Problems with Sediment Load Series and Density

[Camila Souto]

Hi!

I’m working on a sediment model in HEC-RAS 4.1.0, using the International System – SI (Metric) and I’m having the following problems:

1) As boundary condition of the model, I’m using a sediment load series. When I verify the “Mass In” output series on the boundaries cross sections, the program always gives me a solid discharge 2.430168 higher than what I determined as boundary condition for each cross section;

2) When I divide (for any given sand range size) the “Mass In” (in tons) of a specific cross section with the “Volume In” (in cubic meters) of this same cross section, I get a density of 127.942346 t/m³, which has an order of magnitude a lot different from the default sand density of the program (1.489 t/m³). This same density (127.942346 t/m³) is found when I evaluate the sediments that pass or the ones who are retained in the cross section.

Can anyone give me an explanation for this problem? Is there any bug on the transformation from mass to volume in this HEC-RAS version?

Thanks,

Camila

[Mario Grüne]

Hi Camila,

I’m having the same problem with my HEC-RAS (4.1) sediment model (using SI units also)! I was modeling a complex reservoir when I started noticing that the sedimentation was unrealistic.

Then, I created a simple flume model to try to understand what was going on. My boundary condition is a constant sediment influx of 3.456 tons/day. However, HEC-RAS says that the sediment flux into my first cross section is 4.20 tons/day (1.2 times higher).

I still haven’t figure it out if I’m doing something wrong or if this HEC-RAS version (4.1) has a problem in the sediment model.

If I discover something, I’ll let you know. In the mean time, let’s hope that someone can give us an answer.

Sincerely,

Mario Grüne

[Priyankara]

1. I am having the same error with SI units. When I input a sediment load series of 1 tonne/day, Mass input for the relevant cross section shows a mass series of 2.43 ton. Has anyone found a solution??

2. I am modelling a river for sediment transport and the boundary conditions I use is Sediment load series.
Other than the upstream boundaries, I have defined lateral sediment flow series also. But when I run the model and check the results what I saw was HEC-RAS didn’t take those lateral sediment flows to calculations.

3.Is it essential to define downstream boundary condition for sediment also. My model runs without downstream sediment boundary conditions. No need to worry about that, right???

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