Hello. Thank you for the video. I have a question though. My question is, because Manning's equation is for uniform flow, why are we allowed to use it to find the slope of the energy grade line at a specified cross section in the channel since we are dealing wiht gradually varied flow which is non-uniform? Also, if we are allowed to use the Manning's equation to find the slope of the energy grade line at a certain cross section, does that entail that the flow and depth at that cross section is the normal flow and normal depth corresponding to that EGL slope?
If the conditions are non-uniform then we use Manning's equation to find the slope of the energy grade line only at a single POINT, rather than for a longer reach of some distance. By breaking the gradually varied flow section into multiple segments, we can approximate the shape of each curve as a line. The Direct Step Method treats a curve as multiple straight line segments; it isn't perfect, but the approximation is typically 'good enough' if you break the section up into several sections.
Thank you very much , Isaac. Your class is very useful. I am a Master degree student in Hong Kong. May I have your e-mail to ask further questions about fluid related topics? e.g. well point dewatering . Just academic questions not related other stuff. Thank you very much for your help.
