Critical conditions for rill flow erosion on hillslopes are investigated using numerical simulation and laboratory data for large variation in slope gradients. Several factors have been considered in this study

i.e.

slope length

gradient

projected length on a horizontal plane

etc. Shear velocity is used as the parameter for establishing a critical condition

and two cases have been considered

i.e.

(1) the critical shear velocity may change with slope gradient

or (2) it may not change. For given plot size

net rainfall intensity and original topography

the minimum slope gradient has been found out at which shear velocity of rill flow can achieve the critical value.