A surface-based hiding function linking flume and field data

The quantification of the sheltering and exposure effects of non-uniform sediments has been widely achieved through hiding function models. Big challenge exists so far in the model parameter that is highly variable and differs greatly between laboratory flumes and field streams. This paper presents an improved surface-based hiding function. The force balance for particle inception was formulated and the allocation of the overall bed shear stress into each group of sediments was mimicked. The new hiding function was examined against and agrees well with the documented field and flume data. It was shown that the hiding function is closely related to the relative flow depth and the reference elevation in the velocity profile in addition to the bed material gradation. The power law of velocity profile that applies to both flume flows and natural streams can link the flume and field data together. The hiding function with b = 1/6 and b = 1/2 is applicable to natural streams and laboratory flumes, respectively. The value of b = 0.263 also works well for gravel bed rivers. The range of the reference elevation, namely z₀ = 0.4D_m–1.4D_m, is recommended for either the flume or field data. The new hiding function contributes to addressing clearer physical meanings and a useful perspective for further improvement.