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



and shows a great saving in material, for the reason that the amount 

 of water entering the channel leading to the gate can be so easily 

 controlled that there is little danger of failure from freshets, and 

 no excessive amount of money was necessary to build expensive wings 

 and a high bulkhead. 



In the following pages the diversion works of several systems, 

 illustrating both the simple and more elaborate types of structures, 

 are described. 



DIVERSION WORKS OF THE SOUTH SAN JOAQUIN AND OAKDALE IRRIGATION 



DISTRICTS. 



The combined structures shown in Plate IV furnish a general 

 idea of arrangement for an efficient method of handling of water at 

 the head of a canal. The joint headworks of the South San Joaquin 

 and Oakdale irrigation districts are located in the canyon of the 

 Stanislaus River about 18 miles above Oakdale, Cal. 



The river has a maximum flood flow, as shown by two floods within 

 six years, of 62,000 second- feet. The low-water flow is about 100 

 second- feet. Of the 1,500 second-feet which the structure is designed 

 to take from the river but 1,370 feet will be delivered into the head 

 of the canal below the lower gates, the surplus being wasted over the 

 spillway or out through the sand and waste gate, back into the 

 canyon below the diversion dam. 



The complete heading consists of the diversion dam of two arch 

 spans with an intervening buttress, 466 feet in crest length, and a 

 maximum height of 78 feet, <and the joint headworks on the north 

 end of the dam and of the separate Oakdale headworks on the south 

 end. The following description is confined to the joint headworks: 



The joint headworks are built of concrete, part plain and part 

 reinforced, installed upon and against solid rock foundations. 



There are four principal elements in the headworks: First, the 

 head wall, with five openings designed to be closed with stop logs 

 in case of accident to the gates below ; water covering the diversion 

 dam more than 3 feet in depth tops this head wall. Second, a gravity 

 dam placed on a tangent to the curve of the diversion dam, diverging 

 about 16° from a right angle with the center line of the canal. There 

 are three gate openings at right angles to the line of the canal, each 

 6 by 9 feet, regulated by massive cast-iron gates raised by screw stems 

 through geared hoists located on top of the gravity dam. The top 

 of the gravity dam is 25 feet above the crest of the diversion dam 

 and careful estimates show that maximum flood crests will top the 

 diversion dam about 23 feet. Third, an automatic spillway about 

 30 feet long just below the gravity dam at an elevation of H feet 

 below the crest of the diversion dam, and a sand and waste gate 

 just downstream from the spillway. Fourth, three gates, each 6 feet 



