Change of groundwater discharge as response to varying climatic conditions- a model study at catchment scale at the Wismar bay/Baltic sea

Category Other
Group GSI.IR
Location International Geological Congress,oslo 2008
Author Schafmeister, Maria-Theresia۱; Darsow, Andreas۲
Holding Date 05 October 2008

Climate change i.e. changes in temperature, precipitation and sea level will have a strong influence on the hydrodynamics of coastal aquifers. Recently the contribution of fresh terrestrial groundwater and its potential load of nutrients and other contaminants are discussed, but little is known on the variety of discharge processes depending on the geological and hydrogeological conditions. However it is expected that groundwater discharge (GD) will change quantitatively and qualitatively in response to changes in land use, recharge, groundwater management and civil engineering measures in coastal areas induced by climate change.
340 km of the southern Baltic coast build the northern border of the state Mecklenburg-Vorpommern. It exhibits all characteristics of a typical simplification coast with its long sandy bars and lagoons and its steep slopes of glacial tills. It is therefore the result of a long and highly dynamic geological history which started with the Litorina transgression (7800y BP) and is still ongoing. As a consequence the coastline, which builds the interface between the brackish sea and the terrestrial surface and subsurface waters, has moved landwards.
A medium scale catchment area northeast of Wismar is selected in order to demonstrate the possible change in fresh groundwater discharge (GD) to the Baltic by means of a numerical Finite-Element groundwater flow model. The flat area is dominated by agricultural use and tourism. The heterogeneous sediment sequences consist of glaciofluvial sands separated by glacial tills and are thus exemplary for the south-western Baltic coast. The area comprises several small river catchments and one storage reservoir. Other controlling factors are locally enhanced leakage between the aquifers, groundwater extraction and spatially varying groundwater recharge of 8 up to 47 percent of precipitation (600 mm/a). The aquifer geometry and hydraulic properties are estimated by geostatistical regionalization tools.
First the actual groundwater dynamics within this heterogeneous layered coastal aquifer system is modelled resulting in 71 mm/a (12 % of precipitation) indirect GD via the rivers and 86 mm/a (14 %) direct GD into the Baltic. These values are representative for a Pleistocene coastal aquifer system at the southern Baltic border.
Subsequently the climatic change will be considered by a change of boundary conditions (outer boundaries and groundwater recharge) in different model scenarios. The scenarios are designed according sea level variations and change in groundwater recharge. The former data are derived from climate scenarios calculated by SMHI for the Baltic Sea region which predict 21, 42 and 82 cm sea-level rise until 2100 depending on the IPCC emission scenarios. Groundwater recharge is varied according to predicted changes in precipitation and land use. According to these scenarios the impact to the near coastal aquifer systems are investigated and possible consequences are discussed.