[Robert]

Courant number or Courant condition is used for stability and accuracy of unsteady model. When you define a computation time step for your unsteady model, so your Cr have to smaller than or equal 1.0. I recomnend you look HEC-RAS 5.0 Users Manual, p. 387.

regards
Robert

[Robert]

Hello Giacomo,

Do you solve your problem?
You can send me your model using Hec-RAS- File-Debug report. I will check your bugs during weekend.

have a nice day
Robert

[Robert]

Hello,

If you want to advise, so you should provide more information or you can send your model using Debug report (File-Debug report).

see you!
Robert

[Robert]

Hello,

If you solve your model using 2D, so the better solution is using of dtm with buildings (https://www.google.sk/search?q=dtm+with+buildings&tbm=isch&tbo=u&source=univ&sa=X&ved=0ahUKEwif94qq27LKAhUDCBoKHUyhAv0QsAQIHQ&biw=1600&bih=775#imgrc=zRnzZ5PB8ERc-M%3A)

Mrs. User suggested to use higher n-values. But when you use higher n-values, so your flooding area will be incorret. Using higher n-values (also ineffective areas) are good solution for 1D modelling.

regards
Robert

[Robert]

Hello Kong,

In the case when you solve an unsteady flow in the river (upstream c.: flow hydrograph and downstream c.: normal depth, or rating curve or hydrograph), so the hydrograph (wave, dam break wave) should be transform (Translation and Attenuation wave) in the downstream direction.

But you use a storage area for downstream condition. Terefore I don´t know to reply you without view your model.

I suggest you send me your model (URL location) using Debug Report (Hec-RAS- File – Debug report).

regards
Robert

[Robert]

Hello Katarina,

I think, that the problem can be in the Flow Regime or in the Manning´s values.
1. You could check a Freude number, if these values are around 1, so you have to use a mixed flow regime.
2. The error can be also in the Maninng´s values- roughness parameters. If you defined high values or you have big difference between channel n-value and floodplains n-values in the CS.

Let me know, if my proposal help you.

regards
Robert

[Robert]

Hi Darwin,

Do you need to advise with arrival time, still?

bye
Robert

[Robert]

Hi

I do stabilization your model:
1. Water out of channel
You have to remember, that Hec-RAS is 1D model. Therefore you must define Levees or obstructions blok, when Water out of channel, while banks are above water surface in the channel.

2. Hydraulic Tables CS and Bridge (HTAB Curves)
When EGL (Energy Grade Line) is unstable (increase- decrease) you have to edit parameters of HTAB.
Chris wrote excellent articel for this problem (see url)
http://hecrasmodel.blogspot.sk/2011/03/more-on-htab-parameters.html
http://hecrasmodel.blogspot.sk/2009/02/crazy-energy-grade-line.html
http://hecrasmodel.blogspot.sk/search/label/HTab
… .

You wrote about dam in your contribution, but you haven´t dam in your model, only bridge?!

regards!
Robert

1517_Beinwil.rar

[Robert]

thanks!

[Robert]

Hi Stephanie,

HecRas 5.0 (2D) hasn’t ability to define the obstacles by Obstructions. I hink, the best option is use dtm with buildings.

I think, that increase n-values isn’t well solution, Lonnie. Because you change only properties of flow, but the houses will be flooded.

regards
Robert

[Robert]

Hi Matt

Sorry, I am busy, therefore I write you today.

I was looking your model and your issue is a downstream condition (steady flow, reach boundary conditions).
Why did you choose a Know WS for the downstream condition? You cann´t use one WS for all flow (10,20,50, …)!!! You should use it, when you simulate one flow a you know a WS for this flow in the downstream cross section.
Do you understand me?

I changed:
upstream condition: from 0.01 to 0.006 Normal depth
downstream condition: from Know WS to Normal depth 0.01

Using URL I send you your edited model.
https://onedrive.live.com/redir?resid=76FE2B3DBFE48BD3!4657&authkey=!AHSbaEZxmdRgO2s&ithint=file%2czip

I hope, that I help you 🙂
regards Robert

[Robert]

Hi Mat,

Why do you choose a interpolation 1 or 2 m? You should estimate a distance between cross section using Samuel equation and Fread’s euatione (see manual hec).

Can you send me your model? (using File- Debug report) I think, that you have more bugs in your model (ineffective area, abrupt change of bed of channel, …)

regards
Robert

[Robert]

Hi

My errors (abrupt increase of WSE) are results of abrupt decrease velocity before the bridge.
What method can I solve this problem?
My bridge are small obstructions without pillar!

Robert

[Robert]

GD,

I studied your document, but this is only steady flow (sub, super-critical and mixed).
What direction does hec-ras compute, when i solve unsteady flow (gradually or rapidly varied flow)? I was looking also other documents, but i found nothing

thank you very much
regards
Robert

[Robert]

Hi

I recognize you these documents:
1. Create of model by HEC-RAS
https://drive.google.com/file/d/0B6wWUzbPUM0dNmo3RnViUDJwR28/view?usp=sharing

2. Estimating of breach parameters and Downstream flood-wave routing
https://drive.google.com/file/d/0B6wWUzbPUM0delV2ZmFlTTB1Q0k/view?usp=sharing

I hope, that I help you. In case of uncertainty, you can write me!

have a nice day
Robert

[Author]

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