Upstream Distance & Culvert Length

[Jmill]

I've just updated My RMS 2000 with the latest update so I can run it inside AutoCAD 2002. After some clean up of the dwg's configuration settings I went to "generate data and run analysis" in the Hec-Ras module. The first error I got was to specify the "bridge rail to section distance" in the "input > openings > weir flow parameters" dialogue. I set this to 0.1'. Then I ran it again and I get the following:

ERROR: The culvert length and upstream distance is greater than the channel length at culvert area 1 of cross-section 25859.

My culvert length is set to 130 and my upstream channel length is 147 and my roadway width is set to 50

I'm having trouble finding where the "upstream distance" is even defined. I searched for it in your manual but there's only one reference to it when defining an inline weir. But I don't have an inline weir... do I? Aren't the roadway weir over a culvert parameters defined under the "weir flow parameters" for the culvert opening? Or do I need to define an inline weir at each culvert?

[Chris Maeder]

Dear JMill:

Note that HEC-RAS 3.01 has now more strict checking of the bridge geometry. Therefore, we have implemented more strict checking of the HEC- RAS input data in RMS and RiverCAD.

If you add the "culvert length" and the "bridge rail to section distance" together, this total length must be less than the "channel flow length" defined at the next upstream cross-section (flow lengths are measured in a downstream direction). Otherwise, you will get an error, as you have reported.

I am fairly certain that if you review these numbers in your model, you will see what I am describing

Sincerely,

Chris E. Maeder, M.S.
Senior Technical Engineer
chris.maeder@bossintl.com

[Support Staff]

You need to have an upstream distance in the new version of HEC-RAS (3.0). The HEC-RAS user manual on the Army Corps of Engineers website at the following link:

http://www.hec.usace.army.mil/public...user/user.html

That should give you an explanation - let me know if you need anything else.

Thanks,
Mary Paist
mpaist@schoordepalma.com

[Support Staff]

The sum of your 1-culvert length and 2-roadway width and 3-bridge rail to section distance cannot be longer than your upstream channel length. Also keep in mind the values you have set for your bridge side slopes and acocunt for them.

[Support Staff]

Chris M.,

There is reason that JMill (and we) were having difficulties with this. In the regular version of RAS, it asks you to enter two different values: BOTH the distance from bridge deck (rail) to upstream section AND distance from culvert inlet to upstream section, with the former typically larger than the latter. The RiverCAD manual and software doesn't appear to tell you that it will use the rail distance also as the culvert approach distance. So for those of us accustomed to the standard windows version of RAS, we put in a value for rail distance in the same manner we typically do, and RiverCAD fails. To us and within regular RAS, it is OK if culvert length and rail-to-section distance exceed reach length.

It is probably OK if RiverCAD applies the same value to both, but it should also probably be more clear in telling us that. Perhaps a parenthetical comment in the weir input for the rail distance that says, to the effect, this value will also be used as the culvert inlet to upstream section distance. The RiverCAD error message tends to be confusing and could also say something to this effect.

Thanks,
Bob Elliot