  The anisotropic model for landscapes erosion proposed by Pastor-Satorras and
Rothman in [R. Pastor-Satorras and D. H. Rothman, Phys. Rev. Lett. 80, 4349
(1998)] is believed to capture the physics of erosion at intermediate length
scale ($\lesssim3$ km), and to account for the large value of the roughness
exponent $\alpha$ observed in real data at this scale. Our study of this model
-- conducted using the nonperturbative renormalization group (NPRG) --
concludes on the nonuniversality of this exponent because of the existence of a
line of fixed points. Thus the roughness exponent depends (weakly) on the
details of the soil and the erosion mechanisms. We conjecture that this
feature, while preserving the generic scaling observed in real data, could
explain the wide spectrum of values of $\alpha$ measured for natural
landscapes.
