Deluge — S. Fowler Wright

The “landmark disaster novel” that follows the story of two survivors after a global flood has wiped out civilization (Publishers Weekly).
 
An immediate bestseller upon its release in the early twentieth century, Deluge takes place in the English Midlands as a man struggles to save his injured wife and small children amid the destruction wrought by a catastrophic storm. He is then separated from his family by a sudden and terrifying surge of water. Numb and stunned, he proceeds through a world transformed, where those few who have remained alive against overwhelming odds, with neither the comforts nor the constraints of an orderly industrial society, attempt to survive. The basis of a 1933 film, Deluge is a riveting milestone in post-apocalyptic fiction.
 
“Among the best world-catastrophe novels, grimly realistic in [its] depiction of human nature under stress.” -- Science Fiction Studies