From Longman Dictionary of Contemporary Englishfloodgateflood‧gate /ˈflʌdɡeɪt/ noun [countable] 1 → open the floodgates2 WATERa gate that is used to control the flow of water from a large lake or river
Examples from the Corpus
floodgate• The decision closes the floodgates to hundreds of potential appeals by convicted drink-drivers.• A move like this will open the floodgates.• This easing of restrictions opened the floodgates for commercial Internet access.• The floodgates opened then and Bordon piled up six more goals.• The floodgates were now open and it is from here that the reverse sequence of On the Look-Out commences.• Once this floodgate opens, there will be knightly surcharges for courses, laboratories, lecture hall air and library dust. 