Coastal dunes are valuable ecological reserves providing a range of ecosystem services from coastal flood defence to recreational amenity. An important feature of dune systems is the slack floors, areas of high ecological value that are closely linked to the prevailing hydrological system in the dunes. Dune slacks are sensitive environments that are impacted by external changes, such as rainfall patterns and foreshore erosion as well as conservation management. Understanding the effects of these influences upon the water balance in a dune system is fundamental to the management of the slacks. Occurrence of seasonal flood depths, area and timing and how far the water table recedes below ground in summer are critical to the flora and fauna that the slacks will support. Change in the hydrological regime directly impacts the ecosystem. Experience is drawn from four sites in Wales and west coast England: Ainsdale on the Sefton Coast, Newborough Warren in North Wales, Whiteford Burrows in South Wales and Braunton Burrows in North Devon. Similarities and differences between the hydroecology of the respective sites highlight common mechanisms and processes and those unique to each site. Copyright © 2013 John Wiley & Sons, Ltd.