Data repository: The role of sand fraction in mud-dominant wave-supported gravity flows

Abstract

We performed laboratory experiments to investigate the influence of sand content on the dynamics of wave-supported gravity flows in mud-dominant environments. The experiments were carried out in an oscillatory water tunnel with a sediment bed of either 1% or 13% sand. Low and high energy regimes are differentiated based on a Stokes Reynolds number Re_Delta ≈ 500. In the low energy regime, the sand fraction influences flow dynamics primarily through ripple formation; no ripples form in 1% experiments, whereas ripples form in the 13% experiments that increase turbulence and the wave boundary layer thickness, delta_m. In the high energy regime, small ripples form in both the 1% and 13% sand experiments and we observe high near-bed suspended sediment concentrations. The influence of stratification on the boundary layer flow is characterized in terms of the gradient Richardson number Ri_g. The flow is weakly stratified inside the boundary layer for all runs and critically stratified at or above the top of the boundary layer. In the lower regime, the sand content reduces the relative influence of stratification in the boundary layer, shifting the elevation of critical stratification, L_B, from approximately 1.3delta_m to 2.5delta_m in the 1% and 13% experiments, respectively. In both sets of experiments L_B ≈ delta_m at the strongest wave energy, indicating a transition to strongly stratified dynamics.