Somadeva served as an Assistant Director of the Sigiriya - UNESCO - Sri Lanka Cultural Triangle Project from 1989 to 1994.

He contributed his service as a member of the advisory committee to the Director General of Archaeology in Sri Lanka and to the Department of National Archives.

During that period he undertook several macro-scale reconnaissance surveys and nine archaeological excavations in the Lower Kirindi Oya basin.

The results of the fieldwork were presented to his doctoral degree at Uppsala University as his thesis, The Origins of Urbanism in Southern Sri Lanka.

Somadeva was able to explain how the late Holocene hunter-gatherers were resilient to climate change and how they adapted to floral resource exploitation for their survival.

[10] In 1998 he won the top ten in Sri Lanka Award for the category of Academic Leadership and Accomplishment.