The Collaborative International Dictionary of English v.0.48:

Submergence \Sub*mer"gence\, n. [From L. submergens, p. pr.]
   The act of submerging, or the state of being submerged;
   submersion.
   [1913 Webster]

WordNet (r) 3.0 (2006):

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

Moby Thesaurus II by Grady Ward, 1.0:

49 Moby Thesaurus words for "submergence":
   baptism, breaking water, burial, cadence, catenary, concavity,
   crash dive, de-escalation, debasement, decline, decurrence,
   degradation, demotion, depression, descent, detrusion, diminution,
   dip, dipping, displacement, dive, dousing, draft, droop, duck,
   ducking, dunking, engulfment, hauling down, hollowness, immergence,
   immersion, inundation, lapse, lowering, reduction, running dive,
   sag, sinkage, sinking, slump, souse, sousing, stationary dive,
   submersion, subsidence, surfacing, swag, thrusting under