The "Peace Dam" in Hwacheon, South Korea. The preventive dam was built 35 km downstream from North Korea's Imnam Dam, which is seen as a threat that could kill thousands of people in South Korea if the water held back by the dam was suddenly released by accident or as a deliberate attack by the North Koreans. In 2005, South Korea completed the construction of the Peace Dam, at a cost of $429 million, to protect downstream populations from a potential flood from the North. So far, the risk remains hypothetical and and dam's reservoir is empty. Image © Tomas van Houtryve/VII. South Korea, 2013.