THE DROWNING TREES IN GAT U X LAKE 



When this picture was taken there was only S 2l A feet of water in Gatun Lake, but when the 

 lake is full these trees will be entirely submerged 



the Chagres through its own channel and 

 through the old French canal, thus forc- 

 ing all the water through the west diver- 

 sion channel. 



This enabled the work of building the 

 east half of the dam to be started while a 

 channel was being dug through the Spill- 

 way Hill. As soon as this latter chan- 

 nel was finished the Chagres River was 

 turned into it by damming the west diver- 

 sion channel. 



The bed of the west diversion channel 

 being below sea-level, with soft banks 

 and bottom, and the bottom of the Spill- 

 way channel being 10 feet above sea- 

 level, this last diversion of the Chagres 

 proved to be a troublesome undertaking. 

 As soon as this last diversion was accom- 

 plished work on the west half of the dam 

 was commenced. 



The watertightness of the Gatun Dam 

 was never a subject of serious apprehen- 

 sion. The material under it and that in 



the center of it are practically imperme- 

 able. The great problem concerning the 

 Gatun Dam has been to make the mate- 

 rial on which it was built carry the load. 



I referred to the rock being 200 feet 

 below sea-level on one side of Spillway 

 Hill and 260 feet on the other. These 

 old gorges, so the geologists say, were 

 made by the Chagres River when all the 

 country in the vicinity of Gatun was 

 about 300 feet higher than it is now. 

 When the site of the Gatun Dam was 

 lowered 300 feet during some early vol- 

 canic disturbance and its old beds low- 

 ered 200 feet below sea-level, the sea 

 backed up the Chagres Valley and in time 

 filled these old gorges with deposits, 

 largely of clay, which in some places were 

 soft. In order to make such a founda- 

 tion carry a heavy load, an exceedingly 

 broad base was necessary. 



Dams are ordinarily built with quite 

 steep slopes, one in two, or one in three, 



175 



