pass roughness to SWAN?

[nganju]

Right now ROMS does not pass bed roughness to SWAN. In a case with changing ripple dimensions, the roughness field should be passed to SWAN to adequately represent the effect of bed friction on the wave field. This seems straightforward, except a calculation would need to be done internally to convert zo into a madsen kN. Also, it appears that zo is calculated at each location individually (as opposed to zo(i,j)) within the bbl routines, so I don't know if the roughness field can be passed as-is.