Rødekro Valley

5.3 Rødekro Valley
5.3
Rødekro Valley
5.3.1 Introduction
The Rødekro pilot area is situated in the south
eastern part of Jylland in the county of Sønder2
jylland. The area covers more than 250 km (Fig.
5.3.1). Population and industry concentrate in
and around the towns of Aabenraa and Rødekro.
The major part of the rest of the area is
characterised by intensive farming and to a lesser
extent by forestry. In addition extraction of gravel
has been increasingly more intensive since the
middle of the last century.
As is the case in the rest of Danmark the water
supply structure is quite decentralized. Thus at
time of commencement of the BurVal project the
public water supply of the area was operated by
19 different waterworks mainly owned by the
consumers. The waterworks in Aabenraa are
integrated in a single institution owned by
municipality while the two waterworks in
Rødekro are both part of the consumer owned
Rødekro
Vandværk.
The
joined
annual
groundwater abstraction of the waterworks of
3
the area amounts some 5 million m , which, as
far as the waterworks of Aabenraa and Rødekro
are concerned, are mainly extracted from
Quaternary aquifers via deep-seated screens in
3
deep wells. In addition nearly 3 million m of
ground water are extracted primarily from
shallow Quaternary aquifers by more than 100
separate irrigation systems scattered across the
countryside.
Prior to the start of the project the existence of a
buried valley underneath the terrain surface of
the Rødekro-Aabenraa area was known first and
foremost from groundwater abstraction wells. In
1994 Danmarks Geologiske Undersøgelse (DGU,
presently GEUS) published a national-wide
contour-map displaying the level of the
Prequaternary surface and with that the outline
of the base of the buried valley at RødekroAabenraa. In this representation the valley
exposed as a, in the eastern part, more than 8
kilometres wide subdued continuous structure
extending from Aabenraa Fjord in the east WNWward on to Rødekro from where it extends
further to the west (the contours from the DGUmap are shown in Fig. 5.3.1).
Since the publishing of the DGU-Prequaternary
contour-map a large vibro seismic reflection survey (COWI-report 2002) as well as two deep
investigation wells, 205 m and 225 m, (DGU nos.
160.1526 and 160.1561 respectively) carried out
by Sønderjylands Amt in 2002 and 2003 have
contributed new information about the extent
and the hydrogeology of the buried valley.
The main stationary line from the Weischel
glaciation stretches in a N-S direction as the Den
jyske Højderyg (“The Ridge of Jylland”) through
the central zone of the pilot area, where it
crosses through the eastern parts of Rødekro.
Within a 5–15 kilometres wide zone along this
ridge a significantly increased infiltration of water
is observed. Especially the wide extending
Miocene aquifers, e.g., the Ribe Formationen in
the western direction, benefit from this escalated
infiltration. The reason for the increased infiltration to the Miocene aquifers underneath the area
is primarily the absence or thinning out of the
marine Miocene micaceous clayey layers, e.g., the
Arnum Formation, towards the east of Jylland.
Normally these clay-layers cover and quite
effectively shield the Ribe Formationen against
infiltration and pollution from above in most
parts of Sønderjylland, in particular in the
western regions.
In this context it should be mentioned that one of
the most polluted industry grounds of
Sønderjyllands Amt is located in the town of
Rødekro. The contamination was caused by a
former dry-cleaners company which was
previously operating at the site. During 2006
Sønderjyllands Amt are conducting a cleaning of
the ground whereby the source of the pollution,
approximately 5 tons of chlorine solvents
presently residing in the soil and the shallow
aquifers below the ground, is expected to be
removed. Following the cleaning process a
considerable plume of pollution will still be
present in the aquifers of the area. The plume as
is now can be traced more than 2 kilometres
away from the location of the source.
For this and other reasons it is vital to improve
the knowledge of the hydrogeological setting of
the Rødekro area in order to assemble a solid
basis for a concerted effort with the aim to
protect the ground water of the region for
present and subsequent generations.
191
STEEN THOMSEN & HANS GULDAGER
Fig. 5.3.1: Project area. Locations of waterworks active at the commencement of the project are indicated by
blue quadrangles. Contours show the elevation (m asl) of the Prequaternary surface as published by DGU (DGU
1994). Regridded version.
5.3.2 Basic knowledge
At Rødekro the bedrock is located relatively
shallow and is descending towards the south.
Thus in the oil exploration well just north of
Rødekro, Rødekro no. 1 (DGU no. 160.286) the
bedrock is found at 1600 m bsl, while some 6.5
km south of here at the only other really deep, oil
exploration, borehole of the pilot area, Aabenraa
192
no. 1 (DGU no. 160.101) the bedrock is not
found until 2200 m bsl. This topography of the
bedrock surface is clearly reflected in the Bouguer
gravity field of the area, which appears with a
pronounced regional maximum just north of
Rødekro (Fig. 5.3.2).
5.3 Rødekro Valley
Fig. 5.3.2: “Total” Bouguer anomaly gravity field based on observations carried out during the project. Datum is
IGSN71. The area covered is identical to the project area (cf. Fig. 5.3.1).
In Aabenraa no. 1, located at Årslev, the bedrock
is succeeded by 450 m of Permian evaporites,
which is followed by some 900 m of Triassic
Keuper Clay and nearly 550 m of Limestone and
Chalk. At Rødekro and further to the north the
evaporites are missing and the thickness of the
Keuper Clay succession is reduced to
approximately 700 m. The topside of the Chalk
exposes a gentle positive gradient in the
northeastern direction with the surface located at
360 m bsl to the southwest and at 310 m bsl at
the northeast. The Chalk is overlain by 155–185
m of Paleogene clays and marls.
The Paleogene is followed by Neogene micaceous
clay and sand reaching a combined thickness of
nearly 100 m at locations where the buried valley
system is not incised into these sediments. The
Neogene succession includes the most important
aquifers of the region, first of all represented by
the Miocene Ribe Formation. Predominantly in
the western parts of the region marine micaceous
clays and fine-grained sediments of the Arnum
Formation cover the Ribe Formation. The
thickness of these layers is increased toward the
western parts of Sønderjylland where they may
total substantial more than 100 m. In the major
parts of the region the Arnum Formation
constitutes a quite effective shield against
infiltration and thereby contaminants from the
terrain surface, e.g., to the Ribe Formation,
because of the fine-grained character combined
with a frequent considerable thickness of the
Arnum Formation.
193
STEEN THOMSEN & HANS GULDAGER
Fig. 5.3.3: Map showing the obtained data and other information utilised during the project.
194
5.3 Rødekro Valley
While the topside of the Paleogene, which in
reality represents the deepest level from which
abstraction of fresh groundwater can be
performed, appears as a level surface with a very
subdued topography, the Neogene-Quaternary
interface, the Prequaternary surface i.e., expose a
highly irregular topography which reflects the
existence and courses of buried valley systems
(e.g. Fig. 5.3.5 and 5.3.7).
The Quaternary sediments in the western part of
the pilot area consist of up to 30 meter of melt
water sands pertaining to the Tinglev Hedeslette
(“Tinglev Outwash plain”). These sandy deposits
constitute the basis for a substantial part of the
ground water extraction in the area. Within a 1–3
km wide zone along the main stationary line,
which traverses in a N-S direction through the
pilot area and through the town of Rødekro, up
to 20 m thick fans of very coarse outwash sand
and gravel are a common phenomenon. Further
eastward on in the area the Quaternary
succession is dominated by tills and melt water
sand deposits. The Quaternary appears very
complex and heavily marked by several
glaciations.
The most important deep seated aquifers of the
area are constituted by the Miocene sand bodies
which are relatively thin but with a huge lateral
extension, and by the Quaternary elongated sand
bodies localized inside the deeper parts of the
buried valley system.
The Miocene aquifers are primarily represented
by the Ribe Formation, which stretches from a
zone along the median crossing through
Aabenraa and westward on underneath
Sønderjylland where it thins out a few kilometres
east of the coast bordering the Vadehavet (“the
Waddensea”). While the surface of the Ribe
Formation in the central parts of the pilot area is
located at approximately 70 m bsl this surface
gradually descents in the western direction. In the
westernmost extension of the Ribe Formation it is
located at a approximately 280 m bsl.
The deep seated Quaternary aquifers are
represented by, e.g., the sand body in the deep
production well at Rødekro Vandværk (DGU no.
160.1359). The surface of this sandy aquifer is
localized at a depth of 123 m below almost 60 m
of clayey till. At the waterworks Farversmølle of
Aabenraa Vandforsyning abstraction takes place
from a Quaternary sand body situated at a depth
of 83 m below tills and melt water clay ayers with
a thickness of more than 60 m (DGU no.
160.1245).
5.3.3 Pilot area mapping
5.3.3.1 Considerations of mapping concept
The overall purpose of investigations in the
Rødekro project area has been to improve the
understanding of two issues: 1) to which extent
the buried valleys of the area influence infiltration
to the Miocene aquifers; 2) which methods are
best suited for mapping buried valleys in an area
like the Rødekro project area where the
substratum beneath the valleys frequently is
constituted by sand as may as well be the case
with the basal layers in the valleys.
As regards the first issue, an attempt of detailed
mapping of the Prequaternary surface across a
2
more than 200 km wide area was accomplish as
a mean of delineating the extent and possible
depth of buried valleys in the area. In this way it
would be possible to assess to which extent the
Miocene micaceous clayey or fine-grained layers,
e.g. the Arnum Formation, which normally covers
and protect underlying, Miocene too, aquifers
have been eroded away, and thereby estimating
at which scale infiltration from Quaternary more
shallow aquifers may occur. In addition the actual
existence of the fine-grained mica clay was
evaluated by mean of detailed interpretation of
information from deep wells and reflection
seismic. Finally three weeks of test-pumping of a
centrally located deep well with the “testpumping-intake” placed in the Ribe Formation
was conducted. More than half a year in advance
of the test-pumping high-resolution registrations
of ground water pressures have been operated.
These registrations took place from a
comprehensive set of screens located in
Quaternary as in Miocene, deep seated as in
shallow aquifers in the area. This part of the
investigations has been carried out in a mutual
cooperation with the water works of Rødekro.
The second topic was to evaluate the usefulness
of different methods and combinations of
methods for mapping buried valleys. This goal
has been approached by collecting different types
195
STEEN THOMSEN & HANS GULDAGER
of data by use of different methods at – as far as
possible – identical positions. The project area
had been subject to more hydrogeological
surveys prior to the commencement of the
project. So a considerable number of data of
different origin and type already existed at that
time. Therefore it has been an aim during the
project to complement the collective set of new
and existing data. The clear objective with this
was to improve the basis for comparing strengths
and drawbacks of different methods. Caused by
the huge number data and the diversity of these
data in the final set, analysis will extent still some
time until a final conclusion can be drawn. Thus
the analyses throughout the project period have
primarily focussed on the data obtained in
project. Nevertheless still at the present stage
assumptions on which methods gives the most
fruitful results in an area with a hydrogeological
setting like the project area may be stated.
5.3.3.2 Field surveys and obtained data
The field surveys carried out during the project
are listed in Table 5.3.1.
5.3.3.3 Results
Results of the field surveys and subsequent
analysis are shown in the Figures 5.3.5 – 5.3.8.
Table 5.3.1: Investigations carried out in the Rødekro area (RUB = Ruhr Universität Bochum,
KMS = Kort og Matrikel Styrelsen, GI AU = Geologisk Intitut, Århus Universitet)
Method/
Survey
Survey
area, km2
SkyTEM
85
Gravity
Gravity
Seismic
200
–
–
VSP
–
Logging
–
GPR
–
Survey
length, km
Number
of
surveys
Parameters
Field operator/contract
72
1
GI-AU
–
26.4
5.5
1
1
7 lines
594 soundings
varying spacing
1456 stations
32 points
2.5 m CMP
spacing,
Vibroseis
P– and S–waves
3 wells:
205 m
205 m
225 m
0.300
196
GEUS
1
–
GI-AU
GEUS
Test
pumping
Passive
Ground
Level registr.
Samples,
water
SJA / KMS
RUB / KMS / SJA
GI-AU
–
7 wells
17 screens
1 air
pressure
1
65 m3/h
21 days
500 days
SJA / Rødekro VV / Ribe BBF
11 samples at 2
locations
GEUS
SJA / Rødekro VV
5.3 Rødekro Valley
Fig. 5.3.4:
Band passed residual gravity field extracted from the field displayed on the map of Figure 5.3.2
supported by regional data during the filtering process. Cut off wavelengths are 0.3 and 6.5 km.
197
STEEN THOMSEN & HANS GULDAGER
Fig. 5.3.5:
N-S profile showing an excerpt from the vibro reflection seismic sections on the northern outskirts
of Rødekro together with inline residual gravity data. The seismic sections were recorded and processed for
Sønderjyllands Amt by COWI (COWI-report 2002). Interpretation was carried out during the project. Inline and
neighbouring well profiles are projected onto the seismic section. Notice: Prequaternary elevations extracted from
the model exposed in the map of Figure 5.3.7 are projected onto the reflection seismic part of the Figure as a red
dotted line. The position of CMP-points may be obtained from the map in Figure 5.3.4.
198
5.3 Rødekro Valley
Fig. 5.3.6:
N-S profile displaying line 107 from the vibro reflection seismic survey recorded, processed and
interpreted by Geologisk Institut, AU. The line is running from Årslev to Bolderslev Skov ESE of Hjordkær (cf. Fig.
5.3.1). The position of CMP (SP) points may be obtained from the map in Figure 5.3.4. The inline residual gravity
data are extracted from the residual gravity field exposed in Figure 5.3.4. Notice: Prequaternary elevations
extracted from the model exposed in the map of Figure 5.3.7 are projected onto the reflection seismic part of the
figure as a red dotted line.
199
STEEN THOMSEN & HANS GULDAGER
Fig. 5.3.7: Contour map exposing the elevation of the Prequaternary surface as modeled on the basis of the
residual gravity field and information on the level of this surface from well and seismic data. The map is blanked
from a distance of 600 m away from gravity data points. CMP-points corresponding to the reflection seismic
section exposed in Figure 5.3.5 are displayed as red stars with a red label indicating the number of every 50th
point. CMP (SP) points corresponding to the reflection seismic section exposed in Figure 5.3.6 are displayed as
violet stars (a continuous line) and a violet label indicating the number of every 100th point. Also displayed on the
map are the locations of wells supplying information on the level of the Prequaternary surface to facilitate
comparison of the contoured model and existing well information. The blue rectangle around Rødekro indicates
the area covered by the maps shown in Figures 5.3.8 and 5.3.11.
200
5.3 Rødekro Valley
Fig. 5.3.8: 3D version of the elevation model of the Prequaternary surface exposed on the contour map in Figure
5.3.7. The map on this figure covers the small area around Rødekro as indicated by the blue rectangle in Figure
5.3.7. Notice: the positions of the deep wells are in the area shown.
5.3.4 Integration of results and modelling
5.3.4.1 Test pumping and geological model
Examples of integration of data and modelling
are illustrated by test-pumping results and by the
combined display of 3D geometrical model of the
buried valley at Rødekro together with a SkyTEM
contour map showing infill at a the elevation of
50 m bsl.
A constant discharge pumping test was
performed on well no DGU 160.1561 in order to
determine the hydraulic properties of the aquifer
in the depth range 75 – 115 m bsl and to
indicate possible boundary conditions.
201
STEEN THOMSEN & HANS GULDAGER
The test was performed by pumping with a
3
constant discharge of 65.7 m /h for a period of
22 days. During the pumping and the subsequent
recovery period changes in water levels were
recorded in the pumping well and in a number of
screens in observation wells in the vicinity.
Two observation wells, which are screened at the
same level as the pumping well, were clearly
influenced by the pumping. The wells are located
1380 m (160.1526_2) and 1740 m (160.1359)
from the pumping well (see location of wells in
Figure 5.3.6).
A selection of recorded data is shown in Figures
5.3.9 and 5.3.10.
Fig. 5.3.9: Drawdown curve for pumping well.
Discharge Q=65,7 m3/h. The position of the well is
displayed on the maps in Figures 5.3.3 and 5.3.8.
Transmissivities were determined from all time
drawdown / recovery curves from the pumping
well as well as for the observation wells. Storage
coefficients (S-values) were calculated from the
drawdown data measured in the observation
wells.
A summary of results is presented in Table 5.3.2.
From the calculated results the tested aquifer can
be characterised as a high yielding, extensive,
artesian type aquifer. The cone of depression
extends apparently freely towards west and
northwest in the direction of the observation
wells. The drawdown curve of the pumping well
(Figure 5.3.9) shows a slight change of slope
after approximately 250 minutes of pumping.
This may indicate a decrease in the aquifers
hydraulic conductivity at a distance from the
pumping well. As a similar change in slope is not
observed in any of the observation wells the low
conductivity area may be assumed to be located
to the east of the pumping well. This corresponds
well with other investigation results from the
project area.
Fig. 5.3.10: Drawdown curve for observation
wells. The positions of the two wells are displayed
on the maps in Figures 5.3.3 and 5.3.8.
Table 5.3.2: Results of pumping test analysis including calculated hydraulic parameters.
202
DGU
Well no
Distance
m
Drawdown
m
160.1561
160.1526_2
160.1359
0
1380
1740
0.82
0.68
Δs
Drawdown
m
Δs
Recovery
m
Transmissivity
m2/s
t0
S
min
0.39
0.49
0.44
0.43
8.1E-03
6.8E-03
7.5E-03
410
680
0.45
2.0E-04
2.3E-04
5.3 Rødekro Valley
Fig. 5.3.11: Contour map displaying the elevation model of the Prequaternary surface as seen in Figures 5.3.7
and 5.3.8. At the level of 50 m bsl the contours are blanked thus opening for a view on the mean electrical
resistivity map as calculated for the same elevation from the SkyTEM soundings.
Formation, thereby allowing for increased
infiltration to huge Miocene aquifers,
primarily the Ribe Formation.
5.3.5 Conclusion
■
■
The Aabenraa-Rødekro valley has proven to
constitute an intricate system of buried
valleys extending across the major part of the
surveyed area. Compared to the original
conception of the topography of the
Prequaternary surface, the result of the
project implies a thorough revision.
Generally speaking the valley system is not
incised rather deeply into the Tertiary
substratum and incisions to levels of more
than 100 m bsl are seen only in local areas.
However at all surveyed locations the valleys
do actually cuts through the fine grained
layer of, where present, the Arnum
■
The buried valleys in the area west, north and
northeast of Rødekro are from mean sea
level down to some 60–70 m bsl normally
filled with clayey sediments, frequently rather
thick sequences of tills. These layers reduce
the direct vertical hydraulic connection
between the terrain surface and the deeperseated aquifers. Based, e.g., on the results of
the gravimetric survey these clayey layers
probably extent through large parts of the
entire buried valley system.
203
STEEN THOMSEN & HANS GULDAGER
■
■
■
The hydraulic connection between deep
seated aquifers inside the buried valleys and
the contiguous Miocene sand layers is good
and the flow of ground water between these
aquifers presumably occurs quite unimpeded.
The lateral flow, however, in the deep seated
aquifers appears to a certain extent to be
affected by thick clayey sequences inside the
buried valleys
The geological setting of the RødekroAabenraa area, where the buried valleys are
frequently eroded into a substratum of
Miocene quartz sand layers requires special
demands on surveying methods to be used.
The combination of primarily reflection
seismic, gravimetric and electromagnetic
methods extensively supported by information from deep wells has demonstrated very
fruitful results. While the topography of the
Prequaternary surface has been successfully
mapped quite detailed by the combined
information from reflection seismic,
gravimetry and wells, the electromagnetic
results supported by well data and seismic
information have given details on which type
of sediments are actually comprising the infill
of the buried valleys as well as the
contiguous Miocene geology.
5.3.6 References
Aarhus University (2005): Rapport om en
refleksionsseismisk undersøgelse mellem Rise
og Bolderslevskov, Sønderjyllands Amt. –
Aarhus Universitet, Geologisk Institut 2006.
Aarhus University (2005): SkyTEM survey.
Aabenraa Røde Kro. Data report. – Report no.
2004.10.01, June 2005, Department of Earth
Sciences, University of Aarhus.
Binzer K, Stockmarr J, med bidrag af LykkeAndersen H, DGU, Kortserie nr. 44.
COWI (2002): Slæbeseismisk undersøgelsese OSD
Rødekro-Aabenraa-Kliplev. Udført for Sønderjyllands Amt. Rapport. COWI, Maj 2002.
Danmarks Geologiske Undersøgelse DGU (1994):
Prækvartæroverfladens højdeforhold.
204
Dybkjær K, Rasmussen ES (2005): OligocænMiocæn dinoflagellat stratigrafi i to boringer
ved Hellevad, Sønderjyllands Amt. Udført for
Sønderjyllands Amt. Danmarks og Grønlands
Geologiske Undersøgelse Rapport 2005/34.
Friborg R, Thomsen S (1999): Kortlægning af Ribe
Formationen. Et fællesjysk grundvandssamarbejde. Teknisk Rapport. – Ribe Amt,
Ringkjøbing Amt, Viborg Amt, Aarhus Amt,
Vejle Amt, Sønderjylands Amt. Tønder 1999.
ISBN nummer 87-7486-360-6.
Korsbech U (2004): Korrelationer mellem SNGlogs fra fire boringer ved Rødekro. – Rapport.
Danmarks Tekniske Universitet, Ørsted-DTU
Nørmark E, Lykke-Andersen H (2005): VSP (Vertikal Seismisk Profilering) i Boringer ved Rødekro. – Aarhus Universitet, Geologisk Institut.
Saxov S (1965): Some gravity measurements in
Sønderjylland. - Geodaetisk Institut Skrifter (3)
XXXVI, 59 pp.
Sønderjyllands Amt (2005): Tidligere renseri, Clip
Rens. Kortlægning af forureningsspredning., –
Grundvandsafdelingen, Sønderjyllands Amt,
Tønder.
Sørensen J, Dybkjær K, Rasmussen ES (2004):
Miocæn stratigrafi I boringen DGU nr.
160.1526,
Lunderup
ved
Rødekro,
Sønderjyllands Amt. Udført for Sønderjyllands
Amt. – Danmarks og Grønlands Geologiske
Undersøgelse Rapport 2004/91.
Sørensen J, Kronborg C, Nielsen OB, Krohn C,
Kragelund A (2005): Petrografisk korrelation.af boringer ved Hellevad, Rødekro,
Åbenrå og Kliplev. Udført for Sønderjyllands
Amt. – Rapport. 04SJ-05. Aarhus Universitet,
Geologisk Institut, Afdelingen for SedimentGeologi.
Thomsen S (1997): Kortlægning af dybtliggende
grundvandsmagasiner i Danmark. Afsluttende
rapport. Sønderjyllands Amt & Kort– og
Matrikelstyrelsen: 83 pp.
Watertech (2004): Rødekro. Borehulslogging I tre
nye
undersøgelsesboringer
DGU
nr.
160.1512, 160.1525, 160.1561. Udført for
Sønderjyllands Amt. – Watertech a/c. Rapport.