Working around dams and powerhouses associated with dams. Providing passage underground for various other reasons. Bureau engineers maintain a database of water conveyance tunnels. The database also contains information on some other tunnels. Tunnel construction begins by excavating the ground.
Miners install initial supports to hold the tunnel open until final supports can be installed.
Sometimes these are the same supports . Bill Thompson, for information on tunnels or these tunnel Web pages. Lowell Pimley, for information on water conveyance systems.