Tunnel 3 : A long underground excavation with two or more openings to the surface, usually having a uniform cross section used for access, conveying flows, etc
National Dam Safety Program, U.S. Department of Homeland Security Federal Emergency Management Agency Interagency Committee on Dam Safety, Federal Guidelines For Dam Safety: Glossary of Terms For Dam Safety (FEMA-148), Washington DC, USA 2004. http://www.damsafety.org/media/Documents/PDF/fema- 148.pdf, (Dam Sfty - Amer) {890}