Sediment Time Series Confusion

[Anonymous]

Hello Everyone

Now this has made me crazy by now and i have no idea what is going on in the model.

I am trying to point sediment load in an unsteady sediment simulation. For this, i am using SEDIMENT TIME SERIES as the upstream boundary condition.

Now, the thing is that i need to mention the sediment load (tons) and the duration(hrs) for which it continued. Basically, a mass rate.

Now take the following example:

ELAPSED TIME || DURATION || SEDIMENT LOAD (TONS)
6 || 6 || 2000
14 || 10 || 0
19 || 5 || 5000

If the above information is fed in the sediment time series, i should get a sediment concentration profile that starts at 0hrs and continue to rise till 6 hrs. After that, the sedigraph should start falling and should become zero until the 14th hr and from their on, 5000 tons of sediment should flow for about 5 hours.

the above explanation is my interpretation which i believe is true. But when i see the HEC Ras sediment concentration vs time profile, my first point load peak starts at 0 hrs uptill 6 hrs and then their comes a large gap until the next point load. This large gap is making no sense to me and i have no clue why hec ras is delaying entry of this point load. it was suppose to enter the system at 14th hour.

Please help. I cannot find any literature or example or even the manual that explains this.

Looking forward.

Regards
Nayyar

[cameron]

There is a new sediment transport manual for HEC-RAS that explains some of the new features in HEC-RAS 5.0. I misplaced my copy and you would probably need to contact HEC to obtain the manual. You may also want to ask if you can beta test the next version as I believe they have fixed a few things with sediment transport sine the release of 5.0.3.

[Anonymous]

Thank you for the feedback Cameron. You mean to say that in addition to user’s manual, hydraulic reference manual and the release notes, there is an additional manual for sediment module??? is it publically avaiable for downloading (i have just started googling it).

Regards

[cameron]

Yes there is a manual just for sediment transport which was in draft a few years ago when I was using it. I couldn’t find it by a simple google search so you may need to ask HEC directly.

[Zain]

Hello Cameron

Got in touch with the Hec Ras guys. They told me that the complete sediment manual has already been provided with the version 5.0 and only the TOE EROSION part is missing and it will be uploaded soon on the website. Since, i am not modeling the erosion phenomena for the emabnkments, this pending pdf document wont going to help.

I have sent them the problem i am encountering and am waiting for their feedback. Meanwhile, i am posting the same problem on the forum in an independent thread. I would appreciate if you could have a look and give your opinion.

Regards

Nayyar

[cameron]

Did they say if the sediment manual was a separate document or as part of another document? Chapter 13 of the reference manual has information on Sediment transport which appears to be updated from 4.1. I could not find the document I had from a few years ago, but it did have discussion on both the new unsteady sediment capabilities and BSTEM (toe erosion) and maybe that is what they will be uploading soon.

I will take a in depth look when I get some time, but that may not be until September.

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