Nickoli,
Friction Slope is that slope (S) in Manning's formula required to convey a specified discharge under uniform flow conditions given a depth, roughness, and shape. Under uniform flow, depth and flow area are constant and the friction slope, the actual slope, and the energy slope are all equal.
You may feel free to email me your details and I will look closer at your assumption. mike.barkasi@bentley.com
Michael Barkasi
Benttley Civil
Professional Services
Application Engineer
Reality Modeling