Island of Falster, Denmark
1. Pre- foresight
Climate change and sea level rise is expected to increase salt water
intrusion and decrease freshwater resources in coastal regions. The
Falster case assesses the impacts of climate change and sea level rise
on available groundwater resources and the risk of flooding in a
coastal region. The project findings and established groundwater model
will provide a tool for future development of sustainable water
extraction schemes for the area. Water extraction (pumping) occurs from
wells for water supply (drinking water and irrigation), and from canals
to avoid flooding of reclaimed land. The project results and the
established model will constitute part of the important knowledge base
for the development of climate proof river basin management plans and
adaptation strategies for the investigated area according to EU
directives and guidelines.
Falster is an island in the south-eastern part of Denmark in the
western Baltic Sea., Marielyst waterworks is located close to the
Baltic Sea at the east-coast of the island. The waterworks supplies
5,200 households with groundwater from a shallow coastal chalk aquifer
at 20-30 m depth. The majority of households are summer and weekend
cottages. The water demand varies significantly between seasons. The
minimum water consumption is 300 m3/day in January, and the maximum is
around 2,000 m3/day in July. The total production of drinking water
form Marielyst waterworks is 250,000 m3/year (2008).
The waterworks already face problems with high chloride content in the
abstracted groundwater. Especially sea level rise and changed
precipitation patterns will challenge the current water supply
management and the abstraction from existing well fields at Marielyst
waterworks. The following climate change effects are expected: (1)
Change in amount and distribution of precipitation during the year, and
increasing evapotranspiration. Most climate models predict an increase
in winter precipitation and a decrease in summer precipitation for the
Danish area, and (2) Sea level rise. Climate models predict sea level
rises between 0.5 and 1.0 m in the area by the end of the twenty-first
century. Secondary effects of the predicted increase in summer
temperatures are increased water consumption in the summer months due
to a longer season for using the weekend houses and also an increased
demand for second homes in the recreational coastal area.
Water abstraction for water supply and drainage of reclaimed land both
increase salt water intrusion in the investigated area. The groundwater
and drainage pumping have to be carefully planned as there is a
delicate balance and conflict between minimizing salt water intrusion
and the risk of flooding of the reclaimed land.
The project activities in the case study area include the construction
of a 3D variable density groundwater model of the above described
aspects of groundwater abstraction from the coastal aquifer. Field
activities for collection of new data as well as compilation of
existing data are key activities of the case study. The vulnerability
of the existing water supply infrastructure as well as the adaptation
capacity of both the water users and waterworks are studied.
Meetings and workshops with key stakeholders will take place throughout
the project period.
The BaltCICA project has made it possible to carry out field work
and data collection including groundwater level and groundwater
salinity monitoring, groundwater and surface water sampling, borehole
geophysics, hydraulic aquifer tests, and to drill three new boreholes
for detailed information of geology and saltwater distribution.
The local office of The Danish Nature Agency (NST) has included the
Falster case study area in their on-going groundwater protection
mapping by the SkyTEM method for the BaltCICA project. SkyTEM is a
helicopter-borne electromagnetic system capable of mapping near surface
groundwater resources up to 150 m below ground surface. Interpreted
SkyTEM data from the case study area has been provided by NST. The data
are primarily used to identify the interfaces between freshwater and
salt water in the subsurface.
Marielyst waterworks has provided the project with data on groundwater
abstraction, groundwater salinity, as well as access to existing and
previous abstraction wells for groundwater sampling and borehole
logging.
The municipality of Guldborgsund issued permissions for new
investigation wells to evaluate fresh/salt water boundaries in the
investigated area and corroborate the SkyTEM measurements.
Other main data sources were the national borehole database Jupiter
with geological logs and groundwater data at GEUS, the Danish Nature
& Environment Portal containing surface water and land use data.
The Danish Maritime Safety Administration web site provided access to
sea level and salinity data.
The
groundwater
model
will
integrate
many
of the collected data and provide
an understanding of how the various parts of the groundwater system are
interacting, and how it reacts to different imposed stresses.
Scenarios will be developed including the impacts of three climate
change effects: Precipitation, sea level and groundwater demand
including its seasonality. The scenarios will focus on the effect of
each of the three issues, as well as on the combined effect.
The outcome of modelling the different scenarios is expected to
pinpoint areas where the current groundwater plans and groundwater
management practice are challenged by climate change. The modelling
results will be illustrated in figures and maps for both written and
oral presentations.
An introduction meeting with key institutional stakeholders was held
to introduce the case study, to seek consensus on how to proceed with
the project activities, and to clarify stakeholders roles and
expectations. The key institutional stakeholders are: Marielyst
waterworks, Guldborgsund Municipality, regional office of The Danish
Nature Agency (Ministry of the Environment) and the land reclamation
association. The ownership of Marielyst waterworks is a co-operative
society. The Geological Survey of Denmark and Greenland (GEUS) is the
BaltCICA partner in the Falster case, and the main actor in data
collection, data analysis, and groundwater modelling.
The project manager from GEUS was interviewed by a local newspaper and
by regional TV news during a field campaign and the drilling of new
wells, respectively. A technical workshop with the stakeholder in
charge of data collection was held to discuss interpretation of field
studies.
A second workshop with the key stakeholders is planned for presentation
and discussion of scenario modelling results. The responses from
stakeholders including ideas, suggestions, and opinions will serve as
input for groundwater modelling of selected adaptation measures like
changed pumping strategies, location of new abstraction wells, change
in drainage channel discharge etc..
The work described will form input to stakeholders in their decision
process on how to deal with the projected climate change. Future
scenarios on three different strategies for responding to climate
change effect are suggested (base on framework
from
the
Danish
Board
of
Technology):
1. Do nothing scenario: No preventive measures are
taken before absolutely necessary.
2. Resistance scenario: E.g. create a hydrological
barrier to prevent increased sea water intrusion into groundwater
aquifer due to sea level rise.
Enforcement of dikes is another important issue for protection of the
area including the water supply. Dikes to prevent flooding were built
at the coastline after a large flooding in 1872. Flooding from the sea
is not the focus of this study but, but flooding risks from the
hinterland due to increased winter precipitation as well as the need
for increased and more efficient drainage and pumping schemes to avoid
flooding are relevant issues to be discussed in this scenario.
3. Resilience scenario: E.g. mixing of groundwater
from different wells to lower chloride content in drinking water; start
enlarging well field less vulnerable to sea water intrusion as part of
the renovation of existing well fields; or change in pumping strategy
for drainage channel to increase groundwater level.
The outputs of the case study will include a workshop with key
stakeholders, interview to the local newspaper and regional TV news,
presentation of case study outcomes in the BaltCICA booklet and book,
on the BaltCICA web site, on an interactive on-line webserver, and in a
scientific paper.
The outputs will focus on highlighting:
- Consequences of the three different climate change
scenarios
- Recommendations for adaptation measures for local
waterworks and water resources authorities
- General recommendations for similar coastal areas
in Denmark and the southern part of the Baltic Sea
- Provide part of the knowledge base for developing
climate proof groundwater abstraction schemes and river basin
management plan according to EU directives.
Involved persons:
GEUS: Klaus Hinsby, Torben O. Sonnenborg, Per Rasmussen
Marielyst waterworks: Claus Clausen
The Land reclamation association: Torben Dynesen
Guldborgsund Municipality: Henrik Andersen
The Danish Nature Agency: Mads Bisgaard (from January 2011), Gheorghe
Goncear, Inken Müller-Töwe, Marie Blanner (until December
2010)
A short news-video about BaltCICA’s work in Falster, Denmark
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