 Before the dam could be built , the Colorado River needed to be diverted away from the construction site . To accomplish this , four diversion tunnels were driven through the canyon walls , two on the Nevada side and two on the Arizona side . These tunnels were 56 ft ( 17 m ) in diameter . Their combined length was nearly 16 @,@ 000 ft , or more than 3 miles ( 5 km ) . The contract required these tunnels to be completed by October 1 , 1933 , with a $ 3 @,@ 000 @-@ per @-@ day fine to be assessed for any delay . To meet the deadline , Six Companies had to complete work by early 1933 , since only in late fall and winter was the water level in the river low enough to safely divert . 
 Before the dam could be built , the Colorado River needed to be diverted away from the construction site . To accomplish this , four diversion tunnels <a href='uninflect' title='1'><mark>were</mark></a> driven through the canyon walls , two on the Nevada side and two on the Arizona side . These tunnels <a href='uninflect' title='2'><mark>were</mark></a> 56 ft ( 17 m ) in diameter . Their combined length was nearly 16 @,@ 000 ft , or more than 3 miles ( 5 km ) . The contract required these tunnels to be completed by October 1 , 1933 , with a $ 3 @,@ 000 @-@ per @-@ day fine to be assessed for any delay . To meet the deadline , Six Companies had to complete work by early 1933 , since only in late fall and winter was the water level in the river low enough to safely divert . 
B4 the dam could be built , da Colorado River needed to be diverted away from the construction site . To accomplish this , 4 diversion tunnels was driven thru the canyon walls , two on the Nevada side and two on tdaArizona side . These tunnels was 56 ft ( 17 m ) in diameter . Their combined length was nearly 16 @,@ 000 ft , or more den 3 miles ( 5 km ) . The contract required these tunnels to be completed by October 1 , 1933 , wid a $ 3 @,@ 000 @-@ per @-@ day fine to b assessed for any delay . To meet the deadline , Six Companies had to complete work by early 1933 , since only in late fall and winter was the water level in thdaiver low enough to safely divert .