Reconstruction of a colluvial body in an ... - Universität Bonn

Reconstruction of a colluvial body using geoelectrical resistivity
by
Marc-O. Löwner, University of Bonn, Germany
Nicholas J. Preston, Macquarie University, Australia
Richard Dikau, University of Bonn, Germany
with 6 figures and 3 tables
Summary. We reconstructed a colluvial fill in a relict gully on the middle slope of a loess
covered area of the Pleiser Hügelland near Bonn, Germany. The morphology of the site gives no
indication of the existence of such a feature, and we adopted geoelectrical soundings as a means
of both detecting and delineating it. Promising results showed that the electrical resistivity of
colluvium and its parent material differs by up to 50%. The volume of the colluvial body has
been reconstructed with the aid of a series of soil augerings. The volume of the linear feature
perpendicular to the slope was calculated as 2641 m 3 ± 383.05 m 3 . Though it is small in size we
argue that the existence of a colluvial body in such an unexpected slope situation has implications
for reconstruction of long-term landscape evolution and for closure of long-term sediment
budgets.
Zusammenfassung. Rekonstruktion eines kolluvialen Körpers mit Hilfe geoelektrischer
Widerstandsmessungen: In einer Mittelhanglage in einem Lößgebiet des Pleiser Hügellandes
bei Bonn wurde ein kolluvialer Körper rekonstruiert. Weil geomorphometrische Eigenschaften
nicht auf die Existenz eines solchen Sedimentkörpers hinwiesen, wurden geoelektrische
Methoden zu dessen Auffindung und Rekonstruktion angewendet. Die Ergebnisse zeigen, dass
sich das Kolluvium in seinem ermittelten elektrischen Widerständen um etwa 50 % von denen
des Ausgangsmaterials unterscheidet. Das Volumen des kolluvialen Körpers wurde mittels
Bohrungen auf 2641 m 3 ± 383,05 m 3 bestimmt. Trotz der geringen Größe des kolluvialen
Körpers ist durch dessen ungewöhnliche Lage ein Einfluss auf die
Landschaftsgenesemodellierung, insbesondere bei der Evaluierung langfristiger
Sedimentaustragsverhältnisse zu erwarten.
1

Résumé. Reconstruction d'un corps colluvial en utilisant la résistivité geoelectrical: Nous
avons reconstruit un colluvial complétons une caniveau de relict sur la pente moyenne d'un
domaine couvert par lœss du Pleiser Hügelland près de Bonn, Allemagne. La morphologie de
l'emplacement ne donne aucune indication sur l'existence d'un tel dispositif. Nous avons adopté
des mesures geoelectricales et en utilisant cette méthode la détection du colluvial éait possible.
Les résultats prometteurs ont prouvé que la résistivité électrique du colluvium et de son matériel
de parent diffère jusqu'à de 50%. Le volume du corps colluvial a été reconstruit à l'aide d'une
série de sondages. Le volume de la perpendiculaire linéaire de dispositif à la pente a été calculé
en tant que 2641 m3 ± 383.05 m3. Bien qu'il soit petit dans la taille nous arguons du fait que
l'existence d'un corps colluvial dans une situation si inattendue de pente a des implications pour
la reconstruction de l'évolution à long temps de paysage et pour la fermeture des budgets à long
temps de sédiment.
1 Introduction
Redistribution of sediment by diffuse and linear erosion processes is the most characteristic
feature of the small-scale landscape evolution of the loess-covered areas of central Europe (Bork
1988), and has been heavily influenced by agricultural land use over several millennia (Bork et
al. 1998). The anthropogenic clearing of vegetation cover represents the removal of a damping
agent between climate and the soil system, forcing the landscape to readjust through
redistribution of soil material. Where diffuse soil erosion processes are dominant, a smoothing
effect on slope morphology masks linear erosional features through colluviation. This effect is
reinforced by soil tillage on arable land (e.g. Lindstrom et al. 1990, Lindstrom et al. 1992, Govers
et al. 1994, Govers et al. 1996). Where this readjustment takes place through linear erosional
processes, like piping and gullying, we observe landscapes with more relief.
Geomorphologists attempt to reconstruct these landform changes using a variety of different
approaches that include process-based models and sediment budgets. Understanding of long-term
sediment fluxes is one of the keys to not only landform change, but also associated nutrient and
particulate fluxes. Further, sediment flux has implications for water quality, floodplain fertility
and natural hazards. Because it is influenced by both, a sediment budget has the potential to
highlight the relative significance of climate and anthropogenically driven environmental
changes. Irrespective of whether modelling is based on empirical relationships or physical laws,
2

the number of factors and processes that must be considered increases with area and time span,
creating problems when dealing with questions of longer-term landscape change (Dikau 1999).
Piping – or tunnel gullies – has been identified as an important process in the loess-covered
landscape of the Pleiser Hügelland to the east of Bonn in Germany (Botschek et al. 1996,
Botschek & Skowronek 1999). In many instances collapsed pipes form gullies, and in some cases
may even become infilled with colluvially derived sediments. The objective of this study was to
map and quantify such a colluvial body. Because these colluvial fills are often small in volume,
detecting them by drillings or trenches is very cost intensive. Geoelectrical techniques have
successfully been tested in permafrost research (rf. Schrott et al. 2003), and have also been used
in the investigation of soil properties (Lück et al. 2000, Koszinski & Wendroth 2001, Koszinski
& Wendroth 2003). We have used geoelectrical resistivity in this study as a comparatively quick
and simple means of remotely detecting infilled relict gullies. We argue that a linear erosional
feature found at the study site is an indicator of an ancient piping process, and that this process
should be incorporated into attempts to reconstruct long-term sediment fluxes. We have estimated
the volume of material stored within the relict gully and compared this to volumes of material
eroded from the slope.
2 Study Area
The investigated slope is sited at Gut Frankenforst, a research station of the University of Bonn
situated in the Pleiser Hügelland, a loess-covered predominantly agricultural area 15 km east of
Bonn (figure 1). The region is characterised by a complex geology made up of Devonian schists
and a series of alkaline basalt and andesite intrusions as well as deep deposits of trachyt tephras
(Vieten 1983, Vieten et al. 1988) that have since weathered to clay.
Loess, derived principally from the alluvial plains of the Niederrheinische Bucht, and
accumulated during the last glaciation (Sieberts 1983), is the parent material for soil
development. Under Holocene climatic conditions and without anthropogenic perturbation the
soil type is Luvisol (Paas 1968), with a typical horizon sequence as shown in table 1 (Heide
1988).
3

Figure 1: The research area within its regional setting. Measurement points and transects are
indicated.
Owing to agricultural land use these soils are highly eroded, and in some locations only the
recently formed calcareous ploughing layer can be distinguished from the parent loess material.
Soil moisture movement and groundwater lead to an additional differentiation of soil type. So-
Symbol Illustration
Ah/p
Al
Bt
Bv
C
humic horizon / ploughing horizon
illuviated horizon (≈ 10% clay) (l = lessiviert, i.e. illuviated)
relatively dense clay (≈ 25% clay) and silt enriched horizon (t = Ton, i.e. clay)
less dense/more porous horizon, lower clay content (v = verwittert, i.e. weathered)
parent material (loess or silty sand)
Table 1: Typical horizon sequence for the Holocene climax soil Luvisol (Heide 1988).
4

called pseudogley variants exhibit characteristic marbled and striped features, reflecting solution
and redistribution of iron and manganese during wet phases and leaching and concretion
development during dry phases. These features are highly variable in the research area. The
current distribution of eroded soils and colluvium on the study site is depicted in figure 2.
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Figure 2: Soil distribution on the research site, as reconstructed from 55 auger points.
The first human activity in the Bonn area is assumed to have been associated with Neolithic
people, who cleared forest from the more convenient sites for agricultural use (Erdmann 1998).
These sites were expanded by the Romans from 50 B.C. to 400 A.D. More widespread
deforestation took place in the 6 th century A.D., and over one hundred settlements were founded
in this period, including Stieldorf, located 1.5 km north-east of the research site. Whereas the
following centuries saw little human impact on the landscape, more widespread deforestation
occured in the 14 th and 15 th centuries (rf. Bork et al. 1998). Gut Frankenforst as an occupied site
5

is believed to have been in existence since at least the 12 th century, although the earliest
documented reference is from 1475, at which time it comprised five cultivated fields.
Considerable research into soil erosion and piping has been carried out in the Pleiser Hügelland
and at Gut Frankenforst (Botschek et al. 1991). Lessmann-Schoch et al. (1991) found colluvium
on a slope near the investigated site that was dated back to the 14 th century on the basis of pollen
analysis and radiocarbon ages. Furthermore, Welp et al. (1999) found approximately 1.5 m of
colluvium overlying moor at a nearby site. Radiocarbon ages from that colluvium are comparable
to those of Lessmann-Schoch et al. (1991); a sample of the buried moor dates back to 1300-1430
A.D. The onset of colluviation at this time has been inferred to be an indication of the initiation
of anthropogenic impact through deforestation and the introduction of agriculture.
3 Methodology
The colluvial body was initially located and identified using a soil auger, and was subsequently
investigated using geoelectrical resistivity. This technique is based on the differential electrical
resistivity of soil horizons and regolith strata as a function of their material properties, moisture
content and porosity. Colluvial sediments often have a different density from surrounding
material, and thus exhibit different soil hydrological behaviour. It was one of the objectives of
this study to ascertain whether this technique could also be applied in cases where colluvial
sediments were very similar to the material from which they were derived (in this case, loess).
Resistivity measurements are made by injecting a direct current into the ground via two
electrodes and measuring the resulting voltage difference at two potential electrodes with the
purpose of determining the subsurface resistivity distribution. The arrangement of the electrodes
determines the configuration, e.g. Schlumberger or Dipole-Dipole. More detailed descriptions of
the physical basis of geoelectrical resistivity are given by Reynolds (1997), Knödel et al. (1997)
and Friedel (1997), and overviews of the application of geoelectrical sounding in geomorphology
by Schrott et al. (2003), Lück et al. (2000) and Koszinsky & Wendroth (2001, 2003). The extent
of the colluvial body was determined using a geoelectrical transect parallel to the slope contours
(figure 1). Both Schlumberger and Dipole-Dipole configurations were tested, with 40 electrodes
deployed at intervals of one metre. While the Schlumberger configuration is less sensitive to
lateral changes in electrical resistivity, the Dipole-Dipole configuration could be used to detect
this (Lange 1997). Geoelectrical transects were duplicated with two soil auger transects (10 mm
and 55 mm diameter augers) in order to verify the results of the geoelectrical survey and to
6

establish boundaries between soil types. The nature of the sediment and soils was determined in
the field on the basis of texture, organic content, CaCO3 content, colour and inclusions such as
allochthonous stones and charcoal. To detect CaCO3 in the sediment and soils, we applied 10%
HCl solution (AG Boden 1996).
We distinguished colluvium from the in situ soil on two bases. First, the occurrence of charcoal
and pottery is noted. The former is assumed to be associated with slash and burn agriculture and
therefore with human impact on the ecosystem. Second, because decalcification is a soil-building
process propagating down from the surface, the presence of detectable CaCO3 content in horizons
above totally decalcified ones provides unequivocal evidence that the CaCO3-bearing layers are
colluvial material accumulated from above rather than an in situ weathering product.
Recorded thickness at each auger point was grouped into three classes, and mean thickness for
each class was multiplied by the mapped surface area of that class in order to estimate the volume
of colluvium. Establishing boundaries between classes involved some resampling in places with
insufficient depth information. Although the sampling density was high (one metre between
points), boundaries are inevitably subjective.
4 Results
A series of geoelectrical surveys were made parallel to the slope contours, encompassing the area
where soil auger investigations had indicated the presence of a colluvial body. Figure 3 shows the
result of a 2D resistivity survey using the Schlumberger configuration. It is notable that the
resistivities measured are extremely low, due to soil moisture resulting from a recent rainfall
event. Nevertheless lateral differences in resistivity can be observed down to a depth of about
four metres, varying from 45 Ωm to 22 Ωm between the 21 st and 25 th metres along the profile.
The highest resistivities can be observed at depths of less than 1.2 m, possibly due to drying
effects, and at the 31 m mark at a depth of 2.2 m.
7

Figure 3: Resistivity tomogram of a Schlumberger survey along Transect T1.
Figure 4 depicts the result of a 2D resistivity survey using the Dipole-Dipole configuration along
the same transect (figure 1). As in figure 3, the observed resistivities are notably low. Aside from
the upper 1.5 m, resistivities of more than 55 Ωm can be observed at four locations along the
profile - at about 8 metres, 20 metres, 28 metres and 35 metres. The values of higher resistivity in
both the Schlumberger and the Dipole-Dipole configurations are restricted to a narrow zone.
Figure 4: Resistivity tomogram of a Dipole-Dipole survey along Transect T1.
8

Figure 5: Stratigraphy of Transect T1 inferred on the basis of indicated auger holes. The question
mark indicates the tentativeness in identifying the horizon in question as a Bv horizon and not an
elder colluvium. Figures 3 and 4 illustrate results of geoelectrical surveys over the interval 29-69
m.
Two soil auger transects (T1 and T2) are depicted in figures 5 and 6, illustrating the form of the
colluvial body. Transect T1 crosses the widest part of the colluvial body. Two auger holes (T1-15
and T1-21) extended to the lower limit of the loess body, revealing weathered tuff at depths of
6.46 m and 5.1 m respectively. The loess consisted primarily of silt with very little clay but
occasionally large amounts of fine sand. Hydromorphic features were extremely variable over the
whole profile, indicating strong horizontal groundwater migration. In situ soil was absent from
almost the whole of transect T1; only auger point T1-10 revealed an in situ Bt horizon. This
implies that ≈ 3 m of the primary loess soil had been eroded from the middle slope. There is a
sharp boundary between the colluvial filling in the centre of the transect and the underlying loess.
We found no in situ soil under the colluvium. Figure 6 depicts Transect T2, situated 15 m
downslope from T1. Auger point T2-04 extended to the base of the loess body at 4.25 m. As in
9

transect T1, hydromorphic phenomena indicate the influence of lateral groundwater migration.
Again, the Holocene soil has been almost totally eroded from this part of the slope, and we found
calcareous loess underneath the colluvium rather than in situ soil.
Figure 6: Stratigraphy of Transect T2 inferred on the basis of indicated auger holes.
Two distinct colluvial units, a calcareous colluvium and a charcoal bearing colluvium (rf. Fig. 5
and 6) were recognised. The stratigraphically lower of the two is characterised by small
fragments of charcoal. These are absent from the overlying colluvial unit, which can be
characterised by the presence of CaCO3. Although this second colluvial unit is indistinguishable
in texture and colour from the B horizon of a Luvisol (rf. table 1), both the CaCO3 content and its
stratigraphic location preclude it from being an in situ pedogenic horizon. Further, the law of
superposition implies that it must be younger than the charcoal-bearing colluvium.
On the basis of these 55 soil auger points, we infer a distribution of three different units: a totally
eroded soil, an eroded Luvisol, and colluvium. The regional climax soil, a Luvisol, could not be
found on the investigated slope (figure 2). Almost all of the upper slope is characterised by totally
eroded soils. Only the ploughing layer, showing a weak CaCO3 content, could be differentiated
10

fom underlying calcareous loess parent material, indicating that all of the solum had been eroded.
The underlying material varied in colour due to hydromorphic action but not in soil texture or
Depth [m] Horizon Colour Carbonate
a) T1-08
0 - 0.4
0.4 - 2.3
2.3 - 3
Ap
b) T2-09
0 - 0.35
0.35 - 2.7
2.7 - 3
loess (reduced)
loess (reduced)
Ap
Bv
Loess
c) T1-19
0 - 0.46
0.46 - 0.73
0.73 - 0.92
0.92 - 0.95
0.95 - 1.53
1.53 - 1.71
1.71 - 3.0
3.0 - 4.0
Calcareous
Colluvium / Ap
Colluvium
Colluvium
Colluvium
Colluvium
Colluvium
Cv / Bv
loess (reduced)
10YR5/4
10YR5/2
mottles of rust
10YR5/2
10YR4/4
10YR4/6
10YR6/6
10YR5/4
10YR4/4
10YR4/4
10YR4/4
10YR4/4
10YR4/4
2.5Y4/6
10YR5/2
Content [% in
mass]
≈ 1
≈ 20
≈ 20
0
0
≈ 20
≈ 5
0
0
0
0
0
≈ 5
≈ 20
Soil Texture Inclusions
Silt Loam
Silt Loam
Silt Loam
Silty Clay
Loam
Silt Loam
Silt Loam
Silt Loam
Silt Loam
Silt Loam
Silt Loam
Silt Loam
Silt Loam
Silt Loam
Charcoal
Red pottery
Charcoal
Charcoal
Charcoal
Table 2: Profiles found on the investigated sites. a) A typical horizon sequence of totally eroded
upper slope soil, b) a typical eroded Luvisol, and c) a typical colluvium.
CaCO3 content (table 2(a)). The second soil type, mainly occurring on the middle and lower
slope, was an eroded Luvisol with some remaining in situ soil horizons (table 2(b)). In
comparison to the first soil type, the second type revealed decalcified horizons, giving evidence
11

of soil building processes. Additionally, in most cases there were clay-enriched layers on the top
of such profiles, indicating that a former Bt horizon had been exposed, possibly by diffuse soil
erosion or ploughing.
The third unit, colluvium, does not occur over the whole lower slope, but only as a linear feature,
perpendicular to the Forstbach channel (figure 2). Table 2(c) gives a description of the deepest
colluvium found here. Noteworthy is the location of the colluvial body and its extension to the
upper slope, implying a filled linear erosional feature. The older, charcoal-bearing, colluvium
extends to the north-western boundary of the research area, i.e. to the channel, and a further 25 m
upslope. The younger colluvium has an even wider distribution. The orientation of the linear
colluvial body does not conform to the contemporary contour lines. Preston (2001) gives three
OSL ages for samples taken at or near the base of the mapped colluvium: 1220 a ± 100 a – 1380 a
± 100 a, 1200 a ± 130 a – 1350 a ± 150 a and 1200 a ± 110 a – 1280 a ± 110 a. An age of 1250 a
is assumed to be representative for the base of the colluvial fill.
Accumulation Class ≤ 1 m 1 – 2 m 2 – 3 m Total
Area [m 2 ]
Class mean [m]
Standard deviation [m]
Accumulated Volume [m 3 ]
1095
0.4537
0.03792
497
1261
1.5717
0.2688
1982
59
2.734
0.0436
162
2415
2641
Table 3: Estimated volume of accumulated colluvium on the investigated site. Row 2 and 3 are
related to the thickness of the layer.
The total volume of accumulated material was calculated as 2641 m 3 ± 383.05 m 3 (table 3). Of
this, 497 m 3 ± 41.5 m 3 accumulated on sites with thicknesses of less then one metre, 1982 m 3 ±
339 m 3 on sites of 1-2 m thickness and 162 m 3 ± 2.6 m 3 on sites with 2-3 m of colluvium. Of the
total volume, 761 m 3 ± 159.35 m 3 belong to the younger colluvium. As figures 5 and 6 suggest,
this is partly cut into the older charcoal-bearing colluvium.
5 Discussion
The main point of this study is the reconstruction of a relatively large sediment sink, which could
not be identified on the basis of contemporary morphometry, using geoelectrical surveys as a tool
for remote detection and targeting of auger sampling. Although the observed resistivities are
12

conceivable small, the extent of the colluvial body as subsequently revealed by augering is
implied from both the Schlumberger (figure 3) and the Dipole-Dipole (figure 4) configurations.
Because the Schlumberger configuration is normally relatively resistant to lateral changes in
resistivity, a variation of more than 50% of the measured resistivity range is considered to reflect
an effective difference in the material properties of the colluvium and the surrounding soil
material. On the other hand, Dipole-Dipole configurations are more sensitive to lateral changes
(Lück et al. 2000), and it is considered that the measured resistivity peaks are associated with the
boundaries of a filled up sediment sink. Thus, while the Schlumberger configuration shows the
centre of the two reconstructed colluvial sinks, the Dipole-Dipole configuration identifies their
boundaries. The nature of this boundary might be a result of soil building processes that occurred
while the gully was exposed to the air. To answer this question more work has to be done to
compare geoelectrical surveys with drilling results.
There are two possible explanations for the existence of this colluvial sink perpendicular to the
contour lines. It can be hypothesised that the feature in which colluvium has accumulated was
formed by either backward incision from a channel bank slump, or by simple linear incision
resulting from high rates of overland flow, i.e. gullying. While the latter seems to be unlikely
because of the small hydrological catchment, such an origin is plausible if it follows the collapse
of a pipe formed by subsurface flow. Botschek et al. (2001) found that loess-covered slopes have
a strong affinity to piping initially caused by interflow (see also Botschek et al. 1996). Botschek
and Skowronek (1999) describe piping on a nearby slope with comparable soil and of similar
size. We interpret the varied hydromorphic features depicted in figures 5 and 6 as an indication of
ongoing lateral throughflow. Therefore a collapsed pipe, enhanced by headward erosion, is
argued to have occurred here.
Nevertheless, piping does not account for the almost complete erosion of soil across the slope.
We hypothesise that this and the colluvial filling of the former gully are related and that the
truncated soils upslope (rf. figure 2) clearly indicate the source area for the gully fill. We believe
that both the sheet erosion of the slope and the filling of the linear feature are the effect of human
impact on the slope through forest clearing and agricultural land use. Under forest the linear
feature is more likely to have both formed and been preserved (e.g. Müller-Miny, 1954; Nicke,
1989). However, while it may have formed and existed under forest for some time, it is likely that
it did not begin to be filled until the forests were cleared, and that gully formation was probably
contemporaneous with deforestation. The charcoal in the older of the two colluvia suggests that it
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was formed at the time of deforestation, and as there is no other colluvium underlying this, it
seems reasonable to infer that the gully was formed at approximately this time. Deforestation
may in fact have indirectly influenced the collapse of the pipe, by contributing to enhanced
infiltration of rainfall into the soils and thus altering the slope hydrology. If the slope had been
forested prior to the formation of the gully, then it is unlikely that the extensive and ubiquitous
erosion of the upper slope occurred before this. Gully formation, therefore, did not post-date land
use change.
Because the optically stimulated luminescence technique dates the last exposure of sediment to
daylight, the burial of the linear feature must have commenced no later than 1250 years ago and
the collapse of the pipe and its evacuation must have occurred either at that time or some time
prior to that. If the gully filling was broadly contemporaneous with deforestation, then it follows
that the age of the colluvium provides an indication of the timing of this, and therefore the
beginning of human influence on the slope. Using the age of 1250 a given by Preston (2001) for
the colluvium, we suggest that this occurred during the early Medieval period, which is some four
centuries earlier than suggested by Lessmann-Schoch et al. (1991) and Welp et al. (1999).
Our evidence thus indicates that a slope as a geomorphic element does not simply represent a
source of sediment input to the fluvial system, but even when considered over longer timescales
also represents a sediment sink. Storage capacity in the form of colluvial footslopes is common in
many landscapes. Bork (1988) describes basal colluvium deposits in many parts of central and
northern Germany, typically formed as a result of diffuse soil erosion. Temporary storage of
sediment on slopes is also common, but would perhaps not generally be expected on such a short
slope with an undercutting channel, such as in this case. In Forstbach, we found not a basal
colluvium at the foot of the slope, but both on-slope sediment storage and a buried linear feature.
Exposures in other parts of the channel reveal in situ soil and loess. Colluvial sediment storage is
locally restricted.
The aforementioned findings have several implications for understanding and reconstruction of
long-term landscape change. First, the fact that the slope acts as a sediment sink invalidates the
top-down approach of evaluating erosion on the basis of fluvial sediment load measurements and
estimations. One cannot properly understand sediment redistribution dynamics simply on the
basis of catchment outputs. Second, because piping or sinkhole erosion is a widespread
phenomenon in loess areas (Botschek & Skowronek 1999, Pécsi & Richter 1996), this process
must be duly considered in sediment budget approaches – at least in these areas. Slopes such as
14

that presented here are found throughout the Pleiser Hügelland and further afield. We argue that
these features are small but potentially numerous in the context of investigation or modelling at
the scale of higher order catchments. Failure to include them may contribute significantly to
errors in assessment of long-term landform development and sediment delivery. Data describing
location and volumes of onslope sediment storage such as revealed here are essential in
estimation of sediment delivery ratios, although clearly calculation of a sediment delivery ratio
requires that further work is needed to quantify volumes of both onslope storage and erosion.
6 Conclusion
There is a relatively large sediment sink on the investigated site, which cannot be identified on
the basis of contemporary morphometry. Geoelectrical surveys can help to detect and potentially
quantify colluvial bodies such as this, especially when using a combination of Schlumberger and
Diplole-Dipole configurations. More work is needed to be done to understand the interrelation of
electrical resistivity and material properties of erosion-derived sediment.
The characteristics and age of the reconstructed sediment body imply that anthropogenic
influence on landform at this site began earlier than previous evidence had suggested. More
importantly, the presence of sediment bodies such as this has implications for approaches to the
reconstruction of longer term landform changes in two major ways. Firstly, landform change
occurs through multiple processes, and over longer time scales it is likely that an increasing
number of these will have to be incorporated. It is inappropriate, therefore, to attempt modelling
of landform change focussing on only one or two processes. Rather, the full range of processes
that may have occurred must be considered. Secondly, use of a sediment budget approach to
validate models of landform change requires a high data density of sampling, enabling the
reconstruction of erosion and deposition sequences. Clearly sediment storage in small landscape
units can be significant even over longer periods.
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