Alexandra Dock is a commercial dock at Kings Lynn, Norfolk, England sited on the Great River Ouse.
At the entrance lock the normal flood protection for the Kings Lynn area totally relies on the closure of one pair of 16m span sector gates installed in 1988. These sector gates have proved unreliable in the past so to minimise flood risk EA contracted Breheny/Taylor & Sons to install a second line of defence.
T&S retained Kenneth Grubb Associates Ltd to investigate and design the second line of defence with the design brief of a 10 tonne maximum lift load due to crane access limitations at the quay.
The design brief included the study of various locations within the existing lock barrel for the new installation, with the final location selected at the sector gate inner abutments.
The second line of defence incorporates 7 No stoplogs 16m span x 9m on-seat design head, each weighing approx 7.5 tonne, which are deployed by lifting chains and a mobile crane sited on the quayside. 3 No bottom stoplogs are 1.2m deep and 4 No top stoplogs are 1.5m deep. Due to civil load restrictions the bottom stoplogs each include 4 non-return flap valves incorporated to reduce the effects of the dock reverse head during lowering of the river level.
The stoplogs, guides and storage racks were manufactured at Taylor and Sons, Cardiff and due to be installed and commissioned in Aug 2006.
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