original: The valleys of the Waimea River and its tributary, the Makaweli River, were once heavily populated.
simplifications: The valleys of the Waimea River and the Makaweli River, were once heavily populated. There used to live many people in the valleys of the Waimea River and the Makaweli River. The valleys of Waimea and Makaweli Rivers were once crowded. The valleys of the Waimea River and its tributary, the Makaweli River, were once home to many people. The valleys of the Waimea River and its tributary, the Makaweli River, once had a lot of people. The valleys of Waimea River and the Makaweli River used to have many residents. The Waimea River valleys and its tributary, the Makaweli River, were once heavily populated. The valleys of the Waimea River and the Makaweli River were once very populated. The valleys of the Waimea River and the Makaweli River used to be heavily populated. The Waimea River valleys and its tributary, the Makaweli River, were once heavily populated.