Photo of the Week

I have seen this picture off and on in different books or postcards and never really paid attention to the significance of what was happening here. This dredge is high and dry, or should I say low and dry. The flooded canal that connects with the Atlantic Ocean can be seen looking north in the distance. This was one very remarkable engineering feat that was just part of the overall engineering marvel called the Panama Canal.

High and Dry Below Sea-Level

One of the most difficult problems at the Gatun locks site was the preparation of a foundation at the lower end of the locks. It was necessary to go 70 feet below sea-level through soft mud to find rock suitable for foundations. The material was so soft that steam shovels could not be supported on it, so it was decided to do the excavation by dredge. A sufficient width of land between the space to be excavated and the canal toward the Atlantic Ocean was left to act as a dam when the excavation was finally completed and unwatered (drained).

A dredge was allowed to cut a narrow channel through this dam into the space where the lock walls were to be built. This dredge dug the entire space to a depth of 40 feet below sea-level, which was the limit. A dam was then placed across the narrow entrance cut, with the result that the dredge lowered itself as it continued its work. When it had lowered itself to 30 feet below sea-level, it could excavate to the required depth - 70 feet below sea-level.

After completing the excavation, the dredge pumped all the water out of the excavated space, leaving itself ground 55 feet below the level of the sea, in which position it remained until the lock walls were completed. Water was then let in from the sea: the dredge floated and cut its way out.

Another historical piece of the great American accomplishments in the Panama Canal Zone.