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3. For pooled stepped spillway (end sill at the downstream end of apron):
0 : 94
d s
D 50 ¼
y 1
D 50
0 : 61
ðÞ
SN
(7)
r 2
¼
0
:
99
5 Design Procedure
The following procedure is presented to estimate the maximum scour hole depth:
1. Upon knowing the unit discharge and the height of spillway, determine the
energy loss through stepped spillway by applying one of the equations presented
in Table 2 . For example, for the case of
h
=' ¼
3
:
5, we get:
0 : 28
q 2
gH 3
1
H ¼
1
:
736
(8)
1
D E
=
2. Determine the amount of energy downstream of the spillway from ( 9 ):
y c D E
3
2
E 1 ¼
(9)
1 = 3
q 2
in which y c ¼
ð
=
g
Þ
3. By simultaneously solving equations of energy ( 10 ) and continuity ( 11 ), one
can obtain y 1 and V 1 :
V 1
E 1 ¼
2 g þ
y 1
(10)
q
¼
V 1 y 1
(11)
4. Determine the stability number from ( 4 ).
5. Determine the scour depth applying the proper equation ( 5 - 7 , whichever
applies).
6 Conclusion
In this study, three types of gabion stepped spillways under different flow condi-
tions and bed materials were tested. Based on stability analysis of a particle at the
point of incipient motion, a general formula was developed to predict the scour hole
depth. With the help of regression analysis technique and the use of experimental
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