Origins of the 1996 Controlled Flood in Grand Canyon

The March 1996 controlled flood in Grand Canyon resulted from a decade-long evolution in scientific thinking about the appropriate role of floods in management of the Colorado River in Grand Canyon. The flood was implemented after 5 consecutive years in which proposals to conduct a similar event were rejected; final implementation of the 1996 flood necessitated revision of the definition of the appropriate basin-wide runoff conditions that would trigger such a flood. The flood partly resulted from a multi-year effort to reform the Colorado River Storage Project Act that had culminated in passage of the Grand Canyon Protection Act in 1992. The flood itself consisted of a 4-day period of steady discharge of 227 m 3 /s, an 11-hr period of increasing discharge to a peak of 1274 m 3 /s that lasted for 7 days, a 45-hr period of recession, and a 4-day period of steady discharge at 227 m 3 /s. This event was partly a demonstration of the potential role of floods in regulated river management and also provided an opportunity for scientists to make measurements about physical and biological processes during flood conditions.