The Collaborative International Dictionary of English v.0.48:

Aggrade \Ag*grade"\, v. t. [imp. & p. p. Aggraded; p. pr. &
   vb. n. Aggrading.] (Phys. Geog.)
   To bring, or tend to bring, to a uniform grade, or slope, by
   addition of material; as, streams aggrade their beds by
   depositing sediment.
   [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

aggrade
    v 1: build up to a level by depositing sediment [ant: degrade]