THE YUMA RECLAMATION PROJECT. H85 



impossible. The type of weir selected is one that has been tried dur- 

 ing the last fifty years at numerous places in India and Egypt under 

 similar conditions, three dams having been constructed on the Xile 

 River M-ithin the past fifteen years on practically this same plan, all 

 having served their purpose efficiently and being in operation to-day. 

 This type of weir consists of a loose rock structure with a p^tving of 

 stones 2 feet in thickness on the downstream slope, the structure 

 being tied together with three parallel walls of concrete run longi- 

 tudinally between the granite abutments on the two sides of the 

 river, and the entire structure being further made secure by an 

 apron of loose rock pitching 10 feet in thickness and 50 feet in 

 width at the lower toe of the dam Ijelow the sloping pavement. The 

 height of this weir is to be 10 feet above low water and the slope of 

 the downstream side is 12 feet horizontal to 1 foot vertical, with 

 the oO-foot apron below. The design calls for the upper core wall 

 of concrete to rest upon a row of sheet piling driven into the bed of 

 the river. 



The handling of the silt of the Colorado is one of the most difficult 

 features of this undertaking. It is known that its amount is very 

 large. The river is on a grade of approximately 1 foot to the mile 

 above the Laguna weir site, so that this weir, 10 feet high, will make 

 a settling basin of relatively quiet water approximately 10 miles in 

 length above it. At each end of the weir, and constructed in solid 

 graiute rock, will be a sluiceway 400 feet wide on the Arizona side 

 and -40 feet wide on the California side with provision for its enlarge- 

 ment to 200 feet when desired, and excavated to the depth of 2 feet 

 below low water in the river. These sluiceways will be closed by 

 large gates operated mechanically. The diversion canals Avill take 

 their water al)ove these gates from the sides of the sluiceways. 

 The area of these sluiceways being so great, the water movement 

 toward the canal will be slow and most- of the sediment will be 

 'leposited before reaching the canal intake. AVhen this has accumu- 

 lated to a considerable extent, the sluice gates will be opened, and it 

 is estimated that their capacity will be approximately 20,000 cubic 

 feet per second. This great volume of water passing through the 

 sluiceways when the gates are opened will carry out with it the 

 sediment dejjosited above the intake of the canal. The ordinary low- 

 stage flow of the Colorado River is from 3,000 to -4,000 cubic feet per 

 second; so the capacity of these sluiceways will be about five times 

 I he low-watei- flow of the river. These figures are given for pur- 

 poses of comparison only. As the result of a number of experiments 

 it has been found that the principal quantity of silt is carried 

 along near the bottom of the river, and that the surface water is 

 relatively free from sediment. It is phmned, therefore, to take the 

 SM I90i 25 



