Page 52


Page 52
Colorado River problem
Is Part Of,8
Full text
ALLISON ON THE COLORADO RIVER PROBLEM 357 of the western slope of the Valley. The fills required crossing the western section of the Valley to attain the altitudes necessary on the western slope, would be as high as 15 ft. above the natural ground. This section of the country is already menaced by ground-water due to seepage from the local canals and if the All-American Canal were carried across this same territory, at such an extraordinary height, this section would be ruined from ground-water. A considerable area of land west of the present West Side Main would be left in its present condition permanently, on account of the low elevation of the All-American Canal. Fig. 16. [CROSS SECTION OF CUT THROUGH SAND RIDGES SHOWING PROBABLE CHANGE IN SECTION AT END OF ONE YEAR] Assuming the All-American Canal to be built, the next consideration concerns its future maintenance. The very fact that the stream is in a cut 50 ft. below the floor of the mesa itself, with crowning sand-hills of heights ranging to 100 ft. above the floor, makes it absolutely certain that the cut itself will receive and hold the entire volume of sand drifted to it by each storm. Where the sand-drift passes across the country without interruption, ofttimes a pass through the sand-hills, such as the Government Pass in which part of the canal is located, can remain fairly open; but where the passage is deliberately interrupted by a cut having a flowing stream at its bottom, then all the sands must necessarily enter and remain in this excavation. Here, again, Imperial Valley must depend on its present canal system through Mexico if interruptions in the delivery of water are to be avoided— interruptions that unquestionably will be fatal on account of the huge quantity of drift involved. The borings taken along the route of the proposed canal indicate porous strata in the canal prism. Especially with the Boulder Canyon Dam built and with some relief from the silt thrown into the canals as at present, this prism cannot possibly seal itself. The water losses from seepage, as estimated from the losses occurring in the present East High Line Canal through similar sections of material, will amount to 27%, unless the canal is lined with concrete. This loss is prohibitive not only because of the interference in regulating the supply to the land about 150 miles distant, but more particularly because the very water lost to the All-American Canal will mean the ruination, from saturation, of all the low-lying lands along the section of the country through which it passes. As an alternative, lining the canal with concrete or tunneling the sand-hills is impractical, principally because the section must be constructed for the maximum irrigation requirement immediately, as it will be difficult to

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