SIMPLE Scheme for open channel flow

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Could anybody help me with applying the SIMPLE scheme to shallow water eqs in which the pressure and depth is implicit coupled? Do I have to transfer the depth to pressure before every iteration and after solving pressure-correction eqs, tranfer it back to depth? Then how to deal with the boundary conditions? When I give known depth at inlet, how about pressure and pressure correction in the interation computation? thanks a lot for any advice!