I assume you considered Gradually Varied Flow (GVF) and close to uniform condition as this question does not have a general closed form answer in RVF.

S_0: Is the bed stream slope, comes from longitudinal geometry

S_f: is the friction slope, it depends on roughness of the channel, surface wind, viscosity of fluid, turbulence ... it is a general measure of how strong are the forces which want to hinder the flow in your channel

Hi

I suggest you read this file ''http://www.ce.utexas.edu/prof/maidment/CE365KSpr14/Visual/OpenChannels.pdf''

Hello

Please help me with your teachers.

Thanks