96 



DAMS AND HEADWORKS 



El. 15H.Q 



El. 1500.8 



operating the worm nuts. The screws are held in a vertical posi- 

 tion and the hoisting chains pass over sheaves at the tops of the 

 gate piers. A machinery tunnel extends the full length of the 

 spillway, a distance of approximately 800 feet, and is built within 

 the dam and contains all the operating machinery. Limit switches 

 are provided to prevent overtravel by cutting off the current from 

 the motor at the proper instant. 



Tilting Gates. This type of flood gate generally consists of a 

 flashboard which is hinged at its lower edge to the crest of the 



spillway, the other edge 

 being free to move from 

 a more or less vertical to 

 a horizontal position. It 

 maintains its upright posi- 

 tion until the water level 

 above the dam reaches 

 the normal level. As the 

 water continues to rise the 

 additional pressure on the 

 gate will cause it to tilt 

 over further until it finally 

 rests in a horizontal posi- 

 tion on the dam crest. 

 As the water subsides the 

 gate will automatically 

 rise until the normal water 

 level in the pond is 

 reached. 



Many different devices 

 have been used for accom- 

 plishing the counterbal- 

 ancing effect, one of the 

 latest being that shown in 

 Fig. 47. This particular installation is designed to operate with 

 a maximum fluctuation in water level of three inches. 



Each flashboard consists of a steel-reinforced timber panel 

 hinged at the bottom and connected at the top to a 17-ton con- 

 crete roller counterweight by two steel cables, which are wound 

 in grooves around each end of the roller. These rollers travel on 

 inclined tracks, each end being provided with a geared drum which 



FIG. 47. Tilting Spillway Gate with 

 Counter Weight. 



