We present a simple model to describe the lowest-subbands surface scattering in locally oxidized silicon nanowires grown in the [110] direction. To this end, we employ an atomistically scaled effective mass model projected from a three-dimensional effective mass equation and apply a quantum transport formalism to calculate the conductance for typical potential profiles. Comparison of our results with hole-transport calculations using atomistic models in conjunction with density functional theory (DFT) points to an intra-subband scattering mechanism from a potential well.