Question about inlet design using HEC-22 1

[ernesto561]

Hello everybody. I'm designing some inlets using the procedures in HEC-22. I'm using the FHWA Hydraulic Toolbox. In some inlets, this message is shown: "The approach velocitiy is greater than the splash-over velocity. Please consider a longer grate or a different configuration." I've checked the HEC-22 and they say that if this happens the frontal interception capacity is reduced. (Pag 4-41). The bypass flow will be added to the next inlet, so this inlet doesn't need to intercept all the flow. My question is, do I need to change the inlet dimensions to reduce the approach velocity? Or can I use these results with the approach velocity greater than the splash-over velocity? Thanks for your help.

 

[TerryScan]

It is a matter of economics and efficiency. By the time one has splash-over, there is probably already considerable bypass flow due side flow. One will be "playing catch-up" at the next inlet.

Without redesigning the roadway, there is no way to "reduce the approach velocity" other than reducing the flow (reduced inlet spacing.)

The "different configuration" that would make sense might be: a different grate (better splashover characteristics), a longer grate, or reducing the spacing between inlets. The message seems to be more of a warning than an error.

 

[ernesto561]

Thanks a lot for your reply. I had to ask, everything seems ok. My problem is that I cannot change the inlet spacing, nor the inlet type, it is a long story. I think that the message seems to be a warning, as you pointed out. But it's kind of weird that in some inlets the efficiency is about 98% although the approach velocity is greater than the splash-over velocity. I'm attaching a print screen. It's just a thought, I think there is no problem. Thanks again.