Pilot area GE1 Störmarsch WP 4 GE1 Störmarsch and Münsterdorfer Geestinsel Wolfgang Scheer Reinhard Kirsch Helga Wiederhold Michael Grinat Mohammad Azizur Rahman
geological survey Pilot area GE1 Störmarsch WP 4
My most important outcomes:
● finalising geological model ● preparation direct-push measurements ● preparation seismic survey ● site investigations for the vertical electrode chain SAMOS (LIAG development) ● resistivity characterisation of near surface aquifers and covering layers
geological survey Pilot area reference WP 4
1 2 Main topics of field work: 1 interaction surface water – ground water, solution of lime stone sink holes
2 testing methods to characterize the hydraulic conductivity of the unsatured zone in the gw- recharge area 3 3 distribution of fresh and saltwater hydraulic properties of the Holocene clay 4 4 dynamic of the fresh/salt water distribution
geological survey Pilot area GE1 Störmarsch WP 4 site investigations for the vertical electrode chain SAMOS
SAMOS: successfully installed on the island of Borkum by LIAG during the project CLIWAT. Monitoring of resistivity changes in the underground, e.g. due to dynamics of freshwater saltwater interface
apparent resistivity (Ωm)
time after installation (y)
geological survey Pilot area GE1 Störmarsch WP 4 site investigations for the vertical electrode chain SAMOS
monitoring target in our area: intrusion of brackish water from the river Elbe Wadden Sea
our area:
40 km upstream ELBE tide ~ 2 - 3 m
Hamburg what will happen when the river ELBE
gets deepened? geological survey Pilot area GE1 Störmarsch WP 4 site investigations for the vertical electrode chain SAMOS
Glückstadt Proposed SAMOS location south of Glückstadt
2D geoelectrical measurements by LIAG show only minor resistivity contrast between aquifer and covering layers
→ high resolution monitoring necessary
SAMOS location
geological survey Pilot area GE1 Störmarsch WP 4 resistivity characterisation of near surface aquifers and covering layers our area is covered with a HEM survey flown by BGR in the project D-AERO
Bild HEM-Karte
to get a detailled look at the resistivity depth distribution in a selected area existing VES data were re-interpreted geological survey Pilot area GE1 Störmarsch WP 4 resistivity characterisation of near surface aquifers and covering layers From the 70ies up to 1996 about 20.000 vertical geoelectrical soundings were carried out by the Geological Survey of Schleswig-Holstein. The raw data are stored as sounding curves.
Although 1D VES are no longer state of the art it gives an overview of the resistitivity conditions if horizontal layering of the underground can be assumend.
geological survey Pilot area GE1 Störmarsch WP 4 resistivity characterisation of near surface aquifers and covering layers
selected area for VES re-interpretation
geological survey Pilot area GE1 Störmarsch WP 4 resistivity characterisation of near surface aquifers and covering layers
horizontal layering should be no problem in this area
geological survey Pilot area GE1 Störmarsch WP 4
In this area we have influence of brackish water from the Elbe and freshwater Stör from the higher situated Geest areas freshwater from the Geest areas
geological survey Pilot area GE1 Störmarsch WP resistivity characterisation of near surface aquifers and covering layers
The sounding curves were digitized and inverted by the programme IX1D (Interpex). Result is the resistivity-depth distribution at the sounding site.
geological survey Pilot area GE1 Störmarsch WP 4 resistivity characterisation of near surface aquifers and covering layers
Result: resistivity depth distribution along profile 1
geological survey Pilot area GE1 Störmarsch WP 4 resistivity characterisation of near surface aquifers and covering layers
Result: resistivity depth distribution along profile 1
Elbe Geest
covering layer
aquifer
increasing electrical resistivity – less influence of brackish water from the Elbe
geological survey Pilot area GE1 Störmarsch WP 4 resistivity characterisation of near surface aquifers and covering layers
a closer look at the resistivity structure of the covering layers – can we say something on the hydraulic conductivities? At least we can try.
aquifer
geological survey Pilot area GE1 Störmarsch WP 4 resistivity characterisation of near surface aquifers and covering layers
The covering layers mainly consist of sandy/silty clay of marine origin (Klei) and peat layers.
If we simplify this Klei by a sand – clay mixture, we can make an interpretation of the measured specific resistivities in terms of clay content based on laboratory results.
after Alali (2011)
geological survey Pilot area GE1 Störmarsch WP 4 resistivity characterisation of near surface aquifers and covering layers Clay-free sand has about 25% sand grains clay minerals pore space. If clay is added, the with pore (much smaller tiny clay minerals fill this pore space (filled than sand space and block the pore e.g. with grains) fill the channels – the hydraulic water) pore space conductivity decreases.
If the clay content is exceeding the pore space the sand grains are embedded in a matrix of clay. 10-4 hydraulic conductivity m/s From this point the sand has no contribution to the hydraulic 10-6 conductivity, the hydraulic conductivity is on the level of sand-free clay. 10-8 clay 20% 40% 60% 80% content geological survey Pilot area GE1 Störmarsch WP 4 resistivity characterisation of near surface aquifers and covering layers specificic electrical resistivity (Ωm)
60 The critical clay-content of the 40 Klei (represented by a sand-clay 20 mixture) is about 20 – 30%.
If the clay content is higher, the hydraulic conductivity is at the level of 100% clay.
At the critical clay content the 10-4 hydraulic conductivity specific electrical resistivity is m/s about 30 Ωm. Lower resistivities indicate low 10-6 hydraulic conductivities.
10-8 clay 20% 40% 60% 80% content geological survey Pilot area GE1 Störmarsch WP 4 resistivity characterisation of near surface aquifers and covering layers
possibility of limited water infiltration no free pore space left
If we do not assume flow paths through fissures in the Klei, groundwater recharge is restricted to areas where the electical resistivity exceeds 30 Ωm
we are working on that!!!!
geological survey Pilot area reference WP 4
My network
+ What data was necessary to achieve my results • geoelectrical measurements by LIAG • old VES by GLA and LANU (now LLUR)
+ Which stakeholders are involved • stakeholders (Deich- und Sielverband, Kommune Krempe) will be involved when reflection seismic measurements are carried out by LIAG
geological survey Pilot area reference WP 4
Challenges & solutions
+ What are the challenges experienced and/or expected • only a few drillings in the project area → geological database is lean
+ Help from other partners would be particularly useful for… • fast mapping of electrical resistivity for the characterisation of covering layers (down to 30 m) • NMR measurements for hydraulic conductivity assessment
geological survey