Inlet Control Nomographs
Inlet Control Nomographs
(OP)
I have been looking at the "Headwater Depth For Concrete Pipe Culverts With Inlet Control" Nomograph. Is the headwater distance from the invert of the pipe or the top of the pipe? It appears to me that as long as the headwater elevation is lower than the top of pipe, it would simply be free flowing and there would be no pressure head to factor in. However, if the headwater distance is measured to the invert of the pipe, my thinking is incorrect. Can someone help me to understand this? Thanks.





RE: Inlet Control Nomographs
RE: Inlet Control Nomographs
RE: Inlet Control Nomographs
RE: Inlet Control Nomographs
The FHWA manual HEC-22 is the "bible" for analyzing and designing piped storm drain systems. All the charts and nomographs you would need are there, enabling you to account for bend losses, inlet losses, benching/sumps at junctions, plunging flow, etc.
That said, if you are designing a new SD system, often normal flow can be used to size pipes without considering inlet/junction losses. This is valid for systems of moderate or steep slope and no funky junctions. The way to see if this approach is valid should be to size pipes based on normal flow (Manning's eqn). If the flow in a pipe is subcritical or close to pipe full be careful and analyze more closely; supercritical and less than pipe full should be okay. If all your pipes are 2% or greater you will likely be in the second scenario. Flatter systems, systems with manhole channeling to improve hydraulics, and systems with a downstream tailwater require more scrutiny.
RE: Inlet Control Nomographs
Most every system I design has tailwater and subcritical flow. Our clients demand that we design for full flow and limit the velocities. The ground is flat and difficult (impossible) to use 2% slope.
Using mannings equation with normal depth in a system of pipes can be an tedious, iterative process. While it can be done using a spreadsheet or even by hand, it is probably much easier and quicker to do with the proper software. Even at our lowest EIT billing rate, it is more economical to buy commercial software to do the analysis.