Water management in the Danube subcatchment „Upper Regen“, Bavaria, Germany
Dipl.-Geogr. Tilman Mieseler, Dipl.-Geol. Till Rubbert, Dr. Steffen Bender
Chair of Applied Geology, Ruhr-University Bochum
Summary
Border regions, which are geologically characterised by hard rocks, combine the disadvantages of limited groundwater
reservoirs and an unfavourable geographical location. In order to optimise water management in borderland regions, Test Site
Šumava was chosen to represent cross-border hard rock regions. Within the TRANSCAT-project this pilot site is used as
reference area to represent natural conditions without anthropogenic impact. By a close bilateral co-operation between
Germany and the Czech Republic it is planned to develop key indicators to be implemented in the intended TRANSCATDecision Support System for optimum water management in borderland regions.
Keywords:
transboundary, catchment, hard rock, water management, TRANSCAT
1.
Introduction
Water management in Southern Germany is mainly focused on groundwater regions with predominating porous aquifers, such
as the hydrogeological region of the Alpine foothills moraine belt. Their groundwater yield is high due to a combination of
high precipitation rates (950-1500 mm/a) and thick porous aquifers. In contrast, the hydrogeological situation of hard rock
areas is characterised by lower recharge rates due to steeper morphology and bad storage conditions in higher elevated areas.
Difficulties for the field of water management in the area of the Czech-German border are caused by insufficient understanding
of the hydrogeologic system as well as by minor interest of the responsible governmental agencies and the private institutions
involved. For that reason, in most cases only local plans for water management exist. Regarding hydrogeological questions
main problems are caused by the nonconformity of national borders with natural boundaries of groundwater regions.
Furthermore, the implementation of the EU-Water Framework Directive (WFD), associating spatial data from GI-systems with
socio-economic indicators, establishes new demands for catchments. To ensure a reasonable and successful water
management, entire catchments have to be monitored. Therefore, the national border may not be considered as a line limiting
interests of local or national authorities, as in fact all users of a transboundary catchment are responsible for water
management. To simplify water related decisions and to consider the EU-Water Framework Directive, the main goal of the
EU-project TRANSCAT (Integrated Water Management of Transboundary Catchments) is to create an operational and
integrated comprehensive Decision Support System (DSS) for optimal water management of catchments in borderland regions.
Input data for developing and verifying this tool originate from five pilot sites across Europe. Due to the fact that a lot of
problems occur in river systems with different adjacent countries, four pilot sites were selected to tend typical questions related
to contamination (e.g. caused by agriculture, livestock farming, industrial activities and settlements) or unregulated water
consumption in the headwater. The exceptional position of the fifth pilot area “Test Site Šumava” is due to the fact that only
small transboundary surface water catchments exist in that area, while the extend of transboundary groundwater catchments is
uncertain.
2.
Geographical classification of Test Site Šumava
The “Test Site Šumava” is formed by the south-eastern Czech part of the Šumava Mountains and the German boundary region
of Eastern Bavarian Forest, around the cities of Bodenmais and Zwiesel (fig. 1). The large mountain range of Šumava forms a
historical border between Germany and the Czech Republic. Since World War Two until 1990 it also represented the contact
between the Western and Eastern political blocks during the Cold War period. On the Czech side, this led to almost complete
evacuation of the local population while the major part of the area became a military zone. Consequently, this whole region
remained almost untouched for long decades, and today it may serve as a case study providing data on the development of an
environment which has hardly been influenced by human activities. “Region Upper Regen”, the German part of the
TRANSCAT-experimental site, is located in the Bavarian part of the Bohemian Massif. The forest areas in higher elevated
locations are part of the “National Park Bavarian Forest”. The area is characterised by a predominance of protected forest
regions with strongly emerging tourism and weak economic basis. Currently the risk of anthropogenic impacts on soil and
groundwater is low.
Figure 1:
Survey of Test Site Šumava (dashed rectangle: spatial extent of fig.2)
Basically, two different areas can be outlined there: the mountainous part with elevations around 1000 m a.s.l. and the
foothills. The studied part of the Šumava Mountains is drained by two important streams, the rivers Vltava and Otava, on the
Czech side. The German part of the area is drained by the river “Upper Regen” which belongs to the Danube stream
catchment.
Figure 2:
Digital elevation model of a part of Region Upper Regen
3.
Hydrogeology
Geologically the pilot area mainly consists of hard rocks, namely paragneisses and granites, which both generally show a very
low permeability. Nevertheless, local parts with increased hydraulic conductivity can be found, such as the transition zones
between lithological units, intensively stressed tectonic zones and former circulation paths. However, groundwater circulation
mainly takes place within the weathering zone and covering layers, which show an extend of up to 40 m and more in depth.
Compared to the other TRANSCAT reference areas, the hydrogeological situation at Test Site Šumava is of greater interest
and more complex as well. It is characterised by a combination of shallow porous aquifers and fractured hard rock aquifers of
the basement beneath. Within the subterranean catchment, transboundary groundwater fluxes most probably occur (fig. 3).
Figure 3:
Scheme of the hydrogeological situation in transboundary hard rock regions
Detailed investigations in the Upper Palatinate Forest show a broad variability of thickness of covering layers, which ranges
from 0 up to 100 m. Spring systems can be influenced by upwelling groundwater from deeper aquifers (Bender 2000, Breuer
1997). Unfortunately physico-chemical information are predominantly available for shallow aquifers, where available data
mainly originate from various springs.
The upper areas with elevations over 1000 m a.s.l. are part of the Nature/ National Parks Bavarian Forest and Šumava,
meaning good protection of groundwater due to limitations of nearly all anthropogenic activities. One of the main problems in
these mountainous regions is the acidification of soil and groundwater due to low buffer capacity of soil layers and weathering
zones.
As a further result of bark beetle activities or lumbering in combination with spruce monocultures and input of atmospheric
deposition (SO2, NOx) groundwater gets more acidic, enhancing the mobility of heavy metals and aluminum. Creation of
pollution load maps using risk analysis methods of Hrkal (2001) point to the high vulnerability of morphologically higher
parts. As a result of this risk analysis fig. 4 displays the vulnerability regarding acidic atmospheric deposition in the Bodenmais
area (spatial extent as in fig. 2) (Vornehm et al. 2003). This theoretical vulnerability map was created by evaluating four
subprocesses influencing the acidic vulnerability of groundwater: geology and petrology, elevation, prevailing wind exposition
as well as vegetation cover. To validate this risk study several groundwater samples were taken. As it can be seen in fig. 4
there exists a high conformity between measured pH-values and theoretical risk assessment.
4.
Water management
While the higher elevated regions are more interesting for Nature Park administration, the lower regions are highly important
for local water management. Due to the high number of springs mostly located in the higher elevated parts of the area, there
was no mandatory need to drill wells for local water supply. Therefore, geological and hydrogeological knowledge of local
hydraulic conditions is extremely weak. In combination with a very heterogenous geology and hydrogeological structure, it can
be stated that the complex system of hydraulic and hydrogeologic interaction in the area has not been well understood so far,
making a well-planned water management hard to obtain. Heterogeneities can not only be found in the lithological,
hydrogeological and hydrochemical environment of the area and the respective data base, but also for inhomogeneously
distributed anthropogenic impacts. Besides the fact that in some parts of the area the amount of existing data is completely
insufficient, another problem is imposed by data sources with and without anthropogenic influence in direct vicinity to one
another, caused by the heterogeneous nature of the local geology. As the anthropogenic impact cannot always be directly
identified, one is dealing with two different, incomparable data sets without even knowing about it. Such a situation may have
a high influence on statistical evaluation methods for regionalisation of data (Bender 2000). In combination with a small data
base, conclusions for these parameters are afflicted with high uncertainties. To adjust measurement programmes with defined
monitoring strategies for a cross border network, the planned DSS can help to simplify arrangements of standardised
procedures.
Figure 4:
Vulnerability for acidic atmospheric deposition in the Bodenmais area (Vornehm et al. 2003)
5.
Conclusions
The main task of the TRANSCAT project is the development of an integrated flexible DSS, which consists of several modules
for simulation of climatic, environmental or socio-economic processes. Working in a test site which is predominantly
characterised by extremely heterogeneous natural conditions as well as a heterogeneous data base of existing information, the
field of “data acquisition” is highly important. First of all, for an optimised usage of the DSS, the co-operation of countries on
both sides of the border is essential. To account for existing problems, communication between local water suppliers,
governmental authorities and the population must be promoted. Regarding water management in hard rock areas, it is
necessary to find evaluation methods enabling predictions of the hydraulic and hydrogeologic interactions in these complex
systems. Starting points for an approach are a) GIS-based calculations using available spatial data in combination with
weighted levels (Hrkal et al. 2003) or b) anthropogenic impacts (street salt, nitrate fertilizers) which can be used as tracers to
understand hydraulic processes.
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