base level

A base level is the level of earth that cannot be eroded.

References - base level

See the following for additional base level information:

Construction Site Work, Site Utilities and Substructures Databook McGraw-Hill Professional; 1 edition, May 2001, Sidney M. Levy, ISBN 71360212
Excavation and Grading Handbook Craftsman Book Company; Rev Sub edition , November 2005, Nick Capachi, ISBN 934041296
Carpentry & Building Construction, Student Text Sterling, January 2008, Marianne Cusato, Ben Pentreath, Richard Sammons, Leon Krier, ISBN 1402736282
Carpentry Glencoe/McGraw-Hill; 6 edition, January 2003, Mark Feirer, John Feirer, ISBN 007822702X
Green Building Products, 3rd Edition: The GreenSpec Guide to Residential Building Materials-3rd Edition ICC (distributed by Cengage Learning); 1 edition, October 2009, International Code Council, ISBN 1435400631