I have calculated surface runoff volume over the catchment (2000 Km2) under antecedent moisture condition –III (AMC-III). In this procedure I have used appropriate prerequisite input data by SCS-CN model such as Soil type, 7-day daily point rainfall extrapolated using Thiessen polygon and land use/cover in GIS environment. I have calculated total volume daily basis and 7-days cumulative over the catchment. I have also observed daily discharge recorded at catchment outlet, now please tell me how modeled volume can be relate with the observed daily discharge or other way to validate it.