Yes, FLOODGATE is a Scrabble word!

Letter values in Scrabble US: F 4, L 1, O 1, O 1, D 2, G 2, A 1, T 1, E 1.

Is it a valid word?

FLOODGATE is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

something that restrains a flood or outpouring
regulator consisting of a valve or gate that controls the rate of water flow through a sluice

Also: sluice valve, head gate, water gate.

Not playable in Scrabble US: SLUICEGATE.