8 BULLETIN 115, U. S. DEPARTMENT OF AGRICULTURE. 



ried by the radial arms of the lower section or all centering on a 

 common axle. With this arrangement water may be taken under, 

 over, or between sections of the shutter. This allows heavy silted 

 water to be held back in the stream and the lighter waters taken over 

 the top of one or more sections of the shutter. The sectional con- 

 struction also allows the upper sections to be lifted out of the way, 

 so that the lower section may be partly raised and still have a low 

 upper crest. This may be used as a wasteway to prevent floods from 

 topping the levees. The ordinary radial-gate panels are closed at the 

 top when the shutter is partly raised. The greatest use for this 

 modification of the old radial gate is probably in river gates for 

 canals and in crest gates regulating the water above a diverting wen\ 

 The solid type of radial gate probabty will remain standard as a gate 

 for a sand sluice where the scour at the bottom is necessary, and for 

 all other gates than the river gates the character of the water and the 

 manner of discharge will dictate the desirability of using the sec- 

 tional type. 



Very large openings probably are more easily regulated by the 

 radial gates than by any other form of shutter used in this country at 

 present, and for this reason they lend themselves readily to places 

 where the openings must pass cakes of ice or small debris. On the 

 other hand, large pieces of driftwood are a continual source of an- 

 noyance during flood times. This is true especially where the water 

 is carried through submerged orifices, as the arms of the gate in such 

 a case are within reach of the driftwood, which easily clogs in the 

 irons of the gate. 



If it is desired that a radial gate be made comparatively water- 

 tight, a strip of rubber belting on each side and at the top may be 

 used. The bottom of the gate may close on a strip of wood set in the 

 concrete floor, or it may close behind a shoulder of wood or concrete. 



There are various ways of balancing a gate of this type so that the 

 net amount of labor necessary to raise it may be reduced, although 

 it is desirable that there be plenty of weight in favor of the gate in 

 order that it may close of its own weight, as a cable or chain, the 

 usual type of lift, can not be used to push the gate down as can a 

 wooden or iron stem. 



Since the pressure on the face of the gate is normal to the surface, 

 then, if the face is a true segment of a cylinder, with the axle at the 

 center, the pressure is transmitted directly to the axle, but if the 

 axle is set below the center there will be developed a pressure passing 

 over the axle and tending to raise the gate. This same effect may be 

 obtained by spiraling the face of the gate so that the resultant pres- 

 sure passes above the axle. 



