Mole drains are unlined tunnels (mole channels) in the clay subsoil formed by a mole plow. A mole plow is composed of a shank (leg) attached to a cylindrical bullet followed by a cylindrical expander. The expander strengthens the channel by compacting the wall. The process of pulling the mole plow results in soil cracks. The effectiveness of mole drains depends on the amount of soil cracks that facilitate water movement toward the mole channel.