lexical error

"great" sounds odd collocated with "a flood". Looking in a concordancer I've found a couple of examples of "the great flood"

And in the dark days after the Great FLOOD of 1927- the worst natural disaster in the state's ...
... and the great FLOOD of the Mekong River

but none at all with the indefinite article. I'd replace it with "bad" or "severe". Some examples :

We had a bad flood and water was everywhere in the house.
Effects of a severe flood on instream habitat and trout populations in seven New Zealand rivers.

thanks

Yes - it can, usually when it means long prolonged periods of heavy rainfall, like a monsoon. Some examples :

When the next RAINS come, instead of the forests on the hillside holding ....
With the spring RAINS the flow rose rapidly due to infiltration in open sewers...
... an embankment that had become soft and spongy from the RAINS, ...

thank you