Some years ago I had the opportunity of traveling to Israel. My daughter was participating in a study abroad program in Jerusalem. Israel seemed like a different world in many respects. The culture, the food, the history, the atmosphere – everything was unique, different, and fascinating.
As a real estate attorney, I took particular notice of the construction that we saw. Both modern and ancient construction practices, methods and materials appeared to be different from United States practices in many respects too numerous to describe here. The ancient ability to construct large and complex structures with limited technology, engineering and equipment was remarkable. But one particular engineering feat especially caught my attention.
In approximately 700 A.D., the King of Israel recognized that the city of Jerusalem was vulnerable to attack by the Assyrians, who were a large, influential and powerful neighboring kingdom. One of the major water sources for Jerusalem was located outside the walls of the city. The King of Israel discovered that the elevation of a portion of the city of Jerusalem was lower than the spring. So the King developed an elaborate engineering scheme to bore through nearly 1800 feet of solid limestone rock in order to allow spring water to flow into the city. If the Assyrians laid siege to Jerusalem, then at least the City would have water while it was fighting off the attack.
The ancient engineers and workmen dug from both ends of the tunnel – one from the spring, and one from inside the city. After many months, the workmen met in the middle, over a hundred feet underground. Their work is still visible today, and as a tourist, you can pay a small admission fee and walk through the tunnel, end to end, with the spring waters still flowing past your feet from the spring into the city of Jerusalem.
Here was the engineering feat that caught my attention. As you walk through the tunnel, the slope of the tunnel floor is for the most part gradual, almost imperceptible. The elevation drop between the start and the end of the tunnel is only a very few feet. So without the benefit of modern laser or leveling equipment, how did the workmen properly slope the floor of the tunnel so that it was neither too steep nor too shallow? At the point where the workmen met, the tunnel floor is smooth and nearly flawless. How did the workmen work towards the same point, so that when they met they were both at the same elevation?
The workmen carved an inscription on the wall to celebrate their accomplishment. But they don’t appear to have left any kind of detailed description of their engineering or construction methods.
One potential answer to these two questions is the use of a water level. I’ve been told by civil engineers that the water level is one of the oldest leveling devices known to man, and these same engineers have also told me that water levels were used in building the Egyptian pyramids.
The concept is both simple and elegant. An empty bowl is placed on a stand, and a twenty or thirty foot hose or tube is connected to the bowl. A stick is fastened to the far end of the hose, and the hose runs several feet up the stick. The bowl and the hose are then filled with water. The water will fill the hose to the same level as the water in the bowl due to gravity. As a result, by placing one end of the stick on a spot on the floor, the builders can tell whether that spot is higher, even with, or lower than the bowl, even if that spot is 10, 20 or 30 or more feet from the bowl. By placing marks on the stick, the builders can tell the exact difference in elevation between the bowl and the surrounding areas.
What does this have to do with California? Homes in the San Francisco Bay Area are often built on expansive soils that move up or down. When soils move after the completion of a home, then foundations often move as well, and when foundations move, then floors will often move. By using a water level, engineers can often track the amount of up or down movement in the floor of a modern California home.