In the Shadow of the Ark by Anne Provoost
Re Jana and her parents have heard stories about a man building an enormous ship in the desert, and decide to leave their home to go there and find work. Re Jana's father becomes the right-hand man to desert patriach, Noah. Re Jana, an attractive girl on the verge of adulthood, teaches the people the benefits of pure clean water and fragrant oils. Ham, Noah's youngest son, succumbs to her charms, confiding in Re Jana that his god intends to submerge the world and that only Noah and his family will be saved. When the Flood finally arrives, Re Jana is smuggled on-board by Ham. Life on the ark is gruelling and dangerous but, when at last the ship runs aground, a pregnant Re Jana realises she will be instrumental in founding a new dynasty in a new world.