Abstract
The measurement of the morphologic characteristics of evolving sediment beds around hydraulic structures is crucial for the understanding of the physical processes that drive scour. Although there has been significant progress towards the experimental characterization of the flow field in setups with complex geometries, little has been done with respect to the quantitative investigation of dynamic sediment bed geometry, mainly due to the limited capabilities of conventional instrumentation. Here, a recently developed computer vision technique is applied to obtain high-resolution topographic measurements of the evolving bed at the base of a cylinder during clear water scour, without interrupting the experiment. The topographic data is processed to derive the morphologic characteristics of the bed such as the excavated volume and the slopes of the bed. Subsequently, the rates of scour and the bathymetry at multiple locations are statistically investigated. The results of this investigation are compared with existing flow measurements from previous studies to describe the physical processes that take place inside a developing scour hole. Two distinct temporal phases (initial and development) as well as three spatial regions (front, side and wake) are defined and expressions for the statistical modelling of the bed features are derived.
Highlights
The interaction among hydraulic structures, water flows and sediment beds is one of the most complicated phenomena in hydraulic engineering
A new computer vision-based technique was employed to monitor the morphological characteristics of an evolving gravel bed at the base of a cylinder, in clear water scour conditions, with very high temporal and spatial resolution
The evaluation of the calculated statistics led to the categorization of the scour phenomenon in two main temporal phases, namely the initial
Summary
The interaction among hydraulic structures, water flows and sediment beds is one of the most complicated phenomena in hydraulic engineering. The prediction of changes in the bed topography due to scour is fundamental for the safe and cost-effective design of hydraulic structures [1]. This problem has been extensively investigated over the last decades through numerous laboratory tests, field observations, numerical simulations, and derivation of empirical relationships. Many of the derived empirical or semi-empirical relationships were recently summarized and evaluated in [2]. These efforts have provided us with important insights on the effects of various parameters on the scour depth in laboratory simulations, physical understanding of the phenomenon is incomplete. Improved engineering tools are needed to advance the design and protection of hydraulic structures
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