Modelling and Analysis of Fine Sediment Transport in Wave-Current Bottom Boundary Layer

205 Pages·2018·10.52 MB·English

by  Liqin Zuo

MODELLING AND ANALYSIS OF FINE SEDIMENT TRANSPORT
IN WAVE-CURRENT BOTTOM BOUNDARY LAYER

MODELLING AND ANALYSIS OF FINE SEDIMENT TRANSPORT IN
WAVE-CURRENT BOTTOM BOUNDARY LAYER

DISSERTATION

Submitted in fulfillment of the requirements of
the Board for Doctorates of Delft University of Technology
and
of the Academic Board of the IHE Delft
Institute for Water Education
for
the Degree of DOCTOR
to be defended in public on
Monday, 4 June 2018, at 15:00 hours
in Delft, the Netherlands

by

Liqin ZUO

Master of Engineering in Harbor, Coastal and Offshore Engineering, Nanjing Hydraulic Research
Institute, China
born in Shandong, China
This dissertation has been approved by the promotors:
Prof. dr. ir. J.A. Roelvink and
Prof. dr. Y.J. Lu

Composition of the doctoral committee:

Chairman Rector Magnificus TU Delft
Vice-Chairman Rector IHE Delft
Prof. dr. ir. J.A. Roelvink IHE Delft/TU Delft, promotor
Prof. dr. Y.J. Lu Nanjing Hydraulic Research Institute, China, promotor

Independent members:
Prof.dr. P. Nielsen The University of Queensland, Australia
Prof.dr. L.C. van Rijn University of Utrecht
Prof.dr.ir. Z.B. Wang TU Delft
Prof.dr.ir. J.C. Winterwerp TU Delft
Prof. dr.ir. W.S.J. Uijttewaal TU Delft, reserve member

This research was conducted under the auspices of the Graduate School for Socio-Economic and
Natural Sciences of the Environment (SENSE)

CRC Press/Balkema is an imprint of the Taylor & Francis Group, an informa business

© 2018, Liqin ZUO

Although all care is taken to ensure integrity and the quality of this publication and the information
herein, no responsibility is assumed by the publishers, the author nor IHE Delft for any damage to the
property or persons as a result of operation or use of this publication and/or the information contained
herein.
A pdf version of this work will be made available as Open Access via http://repository.tudelft.nl/ihe.
This version is licensed under the Creative Commons Attribution-Non Commercial 4.0 International
License, http://creativecommons.org/licenses/by-nc/4.0/

Published by:
CRC Press/Balkema
Schipholweg 107C, 2316 XC, Leiden, the Netherlands
[email protected]
www.crcpress.com – www.taylorandfrancis.com
ISBN 978-1-138-33468-7.
The work is financially supported by the Joint Research Project of The Netherlands
Organisation for Scientific Research (NWO) - National Natural Science Foundation of
China (NSFC) (Grant No. 51061130546) and NSFC (Grant No. 51520105014 and
51509160).

To my family

Abstract
The evolution and utilization of estuarine and coastal regions are greatly
restricted by sediment problems. Inspired by the Caofeidian sea area in Bohai
Bay, China, this study aims to better understand silty sediment transport
under combined action of waves and currents, especially in the wave-current
bottom boundary layer (BBL), and to improve our modelling approaches in
predicting estuarine and coastal sediment transport.
Field observations were carried out in northwestern Caofeidian sea area
of Bohai Bay and field data were collected on several other silt-dominated
coasts. Analysis shows that silt-dominated sediments are sensitive to flow
dynamics: the suspended sediment concentrations (SSCs) increase rapidly
under strong flow dynamics (i.e., waves or strong tidal currents which can stir
up sediments), and high concentrations cause heavy sudden back siltation in
navigation channels. In the following, details of silty sediment transport are
studied, focusing on the BBL and high concentration layer (HCL).
From laboratory experiments and theoretical analysis, an expression for
sediment incipient motion is proposed for silt-sand sediment under combined
wave and current conditions. The Shields number was revised by adding the
cohesive force and additional static pressure, leading to an extended Shields
curve.
To study the HCL, a process based 1DV model was developed for
flow-sediment dynamics near the bed in combined wave-current conditions.
Based on the physical processes, special approaches for sediment movement
were introduced, including approaches for different bed forms (rippled bed
and 'flat-bed'), hindered settling, stratification effects, mobile bed effects,
reference concentration and critical shear stress. The HCL was simulated and
sensitivity analysis was carried out by the 1DV model on factors that impact
the sediment concentration in the HCL. The results show that the HCL is
affected by both flow dynamics and bed forms; the thickness of the HCL is
about twice the height of the wave boundary layer; bed forms determine the
shape of the concentration profile near the bottom, and flow dynamics
determine the magnitude. For finer sediment, stratification effects and mobile
bed effects impact the sediment concentration greatly.
Finally, based on the 1DV model, the formulations of the mean sediment
concentration profile of silty sediments were studied. By solving the
time-averaged diffusion equation for SSC and considering the effects of bed
forms, stratification and hindered settling, expressions for time-averaged SSC
profile under wave conditions were proposed for silt and are applicable for