Abstract

Bedforms in alluvial river beds can often be identified as 2D- or 3D-forms. A complete description of bedforms, and even a full description of the riverbed topography, should distinguish between 2D and 3D bedforms; nonetheless, an objective and general method to assess bedform 3-dimensionality is not available. The paper presents a method for a measurable identification of 3D bedforms introducing a 3-dimensionality Index T-b. T-b is based on estimating the autocorrelation of a random field of bed elevations, between bed profiles orthogonal to the main flow direction, and a reference mean cross-sectional bed profile. The developed method is tested with synthetically generated bedforms, for which sinusoidal functions are used to reproduce characteristics of archetypical natural sediment waves. Additionally, the approach is applied to experimental data under live-bed conditions, where the bed surface was surveyed using a high resolution 3D stereo photogrammetric system. Results show that the suggested method can serve as an objective tool to rank bedforms and bed states 3-dimensionality, with a continuous scale between 0 and 1.