GATE DAMS. 



243 



dam at Port-a-1' Anglais, on the Seine, showed a difference of 30 per cent in favor 

 of the former. These gates also minimize the dangers of scour, since the discharge is 

 from the surface of the pool. 



The principal objection to the Boule dam is that it is comparatively tedious in 





UP-STREAM ELEVATION OF A CURTAIN DAM, AS USED WITH AN OVERHEAD BRIDGE. 



operation, each gate having to he handled separately and perforce slowly. To remove 

 a gate from the top rank takes one or two minutes, and to remove one from the bottom 

 rank, five or six minutes. For this reason the type is not adapted to rivers subject to 

 quick rises. 



