On the feasibility of managed retreat in the Wadden Sea of Schleswig-Holstein

Abstract

Sea embankments along the mainland coastline in the Schleswig-Holstein Wadden Sea safeguard 130,000 people and 19 billion € of capital assets from flooding during storm surges. Due to climate change induced sea-level rise, these defences will become exposed to higher storm surges and adaptation becomes inevitable. As an alternative to strengthening, managed retreat is discussed in literature as a coastal risk management option for climate change adaptation. Based on an evaluation of examples from the Wadden Sea, this paper elaborates managed retreat as alternative climate change adaptation from a coastal risk management perspective. This paper concludes that, conform the principles of integrated coastal zone management, one precondition for successful implementation of managed retreat is local acceptance. With respect to natural resilience to sea-level rise, managed retreat may counteract the loss of Wadden Sea structures and habitats due to coastal squeeze. However, the effectiveness depends on the surface elevation in the opened polder. If large volumes of sediment are needed to restore a natural elevation, regional resilience against SLR-induced drowning may deteriorate. With respect to coastal flood risk management in Schleswig-Holstein, opened polders have no significance as flood retention rooms and managed retreat does not reduce the hazard of flooding in surrounding polders. Further, removal of primary embankments requires large efforts to secure flood safety in adjacent polders. Under certain conditions, removal or opening of embankments may constitute sustainable coastal risk management, e.g., if retreat leads to a shorter line of defence or if other win-win-situations like securing of NATURA 2000 coherence arise.