DFB (Divergence Form for Bed slope source term) was rigorously derived and the error of mDFB using mean water depth at the cell
face in DFB was clearly demonstrated. In addition, DFB technique turned out to be an exact method to the bed slope source term. The
existing volume/free-surface relationship to the PSC (Partially Submerged Cell) has been corrected. It was discussed that treatment for
the partially submerged edge is required to satisfy the C-property in PSC. It is expected that this study will provides a more accurate
means in analyzing the shallow water equations with the approximate Riemann solver.