Ecological approaches to coastal risk mitigation

Natural coastal habitats play an important role in protecting coastal areas from sea water flooding caused by storm surge events. Many of these habitats, however, have been lost completely or degraded, reducing their ability to function as a natural flood defense. Once degraded, natural habitats can potently be destroyed by storm events, further threatening these systems. Much of the loss of coastal habitats is caused by increased human activity in coastal areas and through land claimed for urban, industrial, or agricultural use. As a result, some coastal habitats have become rare and threatened across much of Europe and the world. An associated problem is that of sea level rise, which has the combined impact of both increasing the risk of flooding in coastal ecosystems and increasing the severity of storm surge events. This chapter addresses two key topics: (1) the use of natural habitats as a form of coastal defense focusing on the required management and how to restore and/or create them and (2) ecological considerations in the design of hard coastal defense structures. The habitats that play a role in coastal deface and considered here are: (1) saltmarshes, (2) sand dunes, (3) seagrass meadows, and (4) biogenic reefs, including Sabellaria reefs, oyster beds, and mussel beds. As part of coastal habitat restoration and management, the process of saltmarsh creation, either through seaward extension or managed realignment is discussed focusing on potential benefits. Finally, key cumulative stressors that can hinder ecological approaches to coastal risk mitigation are reviewed