Ward, A.; Trimble, S. (2004). Environmental Hydrology. Boca Raton: CRC Press. p. 122. ISBN 1566706165. 1566706165
Ward, A.; Trimble, S. (2004). Environmental Hydrology. Boca Raton: CRC Press. p. 122. ISBN 1566706165. 1566706165
Fetter, C. (2001). Applied Hydrogeology. New Jersey: Prentice-Hall. p. 41. ISBN 0130882399. 0130882399
Ward, A.; Trimble, S. (2004). Environmental Hydrology. Boca Raton: CRC Press. p. 122. ISBN 1566706165. 1566706165
Ward, A.; Trimble, S. (2004). Environmental Hydrology. Boca Raton: CRC Press. p. 122. ISBN 1566706165. 1566706165