Picture above taken from bedroom window showing short section of Humber Estuary clay bank, meadow in foreground, passing ship and north tower of Humber Bridge in distance.
Clay banks, linear earthen banks to hold back tidal water, have clearly been constructed by Man for centuries along areas of lowland coast. The effectiveness of such a structure will/would have depended on simple factors; the material used in the building of the bank (loose unconsolidated material will quickly be undermined by even gentle tidal ingress and thus weaken the bank), the pitch (gradient) of the slopes on the landward and seaward sides and any additional material added to the seaward slope to make it more resistant to spring and/or storm tidal waters. On these matters Tidal Lands (s.p.b.s) gives some valuable information for its time (published 1918).
The authors state that the gradient of the seaward slope of a sea defence is critical, where the bank has to resist heavy pounding a 1 in 5 slope is most effective thus reducing the force of the wave impact, where the tidal impact on the bank is less forceful a steeper gradient is satisfactory this, presumably, requiring less bulky material/less expense. ‘In Lincolnshire and on the Wash the front slope is generally 5 to 1’ (p. 125). The writers then discuss measures to strengthen the seaward slope. One was ‘piling’, where the base of the slope was strengthened by vertical timbers driven into the mud, this would also help hold in place any rocks reinforcing the face of the slope. The authors state that chalk blocks are/were often set into the seaward face of the bank, these not just dumped but carefully arranged so that as far as possible they knitted together – tis nicely fits with the evidence given in the Geology pdf in the Publications/Articles section of this site when considering local chalk quarries
(To be continued).