Flooding-Erosion Interactions: Implications for Coastal Risk Management

As routinely experienced coastal hazards, flooding and erosion are key considerations within coastal management plans and policy. Flooding and erosion hazards are often analysed separately, without due attention to their interaction. Low lying barrier islands exemplify coastal environments particularly affected by erosion-flooding interactions. Such environments often support substantial human populations, critical infrastructure, and diverse ecosystems. This study undertakes a high resolution, multidecadal shoreline change analysis at Blakeney Point, a mixed sand-gravel barrier on the UK’s North Norfolk coast. The analysis spans two distinct management regimes: the ‘first era’ (1992-2005) where the eastern section of the barrier was periodically artificially reprofiled into a steep-sided trapezoid with a narrow crest; and the ‘second era’ (2006-2016) of no active intervention along the entire barrier. Along the eastern section of Blakeney Point, we observe an increase in shoreline retreat rate between the two eras of 3 to 30 times depending on the choice of shoreline proxy (High Water Line, ridge line, or vegetation line). The lower shoreline retreat rates during the first era suggest that reprofiling fixed the shoreline position of the eastern barrier. Termination of the reprofiling regime in 2006, in combination with storm surge events in 2007, and 2013, resulted in accelerated retreat along the eastern section towards a more landward position. This has had implications for the western section of the spit which appears to have benefited from alongshore westward transport of sediment during the second era, resulting in slowed landward retreat rates during this period as well as westward extension. Our findings suggest a change in the morphological character of the barrier under the non-interventionist management regime, with clear implications for erosion, flooding and their interaction. Firstly, although the management regime change resulted in barrier lowering and increased landward retreat in the eastern section of the spit, the retreat of the western section was reduced. Slowed retreat of the western section represents the resumption of a more natural system dynamic, demonstrating that management change in one section of coast can have positive downdrift impacts. Secondly, this work draws attention to the value of integrating decadal-scale and event-based coastal zone dynamics when seeking to identify the essential behaviours that characterise a coastal system. Management strategies must account for extreme changes during storm surge events, the interaction of extreme changes with flood risk and the role of these events in shaping longer-term landscape evolution. We include a glossary of key terms at the end of the paper.