The components of the vector Fp are available as variables in the Shallow Water Equations, Time Explicit physics interface and can be accessed in 2D using swe.Fpx and swe.Fpy. In 1D only the swe.Fpx component is defined. Note that these variables represent a force per unit length; the total force on a boundary is obtained integrating over the whole boundary.
The Dam Breaking on a Column, Shallow Water Equations Application Library model is an example of how to use these variables. Application Library path CFD_Module/Shallow_Water_Equations/dam_break_column_sw