I have a fully 2D hec-ras model in which I have an upstream boundary condition (flow hydrograph) and downstream boundary (normal depth).
What happens is that after getting the results I measure the flow just after the upstream boundary condition line (across the entire valley to capture all flow) and the measured flow is 30% less than the discharge that I put in the upstream boundary condition.
It seems that some flow is getting lost somewhere. Have you ever had this situation? What could explain this?