The term 'hydraulic radius' is used in open channel flow. It is defined as:

A$)$ The cross$-$sectional area of flow divided by the wetted perimeter

B$)$ The cross$-$sectional area of flow divided by the hydraulic depth

C$)$ The wetted perimeter divided by the cross$-$sectional area of flow

D$)$ The wetted perimeter divided by the hydraulic depth