An ogee spillway has a crest height of 50 ft above the toe a

An ogee spillway has a crest height of 50 ft above the toe and a maximum head of 15 ft. A minimum pressure of -1.5 psi is allowed. The maximum discharge is 16,000 cfs. Determine the crest length of the spillway assuming a compound circular curve for the upstream crest shape. What is the pressure at the crest for the maximum discharge.

Solution

Solution:-

Given

Q_max = 16000 cfs

C = 4.11

H_e = 15 feet

Height (H ) = 50 feet

Length of crest (L ) = Q_max/(C * (H_e )^3/2)

= 16000/( 4.11 * 15^3/2 )

= 67 feet    Answer

Ratio of maximum head to design head = 1.33

H_e/H_d = 1.33

H_d = He/1.33 =15/1.33 = 11.27 feet

Height/H_d = 50/11.27 = 4.43

H_e/H_d = 1.33

P_mini/y = - 0.43 H_d

P_mini = - 0.43 * 11.27 * 64.43

P_mini = - 312.22 pound/feet²

Pressure (P_mini ) = - 2.168 psi     Answer