Derivation of a fractional Boussinesq equation for modelling unconfined groundwater B. Mehdinejadiani, H. Jafari and D. Baleanu Eur. Phys. J. Special Topics, 222 8 (2013) 1805-1812 Published online: 07 October 2013 DOI: 10.1140/epjst/e2013-01965-1