From coastal protection to "low-regret" coastal adaptation. Changing perspectives on impacts and risk assessment when dealing with sea level rise

Abstract

Traditional and contemporary strategies to protect coastal communities from seaborne hazards alone will fail to sustainably deal with future sea level rise. In the last 2000 years, the global climate and mean sea levels have remained relatively stable, which facilitated cultivation and population of coastal areas. Marine resources are an important factor in the development of coastal and island communities, because they secure the livelihood of their inhabitants. But with rising sea levels, coastal areas are prone to be more exposed to increasing seaborne hazards. For example, when the sea level rises, structures are going to be located closer to the shoreline and waves are going to break later due to deeper waters. This, in turn, leads to higher loads on these structures. To protect against seaborne hazards and decrease the vulnerability of coastal communities appropriate coastal infrastructure is needed. To date, coastal protection structures are designed and implemented to withstand predicted loads and stresses within their typical lifetime (i.e. their "design lifetime"). Thus, they provide a certain level of safety from marine hazards. But as the climate is heating and sea levels are rising, requirements on coastal protection changes. In addition, interactions are complex between drivers and impacts of ocean-borne hazards in a heating climate. This complexity induces further uncertainty when estimating future requirements on coastal protection. To account for deep uncertainties, future adaptation strategies to climate change must become more flexible to be support coastal communities to cope with rising sea levels.

This thesis outlines the traditional design approach to engineering structures and its potential to be one of several responses to rising sea levels. But it also shows the limitation of this design approach in a more complex and interdisciplinary approach to deal with climate change effects. The literature review reveals common misconceptions of the disciplinary engineering perspective on a sustainable approach to coastal protection and contrasts this disciplinary viewpoint with interdisciplinary aspects of climate change adaptation. With that, the literature review bridges the interdisciplinary gap and creates a common ground for an interdisciplinary approach to climate change adaptation of "low-regret". In this interdisciplinary approach, engineering expertise still plays a key role – as demonstrated by three studies, carried out within this thesis. The published studies make use of and advance two typical coastal engineering methodologies – numerical modeling and field measurements. These techniques are the basis for a process-based scrutiny of hydro- and morphodynamic phenomena and facilitate assessing the impacts on hydraulic structures as well as the effect of coastal infrastructure on the entire ecosystem (with humans being an integral part of the ecosystem). Accounting for the human domain in the ecosystem requires considering a socio-political perspective as well. Therefore, a fourth study synthesizes the findings of this thesis in the interdisciplinary context it was framed it. This interdisciplinary assessment reveals potentials and pitfalls when looking at sea level rise from multiple perspectives.

Using the example of ports, this thesis demonstrates the benefits of traditional engineering approaches but also elucidates the advantage of a broader, more interdisciplinary perspective on "low-regret" adaptation when dealing with climate change effects. This broader perspective builds on the experience from different disciplines and allows adaptation strategies to acknowledge and implement more recently brought up ecosystem-based adaptation measures – despite a lack of experience considering their efficiency and implementation. But at the same time, a broader perspective also fosters identifying strategies of "low-regret", by avoiding to overemphasize or overrate the potential of any response option (for example traditional protection schemes or ecosystem-based adaptation) to climate change effects, but encourages a flexible and context-based consideration of the entire adaptation portfolio.