The Arizona sentinel., 1908-12-30

estimated velocity of 2 feet per second, which will allow all sus- pended matters that have passed the controlling works at the head to be passed on to the irrigated
 fields and not remain to clog the canals. The canal will cross under the Colorado river by means of a depressed structure known as an inverted siphon. Borings made during the past few weeks along the probable line of this siphon have demon strated that the river bed IS underlaid by sandstone at such reasonable depth that tunnel op. erutions through it may be read ily conducted. The sandstone,
 which appears to be of the same general character as the bluff that now Hanks the eastern bor- der of the river in this vicinity,
 is about 50 feet below the. river bed in mid stream and some 50 feet below the surface at the site of the proposed shaft on the Cal lfornia side. Shafts for the con- struction of the tunnel will be sunk through the sand and silt into the bed rock and then thor oughly sealed to exclude the water above; the excavations in the sandstone will continue until proper thickness for the roof of the tunnel is obtained, when the tunnelling across the river will begin. The presence of this bed rock has greatly simplihed the construction of the siphon and materially reduced its cost as compared with a similar tun-
 nel through river silt. The structure will be maSsively. con- structed and made in every way
 as enduring as the bed rock in
 which it is contained. Tunnels
 under rivers and harbors in vari.
 ous parts of the world have been
 so numerous during the past few
 years that this branch of engin.
 eering is thoroughly understood
 and the operations connected
 herewith have been reduced to
 almost an exact science. The
 investigations of this feature are
 proving that the local conditions
 for such work are almost ideal
 and its construction at an early
 date is confidently anticipated. After passing the siphon the canal will traverse the upper portion of Yuma valley in Ari zona for short distance, when
 it will be separated into two channels. That on the west side
 of the valley will be located along
 the high ground near the river
 and the one on tue east side vii follow along elevated areas neal
 the foot of the mesa. Both o1 these canals will reach southwarC to the Mexican boundary and ar' so placed as to command all tht irrigable bottom lands in thi: portion of the Project. The eas branch will be of sufficient ca pacity to carry water for tht future mesa extension, and th' pumping station for this feature will probably lie near this cana a short distance below Yuma All the canals will have sucl
 dimensions and inclinations a. will allow them to properly per
 form their functions and to main
 tain throughout the system uniform mean velocity of abou l 2 feet per second.
 , LEVEES.
 . While the bottom lands to b, g irrigated are above the norma s and water stages of the rive a they are subject to inundatiol g during floods. In May, June ant - July the annual freshet of tn i Colorado puts large areas unde a water, and the cratic rises o l. the Gila at various portions o l. the year are likely to cause con 2 siderable inconvenience and dam l.. ape ID guard against such