The interactive relationship between coastal erosion and flood risk


A new paper from DREAM PhD student James Pollard explores the complex interactions between coastal flooding and erosion risks.

Coastal erosion and flooding are hazards that, when combined with facilitative pathways and vulnerable receptors, represent sources of coastal risk. Erosion and flooding risks are often analysed separately owing to complex relationships between driving processes, morphological response and risk receptors.

This paper argues for the need to analyse coastal flooding and erosion risks jointly, based on the fact that these risks interact in at least 3 critical ways:

  • Coastal morphology modifies flood hazard. Through its interaction with hydrodynamic conditions (water level, surge and waves) responsible for flooding, coastal morphology can influence flood hazard characteristics (e.g. water height, occurrence of breaching, wave dissipation);
  • Future flood hazard depends on shoreline position. Since shoreline position determines the natural protection provided by coastal landforms and associated ecosystems seaward of settlements, land-based activities and infrastructure; and
  • Simultaneous occurrence of erosion-flooding events. Since the extreme weather conditions necessary for flooding also drive enhanced sediment transport that may permanently alter erosional susceptibility and natural flood defence capabilities of the coastal zone.

Erosion–flooding interactions can be represented as a spectrum of intensity mediated by the coastal setting in question (Figure 1).

Coastal Erosion-Flooding hazard interactions

Coastal Erosion-Flooding hazard interaction diagram, populated with representative coastal settings

Two critical insights stand out as priorities for the development of coastal risk management policy.
First, is the recognition that future extreme events will encounter future coastal morphologies that may differ significantly from the present. When combined with modelled extreme sea levels, the inclusion of (possible) future shoreline characteristics enables an assessment of future erosion–flooding interactions without the simplifying assumption of static shorelines.

Second, is the reality that erosion and flood risk is determined and experienced at the local scale. This supports approaches to coastal risk assessment that address nested scales, by identifying hotspots of risk at coarser national or regional scales which then feed into more detailed local scale assessments.

The full open access article is available here: http://journals.sagepub.com/doi/full/10.1177/0309133318794498