The locks are situated against the high hills at the east side of the valley, after which comes the east wing of the dam, then the spillway, then the west wing of the dam, which terminates on the side of the low mountain that skirts the western side of the valley. With the hills bordering the valley and the dam across it, the engineers have been able to inclose a gigantic reservoir which has a superficial surface of 164 square miles. It is irregular in shape and might remind one of a pressed chrysanthemum, the flower representing the lake and the stem Culebra Cut. The surface of the water in this lake is normally 85 feet higher than the surface of the water seaward from Gatun and Miraflores. The lake is entirely fresh water supplied by the Chagres River. The accompanying figure shows the profile of the canal.
A PROFILE SECTION OF THE CANAL
The Chagres River approaches the canal at approximately right angles at Gamboa, some 21 miles above Gatun. The lake will be so large that the river currents will all be absorbed, the water backing far up into the Chagres, the river depositing its silt before it reaches the canal proper.
With the currents thus checked, the Chagres will lose all power to interfere with the navigation of the canal, although upon the bosom of its water will travel for a distance of 35 miles all the ships that pass through the big waterway from Gatun to Miraflores. This fresh water will serve a useful purpose besides carrying ships over the backbone of the continent. Barnacles lose their clinging power in fresh water, and when a ship passes up through the locks from sea level to lake level and from salt water to fresh, the barnacles that have clung to the sides and bottom of the vessel through many a thousand mile of "sky-hooting through the brine" will have their grip broken and they will drop off helplessly and fall to the bed of the lake, which, in the course of years, will become barnacle-paved. How many times in dry-dock this will save can only be surmised, but the ship that goes through the canal regularly will not have much bother with barnacles.
The engineer who worked out the details of the engineering examination of the dam in 1908 was Caleb M. Saville, who had had experience on some of the greatest dams in the world. In the first place, the whole foundation was honeycombed with test borings, and several shafts were sunk so that the engineers could go down and see for themselves exactly what was the nature of the material below. There are some problems in engineering where a decision is so close between safety and danger that none but an engineer can decide them. But Gatun Dam could speak for itself and in the layman's tongue.
After investigating the site and getting such conclusive evidence that the proverbial wayfaring man might understand it the engineers next conducted a series of experiments to determine whether or not the material of which they proposed to build the dam would be watertight. They wanted to make sure whether enough water would seep through to carry any of the dam material along with it. The maximum normal depth of the water is 85 feet. The material it would have to seep through is nearly a half mile thick. In order to determine how the water would behave they took some 3 feet of the material and put it in a strong iron cylinder with water above it and subjected it to a pressure equivalent to a head of 185 feet of water. Only an occasional drop came through. If only an occasional drop of clear water gets through 3 feet of material under a pressure of 185 feet of water, it does not require a great engineer to determine that there will not be any seepage through more than a thousand feet of the same material under a head of only 85 feet.
And that is only a sample of their seeking after the truth. When they had gone thus far it was then decided to build a little dam a few yards long identical in cross section with Gatun Dam. It was built on the scale of an inch to the foot, by the identical processes with which it was intended to build the big dam. The result only added confirmation to the other experiments. With a proportionate head of water against it, it behaved exactly as they had concluded the big dam would when completed. Every engineer who has read Saville's report pronounces it a masterpiece of engineering investigation. It proved conclusively that the site of the dam is stable, and the dam itself impervious to seepage. The engineers who visited the Isthmus at the time with President-elect Taft unanimously agreed that those investigations removed every trace of doubt.