Reach question

[hogfan]

Ok, since I can't model a reach as a reach (due to tailwater issues) and must model it as a pond, I have a question.
When describing this channel as a "culvert" what do I use as my entrance loss coefficient since my entrance is nothing more than a channel opening?

Thanks,

 

[psmart]

As you're aware, a reach routing is recommended only for normal open-channel flow. This assumes normal Manning's flow, and cannot handle tailwater effects. See

http://www.hydrocad.net/reach.htm

for details.

If there is ponding at the reach inlet, then we recommend using a pond with a culvert outlet. This will model the ponding effect at the inlet, using the culvert as an outlet control.

If you have a smooth channel-to-pipe transition, this will have a relatively low entrance loss coefficient, like a well-rounded inlet. But if you have a protruding pipe end, the value will be higher. The choice of coefficient is really the same as for a "real" pond.



Peter Smart
HydroCAD Software

http://www.hydrocad.net