UNITED STATES DEPARTMENT OF AGRICULTURE 



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BULLETIN No. 831 M 



Contribution from the Bureau of Public Roads 

 THOMAS H. MacDONALD, Chief 



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Washington, D. C. 



PROFESSIONAL PAPER 



August 25, 1920 



SPILLWAYS FOR RESERVOIRS AND 



CANALS. 



By A. T. Mitchelsoa', Senior Irrigation Engineer. 



CONTENTS. 



Page. 



Spillways 1 



Overflow spillways 4 



Spillway control 9 



Flashboards 11 



Sliding gates 11 



Tilting centerweighted gates 12 



Rolling dams or barriers 13 



Page. 



Siphon spillways , — 15 



U. S. Reclamation Service siphons — 28 



European practice 31 



Huntington Lake siphon spillway 32 



Conclusions 38 



Acknowledgments _- 40 



SPILLWAYS. 



In its ordinary use the spillway is a device for removing surplus 

 water from a reservoir or canal, in order that the water level within 

 the reservoir or canal may not rise above the point considered safe or 

 fixed upon as the maximum allowable height. It is distinguished 

 from other types of wasteways by the fact that the surplus water 

 passes over a crest or "spills" instead of passing through openings in 

 the dam or canal bank. 



The conditions necessitating spillways are many and they vary as 

 to the requirement for capacity, the degree of safety factor demanded, 

 by the extent or importance of the structure they protect, the location 

 of the spillway with relation to that of the dam or canal embankment, 

 and the functions they must perform in maintaining a more or less 

 perfect control of the reservoir or canal in times of maximum inflow 

 when a predetermined flowage line or freeboard must not be exceeded. 

 This necessitates the provision for passing the highest floods over the 

 spillway within the safe limit of maximum rise, and the conveyance 

 of this water away without injury to the clam or canal embankments 

 or to their appurtenant structures. 



If a reservoir is to be located in a stream channel where the extent 

 of inflow is not under human control, the spillway must provide for 

 the passage of both normal and flood flow when the reservoir is full 



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