Effects of sea level rise and different coastline management options on the phreatic level in a coastal dune area are calculated, using a scenario with 60 cm sea level rise in the course of the next century, resulting from global climatic changes. Changes in the phreatic level - both lowering and rising - are evaluated for their effects on the dune slack vegetation, using a newly developed interaction model 'hydrology-vegetation'. Some indications of changes in nature conservation values are presented.