Processes and timescales by which a coastal gravel-dominated barrier responds geomorphologically to sea-level rise: Story head barrier,Nova Scotia

Sea-level rise (SLR) is considered to be important for barrier behaviour when barriers are swash-aligned and single-crested, which is typical of only one part of a barrier's lifeterm. Under such conditions gravel-barrier retreat rate correlates with mesoscale (sub-decadal: <10¹ a) SLR rate. Barrier crest overwashing, depending on surge frequency/magnitude, is recognized as the dynamic element that controls barrier retreat rate. Surge characterization of the Halifax tide gauge (using an annual forcing coefficient derived from tide gauge surge residuals) is shown to have high correlation with Story Head (Nova Scotia) barrier retreat rate between 1945 and 1987. Barrier response appears to vary as a function of mesoscale (sub-decadal) SLR and antecedent barrier conditions in combination with the forcing coefficient. Mesoscale (10⁰ a–10² a) rather than macroscale (> 10² a) SLR rate is the critical control on barrier retreat, as mesoscale SLR variation in combination with surge potential is able to raise water level to the elevation threshold sufficient for barrier overwash and hence drive barrier retreat.