EUCOR-URGENT
2. Modelling of Hydrosystems
2.2. Hydrogeologic framework of quaternary Upper Rhinegraben sedimentary fill
Sub-project coordinators:
Dr G.. Wirsing, LGRB, Freiburg
Dr Ph. Elsass, BRGM, Strasbourg
The Quaternary sediments of the Rhine graben host major groundwater resources , estimated at 40-50
billion cubic metres between Basel and Karlsruhe. Deposited by the Rhine river and ist tribitaries from the
Vosges and Black forest, these sediments consist of a complex sequence of coarse grainesd fluviatile
sands and gravels and regionally intercalated lenticular low-energy clays, silts and fine sands. These
sediments can act as a multi-layered aquifer in areas where fine grained horizons are laterally sufficient
continuous to form hydraulic barriers, as seen in the Strasbourg-Offenburg ares (Elsass and Rau, 1995).
In the course of the LIFE project, a map of the base of the aquifer was constructed for the URG (part of
Baden-Württemberg). A more detailed processing was only carried out in the Offenburg-Strasbourg area,
where also fine grained layers within the quaternary sequence were mapped. However, many wells
located away from chosen cross sections were not used.
The aim of this subproject (led by Dr. Elsass and Dr. G. Wirsing) is to define the geometry of the
hydrogeologic units of the Upper Rhinegraben quaternary sedimentary fill. This work is done on the basis
of lithologic and genetic characteristics of the sediments. The results of the subproject 2.1
"Characterization and correlation of quaternary alluvial sequences" represent essential basic information
for this sub-project. In addition, results of seismic, geochemical and isotopic groundwater studies as well
as of hydraulic tests are incorporated. Each individual hydrogeologic unit will be characterized by its
hydraulic parameters. This can be done by relating the data on hydraulic conductivity, gained in the
course of the LIFE project ( Meineken and Stober, 1997) to the newly delimited hydrgeologic bodies.
Starting with a dense net of hydrogeologic crosssections, structure contour maps of hydrogeological
important interfaces are constructed, using also information about drillings between cross sections. For
the most part, this work is based on drilling data, stemming from the data bases of the LGRB BadenWürttemberg and of the BRGM. Consideration will be given to further constrain the geometric model with
Georadar and/or high resolution reflection data. The combined Sparker and Watergun survey, discussed
under subproject 1.5 may considerably contribute to assessing the overall architecture of the PlioQuaternary sedimentary fill. Additionally, a majer input concerning the influence of tectonics on the
sedimentary record is expected from other URGENT projects (e.g. subproject 1.1, 1.5).
The project will produce a great number of hydrogeological cross sections and a digital data set of
interfaces, determined by a uniform method for the entire Upper Rhine Graben. In conclusion a 3dimensional picture of the distribution of aquifers and aquicludes will be developped representing an
important asset for subsequent groundwater modelling (subproject 2.5: Development of hydrodynamic
models).
Developments in the geophysical characterization of physical properties of the alluvial sequences
(thickness, porosity, permeability) are in planning: use of the new RMP (Magnetic Protonic Resonance)
method as well as improvement in electrical methods.
The BRGM and the LGRB B.-W. will cooperate in this project.