1D results error

[SaraA]

Hi,

I am trying to run a 1D model in HEC-RAS. I took only a small part of my complete river to be me first familiar with the results, however, my results do not have sense.

This is the longitudinal profile of my terrain…

and also I have uploaded a video of my results in Ras Mapper, as you can see there is no sense in the results, as the water disappears, or it is coming from different parts of my upstream boundary condition.

My computational time step is 1second, my upstream boundary condition a hydrograph of (time-discharge) 1h-0, 2h-10, 3h-100, 4h-1000, 5h-100, 6h-10, 7h-0, and my downstream boundary condition a normal depth of 0.1 (critical depth).

Someone could give a hint in where is my error?

Thank you,

Best Regards,

Sara

20181211_154250.mp4

[Scott Miller]

The vertical exaggeration of the thalweg in profile is nothing to be alarmed about. Is the vertical datum on the profile relative? There are negative values. Were the cross sections surveyed, or taken from the terrain? How well do the cross section elevations match with the terrain elevations? If terrain does not reveal the depth of the channel, some flow in the channel would not be rendered on the surface. That is not necessarily a problem for model results.

It looks like a low gradient channel. Is that downstream boundary condition normal depth, or critical depth? Use normal depth for the downsteam boundary condition, unless a steep break, like a waterfall, forces the flow through critical depth. Is 0.1 the depth, or is it slope? (0.1 = 10%, 0.001 = 0.1%)

There are problems not obvious to me from the plan animation. Instability and something going on at 11389. Maybe someone else sees what is going on.

Show model output in profile, either static or animated could help.

[SaraA]

Hi Scott,

I could solve the problem. It was an issue of dates. My first hour started on 31 August 2018, this was creating problems with my computer that it is in Spanish (Agosto). I changed the days and it works.

There was also an issue in the base flow. I did not put any initial flow and HEC-RAS was iterating up to maximum (20) when I changed that I re-run without errors.

Thank you,

Regards,

Sara

[Anonymous]

This is your problem:

HEC RAS (in profile view) uses the bank stations that you defined to define the channel profile no matter where the lowest point in the channel is. if you go back and adjust your bank stations appropriately straddling the lowest point in each cross section your river profile will make sense

[SaraA]

Hi Luis,

For my understanding, the banklines are used to differentiate the main channel from the floodplain area. For your message I understand that I should move the banklines to the lowest point to the cross-section to represent well the longitudinal profile of the river, this means, move the bankline to the bed of my channel where more or less I have located the centerline of the river.

I think I do not get your message well. I attached an image where you can see the location of the bank stations for one my cross-section in the model, but I did not understand where I should move them from your message.

Best regards,

Sara

[Anonymous]

move them to the location of your levee. Wherever the user puts the bank stations hec-ras will consider it the beginning of the overbank. The bank also separates your designated mannings values. For your example, if you have imagery or survey that shows that the bank station is NOT at the location where you put the levee, then sure go ahead and leave it, but that does not seem correct. Banks and levees can share the same station

[Author]

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