Street Drainage Flume Entrance Loss

[655321]

I'm trying to determine the capacity of a concrete drainage flume at the end of a reverse-draining cul-de-sac. (A cul-de-sac that drains to the back.)

I've calculated its capacity as an open channel, but I don't think that adequately represents the situation since I'd expect losses at the entrance. I've also looking at as weir, but that result seems unrealistically low. I don’t want to be overly conservative on this one.

Any ideas how to model this?

Attached is a picture. Thanks.

 

[jgailla]

I would model this as an open channel and check it for weir flow. For the size and length of the channel in the picture, I think that an accurate estimate of the HGL due to headwater and tailwater conditions would be more important than the losses at the entrance.
It looks like the entrance is at street level. If this is the case, the weir flow would control until the channel filled up.

 

[gbam]

You said that you checked the capacity, I assume you used normal depth. What regime is the flow in, sub or super? This will dictate on whether the control is at the inlet or outlet, provided there are no tailwater controls. Make sure you use an appropriate entrance loss coefficient. It appears that there will be significant contraction as well. It may be over kill but you can set up a quick RAS model.