Monday, March 2, 2015

Sediment Transport Features in HEC-RAS 5.0

Written by Stanford Gibson, Ph.D. |  Hydrologic Engineering Center
Copyright © Stanford Gibson 2015.  All rights reserved.

The new 2D features and mapping tools are the most anticipated new features in HEC-RAS 5.0. However, HEC also added a couple major new sediment features, as well as many minor features and a few substantial bug fixes (e.g. SI Units). The two major features are the ARS-USDA Bank Stability and Toe Erosion Model (BSTEM) and Unsteady Sediment transport.

USDA-ARS Bank Stability and Toe Erosion Model (BSTEM)
HEC collaborated with Andrew Simon (Cardno) and Eddy Langendoen (USDA-ARS) to couple the HEC-RAS mobile bed model with the USDA-ARS Bank Stability and Toe Erosion model (BSTEM).  This model coupling adds BSTEM’s lateral processes (geotechnical bank failure, groundwater lag and toe scour) to HEC-RAS’ vertical, deposition and erosion processes.  This tool has a separate User/Technical Reference manual available from HEC.

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Goodwin Creek, MS, repeated right bank surveys compared with computed HEC-RAS/BSTEM cross section migration from Gibson et al. (2015).
 
Unsteady Sediment Transport:
Previous versions of sediment transport in HEC-RAS used the quasi-unsteady hydraulic model exclusively, simulating hydrodynamics with a series of steady flows. HEC-RAS 5.0 couples the sediment computations with unsteady flow. Hydrologic mass conservation is the biggest advantage of unsteady sediment transport, making reservoir models and even multi-reservoir cascade models much more practical in HEC-RAS. However, coupling sediment transport to the unsteady flow capabilities also brings several powerful features, native to the unsteady hydraulic analysis environment, into sediment transport analyses including: lateral structures, flow networks, mixed flow (figure), and especially operational rules (Gibson and Boyd, 2014). Version 5.0 even includes sediment based operational parameters, operating structures based on bed change and concentration (e.g. TMDL).

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Initial and bed profile and water surface elevation for a mixed flow sediment transport simulation with equilibrium sediment load and hard bottom. Sediment deposited in the sub-critical reach.
 
Other Features:
HEC-RAS 5.0 also includes a range of other new sediment features including:
· HDF5 Sediment Output and a New Sediment Output Viewer
· Copeland (1993) Sorting and Armoring Method (Exner 7 in HEC 6T)
· Gradational Hotstart
· Sediment Flow Splits
· New Dredging Tools
· Bed Roughness Predictors
· New User Manual
· DSS Sediment Time Series Boundary Condition
· Specific Gage Capabilities

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HEC-RAS 5.0 will be released shortly. To test a final beta version contact Stanford Gibson at HEC.


References:
Copeland, R (1993) Numerical Modeling of Hydraulic Sorting and Armoring in Alluvial Rivers, PhD Thesis, The University of Iowa, 284 p.

Gibson, S. and Boyd, P. (2014) “Modeling Long Term Alternatives for Sustainable Sediment Management Using Operational Sediment Transport Rules,” Reservoir Sedimentation –Scheiss et al. (eds), 229-236.

Gibson, S., Simon, A., Langendoen, E., Bankhead, N., Shelley, J. (2015) A Physically-Based Channel-Modeling Framework Integrating HEC-RAS Sediment Transport Capabilities and the USDA-ARS Bank-Stability and Toe-Erosion Model (BSTEM), SEDHYD Interagency Sediment Conference, April 2015, In Press.
























19 comments:

  1. Dear Stanford and Chris

    Thank you for giving a nice overview of sediment transport capabilities of HEC-RAS 5(beta). The question I want ask may or may not make some sense since I am relatively a new HEC-RAS 4.1 user. But still I want to know that are there some instances when a river or channel cannot (or should not) be modeled by HEC RAS 4.1 but can be done in HEC-RAS 5.0. I am specifically talking about in context of sediment transport analysis.

    Regards
    Ahmed

    ReplyDelete
  2. Hello Ahmed, If the process is fundamentally unsteady, the quasi-unsteady approach in 4.1 (and 5.0) can be inappropriate. The most common example is reservoirs. 4.1 can simulate a singel reservoir if the reservoir stage is the downstream boundary condition. But if you try to model operations through an inline structure or, say, a cascade of reservoirs, the steady flow hydraulics of 4.1 will miss the volume storage. This will affect sediment results. So it is important to use unsteady hydraulics (only available in 5.0) if the system has a lot of storage.

    However, there have been many bug fixes since 4.1, so I'd recomend switching to 5.0 for any application at this point.

    stanford

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  3. Mr. Gibson,

    I have been using HEC-RAS 4.1 as well as 5.0 Beta for the sediment transport and dredging prediction model of Ohio River at Olmsted Locks and Dams area for my MS research. Initially, I have begun with HEC-RAS 4.1 steady flow simulation and QUF for sediment transport model. The reach I have considered is about 10 miles. While performing sediment transport modeling in 4.1 under QUF condition, it displays majority of the deposition in the vicinity of u/s boundary before attaining the equilibrium condition d/s. As a result, there isn’t much deposition at downstream sections as observed from measured data. Is it solely because the sediment inflow series defined at u/s is significantly greater than the transport capacity of river or it’s an artifact of the model itself? I wanted to be sure about the correctness of my model before moving further with HEC-RAS 5.0.

    Meanwhile, when can we expect the full version of HEC-RAS 5.0 for public use?

    ReplyDelete
    Replies
    1. Depositing a bunch of sediment at the upstream cross section is a common problem with sediment transport modeling. It means that the inflowing load, the bed gradation and the transport function are not compatible. When the model over-deposits at the US boundary condition there is either 1) too much sediment or 2) not enough capacity. The first thing I'd try would be a different transport function. Chances are there is an appropriate transport function that will compute higher capacity. Also, make sure flow is contained in the channel or, if not, that you are using ineffective flow areas correctly.

      Delete
    2. Thank you Mr. Gibson for your prompt reply.

      I have one more difficulty in understanding the model. Though it uses 1D Exner sediment continuity equation during the simulation, I am wondering where and how do we define porosity in the sediment characteristics. In other words, how is it incorporating porosity in the calculations?

      Besides, if I am not mistaken the sediment composition we define at the upstream boundary will be used during the sediment mixing process (while checking for sorting and armoring). Am I correct here? Moreover, after series of simulations with the transport functions that are best suited in the sand range, and also updating the bed gradation at u/s, I have been able to reduce the deposition significantly at upstream. But still it is significantly higher than the deposition experienced at site condition. In that case, is it possible to develop the equilibrium sediment rating curve at upstream boundary running the model for each stepped hydrograph? I am looking for your suggestion on how can I approach this problem.

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  4. Hello Mr. Gibson,

    Currently, I am trying observe the difference between the prediction in sediment transport trend using the quasi-unsteady and completely unsteady sediment transport module of HEC-RAS 5.0. However, while using the complete unsteady feature of unsteady flow simulation, I couldn't find several sediment output features available under quasi unsteady-simulation. Model is not unstable either and performing fine as far as hydraulics is concerned. In sediment output prompt lots of output options are missing and sediment output (old) menu is not activated either.

    ReplyDelete
    Replies
    1. Ganesh- Would you please share your email with me? Thanks-
      Chris

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  5. Is it possible to model sediment through an overshot gate?

    ReplyDelete
  6. Estimated Stanford and Chris, you can get results of sediment transport in areas 2d? As I get the updated documentation sediment tranport?

    ReplyDelete
    Replies
    1. There is no sediment transport in 2D areas yet. Look for it in a future version of HEC-RAS

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  7. I am using HECRAS 4.1 and while running the sediment transport analysis, I chose "output Level 6" in the "sediment output options". But I am not getting any sediment discharge in the output. Can you please help me out on this? Thanks in advance.

    ReplyDelete
    Replies
    1. Try the new Version 5.0. Perhaps it will work better. http://hecrasmodel.blogspot.com/2016/03/hec-ras-50-official-release-is-available.html

      Delete
  8. Mr Gibson,
    I have used HEC RAS 5.0 Beta (august 2015 release) to set up and run quasy-unsteady sediment model (Si units). I’ve used MPM equation and Exner 5 Sorting method and I’ve achieved quite good calibration results. But now I have ran the same model in new HEC RAS 5.0 model release and the results are significantly different (e.g. Long. cumulative volume change increases 5 times). Input parameters are the same as I’ve only opened and ran the same file with new model release of HEC-RAS 5.0. Are there known to be any significant changes or bug fixes in final release (compared to last Beta release) of the model that could cause such difference in the results?
    Thank you for the reply.

    ReplyDelete
  9. Mr Gibson,
    I have used HEC RAS 5.0 Beta (august 2015 release) to set up and run quasy-unsteady sediment model (Si units). I’ve used MPM equation and Exner 5 Sorting method and I’ve achieved quite good calibration results. But now I have ran the same model in new HEC RAS 5.0 model release and the results are significantly different (e.g. Long. cumulative volume change increases 5 times). Input parameters are the same as I’ve only opened and ran the same file with new model release of HEC-RAS 5.0. Are there known to be any significant changes or bug fixes in final release (compared to last Beta release) of the model that could cause such difference in the results?
    Thank you for the reply.

    ReplyDelete
  10. Mr Gibson,
    I have used HEC RAS 5.0 Beta (august 2015 release) to set up and run quasy-unsteady sediment model (Si units). I’ve used MPM equation and Exner 5 Sorting method and I’ve achieved quite good calibration results. But now I have ran the same model in new HEC RAS 5.0 model release and the results are significantly different (e.g. Long. cumulative volume change increases 5 times). Input parameters are the same as I’ve only opened and ran the same file with new model release of HEC-RAS 5.0. Are there known to be any significant changes or bug fixes in final release (compared to last Beta release) of the model that could cause such difference in the results?
    Thank you for the reply.

    ReplyDelete
    Replies
    1. Nothing known has changed that would affect that kind of difference. If you want, you can send me your dataset and I'll forward it on to HEC.

      Delete
  11. Mr. Gibbson,
    I am a student and currently learning HEC RAS sediment modelling. in using the model i am getting very high sediment deposition (5 m in 15 days). while i am using similar inputs as given in example model (sediment transport simple). the only difference in my model is that it is in SI unit and the channel cross section is rectangular as compared to trapezoidal as given in example. rest all the flow data and sediment data is same as example still i am getting so high deposition but the example model shows deposition of 1 m. what is the possible cause for this?

    ReplyDelete