Negative Diffusion? The Spread of Seawalls to Adapt to Coastal Erosion and Flooding Along Island Coasts

Sea-level rise and associated coastal erosion and flooding threatens coastal cities and communities across the world. A common response to the threat of erosion and flooding is artificially fortifying the coast through seawalls and similar coastal defence measures. Seawalls present a number of benefits: they are relatively easy and cheap to build, visible and measurable, seemingly robust and require no behavioural change. When well-designed and well-maintained, seawalls can protect the land and property behind it, although this typically comes at the expense of the beach in front of the seawall, which erodes and disappears. Yet, in many cases, seawalls are not well-designed and well-maintained, and hence not only erode the beach, but also fail to protect property and land, and may even collapse shortly after construction. Given these problems, seawalls often are maladaptive, increasing rather than decreasing the vulnerability of those behind. To what extent can policy diffusion explain the continued popularity and widespread use of seawalls against coastal erosion and flooding? This paper focuses on the coasts of tropical small islands, most of which are classified as developing and receive significant donor funding for climate change adaptation. The paper examines learning and emulation as central mechanisms of the diffusion of seawalls along these coasts. It argues that donors, who often have heavily fortified coasts at home, fund well-maintained and well-designed seawalls along core island coasts, such as on main islands and in capitals, to protect the local infrastructure and settlements. Local communities in turn learn from these examples of seemingly successful coastal defence, and build seawalls in their more rural regions, but typically lack the resources to design and maintain them to minimise negative effects. The result is heavily fortified coasts that are nonetheless eroding and subject to flooding. Two case studies of small islands – Fiji and Seychelles – illustrate the argument. For both islands, historical aerial photographs are used to trace the emergence and spread of seawalls over time. While policy diffusion is usually associated with the spread of best practice, this paper shows that the opposite may also be the case: “negative diffusion” helps to understand why ineffective and potentially maladaptive responses to a problem can also spread, particularly when alternative responses require substantial behavioural change.