Geomorphology 135 (2011) 191–202
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Geomorphology
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Accelerated overbank accumulation after nineteenth century river regulation works:
A case study on the Maros River, Hungary
Tímea Kiss a,⁎, Viktor Gy. Oroszi a, György Sipos a, Károly Fiala b, Balázs Benyhe a
a
b
Department of Physical Geography and Geoinformatics, University of Szeged, Szeged, 6722, Egyetem u. 2-6, Hungary
Directorate for Environmental Protection and Water Management of Lower Tisza District, Szeged, 6722, Stefánia 4, Hungary
a r t i c l e
i n f o
Article history:
Received 24 January 2011
Received in revised form 2 August 2011
Accepted 12 August 2011
Available online 22 August 2011
Keywords:
Overbank sedimentation
Regulated floodplain
Accelerated accumulation
DTM
Invasive plant species
a b s t r a c t
In the nineteenth century, the meandering rivers of the Carpathian Basin were extensively regulated, and their
large (up to 100 km wide) floodplains were confined by artificial levees. On the narrow (0.5–4 km) artificial floodplains confined by these levees, overbank sedimentation has become the dominant geomorphological process,
resulting in rising floodplain levels during the last century. The Maros River is an extreme example of this process,
as it carries a significant amount of suspended sediment (4.6 × 106 m3/y) and because its lowland reach was drastically shortened by cutoffs, resulting in bed scour and an increased sediment load. Simultaneously, a flood embankment system was constructed, reducing the floodplain width by 70–80%. The resulting accelerated
overbank sediment accumulation increases the flood hazard along the river.
The aim of this study is to determine the spatial and temporal pattern of overbank sediment accumulation on the
artificial floodplain of the lower Maros River over the last 150 years and to identify its influencing factors. The
lateral slope of the protected (natural) floodplain was projected towards the present-day channel, allowing
the volume (m3) and rate (cm/y) of overbank sedimentation to be calculated using digital terrain modelling
(DTM). Changes in the rate of sedimentation were determined by pollen analysis.
The studied reach was divided into five sections based on the rate of aggradation: (i) the distal surface of the alluvial
fan, where no sedimentation was measured, only incision; (ii) the original front of the alluvial fan (1.0 ±0.4 cm/y);
(iii) the recently formed secondary alluvial fan (1.4±0.3 cm/y); (iv) the low-lying floodplain (0.4±0.2 cm/y); and
(v) the outlet unit (2.0±0.5 cm/y). The aggradation rate was slower on elevated forms, such as the pre-regulation
natural levee (0.2 cm/y), and greater on the low-lying floodplain (0.6 cm/y). The greatest accumulation rate (1.3–
2.4 cm/y) was measured in cutoffs. The sedimentation rate was high during the regulation period (1.9–2.4 cm/y)
but later decreased to 0.5–0.9 cm/y. The rate of aggradation was determined by the width, height and slope conditions of the floodplain, the impoundment of the main river and the land use in the area.
© 2011 Elsevier B.V. All rights reserved.
1. Introduction
Floodplains are widely studied all over the world because of their
importance in sustainable river management, especially in densely
inhabited plain regions, where flooding is a major hazard. Building
of embankments and levees has always been a first-order approach
to decreasing flood risk. However, these constructions can provide a
false sense of security, as hazard and risk may increase over time as
the floodplain experiences accelerated fluvial processes. One of
these is overbank sedimentation, which can decrease the drainage capacity of the artificial floodplain, thus contributing greatly to the increased frequency of flood stages in recent years.
⁎ Corresponding author. Tel.: + 36 62 544545; fax: + 36 62 4544158.
E-mail addresses: [email protected] (T. Kiss), [email protected]
(V.G. Oroszi), [email protected] (G. Sipos), [email protected] (K. Fiala),
[email protected] (B. Benyhe).
0169-555X/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.geomorph.2011.08.017
Overbank sedimentation is influenced by different regional and local
factors. Sediment influx is a key factor, but the sediment discharge is different in each flood, so the rate of sedimentation is not proportional to
the magnitude or frequency of flood events (Magilligan et al., 1998;
Sándor and Kiss, 2006). Upstream inundation conditions (or levee failures) also influence the downstream sedimentary processes (Kiss
et al., 2002). The most important local factors controlling the transport
and depositional environment of the floods are stream gradient, stream
power, and the duration of inundation (Middelkoop and Asselman,
1998). The vegetation of the floodplain influences flow velocity by increasing surface roughness (Kiss and Sándor, 2009; Schenk and Hupp,
2010), while channelisation alters the connectivity of the floodplain
(Kroes and Hupp, 2010). The relationship between overbank sedimentation and floodplain elevation and distance from the channel are uncertain (Hupp and Morris, 1990; Middelkoop and Asselman,
1998; Oroszi, 2008; Schenk and Hupp, 2010). Moreover, in narrow
floodplains, the deposited sediment could be remobilised, influencing
long-term sedimentation rates (Phillips et al., 2007). The spatial and
temporal combination of these natural factors results in a rather
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T. Kiss et al. / Geomorphology 135 (2011) 191–202
inhomogeneous pattern of overbank aggradation (Brush, 1984; Chorley
et al., 1985; Nanson and Croke, 1992; Gomez et al., 1998; Blum and
Tornqvist, 2000; Phillips and Slattery, 2008).
These natural variables are frequently altered by catchment- or
local-scale human impact, changing runoff, sediment discharge and
storage conditions. Major catchment-scale impacts include deforestation and conversion of grasslands into arable land (Froomer, 1980;
Pasternack et al., 2001; Owens and Walling, 2002; Liébault et al.,
2005), increasing sediment yield. The effects of land-use change
were especially evident in North America and Australia after European
settlement (Brush, 1984; Jacobson and Coleman, 1986; Benedetti,
2003; Florsheim and Mount, 2003; Knox, 2006; Rustomji and Pietsch,
2007; Hughes et al., 2010). For example, in the Murrumbidgee–Murray
River system, overbank sedimentation doubled after Europeans
arrived (Gell et al., 2009). Similar changes can be measured as a consequence of intensified agricultural activity (Mücher et al., 1990; Lecce
and Pavlowsky, 2004), timber harvest (Gomez et al., 1998; Constantine
et al., 2005), or mining (Lecce and Pavlowsky, 2004; Knox, 2006). Artificially altered hydrology also yields higher sedimentation rates
(Hohensinner et al., 2004; Owens et al., 2005).
Local-scale human interventions significantly alter the geomorphological setting and microtopography of the floodplain and thus affect
overbank hydraulics (Nicholas and Walling, 1997; Walling and He,
1998). For example, on the Rhone River, local-scale river engineering
measures were responsible for a sudden increase (40 to 230 mm/y) in
sedimentation rate (Provansal et al., 2010). Revetment- and groyneconstruction and river regulation increase near-bank deposition rates
(Károlyi, 1960; Brown, 1983; Ten Brinke et al., 1998; Wallinga et al.,
2010). Meanwhile, the construction of narrow artificial floodplains has
an important role in accelerating floodplain aggradation (Gábris et al.,
2002; Hudson et al., 2008). In addition, the type and density of riparian
vegetation has been altered by human activity in many cases, influencing roughness and thus the rate of aggradation (Steiger et al., 2001;
Oroszi and Kiss, 2008; Kiss and Sándor, 2009). The distance from
urban-industrial areas also influences the rate of floodplain aggradation
downstream of these areas (Hupp and Morris, 1990; Hupp et al., 1993).
Accelerated overbank sedimentation is a widely observed phenomenon. In general, the rate of floodplain aggradation has increased by approximately one order of magnitude since the appearance of intensive
agricultural techniques (i.e., Brush, 1984; Knox, 1987; Owens et al.,
1999, 2005; Pasternack et al., 2001; Benedetti, 2003; Florsheim and
Mount, 2003; Soster et al., 2007; Pierce and King, 2008). Nevertheless,
in some cases, aggradation has been mitigated by better land management and soil conservation practices (Jacobson and Coleman, 1986;
Knox, 1987; Benedetti, 2003; Florsheim and Mount, 2003; Rustomji
and Pietsch, 2007) or by forest regeneration subsequent to depopulation (Keesstra, 2007). Channelisation can also decelerate floodplain aggradation in various ways. The resulting river incision raises the relative
elevation of the floodplain compared to the riverbed, thereby decreasing the frequency of inundation (Wyzga, 2001; Kroes and Hupp,
2010). In addition, drainage of floodplains exposes the organic sediments of the wetlands to decomposition, resulting in compaction,
which decreases the total rate of overbank aggradation (Kroes and
Hupp, 2010).
The rate of overbank sedimentation is a key problem from the perspective of flood hydrology and flood forecasting. It can significantly
reduce the drainage capacity of the inter-levee artificial floodplain
(Keesstra, 2007), which might consequently necessitate heightening
of levees. According to the calculations of Gábris et al. (2002) and
Kiss et al. (2002) along the River Tisza (Hungary), the crosssectional area of the floodplain has already been reduced by 5–16%
as a result of overbank sedimentation, helping to explain the series
of record flood levels between 1998 and 2006.
The spatial distribution of sediment deposition has been less widely
studied, as earlier research focused mostly on at-a-point sedimentation
or aggradation along discrete transects (e.g., Hupp and Morris, 1990;
Hupp et al., 1993; Lecce, 1997; Middelkoop and Asselman, 1998; Schenk
and Hupp, 2010). Nevertheless, a few attempts have been made to investigate larger scale sedimentation patterns in relation to single modern flood events (Magilligan et al., 1998; Steiger et al., 2003; Benedetti,
2003) or longer periods (Kroes and Hupp, 2010). Based on sedimentation rates and other data from these studies, models have been built
to simulate the process for longer periods (Nicholas and Walling,
1997; Walling and He, 1998; Hardy et al., 2000; Gábris et al., 2002),
but our knowledge of larger spatial trends is incomplete.
The rivers of the Carpathian Basin (especially in Hungary) offer a
great opportunity for such research, as extensive river regulation
works were carried out in the nineteenth century, the negative effects
of which have become increasingly evident over time. The primary
aim of the present study is to analyse the spatial and temporal changes
and relationships of aggradation along a longer section of a regulated
lowland river. Our goals were to (i) determine the rate and longitudinal
distribution of overbank sedimentation along a 34-km-long section of
the Maros River since the mid-nineteenth century regulation works,
(ii) evaluate the relations of sedimentation to different depositional environments, and (iii) demonstrate that the application of a digital terrain model (DTM) can be useful in estimating the rate of overbank
sedimentation.
2. Study area
The Maros (Mures) River is the largest tributary (catchment
area = 30 332 km2) of the Tisza River (Fig. 1). The slope and sediment
discharge of the lowland section are strongly influenced by the river's
alluvial fan. The radius of the alluvial fan is 80–100 km, and its front is
only 20 km from the outlet, making the lowland section of the river
quite short (15 km). The apex of the fan at Lippa (Lipova) is the highest (130 m asl) of the rivers of the Hungarian Great Plain, resulting in
steep slopes on the alluvial fan (0.0028) and in the lowland region
(0.0013) (Laczay, 1975).
The regime of the river is dominated by spring and early summer
floods. Floods on the Maros usually precede those on the Tisza. However,
in some cases, floods can be simultaneous. In these cases, the Maros is
impounded by the Tisza, resulting in extremely long-lasting overbank
floods and record water levels (i.e., 1941, 1970, 1975, 2000, and 2006).
Altogether, 725 overbank flood-days were recorded at the Makó gauge
station in the twentieth century (average 6 d/y). Short, 1- to 2-day-long
floods are the most common; the longest overbank flood (47 days) occurred in 1970, primarily as a consequence of impounding. The mean
and maximum recorded discharges are 161 m3/s and 2440 m3/s
(1970), while the discharges characterising the 1-year and 30-year return
interval overbank floods are 710 m3/s and 1500 m3/s, respectively (Boga
and Nováky, 1986).
The Maros River has a considerable sediment discharge; its bedload transport exceeds that of the Danube while its suspended-load
transport is almost as high as that of the Tisza (Table 1), though the
mean water discharge of the Maros is 14 and 3 times lower compared
to the Danube and the Tisza, respectively (Bogárdi, 1954). The mean
concentration of the suspended sediment is 500 g/m 3, but during
floods, it can increase by an order of magnitude (Mezősi and Donáth,
1954). The median grain size of the bedload is 0.2–0.3 mm, while that
of the suspended load is 0.04–0.05 mm (Bogárdi, 1954; Csoma, 1975).
River training on the Maros was completed in the second half of
the nineteenth century. Its primary aim was to improve navigation.
By 1872, 33 meanders were cut off between the apex of the alluvial
fan and the outlet of the river, shortening the original 260-km-long
section by 33% (Ihrig, 1973). As a consequence, the channel slope
was doubled from 0.0014 to 0.0028, and the river incised by ~1.0 m
(Somogyi, 2000). Subsequently, intensive bank erosion led to an extremely wide channel and a braided pattern (Kiss and Sipos, 2007).
Flood protection works were performed in the first half of the
1880s. Levees mostly flank pre-regulation meanders, such that the
T. Kiss et al. / Geomorphology 135 (2011) 191–202
193
Fig. 1. Location of the study area along the Maros River. The DTM represents its 4-km-wide buffer zone. Sediment samples were taken at three sites (Ve, Zu, Cs). A: inactive, floodprotected floodplain; B: active floodplain; C: artificial levee; D: limit of the main geomorphological units; E: nineteenth century cutoff; F: abandoned meander and channel, G: point
bar; H: scour channel; I: back-swamp; J: sand dune; K: settlement; L: sampling site.
width of the artificial floodplain is irregular, varying between 0.2 and
2 km.
Our research was conducted on a 34-km-long section of the Maros
River (Fig. 1). The cutoffs and artificial levee system on this reach were
created between 1846 and 1885 (Laczay, 1975). The average width of
the active floodplain is 0.7 km, though it varies irregularly between 0.1
and 1.9 km along the river. The land use of the study area has changed
considerably since the eighteenth century. Before river regulation, the
low-lying floodplain sections were covered by riparian forests and
pasture lands; on the higher surfaces, plough-fields, orchards and
vineyards were common. Since the mid-nineteenth century regulations in flood-protected areas, plough-fields have become dominant.
On the artificial floodplains, riparian forests and pastures remain, but
the proportion of poplar plantations has increased (Oroszi and Kiss,
2006; Oroszi, 2009). This artificial forestation and the dispersal of
invasive plant species have doubled the roughness coefficient of the
floodplain (Oroszi and Kiss, 2006, 2008).
3. Methods
To determine the spatial and temporal pattern of overbank sedimentation along the Maros, two approaches were applied. The rate
of sedimentation and its longitudinal variation were calculated from
a digital terrain model (DTM). The spatial and temporal changes in
sedimentation rate were determined by sediment and pollen analysis.
The number of applicable dating methods was limited because of the
short time-span of the investigation. However, the pollen grains of invasive plants appearing at known dates provided adequate means by
which to quantify sedimentation rates.
Table 1
Sediment transport data of the main rivers in Hungary.
(Bogárdi, 1974; Fiala et al., 2006).
River, station
Mean water
discharge (m3/s)
Mean sediment
concentration (g/m3)
Duna, Nagybajcs
Tisza, Tápé
Maros, Deszk
2270
550
161
60
340
500
a
n.d. not determined.
Sediment transport (m3/y)
Sediment discharge (kg/s)
of the largest flood
Suspended
Bedload
Suspended
Bedload
3 210 000
5 900 000
4 620 000
12 000
5 000
16 000
6500
6000
12 000
105
5
n.d.a
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T. Kiss et al. / Geomorphology 135 (2011) 191–202
3.1. Digital terrain modelling (DTM)
The DTM (250 km2) was compiled by digitising the contours of topographic maps in a 4-km-wide zone along the chosen 34-km-long section of the Maros River. The 1:10 000 topographical maps were made in
1983 and have contour intervals of 0.5 m. The accuracy of the topographical maps was determined by comparing them with a LIDAR survey in the western, flood-protected part of the study area. The average
vertical difference was 0.26 ± 0.1 m. Considering the scale and vertical
resolution of the maps, a 10 m pixel size was determined for the DTM.
The terrain model was created and checked using ArcGIS 8.2 (the RMS
error of the model was 0.36 m). Between 28 km and 34 km on the studied section of the river, only the northern area could be studied because
no maps were accessible for the southern, Romanian side.
The study area was systematically divided by parallel cross sections
set quasi-perpendicular to the east–west-flowing river at 1 km intervals.
These cross sections, the banklines of the river and the artificial levees
further divided the area into polygons (Fig. 2). The polygons were considered as 3D-bodies, and the aggradation volume was calculated. The
pre-regulation surface should have had an even lateral slope (from the
river towards the bottom of the floodplain), and this “original slope”
should theoretically be the same as the slope of the present-day inactive
floodplain. This “original slope” was calculated for the areas between
each cross section, but only the slope of the near-levee areas was considered (within the same width as the width of the active floodplain). The
reason for this limitation is that some distant landforms, which were
commonly formed during the Late Pleistocene or early Holocene, were
not an active part of the floodplain before levee construction. The present
active floodplains (between the levees) were cut by these imaginary surfaces created from the “original” slope at the feet of the levees. The
amount of aggradation (m 3/m2) was determined by dividing the volume
of the total aggradation in the polygon by its territory. This represents the
amount of sediment deposited between 1885 (completion of the levee
system) and 1983 (topographical survey), so it was possible to calculate
the rate of sedimentation (cm/y).
cutoffs (e.g., where sandy deposits of the pre-regulation natural levees
were covered by finer floodplain sediments, or in cutoffs where the
change from active bed sediments and silty–clayey post-regulation sediments was also clear). Another type of sampling site was where the deposition of fine floodplain sediments was continuous (e.g., at the
bottom of the floodplain; Fig. 1; Table 2). The geomorphological features of the study area were identified mainly by surface mapping; old
topographical maps and soil maps were also used.
Cutoffs (Cs1, Zu, Ve) were sampled by boreholes (5 cm sampling interval), while at other sites (Cs2 and Cs3), sampling pits were established
(2 cm sampling interval). Under the prevailing climate conditions, only
cutoffs provide reliable (wet) locations for palynological analysis, though
here the rate of sedimentation is higher than on the rest of the floodplain.
The grain size distribution of samples was determined by the Köhn
pipette method (Müller et al., 2009) and by wet sieving, while the organic content (%) was measured following the Tyurin method (Kalembasa
and Jenkinson, 1973). Pollen extraction followed the method of
Zólyomi–Erdtman (Zólyomi, 1952) the sporomorpha were studied
under 400–600× magnification, and identification was carried out on
species, genus, and family levels. Pollen diagrams were drawn using
the Tilia and TiliaGraph software. The arbour (AP) and herbaceous
(NAP) species were divided into allochthonous (representing upstream
catchment areas) and autochthonous (reflecting the local environment)
subsets. Allochthonous pollen was used to identify overbank floods
(Weninger and McAndrews, 1989; Xu et al., 1996; Constantine et al.,
2005). Autochthonous herbaceous species were classified further into
associations of pondweeds (Lemnetea), reeds (Phragmitetea), wet
meadows (Molinio-Juncetea), dry meadow and ruderal weeds (FestucoBrometea +Chenopodietea), herbs of willow stands (Salicetea NAP), and
other herbs. For dating purposes, invasive species and pollen reflecting
dated land-use changes were used (see Brush, 1984). The date of their
appearance was determined on the basis of herbariums and written resources. Only those species that have well-documented invasion histories and no close native relatives were used for dating.
4. Results
3.2. Sedimentological and palynological analysis
4.1. Spatial pattern of aggradation based on DTM
Sediment samples were collected from two kinds of sites. One type
was where grain size distribution changed abruptly because of an increase or decrease in the distance from the river as a result of artificial
The studied reach was divided into five geomorphological units
based on slope conditions, pre-regulation (natural) geomorphological
Fig. 2. The DTM of the study area represents the active and inactive floodplain sections bordered by levees; the lines frame the areas (polygons) that provided the basis for calculating the volume of aggraded sediment.
T. Kiss et al. / Geomorphology 135 (2011) 191–202
195
Table 2
Main characteristics of the sampling sites and observed mean accumulation rates.
Sampling site
Unit
Date of
cutoff
Distance from the
active channel (m)
Floodplain
width (m)
Vegetation
Sampled form
Elevation
(m asl)
Mean accumulation rate
(cm/y)
Sediment analysis
Csordajárás (Cs)
Fan-front
1846
840
1700
Meadow, plough field
Zugoly (Zu)
Secondary
alluvial fan
Floodplain
1864–1872
450
2100
Forests, orchards
1858
1740
2200
Plough fields replaced
by forests
Vetyehát (Ve)
features (see Rachocki, 1981) and active sedimentary processes
(Figs. 2–3, Table 3).
The alluvial fan unit (25–31 cross section) is the highest surface
(83.7–86.8 m asl), characterised by Pleistocene sand ridges and shallow valleys. In this section, the pre-regulation Maros River had a
meandering-anastomosing pattern and a slightly (0.3–1.5 m) incised
floodplain. The artificial levee was built on the edge of this incised
floodplain (slope: 0.00038). During the regulations, this section of
the river was completely straightened. The new channel incised and
later became much wider, the pattern becoming braided (Kiss and
Sipos, 2007). These changes affected floodplain evolution, as another,
lower-lying floodplain level developed along the regulated channel.
Therefore, at present, the artificial floodplain can be divided into a
higher and a lower segment, with a height difference of 0.3–1.3 m.
Consequently, the duration of inundation varies and the lower floodplain is covered by water more often. Because of the formation of high
and low floodplains, calculation of overbank aggradation using the
DTM was not possible for the alluvial fan unit.
The fan-front unit (20–24 cross section) connects the higher surface of the alluvial fan with the lowland floodplain of the river. This
unit is characterised by abandoned meanders and point-bar remnants, while the higher northern part (elevated by 1.2–1.9 m) is dissected by valleys and covered by sand dunes. In this unit, the entire
active floodplain experiences intense aggradation, particularly the
areas near the active channel, although some pre-regulation forms
are still visible. The average amount of the overbank accumulation
between the artificial levees is 1.05 m 3/m 2, indicating an aggradation
rate of 1.0 ± 0.4 cm/y (Fig. 3). However, accumulation is not even on
the two sides of the river, as the overbank aggradation rate is only
0.8 ± 0.4 cm/y on the northern active floodplain but is 1.6 ± 0.4 cm/y
on the narrow southern one.
The development of the secondary alluvial fan unit (9–19 cross section) was the result of levee constructions. The slope of the protected
floodplain of the unit is almost the same as the next two units
(0.00006), so the distinction of this unit is justified by its high overbank sedimentation rate (1.4 ± 0.3 cm/y). Furthermore, this sediment
body is limited to the artificial floodplain and lies considerably higher
(max. 2.5 m) than the protected pre-regulation floodplain. The flood-
Fig. 3. Rates of aggradation (cm/y) on the active floodplain since levee constructions
(1885–1983). The maximum values indicate the rate of aggradation if the lateral
slope of the floodplain is not considered (for a detailed explanation, see section 5.3).
Cutoff (Cs1)
Natural levee (Cs2)
Floodplain bottom (Cs3)
Cutoff
83.0
83.9
83.2
81.5
2.4
0.2
0.6
1.3
Cutoff
78.0
1.8
DTM
1.3
1.0
0.3
protected area of the unit is characterised by scour channels and lowlying floodplain areas. The accumulation rate is highest along those
riverbanks in the form of natural levees, and it decreases downstream. The overbank sedimentation rates of the northern and southern artificial floodplain are almost identical (north: 1.5 ± 0.3 cm/y;
south: 1.4 ± 0.4 cm/y).
The next two units form the former common floodplain of the
Tisza and Maros Rivers, and are characterised by similar geomorphological features: abandoned and silted channels, shallow scour channels and backswamps. Some of the Holocene palaeo-meanders
belong to the Tisza River (with well-developed point-bar systems),
and others to the Maros River.
The low-lying floodplain unit (4–8 cross section) is characterised
by the slowest overbank aggradation rate (0.4 ± 0.2 cm/y). Sedimentation is most intensive on the active point bars and natural levees, so
areas farther from the channel experience moderate aggradation. The
northern and southern parts of the active floodplain exhibit significant differences in aggradation rate (north: 0.2 ± 0.1 cm/y; south:
1.0 ± 0.5 cm/y).
The outlet unit (1–3 cross section) differs from the other units in
the way it was regulated, as here a completely new channel was created, and the cutoff channel is now on the inactive floodplain. The
mean aggradation rate here is the highest of all the units (2.0 ±
0.5 cm/y) and increases downstream. The spatial pattern of accumulation is somewhat different to other areas, as the highest values were
measured on the bottom of the floodplain rather than near the channel. Furthermore, the northern part of the floodplain has experienced
a lower sedimentation rate (1.8 ± 0.5 cm/y) than the southern part
(2.3 ± 0.3 cm/y).
4.2. Temporal pattern of aggradation: analysis of sediment profiles
4.2.1. The sediment and pollen profile of a cutoff (Cs1) located on the
fan-front unit
Based on the physical and palynological character of the samples,
the sediment record of the almost entirely filled cutoff was divided
into three major zones. The middle zone was classified further into
two subzones (Fig. 4).
The lowest zone (I. 380–420 cm) represents the bedload material
of the active channel. The proportion of sand in the samples is high
(77–92%), while the coarse sand (0.1–0.32 mm) is indicative of bedload material. The number of allochthonous corroded and broken pollen grains (Pinus, Abies, Juniperus) is high, signifying an active channel
facies (before 1846). Based on the pollen spectrum, the exact environment of the channel can also be reconstructed and suggests the
dominance of riparian Salix and Quercus species.
Samples from the middle zone (II. 170–380 cm) contain more clay
and silt (25–50%) and organic material, but sandy layers are intercalated
between them. The II/a subzone (245–380 cm) represents an oxbow
lake in an early stage with deep open water. Here, pondweed species
(Myriophyllum, Potamogeton, and Nymphea) appear, and Carex indicates
an extended marshland. Higher surfaces at this time were covered by
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T. Kiss et al. / Geomorphology 135 (2011) 191–202
Table 3
Main characteristics of the geomorphological units in the study area, and the amount (m3/m2) and rate of overbank accumulation.
Unit
Alluvial fan
Fan-front
Secondary alluvial fan
Floodplain
Outlet
a
b
Section
25–31
20–24
9–19
4–8
1–3
Average slope
of the river
0.00030
0.00022
0.00012
0.00005
0.00002
Amount of accumulation (m3/m2)
Southern floodplain
a
n.d.
1.62 ± 0.45
1.38 ± 0.44
1.04 ± 0.57
2.37 ± 0.28
Accumulation rate (cm/y)
Northern floodplain
b
− 0.54
0.86 ± 0.49
1.50 ± 0.36
0.25 ± 0.18
1.85 ± 0.57
Average
Southern floodplain
Northern floodplain
Average
n.d.
1.05 ± 0.40
1.42 ± 0.35
0.43 ± 0.23
2.00 ± 0.55
n.d.
1.6 ± 0.4
1.3 ± 0.4
1.0 ± 0.5
2.3 ± 0.3
− 0.50
0.8 ± 0.4
1.5 ± 0.3
0.2 ± 0.1
1.8 ± 0.5
n.d.
1.0 ± 0.4
1.4 ± 0.3
0.4 ± 0.2
2.0 ± 0.5
n.d. not determined.
Negative value indicates incision.
riparian forests (Salix, Quercus, Populus, and Ulmus), pastures, and
plough-fields. During overbank floods, sand and allochthonous pollen
from the catchment were washed into the oxbow lake. The sandy layers
are covered by finer, organic rich sediments deposited during falling
water levels or smaller floods. The pollen of Amorpha fruticosa, appearing in the area in 1884 (Tímár, 1948) were found in the 300–310 cm
sample. Acer negundo was identified in the 250–260 cm sample and
first appeared in the area in 1889 (Priszter, 1960).
The pollen spectrum of the II/b subzone (170–245 cm) reflects a mature oxbow lake comprised mostly of wetland, with temporal open
water surfaces near the deepest points, and these only during floods
when some allochthonous pollen was still trapped at the site. After
floods, pondweeds appeared, though plants with wetland associations
(i.e., Caltha, Carex, and Lycopus) appear to be continuously present.
Identified patterns reflect rapid sedimentation in the cutoff. The pollen
spectrum also reflects agricultural extension in the close vicinity of the
site (cult. Gramineae, Chenopodium, Orobanche, Plantago, and Artemisia).
The pollen of the invasive Solidago sp. (at 210–220 cm) and Galinsoga sp.
(at 180–190 cm) were identified but could not be determined on a species level. However, their presence has been documented between 1870
and 1902 (Tímár, 1948).
In the upper zone (III. 0–170 cm), higher clay content indicates
the dominance of suspended sediment deposition. By this time, the
cutoff had silted up to such an extent that direct water transport
ceased and only suspended sediments could reach the area. The wetland almost disappeared, and hygrophilous species appeared only
Fig. 4. Sediment and pollen profile of a cutoff (Cs1) located on the fan-front unit. The proportion (%) of pollen grains is exaggerated (10×) for better visualisation. AP: arbour species; NAP: herbaceous species (for the legend of the sediment profile, see Fig. 5).
T. Kiss et al. / Geomorphology 135 (2011) 191–202
transiently during floods. Riparian forests withdrew and pasturing
and ploughing became dominant near the site. The appearance of
Ambrosia artemisiifolia pollen (115–135 cm) on the floodplain can
be used to date this phase to 1955 (Priszter, 1960).
4.2.2. The sediment profile of a natural levee (Cs2) on the fan-front unit
The natural levee studied here (Fig. 1) became inactive when its
meander was cut off in 1846. The sediment profile was divided into
two major zones (Fig. 5). Because the levee was elevated and its constituent material was aerated, no pollen grains were preserved, so
zoning is based on sedimentological evidence alone.
The material in the lower zone (I. 35–138 cm) represents a period
of active natural levee formation. The proportion of sand is very high
(80–85%), but slightly finer (0.1–0.2 mm) than the present-day bedload (0.2–0.3 mm). Sandy sediments are intercalated by silty (40%)
and clayey (20%) layers rich in organic material. These were probably
deposited during the falling stages of floods.
Nevertheless, in the upper zone (II. 0–35 cm), the proportion of
sand decreases to 30–40% and mostly consists of very fine sand.
These samples correspond to the post-regulation period, when suspended sediment was transported and deposited at the site.
197
4.2.3. The sediment profile of the floodplain bottom (Cs3) on the fan-front
unit
This site is situated near the above-described sampling points, but
is enclosed by a meander and its point-bar system (Fig. 5). Unfortunately, sediment samples are also pollen-sterile.
In the lower zone of the profile (I. 198–206 cm), samples certainly
represent a point-bar facies, and they were deposited when the meander was developing and the site was near the active channel. In
this zone, the sand fraction dominates (90%) with 60% being medium
sand. Finer fractions are underrepresented and organic content is
very low. In the middle zone (II. 98–198 cm), the sand fraction decreases (60–80%), and medium sand is replaced by fine sand. An overall fining can be observed above the middle zone (154–198 cm), but
then coarser material appears (98–154 cm). The finer sediments of
the top zone (III. 0–98 cm) suggest that the area was far from the active channel during this period (silt + clay = 40%).
Dating the different zones is possible by comparing this profile to
that of Cs2. The lower and middle zones were deposited when the
meander was still active. Later, sediments became finer as the channel was diverted from the site (early nineteenth century). The fine
sediments of the top zone were deposited after the regulation
(1846), when only fine material could reach the site.
Fig. 5. Sediment profiles of the study areas. The Csordajárás (Cs) site is located on the fan-front unit. The Cs1 coring was made in a cutoff, Cs2 on its natural levee and Cs3 in the
floodplain bottom behind the point bars. The Zugoly cutoff (Zu) is situated in the secondary fan unit and the Vetyehát cutoff (Ve) is in the floodplain unit.
198
T. Kiss et al. / Geomorphology 135 (2011) 191–202
4.2.4. Sediment and pollen profile of the cutoff (Zu) located on the secondary
fan unit
The lowest zone (I. 170–400 cm) consists mostly of sand (90–
100%), indicating the existence of an active channel. The proportion
of medium sand (representing the bedload material) is as much as
10–35% (Fig. 5). These samples are almost pollen-sterile (9–
23 grains/cm 2), making reconstruction of the past environment difficult. Samples at the bottom contain some pollen, while in the upper
samples, pollen density increases simultaneously with silt and clay
content. The pollen spectrum is dominated by allochthonous, broken
pine pollen grains; but some autochthonous species also appear
(Populus, Carex, Phragmites, Gramineae, and agricultural crops).
The middle zone (II/a. 170–90 cm) represents material in the cutoff. The samples contain very fine material, as the proportions of silt
and clay increase to 45 and 25%, respectively. However, sandy layers
also appear (e.g., between 160 and 130 cm), and the sand fraction
(0.2–0.1 mm) has a double peak. Changes in sediment properties reflect the inactivity of the channel, i.e., sand could get into the cutoff
only during floods. The middle zone is rich in pollen, though pollen
density decreases upward (130–160 cm: 54–154 grains/cm 2; 90–
130 cm: 3–54 grains/cm 2). A considerable number of allochthonous
grains were identified, such as Pinus (very often broken), Fagus, and
Alnus. Pondweeds (Nymphaea, Myriophyllum, and Potamogeton) indicate a deepwater juvenile oxbow that was surrounded by reeds. The
riparian forest was mostly composed of Salix and Populus species
mixed with Quercus, Fraxinus, and Ulmus. Some lands were cultivated nearby, as is indicated by cereal and weed pollen. The Amorpha
fruticosa was introduced in 1885 to stabilise the riverbanks (Tímár,
1948; Priszter, 1960) and its pollen appears in the 130–140 cm sample.
In the upper zone (II/b. 0–90 cm), the sediment gets even finer as
the proportion of clay increases to 50%. As the cutoff was aggrading
and becoming shallower, the velocity of the flood water decreased
considerably, such that only suspended material was transported
and deposited. The intensive silting-up is also reflected by a 1914
map, which already depicts a filled-up cutoff covered by a wet meadow. The pollen density of the samples is low (1–20 grains/cm 2). The
environment of the cutoff did not change significantly, and mixed willow stands grew nearby. Phragmitetea species were continuously present, while the Molinio-Juncetea association reflects the presence of
wet meadows. Ambrosia artemisiifolia was first observed in the area
in 1955 (Priszter, 1960) and its pollen grains are found in samples between 70 and 80 cm. In the upper samples (0–30 cm), the proportion
of arboreal pollen decreases, though Populus sp. becomes dominant
because of intensive poplar planting in the 1960s. The cutoff became
drier as only Carex sp. could grow, but crops and related weeds became
more abundant as well. The pollen grains of Ambrosia are very common, indicating its intensive spreading, which is also shown by air
quality data from the last few decades (Makra et al., 2005).
4.2.5. Sediment and pollen profile of the cutoff (Ve) located on the floodplain
unit
The lowest zone (I. 255–360 cm) contains mostly sand (90%). The
high proportion of medium sand (20–40%) represents the bedload of
the pre-regulation channel (Fig. 5). The pollen density of the samples
is quite low (0–15 grains/cm2), except for one silty sample (330–
340 cm: 77 pollen grains/cm 2). A great number of allochthonous pollen
were found (Pinus, Fagus, and Alnus), but the local vegetation is also
well-represented. Near the channel were riparian forests (Quercus,
Salix, and Populus), while deeper areas were covered by marshes and
wetlands.
The middle zone (II. 110–255 cm) represents an oxbow lake. The
mean grain size and the proportion of sand (20%) decrease. Similar
to the Zu II/a zone, a double peak of 0.1–0.2 mm sandy deposits can
be identified at 255–230 cm. This zone can be divided further based
on its pollen content. In the lower subzone (II/a. 180–255 cm), pollen
density is high (maximum 282 grains/cm 2 at 250–255 cm). Numerous allochthonous and broken pollen (Pinus, Fagus) were counted.
The local forest was dominated by Quercus, Populus, and Corylus sp.
In the oxbow lake, Myriophyllum was common, but other marshland
species were also present (e.g., Callitriche, Lycopus, and Carex sp.).
The elevated surfaces were cultivated, as reflected by the pollen of
corn and some weeds (Chenopodium, Plantago). In the upper subzone
(II/b 110–180 cm), pollen density decreases (0–14 grains/cm 2). The
pollen spectrum is similar to the previous subzone, though the proportion of hygrophilous plants decreased, reflecting a rapid aggradation rate.
In the upper zone (III. 0–110 cm), the sediment fines as the silt
content decreases (30–35%) and the clay content increases (50–
60%). This indicates the increasing importance of suspended sediment in overbank sedimentation. Nevertheless, pollen representing
the presence of riparian forest is still abundant; but in the upper
part of the zone (0–50 cm), Populus sp. becomes dominant because
of intensive afforestation between 1953 and 1964. The increasing
proportion of open-water pondweeds and wetland species indicates
permanent water supply, which can be explained by the artificial
water-retention measures in the cutoff channel.
5. Discussion
Based on the DTM, the average overbank sedimentation rate in the
studied area was 1.2 cm/y, while sedimentological and palynological
data suggest a 0.2–2.4 cm/y aggradation rate. These values are higher
than the sedimentation rate measured on the Tisza River (Table 4),
due to the different hydromorphological character of the two rivers.
In the case of the Maros River the sediment discharge is higher and
flash floods are more common (the average overbank flood time is
1 d/y). In addition, the slope of the Maros is steeper, lateral migration
Table 4
Overbank sedimentation on the artificial floodplain of the Tisza River since the nineteenth century regulation works.
Author
Location
Method
Period
Overbank sedimentation
Károlyi (1960)
Along the Tisza
Comparison of elevations
1838–1957
Gábris et al. (2002)
Szabó et al. (2008)
Balogh et al. (2005)
Tiszadob
Gulács
Vezseny
DTM
Heavy metal markers
Preregulation buried paleosols
1846–1983
1946–2008
1857–2005
Sándor and Kiss (2006)
Nagykörű, Szolnok,
Magnetic susceptibility,
heavy metal markers
1856–2005
Kiss and Sándor (2009)
Szlávik (2001)
Mártély
Middle and Lower Tisza
Cross section surveys
1976–1983
Narrow floodplains:
Wide floodplains:
Floodplain:
Floodplain:
Floodplain:
Point bar:
Oxbow lake:
River bank:
Point bar:
Floodplain:
Riverbank:
Point bar, natural levee:
Total amount (m)
Rate (cm/y)
0.8–1.6
0.2–0.5
0.2–0.6
0.6
0.4–0.7
1.7–1.8
over 1.5
0.6
0.9
0.3
0.3
0.7
0.6–1.3
0.1–0.4
0.1–0.4
0.9–1.0
0.2–0.5
1.1–1.2
over 1.0
0.4
0.6
0.2
5.0
10.0
T. Kiss et al. / Geomorphology 135 (2011) 191–202
199
is less intensive, the floodplain is narrower and more irregular, and
the outlet is very close to the margin of the alluvial fan. The rate of accumulation is not uniform in either space or time.
5.1. Spatial changes
5.1.1. Aggradation rate along the river
Most researchers have found a positive relationship between the
width of the active artificial floodplain and the rate of accumulation
(Lecce, 1997; Magilligan et al., 1998; Gábris et al., 2002), while some
have found a negative relationship (Károlyi, 1960). The positive relationship can be explained by the increased stream power in narrow valleys,
promoting sediment transport over storage. In case of the Maros River,
the total volume of deposited sediment is directly proportional to the
width of the active floodplain, but the rate of aggradation is inversely
proportional to it (Fig. 6). The volume–width relationship was explained
by Magilligan (1985), who found that in wide valleys the volume of deposited sediment was large but thinly spread. This connection can be
explained by the depositional environment. The narrower, southern active floodplain is typically characterised by more intensive overbank accumulation (1.0–2.3 cm/y) than the wider northern floodplain (0.2–
1.8 cm/y). The greatest difference was measured in the low-lying floodplain unit, where the aggradation rate of the southern active floodplain
(1.0 ±0.5 cm/y) was five times greater than that of the northern area
(0.2 ±0.1 cm/y), while its width (640 m) was less than half that of the
northern area (active floodplain width: 1423 m). In the case of the
Maros, both the slope and the sediment discharge are relatively large.
As a result, the active sedimentation-zone along the river is greater
than on other (Hungarian) lowland rivers. According to Oroszi (2009),
the sedimentation caused by a single flood on the Maros is very intensive
along a ca. 300-m-wide zone around the channel, whereas the equivalent zone is only 100–150 m wide along the Tisza River (Kiss et al.,
Fig. 6. Relationship between the width of the artificial floodplain (m) and (A) the total
volume of aggradation (m3) and (B) the rate of aggradation (cm/y).
Fig. 7. Relationship between the rate of aggradation (cm/y) and the average slope of
the river on the different units in the study area.
2002; Kiss and Sándor, 2009). Intensive near-bank aggradation explains
the increased importance of this zone on narrow floodplains.
The geomorphological units of the studied reach all have characteristic aggradation rates (Figs. 2–3). The most intensive overbank sedimentation has been identified in the outlet unit (2.0 ±0.5 cm/y), whereas it
was lower in the secondary alluvial fan (1.4 ± 0.3 cm/y) and the fanfront units (1.0 ± 0.4 cm/y), and its minimum was measured on the
low-lying floodplain unit (0.4 ± 0.2 cm/y). The greatest difference between the geomorphological units is in their slopes, so the relationship
between aggradation rate and slope was also analysed (Fig. 7). The
two parameters seemed to be directly proportional on the secondary alluvial fan and the low-lying floodplain unit. However, the scatter in the
data is considerable, suggesting the influence of other factors (i.e.,
microrelief, vegetation). The fan-front unit can be regarded as a critical
or transition zone (see Phillips and Slattery, 2008) where rapid downstream translation of alluvial fan development is observed, as the accelerated aggradation could be considered to represent currently active
alluvial fan development. In the case of the fan-front and outlet units,
no relationship could be identified between aggradation rate and
slope. The rate of aggradation was greatest in the outlet unit, despite
the shallow slope, probably due to the influence of impoundment
caused by its proximity to the Tisza. This is illustrated by the 1970 record
flood, when the average slope of the flood level was 0.00081 on the
floodplain, decreasing to 0.00033 in the outlet unit, and the pattern of
aggradation also showed a clear increase toward the confluence. Here,
the most intense accumulation can be seen not along the active channel
but in the bottom of the floodplain, illustrating the significance of sediment settling slowly from still water. The fan-front unit has the steepest
slope, but this appears to be unrelated to the rate of aggradation. This
observation is probably explained by other, site-specific hydrological
conditions (e.g., floodplain width, upstream incision, land use changes).
5.1.2. Aggradation rate related to different floodplain forms
The role of topography was evaluated for the fan-front unit. The
sites (Cs1–3) were close to each other but far from the currently active channel (ca. 840 m). The most significant difference between
the sites was their elevation (Table 2). The old natural levee (Cs2),
being the most elevated form, had an average rate of overbank sedimentation of 0.2 cm/y, while on the bottom of the lower floodplain,
the rate was three times greater (Cs3 site: 0.6 cm/y). The most intensive aggradation was measured in the cutoff (Cs1: 2.4 cm/y), the
lowest-lying form in the area. The relative elevation of forms determined the inundation duration, which was the ultimate control in determining local aggradation rates. The relative topography influenced
the accumulation rate, as was similarly found by Walling and He
(1998) and Benedetti (2003).
Although each cut-off meander exhibited intensive aggradation
(1.3–2.4 cm/y), local rates varied and depended on (i) the date of
the cutoff, (ii) the duration of floods, and (iii) the distance of the
site from the active channel. According to one description (Iványi,
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T. Kiss et al. / Geomorphology 135 (2011) 191–202
1948) over the duration of regulation work sediment transport increased tremendously in the straightened Maros River; thus, older
cutoffs (e.g., Cs) could have experienced very intensive aggradation
rates during this period. According to recent measurements of overbank sedimentation on the Maros, only suspended sediment can be
transported and deposited further than 300 m from the channel during normal overbank floods (Oroszi, 2008). Because all investigated
cutoffs are at least 450 m away from the active channel, today only
suspended sediment can reach these areas. Nevertheless, during earlier phases of their infilling, cutoffs could have served as secondary
channels during floods, and could also have trapped coarser material.
5.2. Temporal changes
The results above already suggest that the rate of aggradation has
not been uniform because the regulation works. Subsequent to regulations and up until 1884/1889, the oxbow lakes were in their early
development phase with deep water and high sedimentation rates
(1.9–2.4 cm/y) because of increased sediment load as a result of the
regulations (Fig. 8). During the first half of the twentieth century
(1884/1889–1960s), the sedimentation rate decreased (1.4–2.1 cm/y)
because of a significant decrease in sediment input as a result of
morphological stabilisation after the regulations. The rate of aggradation decreased further after the 1960s to 0.5–0.9 cm/y. Similar
patterns have been identified in the depositional history of other
oxbow lakes (Tamás and Kalocsa, 2003; Félegyházi, 2009). However,
at site Cs1, the sedimentation rate has increased to 2.6 cm/y since
the 1960s. The local reason in this case is land-use change, as in
the early 1960s the pasture was replaced by orchards, gardens and
forests, which increased roughness, resulting in an increased aggradation rate.
5.3. Methodological results
The application of the DTM to overbank accumulation studies is a
useful tool, but its limitations should be considered. The most important
Fig. 9. The total amount of aggradation (Vmax) could be calculated from the level of the
foot of the levee. By applying the slope of the inactive (original) floodplain, the aggradation since the regulation work (Vreg) could be calculated.
limitation is the accuracy of the available resources upon which the
DTM is based. In the present case, the accuracy of the topographical
maps was 0.26 ± 0.1 m, while the total depth of aggraded sediment
was only 0.1–2.65 m (only 10% of the data was under 0.3 m), suggesting
considerable error in some cases. Of course, the applicability of the DTM
depends on the vertical characteristics of the floodplain, because vertical errors are less important for larger elevation differences (see Phillips
and Slattery, 2008). Another limitation could be the shape of the floodplain. Most aggrading floodplains have a convex cross section, as the
near-channel areas experience more sedimentation. Therefore, if the
volume of the aggradation is calculated from a horizontal plain surface,
the rate of aggradation could be overestimated, while if the aggradation
is calculated from the original inclined slope, the calculation might be
more precise. In the present case, the aggradation was calculated
(i) based on the slope of the protected, inactive floodplain, which was
considered to be the quasi-original slope of the floodplain, and
(ii) from a horizontal surface at the level of the foot of the artificial
levee (Fig. 9). Comparison of the two datasets (Fig. 3) suggests that
the floodplain is so narrow (700 m on average) and the lateral slope
so small (active floodplain: 0.19°; inactive floodplain: 0.08º on average)
Fig. 8. Comparison of the profiles of the cutoffs, paying special attention to the proportion of sand in the sediment and the dated appearance of introduced plant species. Based on
the pollen profiles, environmental reconstruction was conducted for the sites.
T. Kiss et al. / Geomorphology 135 (2011) 191–202
that within the given width, the overestimation of the second method is
very small (ca. 0.04 ± 0.01 cm/y).
The advantage of a DTM is that in rapidly aggrading environments
it could be a useful tool for estimating the volume (or rate) of aggradation, if the height of the original surface is known. Besides, it provides data along long sections, giving broad insights into
downstream variations in fluvial accumulation.
6. Conclusions
Accelerated overbank aggradation as a result of mid-nineteenthcentury regulation works was measured along the Maros River. Within 50 years, the cutoffs made during the regulation works silted up
and the active floodplain was elevated. The accelerated sedimentation rate was due to both the establishment of a narrow artificial
floodplain and channel adjustments. The artificial floodplain limited
the area available for sediment accumulation, but the mechanism
for the accelerated aggradation was the increased sediment input as
a result of channel regulation and subsequent natural channel incision and widening.
The spatiotemporal pattern of aggradation was determined by
several factors. After the regulations, the sediment discharge changed
as the river reached its new hydromorphological equilibrium. This led
to increased overbank aggradation during and after the regulation
works. The rate of aggradation was strongly influenced by the width
of the floodplain, as the narrow floodplain sections aggraded more
rapidly, though the greatest total volume of sediment was deposited
on wider floodplain sections. The elevation conditions of the active
floodplain also played an important role, as the rate of aggradation
was greater in lower-lying areas. Consequently, the terrain of the
floodplain became more uniform, which could have altered the
flood hydrology and the riparian habitats. The confined floodplain restricted deposition to a very narrow zone, leading to the development
of a secondary alluvial fan at the base of the large primary fan and
resulting in accelerated accumulation near the confluence of the
river due to impoundment.
The measured rate of aggradation is uniquely high in the Carpathian
Basin, especially if the duration of floods is considered. The total duration of floods at least 1.0 m deep is only 1 d/y (Csoma, 1975), and the return period of floods deeper than 2.0 m is 30 years (Boga and Nováky,
1986). According to our calculations, the floodplain was covered by a
flood at least 1.0 m deep for only 88 days over 105 years. This means
that the rate of accumulation was 1.5–2.7 cm/d during floods.
Because of intensive aggradation, the cross sectional area of the
active floodplain decreased by 19–35%. The levees should therefore
be heightened to keep the flood hazard at its historically low level.
This study has shown that the rate of sedimentation is higher on narrow floodplains. Therefore, in future regulation works, greater attention should be paid to planning the necessary width of the active
floodplain.
This study has shown that long-term overbank accumulation can
be studied on longer reaches, enhancing our understanding of longitudinal trends. Some problems with the application of the DTM still
exist. However, despite these difficulties, the rate of overbank accumulation as calculated by both the DTM and sediment profiles is remarkably similar.
Acknowledgements
The research was supported by the HURO/0901/266/2.2.2 and
HURO/0801/194 projects. We thank Attila Botlik for his help in creating
the DTM, Dr. Károly Barta, and several students for their support during
sampling.
201
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