THE PANAMA CANAL 



181 



may be briefly stated that the underlying 

 material is impervious to water ; that it 

 possesses ample strength to uphold the 

 structure that will be placed upon it, and, 

 the subsoil being impervious, that there 

 is no connection between the swamps 

 above and the sea below. 



Because of the sluggish current of 

 the river in the vicinity of Gatun and 

 above, the deposits consist of the finer 

 sands and silts interspersed with beds of 

 clay. By constructing experimental dams 

 of this material and subjecting them to 

 the full head of water, it was conclu- 

 sively demonstrated that this material is 

 suitable for the interior or the impervi- 

 ous core. 



The dam is constructed by forming 

 two dumps on the outer lines of the 

 structure and depositing waste material, 

 mostly rock, obtained from Culebra, the 

 lock site, and Mindi. The area between 

 the piles thus formed is filled with the 

 material pumped in by hydraulic dredges, 

 the natural surface of the ground having 

 been previously cleared of vegetation 

 and a suitable bonding trench excavated. 



THE SPILLWAY 



Fluctuations in the lake due to floods 

 are to be controlled by regulating works 

 constructed in Spillway Hill. Objections 

 were made to constructing such works in 

 the line of the dam, but because of the 

 natural configuration of the ground, irre- 

 spective of the location of the spillway, 

 provision had to be made for tying the 

 dam to the sides of the hill ; moreover, 

 the extent and elevation of the hill, as 

 well as the material composing it, make 

 it a suitable and desirable place for the 

 waste weirs. The channel has been cut, 

 the floor and side walls of concrete com- 

 pleted, and the Chagres River now dis- 

 charges through it. As the reference of 

 the floor is at 10 feet above sea-level, the 

 lake is already formed at least to this 

 height. 



The spillway dam will be of concrete 

 with its crest at elevation 69. Piers 8.5 

 feet wide will be built on top of the 

 crest, 53.5 feet centers, grooved for 

 Stoney gates, which will close the open- 



ings and complete this portion of the 

 dam. The trace of the dam will be the 

 arc of a circle 740 feet long, with 14 

 openings, which, when the gates are 

 raised to the full height, will permit a 

 discharge of 140,000 cubic feet per sec- 

 ond. The water discharged over the 

 dam will pass through a diversion chan- 

 nel into the old bed of the Chagres. (See 

 map, page 201.) 



The dam is to contain 21,145,931 cubic 

 yards of material. On January 1, 191 1, 

 there had been placed 12,001,592 cubic 

 yards, making 56.72 per cent of the dam 

 complete. The spillway will contain an 

 estimated quantity of 225,485 cubic yards 

 of concrete, of which 113,269 cubic yards, 

 or 50.23 per cent, were completed on 

 January 1. 



THE LOCKS CAN BE FILLED OR EMPTIED IN 

 8 MINUTES 



The locks are in pairs, so that if any 

 lock is out of service navigation will not 

 be interrupted. Thus, also, when all the 

 locks are in use, the passage of shipping 

 will be expedited by using one set of 

 locks for the ascent and the other for 

 descent. The locks are no feet wide 

 and have usable lengths of 1,000 feet. 



The system of filling adopted consists 

 of a culvert in each side wall feeding 

 laterals perpendicular to the axis of the 

 lock, from which are openings upward 

 into the lock chamber. This system dis- 

 tributes the water as evenly as possible 

 over the entire horizontal area of the 

 lock, and reduces the disturbance in the 

 chamber when the latter is being filled 

 or emptied. ( See diagram, page 202, and 

 illustrations, pages 206-207.) 



The middle or separating wall con- 

 tains a single culvert of the same area 

 as the culverts in the side walls, which 

 feeds in both directions through laterals 

 controlled by valves designed to operate 

 against a head from either direction. 

 This arrangement permits communica- 

 tion between the chambers of twin locks, 

 so that water may be passed from one 

 lock to the other of the pair, effecting a 

 saving of water. The main culverts are 

 controlled by Stoney valves, and the lat- 



