EFFECTS OF FUTURE CLIMATE CHANGE ON GROUNDWATER LEVELS AT A SUB-GROUNDWATER TABLE MOTORWAY CONSTRUCTION IN DENMARK

A motorway is planned trough the city of Silkeborg in the central part of Jutland, Denmark. In order to minimize disturbance from the motorway it was decided that the stretch through the city should be below ground level, in average 6 m. Sheet piling will be put down from ground level penetrating the upper aquifer and only leaving a few meters at the lower part of the aquifer undisturbed for flow beneath the construction. This will affect groundwater flow and also groundwater table in the perimeter of the construction. The objective of the research was therefore to; a) analyse the effects imposed on the naturel groundwater system from the motorway, b) predict these effects under possible future climate conditions. In order to do that an integrated surface- and groundwater model was build using the MikeShe code. The hydrological surface and groundwater model is driven by its climatological input such as precipitation, temperature and reference evapotranspiration. Therefore, uncertainty in predicting these future climatic parameters should be propagated to the hydrological model predictions. In this study 24 different climate projections have been chosen to represent future climate at Silkeborg. The climate projections are composed of different combinations of global climate models, regional climate models and statistical downscaling methods, all based on the A1B emission scenario. The results from the study primarily focus on groundwater elevation because houses close to the motorway may be adversely affected by rising groundwater table. It is important to know whether possible rising groundwater is caused by the planned motorway, different climatic conditions in the future, or a combination of both. Therefore prediction uncertainties of groundwater changes due to the motorway construction and due to climate change will be assessed.