a gate that can be opened or closed to control a flow of water
Idiom
open the floodgatesidiom引发更多同类事件;放开限制
If an action or a decision opens the floodgates, it allows something to happen a lot or allows many people to do something that was not previously allowed.
Officials are worried that allowing these refugees into the country will open the floodgates to thousands more.官员们担心，允许这些难民入境会引发数千其他难民的涌入。