Developing proxy flood records from sediment stacks in palaeochannels: the 'Bloody Inches' on the River Tay, Scotland

Assessing the frequency of recent large floods in Scotland is hindered by short river records and non-homogenous flow series. Proxy flood records can be generated from sediment stacks in floodplain palaeochannels which steadily infill with silts during normal winter floods and fine sand during catastrophic floods. The ‘Bloody Inches’ (a meander cutoff on the lower River Tay, Scotland) has been infilling with flood deposits since c. 1763. Agricultural flood embankments near this site locally breach with flows > 850 m3s-1 which introduce silts into the palaeochannel and extensively fail with flows > 1200 m3s-1 which deposit fine sand. Repeated cores (up to 1.4 m in depth) at the site consistently reveal sand-rich flood units. In the upper core sections 137Cs dating enables these to be correlated with floods >1200 m3s-1 in the post-1950 discharge record at the Caputh gauging station 5 km upstream. Sand units in the lower part of the profile are correlated with floods from 1780 onwards using a 210Pb-based chronology and independently supported by a detailed record of flood marks inscribed on Smeaton’s Bridge in Perth, 15 km downstream. This ability to recover proxy flood records from sediment stacks in floodplain palaeochannels provides a new tool for assessing the return periods of recent major floods in Scotland and useful natural analogues for assessing flood risks under the warmer wetter regimes predicted by climate modellers for the 2050s