GATE STRUCTURES EOR IRRIGATION CANALS. 21 



concrete division wall 8 inches thick. The gate shutters are each 2 

 feet 4 inches wide, sliding in 2 by 3 inch grooves. The individual 

 boards are of 2-inch stuff firmly bolted to a wide gate stem of the 

 bame thickness, which is bound around the edge securely with an iron 

 strap. Small bolts pass completely through the gate stem edgewise 

 and hold the strap to the stem. The outside gate slots are cast in the 

 concrete, while the inside slots are built up of timber secured to the 

 division wall by anchor bolts. The 4 by 4 inch cap for the locking 

 device is secured to the side and division walls by anchor bolts. 

 Staggered holes for the locking pin are bored in the stem shutter and 

 cap. The concrete is a mixture of one part cement to six parts sand 

 and gravel found near the site. The total cost was $225. The items 

 were not obtainable. 



As the canyon is subject to very rough flood waters which may 

 overtop the gate at any time it was desirable to keep the superstruc- 

 ture as low as possible, so that the gate standards were not set high 

 enough for the locking holes to be bored in the stem alone, which 

 would leave the shutter proper a solid panel. In order to secure a 

 locking position for the shutters when wide open, it was necessary 

 to bore the holes nearly to the bottom of the gate, and these cause a 

 bad leakage when the gate is closed. A better construction to secure 

 the low superstructure probably would have been a wooden radial 

 gate extending from one side wall to the other, omitting the division 

 wall; or, if desirable to use a slide gate, the use of the angle-iron 

 stem shown in Plate I, i. The double concrete flume below the shut- 

 ters is covered with a timber footbridge for a trail leading up the 

 canyon. 



BIFURCATION WORKS. 



These structures are used to divide the water of one canal or lateral 

 between two or more canals or laterals. This division may be on a 

 proportionate basis or otherwise. A structure may be used to divide 

 water all of which is handled by one company, or it may be used to 

 segregate for one company water which has been carried in the canal 

 of another company up to the point of bifurcation. If the conditions 

 of water rights and the arrangements between the companies call 

 for a proportionate division of whatever flow is in the supplying 

 canal, then the openings should be so arranged that any change in the 

 head of water will affect the discharge of both proportionately. 



Where the division of water is to be nearly equal and the topog- 

 raphy permits, it is usual practice to design a twin structure placed 

 symmetrically with regard to the supply canal. In this way each 

 gate is affected equally by the various factors of approach velocity, 

 contraction, etc. If one division is to receive only a small portion 

 of the water, the usual practice is to hold the alignment of the sup- 



