave parameters. The model is executed by computing the initial near-bottom concentration and the transient concentration profile using experimental wave data form. It was found that the estimated initial concentration in the bottom region is compatible with those obtained from the measured data and then calculated transient concentration profiles show good agreement with the measured profiles.