Abstract
The composition or bed material plays a crucial role in the physical hydromorphological processes of fluvial systems. However, conventional bed material sampling methods provide only pointwise information, which can be inadequate when investigating large rivers of inhomogeneous bed material characteristics. In this study, novel, image-based approaches are implemented to gain areal information of the bed surface composition using two different techniques: monocular and stereo computer vision. Using underwater videos, captured in shorter reaches of the Hungarian Danube River, a comparison of the bed material grain size distributions from conventional physical samplings and the ones reconstructed from the images is carried out. Moreover, an attempt is made to quantify bed surface roughness, using the so-called Structure from Motion image analysis method. Practical aspects of the applicability of image-based bed material mapping are discussed and future improvements towards an automatized mapping methodology are outlined.
Highlights
There is a permanent interaction mechanism between the water flow and the riverbed, which on the one hand determines the sediment transport capacity of the river yielding to different morphodynamic processes, and on the other hand, the riverbed itself, through the hydraulic resistance, influences the flow features
There were samples, where the grain size distributions constructed from the images showed a good match with the sieving based GSDs
Two different approaches were tested in shorter sections of a large river: monocular and stereo vision methods
Summary
There is a permanent interaction mechanism between the water flow and the riverbed, which on the one hand determines the sediment transport capacity of the river yielding to different morphodynamic processes, and on the other hand, the riverbed itself, through the hydraulic resistance, influences the flow features. This back-and-forth effect eventually leads to a complex and continuously changing system of the rivers, possessing great practical importance. Bank infiltrated drinking water production depends on, e.g., porosity, stratification, permeability, armoring, colmation, and characteristic sediment grain sizes [1,2]. When analyzing reach scale hydromorphological processes, there is a strong need to gain detailed information on the flow features, the riverbed morphology, the sediment transport, and as a crucial boundary condition: the composition of the riverbed
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