 Legislation to authorize the dam was introduced repeatedly by Representative Phil Swing ( R @-@ <unk> . ) and Senator <unk> Johnson ( R @-@ <unk> . ) , but representatives from other parts of the country considered the project as hugely expensive and one that would mostly benefit California . The 1927 Mississippi flood made Midwestern and Southern <unk> and <unk> more sympathetic toward the dam project . On March 12 , 1928 , the failure of the St. Francis Dam , constructed by the city of Los Angeles , caused a disastrous flood that killed up to 600 people . As that dam was a curved @-@ gravity type , similar in design to the arch @-@ gravity as was proposed for the Black Canyon dam , opponents claimed that the Black Canyon dam 's safety could not be guaranteed . Congress authorized a board of engineers to review plans for the proposed dam . The Colorado River Board found the project feasible , but warned that should the dam fail , every downstream Colorado River community would be destroyed , and that the river might change course and empty into the <unk> Sea . The Board cautioned : " To avoid such possibilities , the proposed dam should be constructed on conservative if not ultra @-@ conservative lines . " 
