38 BULLETIN 831, U. S. DEPARTMENT OF AGRICULTURE. 



under a minimum head of 36 feet. The calculated discharge of the 

 battery is 16,600 second-feet with an assumed coefficient of 0.70 and 

 a minimum head of 36 feet. The total capacity of the siphons and the 

 overflow spillways at the south end and center is now estimated to 

 be 50,000 second- feet with 5 feet of water flowing over the center 

 spillway. Figure 1, Plate XV, shows a cut of the south-end spill- 

 way. About 300 feet below the dam proper there is a reinforced con- 

 crete hollow-type dam built to provide a stilling pool and neutralize 

 the energy of the water falling from the three spillways. 



CONCLUSIONS. 



The purpose of this bulletin is to assemble, as fully as possible, 

 all the best information known to the writer in such a way as to be 

 of use to anyone interested in the subject. It is the intention of the 

 writer to point out, in as brief a manner as he can, the advantages of 

 the siphon spillway when it is desired to facilitate the escape of high 

 flood crests, and at the same time to conserve crest length, and cost 

 of construction and maintenance, fey eliminating the use of mechani- 

 cal or other energy necessary to operate partially or completely 

 automatic spillways of other types. 



It is not too broad a statement to say that the siphon is the only 

 absolutely " foolproof " method of maintaining adequate spillway 

 capacity without the addition of moving parts to be constantly cared 

 for and frequently replaced, and which very often fail to operate 

 automatically or because of the absence of an intended operator. 



Furthermore, the siphon permits of (1) closer regulation of the 

 pond level, (2) the heightening of the spillway crest and therefore 

 additional storage capacity where each unit of height is of greater 

 value, (3) the coming into full and efficient action almost at the mo- 

 ment the danger point is reached, instead of having to depend upon 

 additional danger-producing head to increase discharge, and (4) 

 maintaining the desired pond level by quickly ceasing to act when 

 the danger is passed. 



It is evident that having provided adequate spillway of the si- 

 phonic type in about one-half the area required for any other known 

 automatic type, the escaping water is concentrated to a narrow jet. 

 This allows a more economical arrangement of the channel intended 

 to neutralize the accelerated flow and convey it to a natural drainage 

 course. 



The writer has never heard any question raised as to the possibility 

 of damage to land or structures below the point of installation of a 

 siphon spillway, but it has occurred to him that such possibilities do 

 exist and that provisions may be considered to counteract such dam- 

 age. The spillway of a reservoir may be called upon to discharge a 

 larjre volume of water. 



