Phnom Penh (pronounced p-NOM PEN) is the capital city of Cambodia. It is just west of the four-way river intersection, which is called the Chattomukh ("Four Faces"). From the northwest and northeast, respectively, flow the Tonle Sap and Mekong Rivers. These waters merge and split into the Basak River and the Mekong, which flow southeast to the South China Sea. The Mekong river is the 12th longest in the world, flowing from western China to the Mekong Delta in southern Vietnam. Every autumn, monsoon rains are too great for the Mekong to carry, and it floods a large area of Cambodia. This flood even reverses the flow of the Tonle Sap River, northward to the Tonle Sap ("Great Lake") which can expand to ten times its normal size. This serie of images shows how the capital city expanded and is surrounded by a flood zone.