10 



BULLETIN 831, U. S. DEPARTMENT OF AGRICULTURE. 



life and property. Sometimes legal requirements fix the flow line 

 or it may be desirable to maintain a constant head in the reservoir. 

 Long crests to keep the rise of the pond level within a minimum 

 limit have been built and where the site did not permit of a straight- 

 line crest, modification of the form has been made as in the case of 

 the East Park reservoir of the Orland project, where crest length 

 was gained by forming it in a series of nine semicircular arches 

 resting against piers 8 feet wide. The arches have a radius of 13.5 

 feet and the whole structure is curved to a radius of 474 feet, the total 

 length of spillway crest being 460 feet. It was designed to care for 

 a discharge of 10,000 second-feet with a depth of 3.7 feet of water 



Fig. 2. — Plan and cross section of East Park reservoir spillway, Orland project, Cali- 

 fornia. Form of dentated type of spillway composed of a series of nine piers, each 8 

 feet wide. 



flowing over the crest. The spillway is located in a saddle about one 

 mile from the dam and its outline is shown in figure 1, Plate VI, and 

 in text-figure 2. 



The Little Falls dam of the Washington Power Co., near Spokane, 

 where the crest was built in the form of the letter " L " is shown in 

 figure 1, Plate IV. The accomplishment of the above results, how- 

 ever, will add greatly to the cost of the structure if the longer crest 

 has to be provided by the lengthening of the dam. 



When acceleration is due to a shorter crest length and a resulting 

 increase in the head to effect discharge, the devices serving to pro- 

 duce a regulated pond level must be under direct control. The 



