I was basically taken from the geology of the riverbed as it goes across and for the placement of the powerhouse and the pin-stocks. It does not go strait across. Then it has a slight bend to the southeast east towards where it ties into the abutment. How the dam lays across the valley floor was based on the geology report from all the exploration that they did before construction. There was a lot of drilling checking to see what type of soils were at different levels and based on the results of that and all the other checking, that s how they laid out the center line of the dam.
Earth dams stay in place because of mass.
It depends on the amount of dirt that is placed down, how it is compacted and the types of soils that are used. 24ft in diameter. Also some of the earth moving equipment, the steam shovels and trucks, were built specially for this project and were the largest of their kind in the world at that time. The original authorized purpose for the project were flood control, hydropower, irrigation and navigation. Since then some items have come up.