100 yr flood in HEC_RAS

[sujanshakya]

I am running HEC_RAS for the proposed culvert.The 100 yr flow seems to jump up at the culvert. Is this because of the ineffective flow area that I set.

 

[chicopee]

"seems to jump up" do you mean flow is over the top of the culvert?

 

[sujanshakya]

yes,overtops the culvert. and also,do I have to consider T6 rail in my model. I think, it has only a minimal effect on 100 year discharge.

 

[saruman26]

Sounds like a hydraulic jump, which isn't uncommon. If the model is set correctly, this probably means that there isn't enough capacity to convey the 100-year storm event.

As for including the rail, I don't know, but if the goal is to prevent overtopping, use the lowest elevation part to which point some flooding is tolerable.

 

[sujanshakya]

The Hec_Ras output showed a critical WSE upstream of bridge for 2 and 5 yr frequency, Froude#1.01, what could be the reason? The stream bed seems little steep U/S to bridge.

 

[sujanshakya]

And also there was about 1ft of scour hole at U/S of bridge.

 

[prabhashjoshi]

i am running Hec-Ras model and i have to skew a bride about 15 degree but as i skew the bride water goes up is there negetive skew in hec ras program anybody help please

 

[RWF7437]

prabashjoshi,

Start a new thread.

 

[sujanshakya]

Prabhash, I don't think there is -ve skew. Why don't you tweak little bit the 'n' valves U/S and D/S of bridge to lower the WSE.as, you can have concrete riprap at the bridge... And also, check your U/S and D/S cross section distance.

 

[sujanshakya]

The Hec_Ras output showed a critical WSE D/S of existing bridge for 100 yr frequency, Froude#1.0, what could be the reason? The WSE profile showed sharp fall down from D/S bridge face. Is it a glitch on Hec_Ras program .

 

[prabhashjoshi]

sujancha, check your boundary condition may be the slope is too high.This may help you.

 

[civeng00]

hec ras program goes off as i try to skew my culvert.

 

[sknight701]

civeng00,

You may need to download and reinstall RAS. Save the geometry, plan, and other files somewhere safe before you reload the program.

 

[sujanshakya]

skew the bridge first and then set ineffective area OR set ineffective area then skew the bridge. which one to perform first!!

 

[sknight701]

sujancha,

I always set the ineffective flow areas first and then skew the bridge and the cross sections afterward. This takes the ineffective flow areas into account when skewing the cross sections. Just remember that you have to tell it to skew the cross sections as well as the bridge.

 

[civeng00]

In the Hec-Ras i interpolation cross section on every 100' but when i generate my report it shows me more than 2000 pages, how can i get rid of those interpolated sections (in report generation)??Thanks.

 

[sknight701]

civeng00,

When you generate the report, you can tell RAS not to include geometric data. It's either no geometric data, or all of it.

 

[sujanshakya]

When I skew the bridge/culvert and cross section, the ineffective area I set (before skewing), falls on the channel. It appeared that I set the ineffective area inside the channel containing flow. Do I have to adjust the ineffective area again after skewing or leave it as it is. I think, I should not skew again just to make the schematic look normal? Am I correct. Because, adjusting ineffective area again, leads to jumping of WSE above the bridge U/S on the schematic.
Any idea, please.

 

[sknight701]

sujancha,

Why was your ineffective area in the channel? If the channel is actively flowing, then it cannot be ineffective. Sounds like you need to un-skew your culvert and bounding cross sections, set new ineffective area boundaries, and skew the culvert and cross sections again. And don't worry about what the WSE does until after you get the geometry modeled correctly. The culvert may be causing an increase in WSE, which would indicate it may be too small.