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Hello there,

One question arised while simulating bed evolution in a river reach. I wanted to add a constant sediment discharge at the inflow boundary and I´m asking if there is a option to add a constand sediment discharge (bedload) with a specific grain size distribution, i.e. the ratio of different sediment classes.

According to the GAIA manual there can be added a (total) value of constant sediment discharge at boundaries but not addressing multiple grain size inflow.


Would appreciate any solution or idea regarding my question a lot.

Thanks in advance,
Mati

Hi Mati,

Does the keyword CLASSES IMPOSED SOLID DISCHARGES DISTRIBUTION work for you? This works with the same classes as provided in CLASSES SEDIMENT DIAMETERS, but allows the specification of different proportions for influx.

If you are wanting to specify different classes for influx than for initial composition, I would suggest having up to 5 classes for influx and 5 for initial composition (GAIA being limited to 10 classes).
For exampleith a total of 4 classes where the initial fraction is coarse and the influx is fine, this could look like:

I hope this helps!
André

Hi André,

I am trying to simulate both suspended and bedload in Gaia. I put variables for graphic printout in gaia cas= U,V,S,H,B,Q,M,E,QSBL,TOB,KS,kAi,kRi.
And I got these variables in the result. I didn't understand what is bedload and sediment load results here. Also, what are these layer1,2,3...?? I didn't find an explanation of these in the manual.


Thanks,
Sumaiya

Hi Sumaiya,

QS BEDLOAD is bedload flux in kg/m•s. I am less familiar with the values for LAYER1 and LAYER2 as these look like suspended load (and I only work with bedload), but from reading the source code, CONC is concentration or density of a layer, TOCEMU is the critical shear stress (tau_c) for mud, and PARTHE is the Partheniades constant for mud.

I highly recommend first reading the GAIA user manual section 6.1, as there is a handy reference list, then exploring $HOMETEL/sources/gaia/nomvar_gaia.f (especially line 351 and on) to understand all the keywords. The open-source nature of the OTM suite is very helpful to understand parts of the suite that aren't fully documented.

One thing that is not necessarily clear is that to print out, for instance, the "fraction of non cohesive sediment of class i, in k layer" (nominally kAi), you have to use either explicit numbers (2A3 -> layer 2, class 3) or asterisks to print all values (*A* will return all layers and classes).

Hope this helps,
André Renault

Thank you very much for your response.
This is exactly I`m aiming for.

Another problem in this context appears while testing your Keywords.

---

ITERATION 0 TIME: 0.0000 S

GAIA COUPLED WITH: TELEMAC2D
TELEMAC2D INITIALIZED
USING STREAMLINE VERSION 7.3 FOR CHARACTERISTICS
DISIMP_GAIA : PROBLEM ON BOUNDARY NUMBER 2
GIVE A SOLID DISCHARGE PROFILE
IN THE BOUNDARY CONDITIONS FILE

PLANTE: PROGRAM STOPPED AFTER AN ERROR
RETURNING EXIT CODE: 2
....

---

I don´t unterstand how to give a solid discharge profile, bc in my understanding (according to gaia user manual) only a profile has to be implemented in T3D cases (throuh VERTICAL PROFILE OF SUSPENDED SEDIMENTS).

Perhaps someone can help how to fix the problem / how to give a solid discharge profile ?

Thanks a lot in advance,
Mati

Hi Mati,

Do your boundary conditions look like this example, where column 8 is 4 or 5 ?
hydro-informatics.com/numerics/gaia-basi...#boundary-conditions

Hello,
Yes in my case I used "4" for column 8 and
1. added in .cli file (kg/m s) value for Q2BOR - same result /error
2. added in gaia.cas file the Keyword PRESCRIBED SOLID DISCHARGES in real total value (kg/s) - with the same result /error

Another test with a succesful run / simulation was possible with a smaller value of 40 kg/s (in the example above total sed. discharge 92 kg/s)

So looks like it depends on the amount of prescribed suspended sediment not on the drafting of .cas /.cli files.

So perhaps somebody knows the reason.
Thanks so far