416 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1947 



quired if locks wider than the 140 feet originally planned were deemed 

 necessary. Should the third locks idea be abandoned, this plan thus 

 provides an effective way to save a large part of the investment already 

 made in that project. 



Two variations of the conversion locks have been studied, one using 

 a single-lane lock, the other a double lane. Since two lanes for traffic 

 must be maintained during all lake-lowering stages, adoption of the 

 single-lane conversion lock would require also that first one lane and 

 then the other of the existing locks be modified to operate at the lower 

 lake stages. This would entail a construction operation of consider- 

 able magnitude and difficulty, since the center wall between the existing 

 locks would have to be underpinned during the time that the upper 

 chamber of one lane was being removed so that this lane could be 

 available for traffic when the lake was lowered to elevation 50. Later, 

 when the other lane was cut down from elevation 85 to elevation 20 to 

 serve traffic at this lake level, the same ticklish operation would have 

 to be repeated. As a corollary of the construction difficulties of this 

 method there would be considerable risk, for a failure of the center 

 wall might result in draining the lake. 



The two-lane conversion plan is both simpler and more certain, for it 

 would permit complete abandonment of the existing locks during the 

 lowering stages. The idea would be to make the conversion lock of 

 one-lift design, capable of being used at all stages from elevation 50 to 

 sea level. While the lock at the Atlantic end, for example, was being 

 built in the third locks cut, seaward from the unexcavated plug that 

 separates the cut from the lake, the deepening of the channel in the 

 lake would be carried out. This would entail dredging to a maximum 

 depth of about 85 feet (present water surface, elevation 85, minus 

 future water surface, elevation 50, equals 35, plus a 50-foot channel 

 equals 85 feet). Such a depth is well within the capabilities of con- 

 temporary dredging equipment. 



Once the channel was deepened, the plug ahead of the conversion 

 lock would be blown out, and the lake water surface rapidly lowered to 

 elevation 50. Then, with the two-lane conversion lock in constant 

 service, the channel could be deepened as the water surface was progres- 

 sively lowered until the bottom of the excavation reached project grade 

 of 50 feet below sea level (and increasing to 60 feet at the Pacific end 

 because of the greater tide variation there) . 



At the Pacific end the conversion plan would be only slightly differ- 

 ent. The single-lift conversion lock would be built in the third locks 

 cut at Miraflores. When it went into service, as the Gatum Lake water 

 level was dropped to elevation 50, Pedro Miguel lock, which operates 

 between elevation 85 and elevation 50, would be high and dry. Since 

 the third locks cut at this location was hardly more than begun before 

 that project was shut down, a bypass around the existing lock would 



