The distribution of flow between the channel and floodplain must be determined. The portion of the flow in the channel is given by:

1) \phi _j = \displaystyle \frac{Q_{cj}}{Q_{cj} + Q_{fj}}

Fread (1976) assumed that the friction slope is the same for the channel and floodplain, thus the distribution is given by the ratio of conveyance:

2) \phi _j = \displaystyle \frac{K_{cj}}{K_{cj} + K_{fj}}

(2) is used in the HEC-RAS model.