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In recent decades both physical modelling and computer simulation of fl uvial processes has undergone rapid progress. The paper summarizes the achievements of both international and Hungarian laboratory experiments in fl uvial geomorphology. Then, the new auto-matically governed fl ume facility, called PTETHYS (Project for Tectonical and Hydrological Simulations) recently set up at the Faculty of Natural Sciences, University of Pécs, is pre-sented. Finally, some of the new opportunities it off ers for research in fl uvial geomorphology are briefl y demonstrated: the identifi cation of geomorphological thresholds; modelling the generation of (fl ash) fl oods and its application for the reconstruction of the architectural elements and geomorphic evolution of fl oodplains. Some important channel parameters can be quantitatively investigated: channel cross-section change, amount of bedload infl uencing braiding, current velocity distribution etc. The novelty of the facility is the easy adjustment of channel slope and continuous experimenting (no need for interruption as in the case of laser-scanned experiments). The scaling necessary for quantitative analyses is also tackled.
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Hungarian Geographical Bulletin 63 (4) (2014) 425–436.
DOI: 10.15201/hungeobull.63.4.4
New opportunities for experiments in uvial
geomorphology: the ume PTETHYS
Ervin PIRKHOFFER1, Ákos HALMAI1, Szabolcs CZIGÁNY1, Titusz BUGYA1,
Andor RÁBAY1, Tamás BÖTKÖS1, Gábor NAGY1, Bettina BALASSA1,
Ildikó JANCSKÁRNÉ ANWEILER2 and Dénes LÓCZY1
Abstract
In recent decades both physical modelling and computer simulation of uvial processes has
undergone rapid progress. The paper summarizes the achievements of both international
and Hungarian laboratory experiments in uvial geomorphology. Then, the new auto-
matically governed ume facility, called PTETHYS (Project for Tectonical and Hydrological
Simulations) recently set up at the Faculty of Natural Sciences, University of Pécs, is pre-
sented. Finally, some of the new opportunities it o ers for research in uvial geomorphology
are briefl y demonstrated: the identifi cation of geomorphological thresholds; modelling the
generation of ( ash) oods and its application for the reconstruction of the architectural
elements and geomorphic evolution of oodplains. Some important channel parameters can
be quantitatively investigated: channel cross-section change, amount of bedload infl uencing
braiding, current velocity distribution etc. The novelty of the facility is the easy adjustment of
channel slope and continuous experimenting (no need for interruption as in the case of laser-
scanned experiments). The scaling necessary for quantitative analyses is also tackled.
Keywords: physical modelling, ume, channel pa erns, ood generation, oodplain re-
habilitation, scaling
Introduction
In recent decades monitoring has been launched in many instrumented
catchments all over the world and numerous computer models have been
elaborated for the explanation of some of theeternal” questions of uvial
geomorphology. At the same time, the weaknesses of the rst (a labour and
1 Institute of Geography, University of Pécs, H-7624 Pécs, I úg útja 6.
E-mail: pirkho @gamma. k.pte.hu
2 Pollack Mihály Faculty of Engeneering and Information Technology, University of Pécs,
H-7624 Pécs, Boszorkány u. 2. E-mail: jancskarne.ildiko@pmmik.pte.hu
426
time-consuming activity involving high expenses) and the second approach
(e.g. magnifi cation of errors springing from incorrect parametrisation or lim-
ited applicability to real-life situations) have also been recognized.
Observing the scaling rules, the small-scale physical models, long es-
tablished in water engineering, seem to be capable to bridge the gap between
the two approaches. If the results of experimentations could be quantifi ed,
physical modelling may also be helpful for the theoretical foundation of vari-
ous water management tasks (including dam constructions, designing ood
control alert and warning or river rehabilitation).
The aim of the project is to apply quantitative methods for the model-
ling of braided (and in the future meandering) channel evolution. Hopefully,
the results can be used in designing river restoration, too. The experiment also
helps students to combine their knowledge in laboratory studies, experimental
geomorphology and remote sensing.
Previous ume experiments
Reaching back to the end of the 19th century, physical modelling has a long
tradition in water management. It is particularly frequently applied in river
channel studies for diverse purposes. The largest hydraulic model ever built
in the world replicates the Mississippi River and its major tributaries (the Ten-
nessee, Arkansas and Missouri Rivers) in ca 170 hectares area near Clinton,
Mississippi. Meant to aid ood control planning, it was built by 3,000 German
and Italian prisoners of war for the US Army Corps of Engineers in 1944 (Fos-
ter, J.E. 1971). (It still exists now but in a neglected condition.)
In the United States smaller-scale laboratory studies on river channels
began by the US Army Corps of Engineers in Vicksburg, Mississippi, in 1929.
The rst experiments, however, only modelled the origin of a meandering
thalweg instead of a meandering channel (a famous example being Friedkin,
J.F. 1945). A later recognition that pa ern changes occur rather abruptly in
rivers in the course of a punctuated evolution and are driven by channel gra-
dient and the mode of sediment transport (Leopold, L.B. and Wolman, M.G.
1957; Schumm, S.A. and Khan, H.R. 1972; Miall, A.D. 1996). These led to
experiments where gradient and sediment supply were changed, while wa-
ter discharge was kept constant, and parameters like channel width/depth
ratio, mean current velocity, bedload discharge and concentration, shear and
Froude number were recorded (Schumm, S.A. 1973). The morphodynamics,
particularly the depositional activity of braided rivers have been intensively
studied in experiments (e.g. Ashworth, P.J. et al. 1994).
In uvial geomorphology the second half of the 20th century was a
period of identifi cation of important thresholds. Such are the critical channel
427
gradient values which separate straight, meandering and braided channel
pa ernsa major issue in uvial geomorphology of the 1970s (Schumm, S.A.
and Khan, H.R. 1972; Schumm, S.A. 1973; Brotherton, D.I. 1979).
The importance of bank strength was also recognised in determining
channel pa ern (Kleinhans, M.G. 2010), rivers with stronger (o en vegetated)
banks being narrower and deeper, and alternate bars common in their chan-
nel. Although it is widely accepted that bank-erosion rate and oodplain
sedimentation, infl uenced by more complicated factors than just channel ow
and sediment transport (Friedkin, J.F. 1945; Fraselle, Q. et al. 2010), are ex-
tremely di cult to scale (Ashworth, P.J. et al. 2004), it is also noted that even
small-scale experiments adequately reproduce spatial pa erns and the natural
system dynamics (Paola, C. et al. 2009).
The importance of sediment transport was also recognised internation-
ally (Ferguson, R.I. 1987) and in Hungary, too. In 1951 László Kádár began to
set up a ume at the Kossuth Lajos University of Debrecen, Hungary, to study
uvial geomorphological processes and drew a ention to the part sediment
transport plays in the (trans)formation of channel pa erns. On the basis of the
visual observations made in the ume, he published papers (Kádár, L. 1954,
1955, 1969), where he presented a geomorphologically more consistent picture
of meandering than it was usual at the time when thetheory of types of river
reaches”, borrowed from Germany, prevailed (Sipos, Gy. and Kiss, T. 2008).
In Hungarian water engineering model experiments started in 1928,
when Sándor Rohringer installed a hydraulic laboratory of 670 m2 area at the
Department of Water Construction, Budapest Technical University. T he aim of
the rst experiment was to investigate the hydraulics of the Danube channel
at the artifi cial cut-o of Bogyiszló (Sárköz, South Hungary) (Fejér, L. 2001).
In 1967 the Research Institute for Water Resources Management (VITUKI)
established a hydrological model at the village Nick (Pannonhalmi, M. 2004).
A ume of 40 × 6 m size supplemented with a glass channel 15 m long and
0.5 m wide was built to model a section of the Rába River. The experiments
were conducted with the purpose of modelling meander shi s and the im-
pacts of river regulation and served the basis for 48 river regulation proposals.
However, the modelling of sediment transport was not satisfactory. A er 2007
the facility was not used.
The largest physical model in Hungary served the checking of the
rehabilitation plans for the Danube oodplain in the Szigetköz a er the con-
struction of the Bs (Gabíkovo) Barrage and diversion of the main chan-
nel in 1992. The upper Szigetköz section of the Danube (from Dunakiliti to
Dunaremete) was modelled at 1:500 scale, while the lower (from Dunaremete
to Medve) at 1:700 scale in the Ecopark of Dunasziget. The impacts of river
regulation are also reconstructed through the use of physical models (see e.g.
Kornis-Akantisz, Zs. 1977).
428
Flume parameters
The new ume of the University of Pécs is intended both for educational and
research purposes (Photo 1). It was designed by experts of the Department of
Physical and Environmental Geography, Institute of Geography, and the De-
partment of Mechanical Engineering, Pollack Mihály Faculty of Engineering
and Informatics, University of Pécs, in 2012. The technical documentation,
manufacturing and installation was the responsibility of the CsavarKON-
TROLL 2004 Ltd.
The versatility of the ume is demonstrated by its technical param-
eters, which are the following:
size: 4.2 × 2.5 m;
maximum ll weight: 2,500 kg (wet sediment in 150 mm depth);
maximum tilting: around longitudinal axis: ±7.5, around transversal
axis: +10;
adjustable parts: 6 sections can be moved vertically ±120 mm at 10–200
mm per day speed;
lateral deformation: possible through the displacement of 4 push-
blades to the extent of 100 mm;
closed equipment, water and sediment can only leave it through the sink.
Photo 1. View of the PTETHYS ume before installation
429
All motions in the ume are executed by computer-governed electro-
engines. The speed of movements allows the modelling of both very slow and
rather rapid changes. The rate of motions is checked by Leica Disto D3a BT
laser meters (automatic feedback through Bluetooth).
Discharge is regulated through a 1-m-high water column, adjusted au-
tomatically to the position of the table. Water is recycled by a pump system.
The processes are detected through two devices. On the one hand, de-
tailed picture information is collected and all physical parameters of the proc-
esses taking place in the ume are recorded by the use of eight Canon EOS 1100D
cameras (Photo 2). The cameras are xed on a system of cantilevers at 30 cm dis-
tance from each other and at 1.2 m height above bed. At 18 mm focal length the
overlap between photographs is ca 80%, which allows 3D imaging. The cameras
are connected to the PC and governed by a so ware of authors design.
In addition to the photographic cameras, a VarioScan 3021 ST type
thermal camera is also used to establish the actual position of owing water,
the confi guration of active channels, current velocity and the horizontal dis-
tribution of sediment ll saturation. The observation province of the thermal
camera is between 8 and 12 m and its thermal resolution is ±0.03 K.
Since the moisture content of the modelling medium (sediment) of the
ume is of utmost importance from the point of view of uvial processes, the
moisture content is recorded at several depths by sensors of Decagon 10HS
TDR system and the data are stored by Decagon EM50 data loggers.
Photo 2. The cameras installed to record geomorphic processes
430
The material used for the sediment ll is also carefully designed and
manufactured particularly for this purpose. The colours of grains indicate
grain size and density: coarse grains (1.0 and 0.8 mm diameter) are ground
basalt and andesite of grey and black colour, while the 0.6 mm diameter grains
are of red marble and those of 0.2 mm diameter are of beige limestone.
The functions of governing ume position on the one hand and imag-
ing and data logging on the other are shared between di erent computers. For
imaging an Asus P9X79 PRO computer with Intel Core i7–3820 processor and
nVidia GTX 660 Ti video card is applied. The operating system and processing
is based on two Samsung 250 GB SATA3 2.5 Basic (MZ–7TD250BW) SSDs,
while data are stored by Seagate Barracuda 3 TB 64 MB 7,200 rpm SATA3 3.5
(ST3000DM001) HDDs.
Image processing of stereo pairs and the representation of topography
is performed by Agiso StereoScan program. For the interpretation of the DEM
and detection of processes ArcGIS 10.2.1 so ware is available.
Possible applications
The objective of the rst experiment with the new ume was to nd out how
reliably the development of channel pa erns can be modelled. The ume was
lled with material of 8 cm depth and tilted at 5 degrees (~0.087). Imaging
interval (both photographic and thermal) was set to 30 seconds.
Preliminary we ing was applied to reach 40 percent of the saturation
moisture content all over the experiment area. In order to trigger and accel-
erate the process of channel incision a longitudinal groove of ca 2 cm depth
wasburnedinto the sediment surface. Previous observations showed that
in lack of such an intervention, no collection of runo into a channel would
take place within an acceptable time span.
To identify active channel ow and current velocities, boiling water
was conducted in pulses into the ume and its motion was detected by the
thermal camera. The resulting channel cross-sections and sediment transport
were studied in 3D images.
Braided channel evolution
Since Schumm, S.A. and Khan, H.R. (1972) found that channels above 0.016
gradient form a braided pa ern, it was expected that such pa ern will be the
outcome from the rst experiment (Figure 1).
In the non-cohesive material increasing discharge led to gradu-
ally broadening channels, providing space for more and more bifurcations
431
and the building of bars of various types. Thus, all the main morphological
requirements for braiding were fulfi lled. Since the banks are easily erodible,
channel width remarkably uctuates, but the width/depth ratio remains high
throughout. During the experiment the following partial processes could be
visually identifi ed:
channel widening through bank erosion;
lateral bar accumulation;
transverse bar accumulation and the resultant diversion of the thalweg;
occasional reduction in the plan curvature of the thalweg, resulting
in channel widening;
emergence of bifurcations and mid-channel bars at regular distance
from each other in broader channel sections;
alternating cut and ll along the thalweg, which leads to a continuous
displacement of braids, a dynamic rearrangement of pa ern.
The observed channel evolution corresponds to the observations by
Bertoldi, W. et al. (2001). The braided sections were locally replaced by anasto-
mosing reaches, where the following partial processes were clearly visible:
with widening channel and lowering water level, some bars rise above
the general surface as more stableislands”;
the distributary channels bordering islands are very shallow just down-
stream the bifurcation and only convey water at high water stages (“ oods”);
Fig. 1. The braided channel pa ern generated in the rst experiment
432
bifurcations are gradually
replaced by avulsions (more perma-
nent displacements of channel) where
sediment accumulation is rapid, the
distributary channels will acquire a
slightly convex longitudinal profi le;
avulsions are concentrated
where bank erosion is not particu-
larly efficient since the banks are
relatively stable but breach abruptly
when reaching a threshold.
Comparing these observations
with some descriptions of eld studies
(e.g. Miller, J.R. 1991), remarkable re-
semblances are seen. The development of
avulsions is of great practical signifi cance
as far as ood hazard is concerned.
Due to the tilting function of the
ume, the adjustable channel gradient al-
lows the experimental establishment of
further thresholds, e.g. between meander-
ing and braided river behaviour (Parker,
G. 1976; Püski, Z. et al. 2005). Its sig-
nifi cance is underlined by recent papers,
where the challenge of physical modelling
of meandering river behaviour is pointed
out (van D k, W.M. et al. 2012).
Delta formation
Another experiment proves that the
equipment is suitable for the mod-
elling of delta formation (Photo 3).
Flume observations show that delta
accumulation is composed of the fol-
lowing partial processes:
the surface of the fan is con-
tinuously raised by accumulations by
the main channel, which is continu-
ously wandering and deposits large
amounts of sediment;
Photo 3. Stages of delta formation in the second experiment
433
the main channel is a ected by repeated avulsions and shi s to the
lowest-lying zone of the delta fan;
if water discharge increases, vertical accretion also raises the level of
inter-channel surfaces.
Similar channelisation, avulsion and backward sedimentation proc-
esses on deltas of homogeneous material were found during experiments in
the Netherlands (Van de Lageweg, W. 2013).
Flood modelling
In addition to in-channel geomorphic processes, overbank erosion and depo-
sition can also be included among the objectives of physical modelling. This
presupposes of creating an exact replica of the oodplain surface. The previ-
ously applied GIS-based modelling of ood hazard (e.g. Czigány, Sz. et al.
2011) can be supplemented by ume experiments locating the potential sites
of dyke breaches and avulsions as well as the predictable extent of oodplain
inundation. If the boundary conditions leading to river ooding are exactly
defi ned during the experiment, rst of all, local ood hazard (Lóczy, D. et al.
2009) can be precisely determined. The morphometric indices derived from
the experiments are useful for estimating local ood hazard along channelized
rivers and designing the necessary ood-control measures.
Floodplain rehabilitation planning
Through modelling channel migration and the related deposition processes,
ume experiments are a potentially useful tool for reconstructing historical
oodplain evolution under natural and human-induced conditions. Their
advantages over eld data are the opportunity to set both initial and bound-
ary conditions and the much faster operation of processes. With appropriate
monitoring technology, morphological changes and the resultant architectural
elements can be recorded without intervention into the processes.
Channel evolution observations may be the starting point for the re-
construction of long-term oodplain evolution (Pizzuto, J.E. 1987; Bathurst,
J.C. et al. 2002; Sellin, R.H.J. et al. 2003; Van D k, W.M. et al. 2013). In the ume
the rate of sediment exchange between the main channel and distributaries
can be measured and deposition pa erns on the oodplain demonstrated.
From data on natural oodplain evolution and human-infl uenced processes
in the oodplain, the measures necessary to create conditions under which
the ecosystem functions of oodplains are optimally fulfi lled (i.e. oodplain
rehabilitation) can be derived.
434
Similarity scaling
Until very recently physical models had been treated as analogue systems in com-
parison to real-world uvial systems. Thus, the results of the experiments only al-
lowed qualitative analyses of processes and the resultant landforms. Modern tech-
nology developed for the documentation of experimentation outcomes (e.g. DEM
representation of high spatial resolution and digital photography of high temporal
resolution) makes measurements and quantitative assessment possible.
A major problem in the quantitative interpretation of the processes re-
corded in ume experiments is seen in the spatial and temporal scaling. For scaling
a set of rules have been established but not yet convincingly checked (Kleinhans,
M.G. et al. 2010). The complexity of scaling to achieve similarity is addressed by
numerous authors (see Paola, C. et al. 2009). Hydraulic scaling involves similar-
ity in ow criticality (Froude number), current velocity, turbulence (Reynolds
number), surface tension e ects and bed roughness, while sediment-transport
similarity refers to sediment mobility (Shields number), shear stress, particle size
(Reynolds particle number) and suspended sediment (which is again the function
of turbulence). We can also mention morphological similarity, i.e. the cumulative
e ect of width-to-depth ratio, channel bar dimensions and wavelength, transverse
bed slope and other morphological parameters. Most of the above scaling factors
have a temporal aspect, too, which also has to be considered.
A task of future research is to further develop the scaling rules in order
to produce realistic and meaningful morphodynamics and stratigraphy (Van
de Lageweg, W. 2013).
Acknowledgements: The project was partially nanced from TÁMOP/SROP-4.2.2.C-11/1/
KONV-2012-0005 (Well-being in the Information Society) and by the Hungarian National
Scientifi c Research Fund (OTKA, contract number K 104552).
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... Computer-controlled electro-engines are in control of these movements. Only a sink in the downstream part of the flume allowed water and sediment to leave (Pirkhoffer et al., 2014;Słowik et al., 2021;Kiss, 2021). ...
... Dams, which alter sediment loads and outflow, typically result in channel narrowing and degradation below the dam (Petts, 1979;Williams & Wolman, 1984;Collier et al., 2000;Schumm, 2007). In this river flow, certain steps are being taken to restore side channel activity and groundwater supplies (Lóczy et al., 2014;Słowik et al., 2021). However, the availability of sediment and water resources in river basins is critical to the success of these endeavors. ...
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... The results of the questionnaire-based survey of the current study, in accordance with the findings of previous studies (e.g. Maor & Fraser, 2005;Pirkhoffer et al., 2014), signpost new challenges in STEM education. This challenge for teachers is reflected in the need for the development of new learning environments by using demonstrational tools (Jonassen & Reeves, 1996) and by combining them with multimedia tools and providing opportunities for critical thinking and higher order learning (Garbinger, 1996). ...
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