flow throus porous media

sid

please help me with the porous jump boundary condition.I am just starting with this software.I need to get the free surface shape and the shear stress on the surface of the soil(porous) when water flows over it When i give the condition of porous jump i am getting an error which says unbound variable.i have tried to understand the help notes but in vain.Could u please help me out in what exactly i am supposed to put in gambit for the porous layer under zone. The sketch is shown.i will be greatful if u tell me wat the various bcs should be at the interfaces

(inlet)--> water =======================================

porous soil ----------------------------------------

rock bed (non porous) ----------------------------------------