Well of Shiuan

"The world of Shiuan was doomed. Rising waters and shattering earthquakes due to the coming of a vast and strange new satellite had sealed the fate of its peoples—flee or die with their world. Their sole escape routes were the Gates, the passages between worlds established by a forgotten cosmic race. And just as this knowledge dawned on the desperate tribes and cities there appeared the woman Morgaine—whose mission was to seal Shiuan's Gates."
Winner of the John W. Campbell Award for the best new writer of the year.
This is the story of Morgaine, and of her henchman, Nhi Vanye, and of their relentless enemy, Chya Roh, who followed them to the drowning planet.