Risks to the Glen Canyon Dam that the resulting flood would scour the bottom few hundred feet of the Grand Canyon, overtop Hoover Dam, and cause severe damage all along the lower Colorado River. In the event of a complete dam failure with Lake Powell at high pool, about of water would surge out of Lake Powell at an initial depth of over . Downstream communities and perhaps every dam along the river, excluding possibly Hoover Dam, as well as riverside lowlands, would be inundated or severely damaged. Located downstream from Glen Canyon Dam are Hoover Dam forming Lake Mead, Davis Dam forming Lake Mohave, Parker
Glen Canyon Dam Sea. After this catastrophe, California and Arizona began to call for a dam to control the tempestuous river. In 1922, six U.S. states signed the Colorado River Compact to officially allocate the flow of the Colorado River and its tributaries. Each half of the Colorado River Basin – the Upper Basin, comprising Colorado, New Mexico, Utah and Wyoming – and the Lower Basin, with California and Nevada – was allotted of water annually, and a treaty between the U.S. and Mexico was signed in 1944 allocating to Mexico. The third lower basin state, Arizona, did not ratify the Compact until