CE 3205 Water and Environmental Engineering. Spillways. SPILLWAY. A spillway is a structure used to provide for the controlled release of flows from a dam or levee into a downstream area, typically being the river that was dammed. to prevent overtopping and possible failure of the dam.
Four Mile Dam, Australia – Ogee Spillway
Baffle apron or chute spillway
Basic equation flow over weirs,
Cd=coefficient of discharge
He=actual effective head
Ha=head due to velocity of approach (sometimes neglected)
Le = effective width of crestL’ = net width of crest(clear waterway x
no.of spans)N = number of piersKp = pier contraction coefficientKa = abutment contraction coefficient
Table 1: Pier Contraction Coefficient (Kp)
Table 2: Abutment Contraction Coefficient (Ka)
*Pier contraction coefficient depends on several factors such as shape and location of pier nose, thickness of piers and velocity of approach.
*Abutment contraction coefficient depends on factors such as shape of abutment and velocity of approach.
x,y= coordinates of the point on the spillway surface
K,n= constant, depend on inclination of the upstream face of spillway
*For overspillway/ogee, the upstream face is vertical
(P/Hd)>1.33, velocity is neglected
Problem 01: An overflow spillway with the upstream face vertical is to be designed for a flood peak of 3000 m3/s. The height of the spillway crest is kept at RL 130.50 m. The average river bed level at the site is 102.50 m. The number of spans is 6, clear waterway between piers is 12 m, thickness of the pier is 2 m, pier contraction coefficient, Kp = 0.02 and abutment contraction coefficient, Ka = 0.20 for the effect of end contraction. Assume the coefficient of discharge is 2.20 and the slope of the d/s face of the overflow section is 0.8: 1.
profile from the origin of the crest.
*R.L is reservoir level
Determine the design head by neglecting the end contraction.
Neglecting the end contraction, so we calculate L= L’
L’ =clear waterway x no.of spans
L=12 x 6 = 72m
b) design head is determined by taking the effect of end contraction of piers and spans
P/Hd = 28/7.11
= 3.94 ~~greater than 1.33
So effect of velocity can be neglected
He=Hd+Ha(due to velocity~0)
He = Hd
c) Determine the tangent point of x ordinate of the downstream profile from the origin of the crest.
For vertical upstream
Differentiate both sides with respect to x at the site
Since slope of the d/s face of the overflow section is 0.8: 1, So...