Concentrations in oscillatory sheet flow for well sorted and graded sands: Fid-Bau Portal

Concentrations in oscillatory sheet flow for well sorted and graded sands

O'Donoghue, Tom / Wright, Scott

AbstractIn wave-generated sheet flow conditions, oscillatory near-bed flow is large, ripples are washed out and sand is mainly transported in a thin layer, a few centimetres thick, close to and below the no-flow bed level. New experiments in the Aberdeen Oscillatory Flow Tunnel have produced a comprehensive dataset of transport processes for well-sorted and graded sands in large-scale sinusoidal and asymmetric oscillatory sheet flow conditions. In this paper, detailed time- and height-varying concentration measurements are analysed. The range and level of detail in the measurements make it possible to quantitatively analyse concentration behaviour more rigorously than before. A new empirical equation is presented which characterises the time-dependent concentration profile in the sheet flow layer. The equation involves two time-dependent parameters: erosion depth and reference concentration. The dependence of both parameters on flow and bed conditions is analysed. New results are presented which make it possible to estimate time-dependent erosion depth, reference concentration and, therefore, concentration profile. The effects of grading on sheet flow concentrations are analysed by comparing results from the large range of sand beds tested.