July 21, 1922] 



8CIENGE 



65 



the top of the irrigation storage and would 

 continue to discharge as long as there is any 

 water in the space provided for flood deten- 

 tion. This permanent opening would prevent 

 encroachment upon that portion of the reser- 

 voir provided for flood detention and will he 

 so designed as not to allow water to pass in 

 excess of the capacity of the levee system in 

 the lower basin. 



Excellent dam sites exist in both canyons 

 and after examining them in February, 1921, 

 Dr. F. L. Ransome of the United States Geo- 

 logical Survey pronounced them as geolog- 

 ically feasible for the construction of a high 

 dam. 



Probably the most difficult task to Ije en- 

 countered in the construction of a dam on the 

 Colorado Eiver is the turning of the river 

 during construction of the foundation and con- 

 siderable thought has been given to this fea- 

 ture. A study of the hydrograph of the Col- 

 orado at Yuma over the period 1902 to 1921 

 shows that, if the discharge at Boulder Can- 

 yon is assumed to approximate that at Yuma 

 with the exception of the flash peaks thrown 

 into the river from the Gila, a diversion 

 works of 50,000 second feet capacity would 

 have been overtopped every year of the twenty 

 and that the average time of submergence 

 would have been about 11 per cent, of the 

 total, the maximum being about 84 days in 

 1920 and the minimum 2 days in 1904. 



Diversion works of 75,000 second feet ca- 

 pacity would not have been overtopped during 

 nine of the twenty years. The average time 

 of submergence would have been 5 per cent. 

 of the total, the maximum being about 50 days 

 in 1907 and 1909. 



Seven of the twenty years of record show 

 peaks of from 115,000 to 190,000 second feet 

 at times occurring in two successive years. In 

 1920 the peak was 190,000 second feet, while 

 in 1921 it reached 185,700 feet, and the pres- 

 ent year promises to be one of high discharge. 



With so great an amount of work to be done 

 in excavating and laying concrete below water 

 surface in so short a season it is essential that 

 diversion works of ample capacity be pro- 

 vided to avoid being flooded out, thus losing 

 much valuable time. It is therefore considered 



necessary to provide for diverting the river 

 during years of ordinary high water and it is 

 proposed to design the works with a capacity 

 of 150,000 second feet. The years 1920 and 

 1921 are the only ones of record when the dis- 

 charge exceeded 150,000 second feet at Yuma 

 and it is thought that the expenditure neces- 

 sary to increase the capacity of the diversion 

 works above 150,000 second feet is unwarrant- 

 ed. Diversion would be by means of coffer- 

 dams and tunnels through the rock abutments 

 of the main dam. 



In order that the diversion problem may be 

 properly attacked and in order that methods 

 to be used in construction of the dam may be 

 properly worked out, diamond drilling opera- 

 tions to ascertain foundation conditions at the 

 possible dam sites were commenced in Sep- 

 tember, 1920, and are still under way. To 

 date three sites have been investigated in a 

 preliminary way and considerable detail infor- 

 mation has been obtained at one of them. A 

 total of 88 holes have been put down including 

 approximately 3,500 feet of wash borings and 

 2,100 feet of diamond drilling. The results 

 of the investigations at Boulder Canyon indi- 

 cate that bed rock will be found at depths not 

 to exceed 140 feet below low water surface. 

 At Black Canyon, bed rock in the deepest hole 

 drilled to date was found at a depth of 62 

 feet below low -water surface. However, the 

 investigations have not been carried far 

 enough for it to be said that this is the maxi- 

 mum depth to bed rock at the Black Canyon 

 site. 



The following recommendations by Director 

 Davis conclude his report as provided for in 

 the Kincaid Act: 



1. It is recommended that through suitable 

 legislation the United States undertake the con- 

 struction with government funds of a highline 

 canal from Laguna dam to the Imperial Valley, 

 to be reimbursed by the lands benefited. 



2. It is recommended that the public lands 

 that can be reclaimed by such works be reserved 

 for settlement by ex-service men under conditions 

 securing actual settlement and cultivation. 



3. It is recommended that through suitable 

 legislation the United States undertake the con- 

 struction with government funds of a reservoir 

 at or near Boulder Canyon on the lower Colorado 



