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# Culvert Modeling in HY-8

## Culvert Modeling in HY-8

(OP)
Good evening, I have three questions regarding culvert modeling in HY-8. I am relatively new to using this software and am unsure if what I am looking to do is possible. I apologize for my naivety in advance.

1. What is the best way to model a culvert system that has two different barrel sizes connected in series with a 49-degree bend? The culvert system I am working with spans a highway with two 8'x8' barrels on the upstream end that tie into two 10'x8' barrels on the downstream end. The change in barrel size occurs under a grassed median that separates the traffic flow direction. Would I model the two 10'x8' barrels for the design flow first and assign the headwater depth as the tailwater depth for the two 8'x8' barrels? Is it possible to link these sections in series?

2. If the only or best way to model the system described in my first section is to model the two sizes separately, what would be the best way to handle the input for the roadway data (crest length, crest elevation and top width) if the change in barrel size occurs under a location that does not span a roadway?

3. s it possible to model the culvert system in HY-8 with the 49-degree bend mentioned in my first question? If not, how would that condition be handled as an input parameter?

Thank you for in advance for taking the time to read these questions and I appreciate the information, responses and recommendations that anyone will be able to provide.

### RE: Culvert Modeling in HY-8

I do not believe that this system (with different sizes in series) can be modelled in HY-8. You can model a "broken back" culvert. Since you have differing sizes in series, I recommend using a storm drain system like STORMCAD, INROADS STORM & SANITARY or other; including spreadsheet analyses.

### RE: Culvert Modeling in HY-8

If I understand the issue, you have two culverts connected in series with varying sizes. Is the 45 degrees bend horizontally or vertical drop? If vertical, then consider using Broken Back culvert option in HY-8. The Broken-back feature can be selected from the drop down menu "Culvert Type", but the barrel diameter has be be uniform throughout the length of the culvert.

### RE: Culvert Modeling in HY-8

If it were straight, I'd say HY-8 might suffice if it were inlet-controlled. Otherwise, you'll need a more advanced tool as mentioned above.

My glass has a v/c ratio of 0.5

Maybe the tyranny of Murphy is the penalty for hubris. - http://xkcd.com/319/

### RE: Culvert Modeling in HY-8

(OP)
Thank you for everyone's responses, they are what I was expecting. The HY-8 software is powerful but limited and I am using Hydrology Studio's Culvert Studio suite to model this system. The 49-degree bend is a horizontal bend with the two 8'x8' barrels on the upstream end and the two 8'x10' barrels on the downstream end with a slight change in slope (single broken-back in HY-8).

I appreciate everyone's help, and be sure to have a great afternoon and weekend.

### RE: Culvert Modeling in HY-8

Scott - If the box culvert cells are not full, you can use HECRAS to model as open channel flow through the box. If under pressure, there are specific headloss equations for angle point bends. The one I use for "kinked" or angle pointed bends is Hb=KbHv, KbA = ((1-((90-A^)/90)^2)Kb90; Kb90= 1.25 to 1.50; if you have radius bend then default to HEC-22. Hope this helps.

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