sluice gate

noun2

1. •
   A portal which may be opened or closed to allow or prevent the passage of water through a man-made channel.

   • "Has the miller a strong high dam to his pond, and a good stout sluice-gate at the end?" — 1877
2. •
   (figurative) Something which restrains or releases a substantial volume, a flood, of activity, emotion, etc.

   • [A]nd then when the fountain of her love was opened, and the sluice gate of her displeasure removed, she told him how she would pray for him till he came back safe from the wars. — 1850