catastrophic, devastating, great, severe
flash
spring, summer, etc.

cause
Heavy rainfall in the mountains caused the floods.

come
No one knew that the flood was coming.

hit sth, strike sth
This summer the region was struck by devastating floods.

inundate sth
The fields were inundated by heavy floods.

cause sth
The flood caused widespread destruction.

subside
The floods are slowly subsiding.

water (usually floodwater or floodwaters)
The floodwaters did not begin to recede until September.

plain
damage
alert (BrE), warning
victim
control, defence/defense, prevention, protection, relief
insurance

be in (full) flood (esp. BrE)
The river was in full flood (= had flooded its banks).

great
constant
sudden

inundate sb/sth
She was inundated by floods of fan mail.

bring, cause
release, unleash

flood of
a great flood of refugees

a flood of memories (esp. AmE)
Writing about St. John's brings back a flood of nostalgic memories.

in floods of tears (= crying a lot)
The little girl was in floods of tears.