Page 53


Page 53
Colorado River problem
Is Part Of,8
Full text
358 ALLISON ON THE COLORADO RIVER PROBLEM enlarge. As it may be twenty years before the entire capacity will be demanded for irrigation, the additional investment at present is prohibitive. However, the main objection to the location of such a canal is the uncontrollable elements injected into the problem in deliberately cutting and maintaining a waterway through the very heart of a desert mesa region, capped with drifting sand dunes. By means of studies herein discussed, these mammoth sand dunes are easily recognized as similar in size and construction and in the phenomena governing their movement, to the most extensive types the world over. As the welfare of thousands of souls in the oasis of the great Sahara Desert, where prosperous settlements have been overwhelmed and blotted out of existence, is intimately connected with the rate of movement and the mode of accumulation of wind-borne sands, so is the fate of one of the greatest irrigation regions of the world coupled inseparably with a similar movement of great sand-hills on the route of the All-American Canal. The lessons taught by engineers and geologists of England, France, and the United States, in their years of study and observation of the sand dune regions of the world, must be applied in this case to avoid disaster in attempting to build the All-American Canal. In addition to the difficulties of construction, there is the question of determining from experiments elsewhere whether or not the sand-hills through a 12-mile section of the All-American Canal can be prevented from drifting into the canal; secondly, it remains to determine the rate of movement in the sands of the character found in this case; and, thirdly, having projected a determined quantity of sand into the canal, it is important as to whether or not conditions can be set up in the canal itself enabling the water to transport the sand without resorting to mechanical means. Although in localities of lesser sand-drifts, fences, trees, and the oiling of the ground surface are useful in stopping their encroachment, under conditions of such overwhelming drift, as in the case at hand, no such means would be successful. The only effect of oiling or planting vegetation is to create other sand dunes. Trees, brush fences, and such obstacles placed in the path of such extreme drift are most readily submerged, emerging, however, as the dunes move on. In the case of the All-American Canal, as the sand rolls over such obstacles, it next encounters the running stream of water which is the only effectual means of stopping it. It follows that the most general method of checking the encroachment of blow sands is to promote the growth of sand dunes; and a sand dune is best promoted by a running stream. Sand-hills on the western shores of the Holy Land, and in a district extending almost from the borders of Egypt, including the neighborhood of Alexandria, are stopped only by the Nile. Sand dunes are invaders far more dangerous than the waves of the sea and only a stream that will carry off the particles will effectively stop them. In determining the capacity of the canal to carry off the sands injected into it, it is necessary to examine the mechanical elements of the materials involved and to determine the quantity to be removed. Table 23 indicates the remarkable similarity in the grading of sand from dunes scattered over the United States. The similarity of sands taken along the route of the All-

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