PUZZLE IN PANAMA — BOWMAN 



421 



the tide at a particular time in the cycle requires. Water levels in 

 the canal during the tests are measured by automatic recorders, and 

 velocities by pygmy current meters or by time-exposure pictures of 

 floating confetti. 



FLOOD CONTROL 



One of the requirements of a sea-level canal will be complete ex- 

 clusion of entering streams. It would be expected that flood flows 

 would have to be kept out, but recent tests indicate that even smaller 

 flows, which could otherwise be carried by the canal, create objection- 

 able currents. Salt and fresh water do not mix quietly. 



.Observed natural 

 tide at Balboa 



6.2 12.4 



Time in Hours 

 FiGiTBE 6. — How tide-control structures would be operated at various stages of 

 tide cycle. Between B and C How would be out of canal through water-control 

 gates, and between E and F the tlow would be into the canal. During these 

 periods ships could use the pass. 



Were the Panama Canal to be converted to sea level, such im- 

 portant rivers as the Chagres and the Gatun from the east and the 

 Trinidad and Cano Quebrado from the west would have to be blocked 

 and the water carried to the sea through diversion channels. A dam 

 would no doubt h^ required at Gamboa on the Chagres to impound 

 the excess run-off of that stream, which is not now held by the existing 

 Madden Dam farther upstream. But it would probably not have to 

 be as high (in view of the supplementary effect of Madden) as the 

 one proposed for the same location in some of the original canal plans 

 and which then caused so much discussion with respect to foundations 



