It had never been necessary before?

This was the first time that the prediction of the water level was above 300cm and made the computer to close it automatically. It closed once before due to water level in 2007 but that was because the threshold was lowered to 260cm during the 2007 storm season. It’s tested every year though. Quite nice to spectate even though it takes two hours and is too slow to really see with the eye.

I find the emphasis on the automatic decision making and operation here interesting. Why does it need to be automatic?

Is it to relieve political pressure on the decision- makers, since closing the barrier prevents traffic in and out of Rotterdam?

Or is it because the algorithm is so complex and it has to anticipate water flow from the Rhine?

On December 21, 2023 the Maeslantkering was closed automatically at the 300 cm threshold for the first time in history. During the day a forecast had been made that the water level in Rotterdam would reach critical height of 300 cm above NAP at around 23:30. There were discussions to close the Maeslantkering manually before that time, and the Port of Rotterdam started reducing traffic at 16:00. Around 18:00 the traffic across the Nieuwe Waterweg came to a complete standstill. Before the decision was actually made to manually close the Maeslantkering, the computer systems intervened and had begun the automatic closing procedure. Closing started at 20:15, a process which takes about 2 hours. The next day at 4:45 the gates were opened again.[8]

From the wiki: https://en.m.wikipedia.org/wiki/Maeslantkering

Exactly your first reason, the algorithm is not complex but politics and economics would make it a hard decision for a human.

Two nitpicks:

- It was completed in 1997.

- It automatically closed in 2018, but the algorithm was adjusted to close at a lower water level, specifically to enforce a closing under storm conditions.

source: https://www.rijkswaterstaat.nl/water/waterbeheer/bescherming...

(that is the Dutch agency responsible for the barrier)