Sediment Transport with HEC-RAS 4.0

[Gkrotti]

Dear all,

I'm using HEC-RAS 4.0 to analyze solid transport in a mountain river. I
started my study with simple cases (for example rectangular channel and
constant slope) to understand as better as possible HEC program. I have some problems to perform a sediment transport simulation.

CASE A
General Rectangular section (10x10 m)
Roughness coefficient: 70 m1/3/s
Slope: 1%
Length: 10 km
Discharge: 200 m3/s ( Normal depth "h0" = 2,17 m, Critical depth "k" = 3,44
m)
Sediment Max Depth: 5 m
Bed Gradation: Medium Boulders (512-1024 mm)
Boundary condition: Equilibrium Load (upstream)

Expected Results: Normal depth and no bed erosion
HEC Results: Critical depth and no bed erosion

CASE B
General Trapezoid section (H = 10 m B max = 12 m, B min = 10)
Roughness coefficient: 70 m1/3/s
Slope: 1%
Length: 200 m (Äs = 10 m)
Discharge: 200 m3/s ( Normal depth "h0" = 2,12 m, Critical depth "k" = 3,40
m)
Sediment Max Depth: 5 m
Bed Gradation: Medium Boulders (512-1024 mm)
Boundary condition: Sediment time series (upstream)
Boundary condition: Sediment time series like upstream (in the middle)

Expected Results: Normal depth, no bed erosion, aggradation in upstream and
middle sections.
HEC Results: Critical depth, no solid transport, aggradation only in
upstream section.

CONCLUSION
I can't obtain a super critical profile. Today I have news about this topic. HEC-RAS default to critical depth when in sediment transport simulation profile going under critical depth.
Internal boundary condition doesn't run although it is the same that
upstream one.

can you help me, please??

thanks

Gianluca

[previde]

Hi,
I have the same problem: I am working on a river flow with steep slope.

In the steady flow analisys I obtain the supercritical profile (also with "mixed") but with the quasi-unsteady flow analisys (that is necessary to simulate trasport) Hec-Ras calculate in all section critical depth (also if the discharge is always the same).

Did you risolve the problem??

All suggestion are accepted.

Thanks!!

[inou-730]

Hello. While I am just a user, let me make some comments. I have same opinion as mr.
previde. It seems to me the fixed bed unsteady can calculate the mixed flow regime in HEC-RAS. But the quasi unsteady option does not do the mixed flow regime. Some books in Japan say the mixed flow of unsteady needs better numerical solution. I think , of course, any numerical solution is possible now, but I have doubt about the relation between the bed load functions and the supercritical flow conditions. There are many unknown factors for the movable bed analysis. But I expect HEC-RAS unsteady will do the sediment transport directly.

I am looking forward to hear some comments from the HEC developer.

Thanks.

Inoue