
Tom De MulderGhent University | UGhent · Department of Civil Engineering
Tom De Mulder
MSc Civ.Eng., PhD
About
97
Publications
17,117
Reads
How we measure 'reads'
A 'read' is counted each time someone views a publication summary (such as the title, abstract, and list of authors), clicks on a figure, or views or downloads the full-text. Learn more
1,197
Citations
Introduction
Publications
Publications (97)
A depth‐averaged (2DH) exploratory model is developed to identify morphodynamic equilibria in short mesotidal inlet systems with arbitrary planform geometries. The water motion is forced by an M 2 tidal constituent at the seaward entrance and is described by the depth‐averaged shallow water equations, whereas the depth‐integrated suspended sediment...
This paper presents a Lagrangian laboratory study of the passive tracer transport in and around a lateral, open-channel (square) cavity. Using 3D-particle tracking velocimetry (PTV), the trajectories of neutrally buoyant seeding particles are measured and analyzed to investigate the processes governing the particle exchanges between the cavity and...
To investigate the historical development of the tidally averaged transport of sandy sediments in the main branch of the Scheldt estuary over the last decades (1950–2013), a 2D exploratory model has been developed. This model comprises the depth-averaged (2DH) shallow water equations, driven by an asymmetric tidal forcing at the seaward side, as we...
The Schelde estuary, characterised as a turbid, polluted and eutrophic system, has nowadays reached a turning point in the
restoration of its water quality. During the past century, human activities have reduced the intertidal areas, essential in
the estuarine ecosystem for nutrient cycling and the self-cleaning capacity. Today, in combination with...
To acquire knowledge of the surface storage effects in the flow separation zone of a T-shaped open-channel confluence, independent Large Eddy Simulations are performed of the flushing with fresh water of a downstream branch which is initially uniformly contaminated by a passive scalar. Based on the ensemble averaged concentration, the spatial distr...
Two ultrasonic anemometers, namely the Gill HS-100 and the Anemoment TriSonica Mini, were placed in the VKI L-1A wind tunnel to assess their accuracy and precision. A comparison was made between these instruments and a Prandtl probe, using a range of wind speeds up to 20 m/s, eighteen azimuth angles (wind directions) at 20° intervals, five tilt ang...
Open-channel confluences are important junctions in natural and human-made channel networks. Different controls of the confluence hydrodynamics have already been studied intensively, often in schematized geometrical configurations. The T-shaped planform with branches having rectangular cross-sections of equal width is a popular geometry in lab expe...
In the context of a T-shaped open-channel confluence, where the tributary flow separates at the downstream junction edge and creates a separation zone in the post-confluence channel, this paper provides a critical reflection upon the terminology and the delineation methods for the separation zone and its proxies: the recirculation zone and the reve...
Channel–shoal patterns are often observed in the back–barrier basins of inlet systems and are important from both an economical and ecological point of view. Focussing on double–inlet systems, the initial formation of these patterns is investigated using an idealized model. The model is governed by the depth–averaged shallow water equations, a dept...
The existence of morphodynamic equilibria of double‐inlet systems is investigated using a cross‐sectionally averaged morphodynamic model. The number of possible equilibria and their stability strongly depend on the forcing conditions and geometry considered. This is illustrated by considering a rectangular double‐inlet system forced by M2 tidal con...
This experimental laboratory study presents a detailed analysis of the surface oscillations inside a square cavity connected laterally to an open channel. For an approaching steady and one-dimensional main stream with a high (subcritical) Froude number, interaction with the dead water volume in the cavity area triggers high-amplitude free-surface o...
3D view of the degraded bed.
Lateral cavities adjacent to open-channel flows are dead zones located on one side of a main stream. With an approaching flow with a high (subcritical) Froude number, the free-surface of the dead-zone oscillates with high amplitudes and generates a so-called seiche. This configuration is reproduced in a rectangular cavity (with an interface length...
Migrating fish species are worldwide in decline due to several global changes and threats. Among these causes are man‐made structures blocking their freshwater migration routes. Shipping canals with navigation locks play a dual role in this. These canals can serve as an important migration route, offering a short cut between freshwater and the sea....
Background
Acoustic positioning telemetry allows to collect large amounts of data on the movement of aquatic animals by use of autonomous receiver stations. Essential in this process is the conversion from raw signal detections to reliable positions. A new advancement in the domain is Yet Another Positioning Solver (YAPS), which combines the detect...
Confluences are important junctions in fluvial and artificial networks of open-channels,
as they regulate the mixing phenomena of substances transported by the merging flows, as well as the scour and deposition phenomena. This paper aims at contributing to the study of how the bed morphology, such as the presence of a scour hole and a depositional...
Background
Acoustic positioning telemetry is nowadays widely used in behavioural ecology of aquatic animals. Data on the animal’s geographical location and its changes through time are used to study for instance movement patterns, habitat use and migration. The acoustic signals are detected by stand-alone receivers, allowing to collect huge amounts...
This work presents the design and application of a Lagrangian measurement and analysis methodology, which is employed to study the flow and passive tracer exchange between a main channel and a lateral cavity in a laboratory experiment. For this purpose, a 3D-PTV system is implemented for which a static and dynamic experimental validation show that...
Background: Acoustic positioning telemetry allows to collect large amounts of data on the movement of aquatic animals by use of autonomous receiver stations. Essential in this process is the conversion from raw signal detections to reliable positions. A new advancement in the domain is YAPS (Yet Another Positioning Solver), which combines the detec...
Background: Acoustic positioning telemetry allows to collect large amounts of data on the movement of aquatic animals by use of autonomous receiver stations. Essential in this process is the conversion from raw signal detections to reliable positions. A new advancement in the domain is YAPS (Yet Another Positioning Solver), which combines the detec...
Background Acoustic positioning telemetry allows to collect large amounts of data on the movement of aquatic animals by use of autonomous receiver stations. Essential in this process is the conversion from raw signal detections to reliable positions. A new advancement in the domain is YAPS (Yet Another Positioning Solver), which combines the detect...
Open-channel confluences are common in nature as well as in hydraulic structures and urban drainage networks. In contrast to natural channels, artificial channels are usually prismatic, with a simple cross-sectional shape (e.g. rectangular) and a smaller width-to-depth ratio. Two confluent artificial channels are often of similar dimensions, follow...
Confluences play a major role in the dynamics of networks of natural and manmade open channels. Since field measurements on river confluences reveal that discordance in bed elevation is common, schematized confluences with a step in the interface between the tributary and the main channel bed have been studied, revealing that the bed elevation disc...
Right-angled confluences of open-channels with rectangular cross-sections are common configurations used to study the complex confluence hydrodynamics by means of lab experiments and numerical simulations. Large-Eddy simulations (LES) of confluences have traditionally been validated using bulk quantities such as water levels and streamwise mean vel...
Confluences of open-channel flows are common in nature as well as in urban drainage networks and in hydraulic structures. The complex hydrodynamics is often studied in schematized, right-angled confluences. In this paper, the influence of the downstream channel width onto time-averaged and turbulent flow features will be investigated numerically, b...
This paper describes the application of four Large Eddy Simulations to an open-channel confluence flow, making use of a frictionless rigid-lid to treat the free-surface. Three simulations are conducted with a flat rigid-lid, at different elevations. A fourth simulation is carried out with a curved rigid-lid which is a closer approximation to the re...
Navigation in inland waterways is increasingly important worldwide and so is inherently the construction and use of navigation locks. However, the impact of navigation locks on downstream migrating fish is rarely documented. In Belgium, the Albert Canal connecting the Meuse River to the Scheldt Estuary may offer migration opportunities for European...
The authors measured and computed the hydrodynamics and passive scalar dispersion in 90-degree open channel confluences over flat and degraded beds with a dominant upstream or tributary inflow. The present discussion essentially deals with the direction of rotation of the secondary currents, reported for the flat bed configuration with dominant tri...
Hydraulic structures such as navigation locks, pumping stations, and hydropower plants play an important role in navigation, water management, and sustainable energy production. However, these structures may severely impact the aquatic ecosystem and freshwater fish in particular. In Belgium, the Albert Canal connecting the river Meuse to the river...
A new depth-averaged exploratory model has been developed to investigate the hydrodynamics and the tidally averaged sediment transport in a semi-enclosed tidal basin. This model comprises the two-dimensional (2DH) dynamics in a tidal basin that consists of a channel of arbitrary length, flanked by tidal flats, in which the water motion is being dri...
The objective of this contribution is to study with Large Eddy Simulations the influence on head losses and recirculation zone dimensions of a bed elevation discordance between the main and tributary channel in a 90° angled open channel confluence.
River confluences are important due to their role on transport of sediments, erosion, transport of nutrients and flood events. Bathymetric surveys show that, typically, in nature, two flows merging into a confluence have discordant beds. The main goal of this paper is to analyse the effect of difference in bed elevations of the tributary and main c...
This paper presents a low-cost and easy-to-implement image-based reconstruction technique for laboratory experiments, which results in a temporal description of the water surface topography. The distortion due to refraction of a known pattern, located below the water surface, is used to fit a low parameter surface model that describes the time-depe...
Confluences with dominant tributary inflow are found to exhibit long-periodic alternations of the flow patterns. They are shown to exist both in laboratory experiments and in numerical simulations. By means of a modal decomposition, insight is given into these long-periodic oscillations. The origin of these oscillations is investigated and their si...
The present work presents an experimental study in which resonant surface oscillations inside a lateral cavity are reconstructed, often denoted as se- iching, which are excited by a shallow main stream flowing past the horizontal basin. Firstly, the flow configurations that trigger transverse and/or longitu- dinal seiching are studied using pressur...
Patches are of central interest to many areas of environmental science because they provide a lower limit of structural detail in synoptic studies, and an upper limit of contextual structure for point measurement-based studies. Identification and delineation of macrophyte patches however, is often arbitrary and case-specific. In this paper we propo...
A key feature of a schematized open-channel confluence is the separation zone that is present when the tributary flow detaches from the downstream corner of the confluence. This zone of recirculating fluid influences head losses, as well as sediment and solute balances. Most laboratory studies on the separation zone were, however, made in flumes ha...
This paper compiles the technical characteristics and operating principles of the Nortek Vectrino Profiler and reviews previously reported user experiences. A series of experiments are then presented that investigate instrument behaviour and performance, with a particular focus on variations within the profile. First, controlled tests investigate t...
The aim of the present contribution is to investigate the effect of difference in bed elevations of the tributary and main channel in a 90˚ angled open-channel confluence onto the hydrodynamics. Large Eddy Simulations (LES) are used to investigate the three-dimensional complex flow patterns for four different discordance ratios (∆zT /hd = 0, 0.1, 0...
The presented model allows for fast simulations of the near-field behaviour of overflow dredging plumes. Overflow dredging plumes occur when dredging vessels employ a dropshaft release system to discharge the excess sea water, which is pumped into the trailing suction hopper dredger (TSHD) along with the dredged sediments. The fine sediment fractio...
The reliability of large-scale particle image velocimetry (LSPIV) methodology to measure a 2D surface velocity field in a vegetated lowland stream is evaluated. To this end, measurements of the free-surface flow field obtained with LSPIV are compared with measurements with an electromagnetic current meter (ECM) close to the surface at four differen...
This paper proposes a new model to determine the head losses at confluences in one-dimensional models of open channel networks, making use of a momentum conservation approach. Momentum conservation has been applied in several theoretical models for confluence head losses, giving satisfactory results in general. However, for larger confluence angles...
Sediment plume predictions are part of the assessment of environmental impacts of dredging. The main source of turbidity while employing Trailer Suction Hopper Dredgers is the release of excess water through the overflow shaft. The near-field plume dynamics below and directly behind the sailing hopper dredgers are traditionally unknown during predi...
Open channel and river confluences have received a lot of attention in hydraulic literature, because of the interesting flow phenomena observed. Features such as flow acceleration, curvature, separation, mixing and recovery are combined in the confluence area into a complex 3D flow pattern. Typically, the analysis of these features is started at th...
In open channel confluences, two shear layers are often present: the one delineating the merging flows, called mixing layer or mixing interface, and the other situated between the separation zone and freestream flow. For the case of a 90° open channel confluence, Dynamic Mode Decomposition (DMD) is applied to time-resolved velocity fields in these...
In the present work, a numerical model based upon the Large Eddy Simulation approach has been set up for predicting the three-dimensional flow around a cylindrical pier, mounted on a flat and fixed bed, a generic case that is relevant for the study of flow and scour around bridge piers. This turbulent flow configuration was studied experimentally b...
The Author is acknowledged for extending knowledge of open channel confluences by providing additional experiments. More specifically, the Author's research offers a dataset with inclined channels, including not only fully subcritical flows (Type I flow), but also flows with supercritical flow in one upstream branch (Type II flow) or upstream and d...
In the original paper, approximate explicit formulae were proposed for the following dimensionless quantities: the filling time , the amplitude and time of the first overtravel peak, as well as the frequency of the chamber surface oscillations around the equalization level. For several reasons, the Authors only discussed the first overtravel peak:...
Despite the ratio of incoming discharges being recognized as a key parameter in open-channel confluence hydrodynamics, little is known about the flow patterns when the tributary provides more than 90% of the total discharge. This paper offers a systematic study of flow features when the tributary becomes increasingly dominant in a 90° confluence wi...
It is important to understand the mechanisms of vegetation establishment on bare substrate in a disturbance-driven ecosystem because of many valuable ecosystem services. This study tested for empirical indications of local alternative stable states controlled by biogeomorphic feedbacks using flume experiments with alfalfa: (1) single flood experime...
Numerical simulations of the sediment-air-water buoyant jet released through the hopper dredgers' overflow shaft have been performed. The release of sediments into the marine environment due to skimming the excess water from the dredging vessel's hopper can lead to increased turbidity and adverse effects on the adjacent environment. Base-case simul...
In this paper, the mixing layer between the two incoming flows in a 90 degree, asymmetrical open channel confluence is investigated. Specific attention is given towards looking into the effect of bed roughness on the flow patterns in the confluence. This analysis is performed in a Serret-Frenet type axis system, in order to come up with a more conv...
The state-of-the-art hydrodynamic knowledge on schematized open-channel confluences is largely based on laboratory experiments in channels with a rectangular cross-section. Since in practice man-made canals often have a non-rectangular cross-section, the question can be raised to which extent the knowledge on open-channel confluences still holds fo...
An upgrade of the present Royers lock at the right bank of the tidal river Scheldt is planned by the Flemish administration and the Antwerp Port authorities. This implies a widening of the lock chamber towards 36 m and a lengthening towards 250 m. The new lock is designed for inland navigation. The design convoy consists of an ECMT class VIb ship a...
New methods have been developed to extract turbulent fluxes of momentum and fine sediments from Acoustic Doppler Velocimeter (ADV) data. The methods were validated with turbidity plume experiments. The ADV's backscatter amplitude signal was used to determine the sediment concentration and its turbulent fluctuations. However, different kinds of nois...
Two-phase Large-Eddy Simulations (LES) of turbidity plumes in a crossflow are presented, representative for mixtures of water and fine sediment particles released through an overflow pipe of a dredging vessel. The model was tested based on experimental data of vertical plumes in a still environment as well as of plumes in crossflow. Simulations inc...
In the weir lock complex of Asper along the river Scheldt in Belgium, two tainter gate weirs were constructed in a new bypass channel, which came into operation in 2009. After the flood wave event of November 2010 a bathymetric survey around the weir lock complex revealed several locations with erosion and sedimentation. The origin and evolution of...
River and canal systems fulfill important societal, economical and ecological functions, such as discharge of water and sediments, waterways for navigation and habitats for unique ecosystems. In a river and canal network, open channel confluences are omnipresent. Confluences are characterized by complex flow patterns, which often induce important w...
In culvert-based navigation lock filling–emptying systems, inertia effects have a significant influence on the filling–emptying time and cause a (damped) oscillation of the water surface in the lock chamber around its equalization level, referred to as the overtravel phenomenon. In this paper, the derivation of analytical formulae for the lock fill...
In this paper, time-averaged flow patterns in a 90° open channel confluence with concordant and non-movable bed are studied, for the case of a tributary discharge largely exceeding the main channel discharge. By means of LSSPIV and profiling ADV, velocity data are gathered in laboratory experiments. A moderate and a small ratio of upstream main cha...
A numerical model based on the 3D shallow water equations is set up for a 90° angle open channel confluence. The model is first calibrated and validated using experimental data by (Shumate, 1998). Then a series of numerical simulations is carried out, systematically increasing the friction coefficient, in order to investigate the impact of hydrauli...
After a major flooding in the north of Belgium (Flanders) in 1976, a masterplan – the so-called Sigmaplan – was elaborated in 1977 to mitigate storm surges in the Schelde estuary as to increase the level of safety. Due to changing physical circumstances and new insights in water management, the Sigmaplan was profoundly updated in 2005 – i.e. the so...
Dredging using Trailer Suction Hopper Dredgers (TSHD) with overflowing lean mixture can generate turbidity plumes in cases when fine sediment fractions are present in the pumped mixture. In view of the increased attention to environmental impacts of coastal and offshore dredging operations, research in this field is increasing. In this context the...