Thesis-2007-Todd-Burley.pdf (49.8 MB)
An experimental study of the transport pathways of individual bedload clasts over a gravel-bed substrate
thesis
posted on 2014-04-29, 11:43 authored by Natasha R. Todd-BurleyThe movement of individual clasts over a water-lain gravel substrate is investigated
in a series of flume experiments. The effects of three experimental variables (mobile clast
size, flow condition and release pocket) on the characteristics of extracted transport
parameters (step length, step velocity, pathway sinuosity and rest period) are examined
using a novel facsimilie of a real gravel bed. As the mobile clast size is increased the mean
step length and mean step velocity of individual steps increases. The sinuosity of
individual pathways increases with mobile clast size. The release pocket, which determines
the region of the substrate over which the clast can move, was also found to influence the
transport parameters. In general, mobile clasts exhibit shorter step lengths and more
sinuous pathways over substrates that have a number of large clasts present in the bed
surface. The mean rest period was found to be dependent on the mobile clast size and the
release pocket. Mobile clasts equal to and greater in size than the median (of the gravel
substrate) exhibited longer rest periods when their pathways coincided with areas in which
large obstacle clasts were present. In contrast, mobile clasts smaller than the median
exhibited longer rest periods when their pathways coincided with areas devoid of the
influence of large obstacle clasts. Examination of the tracer pathways identified a number
of areas that operate as trap areas or transport routes for mobile clasts. Trap areas were
identified in a number of different topographical locations, in both the of and upstream, on
the stoss side of, large clasts. In general, compared to the rest of the bed, the trap areas
exhibit lower than average streamwise velocities, mean vertical velocities away from the
boundary and a dominance of turbulent structures away from the boundary. The ability of
the trap areas to trap mobile clasts was found to decrease with increasing mobile clast size.
Furthermore, this effect was found to be greater at stronger flows. In general, compared to
the rest of the bed, the transport routes exhibit higher than average streamwise velocities,
mean vertical velocities towards the boundary and a dominance of turbulent structures
towards from the boundary. In total, these observations contribute to an understanding of
the elementary parameters of transport and are therefore of substantial value to the future
development of models that deal with the prediction of bedload transport rates and
simulations of bedform development.
History
School
- Social Sciences
Department
- Geography and Environment
Publisher
© Natasha Ria Todd-BurleyPublication date
2007Notes
A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.EThOS Persistent ID
uk.bl.ethos.479273Language
- en