The Collaborative International Dictionary of English v.0.48:

Submerge \Sub*merge"\, v. t. [imp. & p. p. Submerged; p. pr. &
   vb. n. Submerging.] [L. submergere, submersum; sub under +
   mergere to plunge: cf. F. submerger. See Merge.]
   1. To put under water; to plunge.
      [1913 Webster]

   2. To cover or overflow with water; to inundate; to flood; to
      drown.
      [1913 Webster]

            I would thou didst,
            So half my Egypt were submerged.      --Shak.
      [1913 Webster]

WordNet (r) 3.0 (2006):

submerging
    n 1: sinking until covered completely with water [syn:
         submergence, submerging, submersion, immersion]

Moby Thesaurus II by Grady Ward, 1.0:

28 Moby Thesaurus words for "submerging":
   collapsing, deciduous, declining, declivitous, decurrent,
   descendant, descending, down, down-reaching, downcoming,
   downfalling, downgoing, downhill, downsinking, downward, drooping,
   dropping, falling, on the descendant, on the downgrade, plummeting,
   plunging, sagging, setting, sinking, subsiding, tottering,
   tumbledown