Water is a prime natural resource, a basic human need and precious natural asset. Surface runoff is the major source for all the major source for all the surface water bodies such as tanks and reservoirs. The dependable assessment of runoff is scarcely available in few selected locations. In the present study, Soil Conservation Service Curve Number (SCS-CN) method has been applied to assess the runoff for Nambiyar sub-watershed of Thamiravaruni River Basin, Tirunelveli District, Tamil Nadu.