Abstract
Validation and scaling of sophisticated physical and numerical fluvial hydraulic models to real field conditions are limited by temporal and spatial constraints of field measurement technologies. These limitations increase when analyzing hydraulic properties of complex river forms such as submerged bedrock canyons. The analysis of flow under these conditions has demonstrated non-linear behavior, strong secondary circulation and a high level of turbulence. The objective of this paper is to obtain and analyze turbulence and secondary current information for flow analysis, by evaluating the spatial distribution of bed shear stress and eddy viscosity with acoustic Doppler current profiler (ADCP) measurements. The real field-scale case study was the Lourenço Rock Canyon in Tocantins River, Brazil. A total of 10,531 velocity profiles were measured with an ADCP adapted to a moving boat. The data were post-processed by decomposing the velocity data measurements and calculating the standard deviations. Three different methods are compared for bed shear stress: total kinetic energy (TKE), law of the wall and the depth–slope product. The eddy viscosity was estimated with the Boussinesq approach. The initial data processing confirmed turbulence and flow velocity characteristics described in similar literature findings. The results for the bed shear stress for the canyon area were 8 times greater than the outside and for eddy viscosity, 10 times higher. For the surroundings area, the eddy viscosity showed reasonable results with values around the regular 1.0 m2/s used for rivers. It is concluded that turbulent values can be calculated to better represent physical processes with the intention to improve hydrodynamic numerical models calibrations.
Highlights
The understanding of complex flow features, as a consequence of complex geometries or hydrodynamic boundary conditions, is very important for the analysis of transport of substances or sediment in rivers and coastal waters, as well as for navigability analysis in waterway projects.The study of those features generally involves sophisticated physical and numerical modeling approaches [1]
Compared to intrusive and punctual devices, acoustic instruments, such as the acoustic Doppler current profiler (ADCP), have been used in conventional, hydrological river measurements, yielding increased accuracy and greater spatial and temporal resolution due to hardware improvements providing better accuracy for positioning, and having several frequencies combined in the same devices, as well as being robust equipment for field deployment, especially compared to optical (e.g., LSPIV)
The previously described methods have been applied to all measured velocity profiles to obtain shear stress and eddy viscosity distributions for the whole river section
Summary
The understanding of complex flow features, as a consequence of complex geometries or hydrodynamic boundary conditions, is very important for the analysis of transport of substances or sediment in rivers and coastal waters, as well as for navigability analysis in waterway projects. The study of those features generally involves sophisticated physical and numerical modeling approaches [1]. Compared to intrusive and punctual devices (current meter), acoustic instruments, such as the acoustic Doppler current profiler (ADCP), have been used in conventional, hydrological river measurements (discharge, depth, velocity), yielding increased accuracy and greater spatial and temporal resolution due to hardware improvements providing better accuracy for positioning, and having several frequencies combined in the same devices, as well as being robust equipment for field deployment, especially compared to optical (e.g., LSPIV)
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