Lake Delhi Dam in Iowa by Stanley Consultants

Lake Delhi in Iowa was first dammed in the 1920s in order to power a small hydroelectric plant. Since the ’70s, however, the reservoir has had a purely recreational function, which is nevertheless of vital importance to the community. So when the dam was breached in 2010, leading to the evacuation of 8,000 people and the emptying of the lake, the economic consequences were calamitous. In response, local residents joined together to fund a new dam. The resulting structure, recipient of a national engineering award, employs a zigzag ‘labyrinth’ spillway, which effectively triples the ability of the dam to shed excess water without the need for mechanical gates. It has already proven effective: weeks after the dam reopened in 2016, the fifth-largest recorded flood to hit the lake was dealt with successfully by the structure.