Extreme river discharge and associated tide gauge co-occurrences from UK estuaries 1984-2013

Observed total water level (TWL, mODN) data were obtained from 27 class-A tide gauges, which form part of the UK National A-Class Tide Gauge Network, from the British Oceanographic Data Centre (BODC). Skew surge (S, m) was calculated from the detrended TWL. It is the difference between the maximum observed TWL and the maximum predicted TWL based on astronomical tidal constituents for every 12.42-h tidal cycle, and the time of maximum TWL was assigned to each S value.

River discharge measurements were obtained from the Environmental Agency, Natural Resources Wales, and the Scottish Environment Protection Agency for 265 rivers across Britain. Discharge (Q) measurements were taken from the most downstream, non-tidal gauges on each river. River gauges were then selected based on two criteria; 1) they recorded 30 years of discharge from 01 January 1984 to 31 December 2013 (with no data gaps), and 2) they recorded a maximum discharge during this period that exceeded 50 m3 /s to identify rivers that could potentially contribute to flooding. This set 30-year period (1984−2013) was selected to ensure consistency between gauges and to maximise the number of gauges with full data included in the analysis. These criteria isolated 126 gauges, located in 126 distinct estuaries.

A peaks over threshold analysis was then carried out on these data to identify co-occurrences between extreme river discharge and skew surge peaks. The dates and magnitudes of these co-occurrences were recorded in Microsoft Excel spreadsheets (one for each catchment), and these were converted to .csv files.