A tunnel in which an independent pipe is installed should be lined with concrete, even if the rock is competent enough to stand unsupported. Because such a tunnel houses the pressure pipe and provides access to an upstream gate, the lining is needed to protect the pipe and operating personnel against rockfall.

The dam is usually built across a river or other waterway to create a reservoir or impoundment behind it, which can be used to regulate water flow, generate electricity, provide water for irrigation, and/or supply water for human consumption.