It would have been satisfying to hear a great boom and snap as the two gates touched in the middle, but that probably would have meant sloppy engineering. The low purr of the motor cycled down. The engineers whose job it was to make sure that those things worked could go home tonight and enjoy a beer. Other machinery was now engaged to open valves and flood the barrier arcs. The only way you could tell that was happening was that less and less of them showed above the churning surface. The long trusses, formerly parallel to the ground, tilted downward slightly. One had to use one’s imagination a little to visualize the flat bottom of those arcs settling down along the full width, making contact with a channel bottom painstakingly sculpted and inspected to be as flat as a hockey rink. The seal wasn’t perfectly watertight—nothing ever was—but it would hold for a day until the surge had passed.