floodgate
flood-gate
noun
Something that holds back a powerful outpouring of emotions or events.
"Her emotional speech opened the floodgates of public sympathy."
noun
A gate in a dam or barrier controlling the flow of water.
"The engineers opened the floodgates to manage river levels."
Thesaurus
Synonyms: sluicegate, head gate, sluice valve, penstock, water gate