THE CONQUEST OF THE COLORADO 



By C, J. BLANCHARD, Statistician, U. S, Reclamation Service 



THE work of closing the Colorado 

 River, twelve miles above Yuma, 

 Arizona, had a most spectacular 

 finish. The Government engineers 

 have been engaged here for months in 

 building a dam the like of which this 

 country has never seen before. On 

 December 21 the channel of the river 

 was closed^ and the entire flow of the 

 river passed through the giant sluice- 

 ways at either end of the dam. The 

 supervising engineer wired to Wash- 

 ington : "The river is closed and we 

 sat on the lid while a five-foot rise, car- 

 rying 40,000 feet of water, passed by." 



The engineers encountered manv 

 difficult problems in planning the big 

 irrigation systems which the Govern- 

 ment is constructing in the arid West, 

 but no more complicated conditions 

 confronted them anywhere than in at- 

 tempting to control the Colorado River 

 in order that 130,000 acres of exceed- 

 ingly fertile soil in California and 

 Arizona might be made fruitful. 



The size and uncertainty of the riv- 

 er, the shifting channel and unstable 

 banks, the yearly recurring inunda- 

 tions, variations in volume from low 

 water to flood heights and the immense 

 volume of silt carried by its yellow wa- 

 ters, made the problem of the control 

 of the stream unique in the history of 

 American irrigation. With these diffi- 

 culties fully understood and no bedrock 

 for a base, the problem presented to 

 the engineers was to build a structure 

 on the sand and silt that would fully 

 control the river, holding it within cer- 

 tain prescribed limits, and at the same 

 time make some disposition of the silt, 

 one of the most difficult features of the 

 undertaking. 



Constructing Engineer E. D. Vin- 



cent gives the following description of 

 the structure : 



"The most advantageous weir site 

 was found to be at Laguna, twelve 

 miles above Yuma, where granitic 

 mountains encroach on the river valley, 

 leaving an opening about a mile wide. 

 The type of weir selected was one that 

 has been in successful operation for 

 many years in India and Egypt under 

 practically identical conditions with 

 those presented in Yuma Valley. 



"Three concrete core walls 4,800 

 feet in length and fifty-seven and 

 ninety-three feet apart extend from 

 bluff to bluff. The crest wall with a 

 maximum height of nineteen feet 

 above the bed of the stream rests upon 

 a row of six-inch sheet piling from 

 twelve to twenty feet in length, incor- 

 porated in its base to cut off seepage. 

 The space between the walls is filled 

 with broken stone, and an apron of 

 rock extends forty feet beyond the 

 lower wall. The structure between the 

 walls is capped with a concrete pave- 

 ment eighteen inches thick. On the 

 up-stream side of the weir a talus of 

 broken rock, with an incline of two 

 feet horizontal to one foot vertical, pro- 

 tects the concrete structure. The dam 

 is 4,800 feet long between abutments, 

 nineteen feet high in the river channel, 

 and 226 feet in width up and down 

 stream." 



The dam will raise the water about 

 ten feet, backing it up stream nearly 

 ten miles and forming a settling basin 

 covering approximately eight square 

 miles. At the west end of the weir, 

 constructed in solid granite rock and 

 excavated to the depth of low water 

 in the river, is a sluiceway 116 feet 

 wide. At the east end the sluiceway, 

 also in granite, is only forty feet wide. 



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