PUZZLE IN PANAMA — BOWMAN 419 



A great deal of design effort and model study has been expended 

 on the subject of tide control, since the large difference in tide ranges — 

 20 feet maximum on the Pacific side and only 2 feet on the Atlantic — 

 would be expected to generate a considerable current. Actually the 

 maximum velocity has been shown on the sea-level model to be only 

 4.2 knots, and interestingly enough this occurs at the Atlantic end and 

 farthest removed from the high Pacific tides that create it. Never- 

 theless, this is considered excessive for ordinary merchant-ship opera- 

 tion in a canal much of whose bottom and banks would be rock, as con- 

 trasted with the sand in the Cape Cod Canal where such a velocity 

 occurs, and means are being sought to reduce it. 



One method, and the one proposed in the majority report on the 

 original canal in 1904, is to use a barrier dam and locks. But since 

 it would take time to lock every ship entering or leaving the canal, 

 even though the average lift would be only about 6 feet and the maxi- 

 mum 10 feet, the present investigators have been studying a "navigable 

 pass" arrangement similar to those used on the Ohio River by which 

 ships could pass between canal and ocean at certain tide stages without 

 using the locks. Not only would this speed canal operation, but the 

 navigation-pass lay-out would provide maximum security from bomb- 

 ing since, if hit, the closure dam could be quickly dragged out of the 

 way. Then the canal could be used without tidal regulation, which is 

 deemed practicable in an emergency. 



An opening could of course be cleared through a barrier dam and 

 lock, if they should be bombed, but it would be a time-consuming 

 operation. Moreover, it is believed to be the present thinking of the 

 investigators that use of the navigable pass would so familiarize the 

 pilots with open-water operation of the canal that they would be 

 ready for any emergency, whereas the lock-and-dam plan would not 

 permit this advance training. 



ELEMENTS OF NAVIGABLE-PASS PLAN 



The proposed navigation-pass lay-out would include three ele- 

 ments — the pass equipped with a movable dam, a set of locks, and a 

 gated water-control structure. Just how these would be arranged 

 would depend upon the location chosen for the tidal-control works. 

 One of the arrangements tested on the sea-level model places the tide 

 lock, equipped with sector-type gates, in the third locks cut at Mira- 

 flores ; the navigation pass, with a 750-f oot-wide opening, in the ap- 

 proach to the present canal; and the water-control structure, of 

 whatever width necessary, beside it. An interesting aspect of this 

 arrangement is that the tidal lock could temporarily be increased in 

 height and used as the conversion lock should the stage-lowering plan 

 of canal conversion be adopted. 



