Page 50


Page 50
Colorado River problem
Is Part Of,8
Full text
354 ALLISON ON THE COLORADO RIVER PROBLEM The Imperial Irrigation District, with a population of 60,000 dependent entirely on the flow from the river, cannot be subjected to the possibilities of delays in water service. It is proposed, from Pilot Knob westerly, to construct the All-American Canal in a cut ranging from 40 to 160 ft. in depth, through 20 miles of high mesa land and 12 miles of the most extensive drifting sand-hills in America (Fig. 14) along the approximate route of the spectacular California State Highway between Yuma and Imperial Valley (Fig. 15), which is built of portable plank board sections, for raising and lowering the grade and regulating the route with the drifting of the sand. Along this same approximate route is constructed the power line of the Southern Sierras Power Company; its experience alone in maintaining 12 miles of line should be enough to weaken the determination of the most enthusiastic supporters of an All-American Canal. One day 30-ft. power poles are covered to the wires with sand and the next day undermined by a 24-hour sand storm. To build a canal through this section is in itself a most infeasible exploit, not only because of the difficulties of excavation and original construction, but also on account of the hazards and maintenance expense afterward. Fig. 16 shows a cross-section of this work at one of the deeper cuts. It is proposed to make this excavation with suction dredgers at a cost of 20 to 30 cents per cu. yd. Experience shows conclusively that heavy sands and gravels cannot be pumped at this figure even with low lifts, let alone through the gigantic lift of 150 ft. and more which will obtain when the spoil banks are built up along the edges of the cut. "No consideration is given the fact that it is an impossible feat to excavate with hydraulic machines, maintaining such a slope as is estimated; probably 50%, of excess materials must be moved if this means of excavation is utilized. Should even 20% of the excavated materials be waste, the cost of the cut will be increased by between $2,000,000 and $3,000,000. Should the engineer's estimate be exceeded by 5 cents per cu. yd., the cost of the work will be increased $3,000,000. "Not only is the work itself a dangerous experiment, perhaps an entirely impossible task, but the estimates themselves of such an experiment are undependable, as the whole project is at the mercy of the elements. The velocities that will obtain in the canal as planned range from 2 1/2 ft. to 3 1/2 ft. per sec.; these velocities are as high as the engineer dared risk in the loosely knit sand and gravel through the mesa, yet a velocity of 4 to 5 ft. per sec. will not keep in suspension the surface sands which blow in from the surrounding country. In other words, if a velocity is maintained sufficient to keep the drifting sands in suspension and avoid the clogging of the canal, then, at certain seasons of the year, when the silt content from the river water is light, this same velocity will erode the banks in a manner that will ruin the entire section of the canal. A canal all on American territory, designed to serve the western slope of Imperial Valley, would pass along the boundary line north of the City of Calex-ico, crossing New River on an extensive viaduct, costing $915,000 with its wasteway, and enter the West Side Main Canal, which is on the high ground

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