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Background
Gravel bed rivers represent an important
stream type in fluvial environment with regard
to many engineering applications such as
hydropower. Hydropower generation controls
the hydrological regime (e.g. load fluctuations,
hydro peaking etc.), and subsequently affects
exchange processes between surface and sub-
surfaceflows, the so-called hyporheic exchange.
Colmation and decolmation, i.e. the retention of
fine particles in the streambed leading to the
clogging of the river bed and the resuspension
of deposited fine particles, respectively, are two
processes in this respect. In fact, colmation
processes can affect the spawning areas for
salmon and suppress hyporheic exchange by
altering bed porosity and hence the near bed
turbulent flow structure.This study highlights
this issue by focusing on the effect of porosity on
the near bed turbulent flow field, shear stress,
and flow resistance.
Methodology
In order to isolate the influence of porosity, a
novel bed reproduction technique is used to
reproduce the impermeable counterparts
of a natural gravel bed surface. Turbulence
characteristics are determined using
Particle Image Velocimetry (PIV) / Volumetric
3-component Velocimetry (V3V) and Aquistic
Doppler Velocimetry (ADV). Roughness of the
surfaces is determined through Digital Elevation
Models (DEMs). The aquired velocity data will be
analysed based on the Double-Averaged Navier-
Stokes equations.
Department of Civil
and Environmental
Engineering
2013-2017
The Effect of Bed
Porosity on the
Turbulent Flow Field in
Gravel Bed Rivers
Supervisors:
Jochen Aberle
Co-supervisor:
Nils Rüther
Christy Ushanth
Navaratnam
PHD THESIS
Artificially reproduced surface.
Natural gravel bed surface.
Sketch of the experimental set-up.
Sketch of the experimental set-up
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