Below Florence the river enters a gorge at Golfolina and begins its lower course westward past Empoli and Pisa to the sea, where the ancient delta has been reclaimed and the river reaches the sea through a single mouth. The valley of the Arno has been substantially modified by man: in its upper course the Val di Chiana now drains to the Tiber, and in its middle section are flood-control works (some designed by Leonardo da Vinci), though a sudden flood in 1966 inundated Florence.