  We numerically demonstrate a practical means of systematically controlling
topological transport on the surface of a three dimensional topological
insulator, by introducing strong disorder in a layer of depth $d$ extending
inward from the surface of the topological insulator. The dependence on $d$ of
the density of states, conductance, scattering time, scattering length,
diffusion constant, and mean Fermi velocity are investigated. The proposed
control via disorder depth $d$ requires that the disorder strength be near the
large value which is necessary to drive the TI into the non-topological phase.
If $d$ is patterned using masks, gates, ion implantation, etc., then integrated
circuits may be fabricated. This technique will be useful for experiments and
for device engineering.
