noun (n)

• something that restrains a flood or outpouring(noun.cognition)

  Example:
  Suspension of surveillance opened the floodgates to illegal immigrants.
  

  source: wordnet30
• regulator consisting of a valve or gate that controls the rate of water flow through a sluice(noun.artifact)

  Synonym:
  head gate, penstock, sluice valve, sluicegate, water gate
  

  source: wordnet30