CHAPTER VIII. 

 GATE, CURTAIN, AND BRIDGE DAMS. SHUTTER AND A-FRAME DAMS. 



GATE DAMS. 



General. The Boule gate, as it is called, was first used by M. Boule, the French 

 engineer, at the Port-a-1'Anglais dam near Paris in 1875, and has since been applied 

 to important works in France, Russia, and elsewhere. It is a modification of the needle 

 dam, the vertical needles being replaced by horizontal planks, the ends of which rest 

 against and slide upon the faces of the trestles. The latter are hinged to the floor and 

 are raised and lowered in a manner similar to trestles for needles. 



Maneuvers. To raise the dam, the trestles are first set upright, and connected 

 by the floors and service track, and the gates are brought out on a truck and set in place 

 by a light movable crane, or, where small enough, by a pole with a hook on its end. 

 The regulation of the pool is effected by maneuvering the top row of gates, which are 

 usually made from 4 to 12 inches in width, to permit easy movement. The lowering 

 of the dam is done by reversing the operation of raising. 



Dimensions, etc. The trestles for this type of dam are usually spaced from 3^ 

 feet (one meter) to 4 feet apart, with a 

 service bridge 9 to 18 inches above the pool, 

 and are considerably heavier than those 

 for needle dams. Their up-stream face is 

 made smooth, and occasionally provided 

 with a projecting rib, serving as a guide for 

 the gates in sliding. The latter vary in 

 width from 3 to 4 feet for the bottom ones, 

 to between 4 inches and 21 inches for the 

 top ones, the maximum area rarely exceeding 

 20 square feet. They are made of wood, 

 strapped with iron, and are provided with 

 a handle for maneuvering. An example of 

 iron gates is to be found at the Pretzien 

 dam on the Elbe (1875), and also at the 

 new dam at Mirowitz, in Bohemia, where 

 buckled-plates are used, sliding on rollers to 

 reduce the friction. This appears to be an 

 excellent device, as experiments made at the PERSPECTIVE VlEW " B u'- B ' GATES AND TRESTLES 



Marolles dam in France, with gates provided with ball-rollers, showed that one man 



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