floodgate

noun3

1. •
   An adjustable gate or valve used to control the flow of water through a sluice.
2. •
   (figurative) Anything that controls or limits an outpouring of people, emotion, etc.

   • “The floodgates for advertising on cable are down,” says Michael Dann, a leading consultant on cable television. — 1981
3. •
   (no longer used) A stream that passes through a floodgate; a torrent.