[susan53]

"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.