The Collaborative International Dictionary of English v.0.48:

Welldrain \Well"drain`\, v. t. [imp. & p. p. Welldrained; p.
   pr. & vb. n. Well-draining.]
   To drain, as land; by means of wells, or pits, which receive
   the water, and from which it is discharged by machinery.
   [1913 Webster]