Hendrik Antoon Lorentz and the problem of the Zuiderzee tides

In July 1918 the Dutch parliament approved an ambitious plan drawn up by Cornelis Lely, then Minister of Transport and Water. The plan entailed the enclosure of the Zuiderzee with a dike and the subsequent reclamation of large tracts of land in the newly-formed lake. In the discussions preceding the parliamentary decision one important question was raised several times: how would the dike influence the tides along the parts of the coasts of Friesland and North-Holland that lie outside the dike? Under pressure by the parliament, Lely decided to establish a committee to investigate this matter. The famous theoretical physicist Hendrik Antoon Lorentz accepted the invitation to chair the committee. The task turned out to be much more time-consuming and difficult than he had anticipated: Lorentz had to develop new methods to model the tidal flows in the open and closed Zuiderzee and make reliable predictions about the tides. There was no one else on the committee who had the expertise to do this. In the years leading to the publication of the final report of the Committee in 1926, Lorentz spent a substantial part of his time on the Zuiderzee work. In my presentation I will first outline the long history of the plans to close off the Zuiderzee. I will then present in some technical detail how Lorentz approached the problem of the tides and what his results were. I will also briefly comment on the impact Lorentz’s work has had on later work in hydraulics.