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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.


2. Data and inputs

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.

3. Information transmission

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.

4. Interaction

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.

5. Output

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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