What are the parts of an arch dam?
  The Bureau of Reclamation offers excellent photos of the Hoover dam.
  This archive drawing of the Hoover dam will be of interest to those who followed the diagram at left.
  Examples of arch dam construction from the Structurae site.
  Here is a photo of a local arch dam.  It was built as part of the Crystal Springs project that supplies our drinking water.
  This photo offers the best via of the dams's arch shape.  Note the curve of the roadway.
Before we leave arches behind, there is one more common use that you may find interesting.  Start with the diagrams at the left.  The top arch is one unit thick and it can resist a certain maximum force along its length.  The middle arch is two units thick and can support more load.  The bottom arch is three units thick and so can support the most load of the three.

Of course, my diagram at right gives away the surprise.  If arches of increasing thickness are properly stacked, they can be used to create a dam.