The US Interstate Highway system was designed to allow a mass evacuation of cities that were likely target of nuclear bombs during the Cold War, so that some of the population could escape fallout zones and survive.
But while construction was just getting started, bigger bombs were developed, so that such a mass evacuation plan was futile. But by then so many domestic jobs were involved, and so much urban renovation was planned, that the system was built anyway. And it turned out that the economic benefits of this improved transportation infrastructure made it worthwhile. Even without a nuclear attack.
In Egypt, the poverty rate is much higher than the US. I do not know statistics on television and telephone ownership there but it is certainly lower than the US. There is a significant* number of people that would not hear this message unless you knocked on their door.
*I do not mean that word in the technical statistical sense, only that it would be a tragedy if that many people were to perish in a flood.
I think “designed to allow a mass evacuation” is a different think than “conceived specifically because of,” which your second paragraph seems to imply. The Wikipedia article talks about funding to support something not unlike interstate highways being voted in 1916, and Dwight Eisenhower having been impressed by a trip he made in 1919. That would pre-date nuclear weapons.
It seems to me the economic benefits of improved transportation would be obvious and not an unintended consequence of nuclear civil defense.
See my point - Cairo is several dozen square miles of 4 to 10 storey concrete buildings. Escaping a flood would be a matter of climbing the stairs. Plus, they have a massive police presence, so it would not take long for the message to be heard.