SPILLWAYS 227
Fig. 4.18 Siphon spillway, Spelga Dam, UK (Poskitt and Elsawy, 1976)
increase in specific discharge and the automatic control of water levels
within a small range. They are also a very useful alternative when consid-
ering the augmentation of the capacity of existing spillways; on the other
hand, once installed, there is very little scope of increasing the design dis-
charged as Q"H1/2(equation (4.62)).
For further information on siphon spillways, see BHRA (1976),
Ervine and Oliver (1980), Ervine (1998) and Ackers (2000).