Hydraulic Structures: Fourth Edition

SPILLWAYS 207

For a notch of width b, head h, and coefficient of discharge Cd, the
discharge equation is

Q 2
g1/2bCdh 

3/2

(^) 
3/2
 (4.15)
which, for V 0 0, reduces to

Q

2

3

 2

 g1/2bCdh3/2. (4.16)

Cdis about 0.62 (Section 8.4).
Scimeni (1937) expressed the shape of the nappe in coordinates x
andy, measured from an origin at the highest point, for a unit value of H
(Fig. 4.6) as

yKxn (4.17)

withK0.5 and n1.85.
As the nappes for other values of Hare similar in shape, equation
(4.17) can be rewritten as

y/HK(x/H)n (4.18a)

V^20



2 g

V^20



2 g

2



3

Fig. 4.6 Standard spillway crest (after US Army Waterways Experimental
Station, 1959)