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Physical effects of load fluctuations in rivers

Spiller, Stephan Mark
Doctoral thesis
Åpne
fulltext not available (Låst)
Permanent lenke
http://hdl.handle.net/11250/279013
Utgivelsesdato
2014
Metadata
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  • Institutt for maskinteknikk og produksjon [3222]
Sammendrag
The present dissertation describes the consequences of rapid discharge variations

on gravel bed rivers. It consists of a thesis part and eight attached

research papers.

A novel technique to artificially reproduce the surface structure in a

stream-bed is introduced and basic research experiments are performed on

an artificial static armor layer. These investigations, conducted under unsteady

flow, focus on (i) bed-shear stress, (ii) dynamic lift on the streambed

and (iii) spatial fluctuations in the near-bed velocity field. They form the core

of the present study and lead to the following results: Bed-shear stress during

unsteady flow could be very well predicted with the St. Venant equation

and showed no significant dynamic e↵ects as it consistently increased with

increasing discharge. The dynamic lift acting on a patch of the streambed,

however, showed remarkable variations in form of three distinct peaks during

increasing flow. The following hypothesis regarding spatial velocity fluctuations

in the near-bed flow field has been proposed: In uniform flow conditions

the form-induced stresses, being an indicator for spatial velocity fluctuations,

are independent from the discharge. In non-uniform flow conditions the

magnitude of form-induced stresses close to the streambed increases with

increasing discharge, while the qualitative shape of the form-induced stress

distributions is independent from the discharge and unsteadiness of the flow.

Further experimental and numerical studies included in this dissertation

discuss (i) how these basic research findings might a↵ect armor layer stability

and pore water exchange in the hyporheic zone, (ii) how sediments move as

bed load over a fully developed armor layer, (iii) how the flow in naturally

bent rivers might imply additional physical e↵ects of flow fluctuations and

finally, (iv) how mitigation measures could be designed.
Utgiver
NTNU
Serie
Doctoral thesis at NTNU;2014:319

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