386 THE YUMA RECLAMATION PROJECT. 



water into the canals by a skimming process over a long row of gates, 

 so that the entire capacity of the canal can be fnrnished by drawing 

 but 1 foot in depth of water from the surface of the river. Every por- 

 tion of this weir and heaclworks, as designed, would be of rock, con- 

 crete, or steel, with the exception of the sheet piling, which will be 

 driven entirely below the water level, and so will not decay. Every 

 portion of the weir will be what is known as permanent construction. 

 Such character of work will, of course, be expensive, but it has been 

 proved to be sound economy to build in this way. 



The capacity of these canals at their intakes will be 1,600 cubic 

 feet per second on the Arizona side, and 200 cubic feet per second 

 on the California side. The amount of silt that would be daily 

 deliA'ered into the Arizona Canal, if diversion were made directly 

 from the stream, would approximate 17,000 cubic yards of wet mud 

 by volume. It is not believed to be j^ossible for a canal to continu- 

 ously operate successfully for the irrigation of lands along the val- 

 leys of the Colorado River unless some very substantial arrangements 

 are made at the headworks for the handling of silt, and this is 

 believed to be a justi.^cation for the expenditure proposed for these 

 headworks; also the water must be held to a fixed level at the canal 

 heading for all stages of the river. This structure Avill cost approxi- 

 jnately $1,000,000. It is not considered possible to remove all of the 

 silt from the water, but the canals have been designed so that the 

 velocities will be sufficient to convey through to the fields the light 

 material entering the canals from the intake. 



Careful study has been made of the existing canals in the vicinity 

 of Yuma and Imperial to determine the shape that they naturally 

 assume, and tlie i-oughness of the bottom and sides, which tends to 

 retard the velocity. Based upon these chita, the canals have been so 

 designed as to carry water at a higher velocity throughout than Avill 

 be found in the settling basins above their head, and of such velocity 

 as will permit of a minimum loss by seepage and evaporation. The 

 gates and drops of these canals and the ^ uma bridges are designed 

 as steel concrete structures. A distribution system has been esti- 

 mated upon to furnish water to each lOO-acre tract. There will be 

 small ai'cas of laud in the upper (lila Valley, and below Yuma, that 

 will have to be served by ])uniping })lMnts, lifting the water from 

 5 to 7 feet. The power for doing this will be furnished from a 

 water-power [)laut to be erected above Yuma at a drop in the main 

 canal. This ])()wer jtlani will also be used in connection with the 

 (Iraiuage system. 



( )n(' of the most dillicidt pi-oblcnis in connection with this project 

 is the crossing of tlic (Ida Rixcr. Tt has been considered necessary 

 to make this perfertly safe, and for this purpose a structure has been 

 designed that will cross beneath the bed of the river, the top to be 



