Research papersHigh-frequency sea level variations and implications for coastal flooding: A case study of the Solent, UK

- Characterises high-frequency (<6 h) sea-level variability in the English Channel.
- Documents coastal flooding caused by seiching during a neap tide.
- Describes the relevance of high-frequency sea-level variability for coastal flooding.
- Implications for future UK flood risk management discussed.

This study examines the occurrence and characteristics of high-frequency (<6 h) sea level variations in the Solent, UK - a mesotidal estuarine strait located in the central English Channel. A 14-year time series (2000-2013) of sea level observations sampled at 15-min intervals from the Southampton tide gauge was analyzed. The 8 highest-energy events have a mean amplitude of approximately 0.6 m and a dominant period of around 4 h. These events correspond with periods of enhanced meteorological activity, namely a marked reduction in air pressure and onset of strong southwesterly-southeasterly winds. Sea level observations from tide gauges around the Solent and the wider English Channel region (23 in total) were used to assess the spatial characteristics of these events. Analysis of time series and phase information indicates the occurrence of standing waves oscillating across the English Channel between southern England and northern France. This study provides a unique example of standing waves generated by extra-tropical cyclones over a large basin (the English Channel) with implications for flood inundation. The event of 28th October 2013 - the highest-amplitude (1.16 m) event in the record - was associated with minor coastal flooding at Yarmouth, Isle of Wight. This flood occurred during a neap tide, when such events are widely thought to be impossible. Hence, our findings emphasize the relevance of high-frequency sea level variability for regional sea level forecasting and flood risk management.