Given what was decided in the previous blog the building of new clay banks to expand the area of Sunk Island during the early modern period must have been a precarious business. A fully encircling new bank would have taken more than one day to construct so as the tide rose its waters would lap around behind the unfinished section and weaken it on both sides. In the somewhat longer term the rigidity of a clay bank is very much enhanced by the root systems of colonising plants, even a single year’s vegetation would have provided only a fraction of the necessary root systems. Perhaps the ‘navigators’ and their employers had some means of strengthening the seaward face of a new clay-bank in the short term, in the case of Holderness possibly rounded stones from the shore-line, although these would be more common on the German Ocean coast rather than on the Humber Estuary foreshore. Maybe, like later engineers, they realised that a gentle slope on the face of the clay-bank facing seaward reduced undermining by the incoming tide.
Recently an established clay-bank flood defence forming the bank of the River Deeping near Wainfleet, central Lincolnshire (and normally one of the driest parts of the country) was breeched, this leading to extensive flooding of a residential area. If short sections of a clay-bank flood defence are weakened they will become more prone to being breeched. Unfortunately public footpaths over a bank/sand-dune can have this result as the vegetation is worn away.
The photo above, taken on Christmas Day 2013, shows a section of the Humber clay-bank just west of the Humber Bridge, this following the flood of 5th December when the clay-bank was overtopped by a combination of surge water and spring high tide water passing up the Estuary together. Here it was the inland side of the banks that was broken in places, some local issue causing them to be points of weakness.
(To be continued).