"... all those now deceased who have worked on behalf of the Thames Tidal Defences. This includes former employees, colleagues and suppliers who contributed to our work over many years. ... those who lost their lives during the construction of the Thames Barrier and associated defences."
It's not clear but the period covered probably begins when work started on the Thames Barrier in 1974. The barrier opened in 1984 but the memorial was not erected until 2018.
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