Monday, January 12, 2015

HEC-RAS Model with 2D Mesh Only.

Written by Christopher Goodell, P.E., D.WRE  |  WEST Consultants
Copyright © The RAS Solution 2015.  All rights reserved.

There have been many questions lately about whether HEC-RAS 5.0 can perform a simulation with ONLY a 2D mesh (i.e. no cross sections).  The answer is yes.  In fact, in many ways it’s a lot easier.  In this example, the standard Muncie project offered by the Hydrologic Engineering Center has been converted first to SI units, then to a single 2D mesh.  To keep things simple, the levee breach was removed and flow moving into the overbank areas is purely due to overtopping of the levee.  The following figure presents the geometry file for Muncie when modeled with a single 2D area.   

image


Once you’ve drawn your 2D area boundary and have assigned a mesh cell center spacing (DX and DY) and Manning’s roughness value(s), really all that is left is to
assign boundary conditions at the upstream and downstream ends using 2D Area BC Lines.  These were placed at the same location as the upstream and downstream cross sections from the original model. 
The easiest way to set initial conditions is to just apply a single starting water surface elevation for the entire domain, [or start the 2D area out dry].  This will not always work, especially if there is significant changes in water surface elevation throughout the 2D area.  But in this case it worked, with a little help from the Initial Conditions Ramp-Up option in the Unsteady Computation Options and Tolerances window.  I used a ramp-up time of 4 hours to set the model up with a more appropriate initial conditions solution.

image

In the 2D mesh, you’ll also notice I’ve added some refinement to the initial 40m x 40m cell center spacing to better capture the geometry along the levee and to minimize inundation fragmentation. 
Notice in this figure I’ve oriented some additional cell centers to try to align the cell faces with the high ground just to the southwest of the main channel.  This helps to prevent “leaking” through the high ground, which occurs when a cell is large enough to straddle the high ground feature. [orientation of cell faces along high ground features can now be done in the latest version of HEC-RAS quite easily with breaklines]

image

As shown in this figure, I added some resolution and strategic cell center orientation to minimize inundation fragmentation.  A lot more of this could be done with this data set to completely eliminate fragmentation. 

image

Over 2 days of simulation time with a 10 second computation interval and 40 m x 40 m initial cell size ran rather quickly at around 2.5 minutes on my computer. 

image

This sample data set is available from The RAS Solution Google Drive site at:
https://drive.google.com/file/d/0B0bpiyLiUeRXMHhZVU9ibm5faUk/view?usp=sharing

I didn't include the output files, so make sure to run the simulation first.

Please note that this data set is completely fictional and represents no real flood event-past, present, or future.  This data set was originally developed by the Hydrologic Engineering Center and modified by me.  It is meant strictly for demonstration purposes.  Enjoy!

125 comments:

  1. Excellent article, Chris!
    Robert

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  2. When will HEC-RAS 5.0 Full Version come out?

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    Replies
    1. Latest Intel says end of February. I make no guarantees!

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  3. Error with program: RasUnsteady64.exe Exit Code = -1073740940
    This is what I get when following your steps on a project I'm working on. Any suggestions as a fix?

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    Replies
    1. Unfortunately that error message doesn't reveal much. I would check to cells, especially around the boundary, for cell/mesh violations. Things like cells with more than one center, cells with more than one exterior face, cells with no centers, cells with more than 8 sides, etc.

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  4. Hi Chris,

    What would you suggest as alternatives to setting the initial condition in reaches where change in elevation is much greater?

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    Replies
    1. You can explore using a restart (hotstart) initial conditions file. This requires you to run a "hotstart" simulation first to create your hotstart initial conditions file. Given that, I would be more inclined to use a ramp-up time instead.

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  5. Dear Cris,
    I wanted to run your model but it was cut off at the half during unsteady flow simulation although writing geometry info and geometry processor were both completed.
    It says +STOP! Error in the time window
    Unsteady flow encountered an error
    Writing results to DSS

    ReplyDelete
    Replies
    1. Please make sure that your Windows Laguage and Regional settings are to English (United States). That should fix it.

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  6. Thanks much for the articles about HEC-RAS 5.0. Very interesting and helpful.

    My question: Have you had any trouble loading Web Imagery? I am getting the following error:

    Error loading image from file: 'C:\Program Files (x86)\HEC...GDAL\Web map Services\Google Satellite.xml' Dataset:C\Users...AppData\Local\Temp\HEC_RAS_IMAGES\CroppedPicture...tif' could not be opened.

    ReplyDelete
    Replies
    1. The only times I've had issues with loading web imagery have been when:
      1. Projection issues. Either I've forgotten to first load a projection file (Tools...Set Projection for Project) or there is some inconsistency between my geometry data and the projection I've established. Or...
      2. My internet connection was not established.

      Otherwise, it works very well.

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    2. What version of ArcGIS are you using? I am using 10.1 but I have the former library of ArcGIS10.0 ".prj" files, which I placed in the following folder:
      C:\Program Files (x86)\ArcGIS\Coordinate Systems\Projected Coordinate Systems
      ...but still get error when I try to load images

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    3. We've used both, and other software like QGIS as well. Not sure what the problem could be. Sorry. I'll ask around.

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  7. Hello.

    I have downloaded the project, but when I want to run it, I have the next error:

    HEC-RAS Error - Incomplete data, the following errors were found:
    2D Flow Area: 'Muncie2D' has external boundary conditions 'BCLine: Outflow Boundary' and 'BCLine: Inflow Boundary' that use the same face. Boundary conditions cannot overlap on the same mesh face.


    https://www.dropbox.com/s/u8awi6d6x51474n/error_boundary.png?dl=0

    Regards.

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    Replies
    1. I just downloaded, unzipped it and ran it with no problems. You must have made some change before running it. Somehow, the outflow and inflow BC Lines are now in the same place. You can either redownload the project again and rerun it, or you can just put the BC Lines back where they should be. See the "Outflow Boundary" and "Inflow Boundary" on the first figure above. Please respond back and let us know how you resolve this. Thanks.

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    2. I'm getting the same error with my own project. Boundary conditions are clearly shown at upstream and downstream ends and are not on the same face. Tried deleting and redrawing and still get the same error. Anyone know of a possible cause/solution?

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    3. Ian. It is a bug in the March version of 5.0. In my experience this has only come up when using SI units. In any case, this bug has been fixed for the next release. While we wait for that to come out, you can bypass this error by unchecking "Check Data Before Execution" which is in the Options menu item in the unsteady flow analysis window.

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  8. Hello Chris.

    Thank you for your answer.

    I'm afraid I didn't change anything (at least consciously). I have upload it.

    https://www.dropbox.com/s/ow6a3er2wvr3txi/Muncie2DOnly_2015_03_07_SI.rar?dl=0

    It seems like I can't have the inflow and outflow boundaries in the same 2D-Storage area.

    I use the version the version beta 2015-02-09 HEC-RAS 5.0 and windows 8.1 in Spanish (but language format English US).

    Regards

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    Replies
    1. Ok. Try the October 2014 beta version instead. That is what I have been using. If it works in the icy version them that means something changed and might be wrong with the Feb 2015 version you have.

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  9. Hello Chris.

    I'm afraid I have the same problem. I can´t run correctly the modell with the October 2014 beta version. I will try in another Windows OS, for example, Xp (at work). I tell you, when I'll test it.

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    Replies
    1. Yes, please do let me know what you find out.

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    2. Hello Chris.

      I tried it at work (Windows 7 as OS in German language), and the model runs perfectly. So I guess the problem is with Windows 8.1 (which is in Spanish).

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    3. Good to hear. Thank you for sharing this.

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  10. Hi Chris!

    I've been trying to run a simulation with an upstream 2D mesh followed by a 1D river reach but I see the message:

    HEC-RAS Error - Incomplete data, the following errors were found:
    2D Flow Area: 'Montante2D' has external boundary conditions 'BCLine: Saída2D' and 'US XS: RS=1964' that use the same face.
    Boundary conditions cannot overlap on the same mesh face.

    I believe I've drawn the BC downstream line exactly on the first cross section, so I don't know what else this error should be pointing out. Any tips?

    Thanks a lot!

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    Replies
    1. Either you have 2 BC lines overlapping, or you the intersection between your 2D mesh and cross section have both a BC line and a cross section boundary condition applied. In short, you can't have 2 boundary conditions at the same location.

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    2. I have a BC upstream the 2D mesh (flow hydrograph), a BC downstream the 2D mesh (normal depth) and a BC downstream the 1D reach (normal depth).. Initial conditions were set up as initial elevation (2D mesh) and initial flow (upstream 1D reach) that is equal to the first flow value of the hydrograph..

      When I zoom in the first cross section I can see a millimeter offset between it and the 2D Mesh downstream boundary.. Do you think this is the problem? I'm trying to minimize it to zero, but it's kind of impossible..

      Thanks a lot!

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    3. You cannot have a BC line on the downstream end of your 2D mesh where it connects inline to cross sections. I believe that is the problem. Remove that BC line and make sure the 1D reach is connected to the 2D Area.
      Also, you don't have to have the first cross section exactly on top of the 2D boundary. Just get it close so that the conveyance distribution over the cross section is close to the conveyance distribution over the 2D edge that is connected.

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    4. Hey Chris!! Thanks a lot! I've done it this morning.. Just removed the downstream BC and it went OK!

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    5. Great! If you can, send me a video of the flood animation, I'll post it up here.

      Thanks

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  11. Chris,

    It seems to me that whe 5.0 was first announced it was more of a tool to use in place of the storage area feature of RAS. How do you see the 2d feature being utilized with the official release of the program? Is there an intended use or set of limitations for use on 2d only models?

    I am envisioning setting up a quick 2d model to help me decide how to effectively set up a 1d model at complex junctions or flood plains. I see it giving me a solid basis for where/how to cut cross sections. Or maybe it takes place of the 1d model completely? I'm just thinking out loud at this point...

    Thanks for the great posts.

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    Replies
    1. Actually 2D has been planned for RAS for some time now. It's not just a tool to use in place of storage areas, although that is one inteneded use. It's more about adding the functionality of using 2D to model areas that just can't be (or shouldn't be) done in 1D. To your second point, if you go to the effort of setting up a 2D area, I'd just use that instead. Unless you want to use the output plots specific to cross sections.

      Thanks, and good luck!

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    2. Thanks Chris! Do you know of any good documentation showing how RAS 2D compares to some of the other popular 2D models?

      My biggest problem would be convincing the client that a pure RAS 2D model is trustworthy. You know how a lot of engineers can get caught up with "standards". It can be tough to break through some times. RAS 5.0 offers some unique opportunities though, being from such a reputable source. And of course it doesn't hurt that its free!

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  12. chris good day. can only be performed in the simulation area 2d stretch of a river regardless floodplains? project since my college thesis Floodplains not overflow and the water only stays in the stretch of the river and let me know if I can get results only from this area 2d creating computational mesh only the river.

    thank you very much

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    Replies
    1. Hi Chris, I have the same problem of "Anonymous"...
      After some good working simulations, suddenly I have this error :
      "2D Flow Area: 'Prova' has external boundary conditions 'BCLine: cond_monte' and 'BCLine: cond_valle' that use the same face. Boundary conditions cannot overlap on the same mesh face".
      I didn't change the Boundary Conditions, but the only variation that occured was the update (automatic) of the Antivirus and my Windows(vers. 7 Home Premium).
      Now, I can't continue my simulation (I tried also with another pc- Windows vers.8, but I have the same problem).
      How could I solve?
      Help me, please.
      Thanks

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  13. Hi Chris, I have the same problem of "Anonymous - March 6, 2015"...
    After some good working simulations, suddenly I have this error :
    "2D Flow Area: 'Prova' has external boundary conditions 'BCLine: cond_monte' and 'BCLine: cond_valle' that use the same face. Boundary conditions cannot overlap on the same mesh face".
    I didn't change the Boundary Conditions, but the only variation that occured was the update (automatic) of the Antivirus and my Windows(vers.7 Home Premium).
    Now, I can't continue my simulation (I tried also with another pc but I have the same problem).
    How could I solve?
    Help me, please.
    Thanks

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    Replies
    1. I think this might be a bug. Send me an email and I'll see if I can help.
      Chris

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    2. Thanks to a tip by Rob, you can bypass this buggy error message by unchecking "Check Data Before Execution".

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  14. Hi Chris, i've experienced the same problem with overlapping BC lines in March 22 version while i was studying with the 2D only domain. But once i tried to run the same model in the october version, there is no problem. Although it has some key improvements like drawing breaklines and manning's n regions through the geometry editor, the March-22-2015 version needs to be checked in that regard.

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    Replies
    1. Thanks to a tip by Rob, you can bypass this buggy error message by unchecking "Check Data Before Execution".

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  15. Hi Chris, after I run the 2D simulation, can I cut cross sections to see the results?

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  16. Hi Feng. Not yet, but I'm hopeful that a feature like this will be included in the optician release.

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    Replies
    1. Hi Chris I have another question. In 2D only simulation how can I choose different terrains. For example I want to run existing Terrain and Project terrain in 2D only model I only have to make 2D mesh and flow is I make different terrain layers how can I choose

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    2. Feng- Make a copy of your geometry file. One will be for the existing terrain, one for the project terrain. Each geometry file will be in its own plan.

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  17. Dear Chris

    I have a model 2d storage is connected to 2d flow area. The connection of areas are done by weir. The weir breach model is not working properly. It gives the warning below :

    Warning with Connection

    The SA 2D Connection at baraj
    has a weir breach lower than the cells they are connected to
    for 2D Area Sungurlu

    The cells are not lower than breach and Although I increased the breach level, It has not proper solution. The flow area, even is not wet after the dam. The map of depth and elevation is not meaningfull. Thanks in advance

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    Replies
    1. There have been a number of issues in the March version with 2D area connections and the weir or weir breach being "lower than the cells they are connected to" when that is actually not the case. This bug seems to be more prevalent when using SI units. I've found that 2D area connections inside of 2D areas don't have the same problems. Hopefully this will be resolved when HEC releases the official 5.0 version.

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  18. Hello Chris!

    I have basically the same issue with a weir connecting two 2D areas. I changed to US units in order to avoid the error and it worked well for one case, but at the next model it reappeared.

    Actually I've planned to use HEC-RAS 5.0 for my master thesis but since it seems to me that the actual beta version is still not working for my problems I might discard that idea.
    Any idea when the official Version will be released? Or is there another beta version coming out?

    Best regards

    Sebastian

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    Replies
    1. Sebastian-I expect the official 5.0 version will be out by the end of the summer-but no guarantees.

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  19. Hi,

    I've set up a 2d model with no 1d elements to evaluate the performance of a weir across a channel diverting water to a side channel. I've drawn boundary lines in the following locations: 1 in the main channel upstream of the diversion, 1 in the main channel downstream of the diversion, and 1 in the side channel downstream of the diversion. When I try to assign boundary conditions in the unsteady flow dialogue box, the program will only allow me to enter a boundary condition for one of the downstream conditions. When I select the other downstream boundary line, none of the boundary condition options are available. When I model with 1 boundary condition (normal depth) crossing both the main channel and side channel, the model works, but is not accurate as the downstream slope in the channels is significantly different. Has anyone encountered this? It seems from the associated tutorial, it is possible to enter multiple boundary conditions, but I can't figure out how to make it work.

    Also, does anyone know when the full version of 5.0 will be released? I assume there will be manuals associated with it similar to hecras1d. The tutorial provided with the beta version is very helpful but seems to be geared toward 2d/1d combo modeling.

    Thanks in advance.

    Ty

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  20. Also, my models seem to be working ok and I'm able to map depth and elevation in the ras mapper output but I'm unable map velocities or flows. Is this a problem with my model, or have they disabled these features in the beta version?

    ReplyDelete
    Replies
    1. Ty-
      Are you using the March 2015 version? If not, try it: Here is the link to the latest version:

      https://drive.google.com/file/d/0B57QUvyA_BsYZkZILUFXMGJsdUE/view?usp=sharing

      This link lets you download a self extracting archive file called "HEC-RAS_5.0_Beta_2014-10-01.exe"

      Download the file to a separate directory and run the self extracting archive file. The self extracting archive file contains:

      1). The installation setup package called: " HEC-RAS_5.0_Beta_2015-03-20_Setup.exe"

      2). A updated PDF version of the User's Manual called "2D Modeling with HEC-RAS 50_Draft.pdf"

      3). Two 2D Test Data sets in a directory called "RAS_50 Test Data"

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  21. Hi Chris,

    I've also been unable to export velocity grids from RASMapper using 5.0. To get around this we thought we'd do some post processing of the data in HDF5 file to derive these grids ourselves. Thinking that the cell velocity displayed in RASMapper is an average of the velocity across that cell, we've tried calculating this value by averaging the X & Y point velocities for given cell. We're able to 'sort of' get a similar value but unable to replicate them exactly.

    Would you happen to know how the velocities displayed in RASMapper are calculated and on what data it is based?

    ReplyDelete
    Replies
    1. Sorry about the delayed response. Velocities (x and y) are computed at the cell face points. I believe the cell velocity used for the velocity grid is the resultant velocity for all of the face point velocity vectors for that cell. Not 100% though.

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  22. Oh, and one more thing in connection with my latest comment: the simulation goes without any error, but in the velocity profile view, the max profile gives a look, which can't be found during the animation. I'd ran the simulation on two different computers, both with the october beta, but same solution.

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    Replies
    1. The max ws profile is not a true profile, in the sense that it is not associated with a specific date/time. It is an aggragate of all of the maximum water surface elevations that occured at each location during the simulation, regardless of when they happened. The max ws profile is what is typically used for flood inundation maps.

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    2. I see, it's clear, I had some thoughts, that this could be the reason, but I had to be sure, thanks!

      Have You read my comment before that? About that I have a simulation, which worked properly, without errors, but if I add flow, or depth times velocity profiles, the animation shows nothing. I tried it with the test projects, but it worked the same way. I'm using the october beta, but I read here, for a commenter named Ty, You've shared a 2015-03 beta, but that googledrive link is now deleted, and the sidebar link only allows the 2104-10 beta to download. Is it possible to share it again? It would be great!
      Regards
      G

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    3. This comment has been removed by the author.

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  23. amongergely@gmail.com and thanks gratefully!

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  24. Hello
    I am Colombian.
    I do not speak English
    I want to know the procedure to load the mesh geometry or 2D, to generate the 2D area tells me that no cell / mesh. I appreciate your help or can send me a link to your procedure. I hope you understand me.
    Thank you

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    Replies
    1. Please read the manual. It does a good job explaining the procedure.

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    2. i also face the same problem..using HEC-RAS 5.0.3. when i put value for spacing DX and DY, it shows "Current mesh contains no computation points. is it problem with my terrain/coordinate or else..

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    3. It could be, but I dont know for sure. Maybe try some different cell center spacings. And make sure your 2D area doesn't have sharp angles and narrow protrusions. Those tend to create cell violations.

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  25. Hi Chris!

    I'm a constant visitor of http://hecrasmodel.blogspot.com, especially if I need to be enlightened about setting up HEC RAS.

    Lately, I've been testing the pure 2D functionality of HEC RAS 5.0 (8/21/2015 version). I'm testing how it would perform if I'm using terrain data of varying spatial resolutions.

    I would like to ask regarding the algorithm used by RasMapper when computing depths. I noticed that I can compute a depth grid using a terrain file that is different from the one I used during the simulation.

    For example, i did a 2d simulation using a 30-m resolution terrain, and I was also able to have the dynamic flood depth maps using the same 30-m resolution (i.e., "Raster with Associated Terrain").

    But by exploring the "Manage Results Maps.." functionality of Ras Mapper, I found that it is possible to compute for the flood depth maps using a more detailed Terrain (i.e., 1-m spatial resolution).

    I'm now interested on how does RasMapper computes for flood depths using a finer Terrain even though the simulation was done using a coarser terrain.

    Thanks and regards,

    -- Jene

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    Replies
    1. Thanks for visiting the RAS Solution. Glad you are finding it useful. It’s funny, I just recently asked the same question to Gary Brunner at HEC. He said that indeed you can use a different terrain for mapping (i.e. your results layer) versus computations. However, using a different Terrain for mapping does not change the computed results. It simply takes the computed results (i.e. stages) that are based on the original Terrain and projects them onto the new Terrain. A more refined Terrain should make the depth grid look more detailed, but keep in mind, the stages will still be based on the old, less refined Terrain.

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  26. Hello Chris.

    I´ve been visiting the blog for quite a while, but I haven´t had the opportunity to write something. But now I´m doing it because I´m experiencing stability problems with a coupled 1D/2D model I have been working on for a few weeks. It is located at a watershed in Chile. Since I have done everything posted here in order to increase the stability of the model without having any good result, I wanted to ask you if it is possible to send you the files so you can see them and tell me any tip or suggestion that could help me with this.
    I appreciate your attention.

    All the best,
    Camilo

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    Replies
    1. Hi Camilo, yes, please send me your files and I'll see what I can do.

      Chris

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    2. Thanks a lot Chris for your answer. In the following link you can find the HEC RAS project. The one that I´m using is called Temuco, because that is the city in CHile that I´m trying to model (Imperial river). It is in UTM wgs84_18s projection and SI units.
      Hope you can help me with it. Thanks a lot!!!

      https://www.dropbox.com/s/9v0dzu590j9i0lo/HEC-RAS_Camilo_Chile.rar?dl=0

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    3. Hi Chris. I sent you the files as a reply in a dropbox link. Did you receive it? If not, here it is again.
      Best regards!

      https://www.dropbox.com/s/9v0dzu590j9i0lo/HEC-RAS_Camilo_Chile.rar?dl=0

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    4. I have them and I am looking now...

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    5. I need your projection file "CoberturaUTM_2.prj before I can proceed.

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    6. Off course! Here it is:
      https://www.dropbox.com/s/glhneh500lf0q4n/Shapefile.rar?dl=0

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    7. Here are some things I did to get your model to work.
      https://drive.google.com/file/d/0B0bpiyLiUeRXQVh6OUwxN1cxd3M/view?usp=sharing

      Good luck!

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    8. Thanks a lot Chris. I really appreciate it! I will take a look to the files. Meanwhile I made a full 2D version of the model and it worked without any complain. But I find it very useful to learn about 1D/2D models as well. Thanks again and I´ll get in touch again.
      All the best.
      Camilo

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  27. Hi Chris,

    Is there a way to export or see hydrograph at the downstream side BCline in RAS2D model?

    Thanks and regards,

    Hongyu

    ReplyDelete
  28. Hello Chris,

    I am a recent learner of HEC-RAS 5.0 and am coming across a problem, where I am unsure why my channel-only data does not override the base terrain data so that the water will flow underneath bridges instead of acting like a "wall", which forces the water to go around it. I first thought that you have solved this issue by using the Rating Curve for Inflow BC, but it seems you did not. I tried to incorporate the 2D Area Break Lines, but could not get it to work as it should (do you have a link where I can learn about the Break Lines feature in detail by any chance?)

    Please guide me in the right direction how to solve these cases of flooding through barriers/bridges or if the potential causes that I have listed is not even the actual cause of the problem. I have attached an image of the begging of my simulation, showing how the first bridge is obstructing the flow path like a "wall".(Please also note that my creek is not "active" as your model's; I wasn't sure why exactly this was happening either).

    https://drive.google.com/file/d/0ByOXokCMkIBSanBBSDhlT0dwc28/view


    Best Regards,
    Daniel Kang

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    Replies
    1. I see that a lot when there's a problem with an inline connection. Are you doing a single 2D area? Multiple 2D areas, 2D and 1D? If there is a connection at the "wall", make sure it is really connected. If it is a single 2D area and there truly is a "mound" of terrain blocking flow, read this and see if it helps: http://hecrasmodel.blogspot.com/2015/06/lifting-terrain-in-hec-ras-50.html Although this post is about lifting terrain, the same process can work for lowering terrain to the active creek channel.

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    2. Hey Chris,

      Sorry I am trying to do the exact same demonstration as yours, modeling with 2D Computational Mesh only! Which is why I am more puzzled, because I am using the same data set, but I am getting a different simulation than yours. Manually lowering terrain for bridges is definitely helpful and feasible, but was curious if this method is the most efficient/accurate way of dealing with bridges (within 2D Modeling features only), especially if I don't have access to the actual cross-section measurements?

      fyi to guide me in the most appropriate direction, my main goal of using HEC-RAS is to learn dam breach modeling, intensively using the new 2D Modeling features in 5.0.1. I simply came across this project, as I was searching for dam breach modeling with "2D only" on your blog :)


      Big thanks for the quick response!

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    3. Youre welcome! If you don't have cross sections to use to create a cross section terrain for merging with the overall terrain, you will have to remove the bridge remnant from the terrain manually in GIS.

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    4. Hello Chris,

      Just curious, how were you able to present the creek's channel to be already impounding water in the simulation?

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    5. I set an initial water surface elevation for the 2D area and then 4 hours of ramp up (initial conditions) time.

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  29. Hi Chris - great article! I'm very familiar with 1D but trying to make the jump to 2D. I tried running a 2D model of my own (with my own surface, etc) but I keep getting strange results. My upstream BC is a flow hydrograph, 100 days, with flows ranging from 10 cfs up to 500 cfs. When I run the simulation I get convergence errors but the model still runs. The end results give channel depths thousands of feet deep and extremely high velocities on the leading edge when it "wets" the dry cells at upstream end. Any thoughts on what might be causing this? I've tried everything and am pulling my hair out now!

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    Replies
    1. Thanks! Sounds like instabilities. They can result from any number of things. Typical culprits are too large cell size, too large computation interval. Make sure you are keeping your Courant number close to 1.

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  30. Hi Chris - Great article. I'm very familiar with 1D HEC-RAS but am trying to make the jump to 2D. I used my own data set (terrain, hydrograph at upstream BC and normal depth at downstream BC...very similar to this example) and everything seems fine but when I run the simulation I get convergence errors and water depths in the channel modeled to be thousands of feet deep! This is for flows ranging from 5 cfs up to 500 cfs with a channel ~100' wide. When the flow enters from upstream and wets the dry cells, also the leading edge of the flow is modeled with extreme velocities. I've tried adjusting all I can think of and nothing seems to work. Any clue what is going on? Thanks! - Eric

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    1. Daniel, I imagine that going from 20 to 5 for your cell size is different mostly because of where your cell faces end up. I suggest looking at your 20 m mesh and look for areas where water leaks through high ground features or other barriers to flow. Make sure that your cell faces align to those features by using breaklines. Time steps (also called computation interval) can be found in the unsteady flow analysis window. I'm not going to have time to look at any projects for a couple of weeks at least, but if you still are having issues after then, check back with me. Good luck-
      Chris

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  32. Hi Chris
    I am running a fully 2D stream model. In this project the flow changes along the reach. I tried to create two storage areas (one for the US area and one for the DS area), so I could put a new BC in the middle of the reach. However, a boundary condition and a connection canNOT share the same cell face. Could you help me to find a way to put a hydrograph inside my 2D area? Maybe there is a way to put an internal condition.
    Hope you can help me with it. Thanks a lot.

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    1. In the current version RAS does not have a way to put an internal flow hydrograph in a 2D area. You might try putting a "slot" in your 2D area perimeter as a way around this limitation.

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  33. I'm trying to find a way to figure out the max flow across an arbitrary internal line in a 2D area. Alejandro Sanchez at the HEC suggested I "compute approximate fluxes by getting the velocities and water levels at the faces". I installed HDFView and browsed to ????.p01.hdf:/Results/Unsteady/Output Blocks/Base Output/Summary/2D Flow Areas/Wash 1/Maximum Face Velocity. I right-clicked and looked Properties to see that Row 0 is velocity in ft/s and Row 1 is Time in Days. I found the velocity for a Face of interest. But the face belongs to two cells, each of whom have a different water surface. How do I get the appropriate water surface at the face to calculate the flux/flow? Do I simply straight-grade between the centroids of the two adjacent cells to the face?

    All this hints at a general question that I am not finding answered anywhere yet. If cells have a single water surface for computation purposes, how are the differing water surfaces resolved at faces? Or am I misunderstanding, and it is faces that have a level water surface for computation purposes?

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    1. Thomas- It's easy to do, just add a profile line (Version 5.0.3) on your map anywhere. Once you add the profile line, you can right click on it and get flow flux across it. You can also use a SA/2D area connection (what we did before version 5.0.3). http://hecrasmodel.blogspot.com/2015/09/transect-for-extracting-flow-in-2d-area.html

      To get a little bit into the theory, RAS calculates velocity at face points during the computations by using a staggered grid (called the dual grid). The face points are the center points of the cells in the dual grid. Velcities are determined during the matrix inversion and not back-computed from water surface elevations as you are trying to do. The velocity you see at a face is simply the resultant velocity from the two face points on either side of the face. You might read through the theory section in the manual if you want more information on this. However, with the profile lines, or SA/2D Area connection, you should be able to easily get max flow across an arbitrary internal line. Good luck!
      Chris

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    2. Thanks on both questions. I didn't see part A soon enough, but I eventually discovered it another way. Part B is very helpful. I am really enjoying the 2D capability.

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  34. Hello Chris,
    I run the unsteady flow with hec-ras 5.3, using a new terrain (XS data with existing terrain. It could not run and alway alert as follows: Computing 2D Flow Area 'Floodplain' tables: Property tables do not exist. Error completing geometry for computations: Unable to compute face tables. The terrain associated with this geometry does not completely cover the 2D Flow Area 'Floodplain'. I would appreciate, if you could provide any direction and advice. Khem

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    Replies
    1. Make sure your 2D area(s) does not extend beyond the spatial limits of your terrain. Also, make sure that you have associated a terrain with your geometry.

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  35. Hi Chris,

    I'm looking for a way to define different areas(polygons) of varying cell size within the same 2D-area. So far I've only been able to define varying cell sizes along breaklines.

    Online I found a statement:

    "Currently the HEC-RAS 5.0 mesh generation tools are somewhat
    limited, but by applying 2D coastal modeling mesh development
    techniques, the 2D geometry file can be manipulated to allow for
    variable cell sizes within the computational mesh".

    http://www.gafloods.org/pdf/2016/SpringConference/magnolia/03242016%20Managing%20Flood%20Risk%20with%20HEC-RAS%205%20thru%20Case%20Studies.pdf

    I haven't found a way to "apply 2D coastal modeling mesh development
    techniques". Do you have any suggestions?

    Thanks! //Alexander

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    1. I would check with Dewberry and see how they did that. I'm guessing they used a third-party mesh development application, then just copied the cell center coordinates into the RAS 2D Area editor.

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  36. Hi Chris,
    it is a nice work.

    Can we get a results table showing us how much higher the water level in the cells as well as data on the flow in the cells and the amount of flow inside and outside of the cell.or just have this simulation map.

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    1. Thanks. I would try using profile lines to extract data from cells inside the 2D area. Also, you can get into the HDF file using an HDF Viewer if you want to see all of the numbers for every cell. Finally, there's a good real-time query in RAS Mapper. You can click on any cell and get information in time series.

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  37. Hi Chris, how are you? I'm a new user of HEC-RAS 5.03, and I want, first of all, to thank you. Your posts and explanations here are very very usefull!. Well, backing to my problem: I have been trying to run a dam break using only a storage area conected to a 2D mesh area trhough a "SA/2D Area conection". When I run my simulation, totaly in 2D, a lot of messages apear in "Computation Messages" Box. And I'm don't know how to interpret them, especially the "1D/2D flow error". This "flow error" is a numerical error? What is the unit of this error?. Could you help me in this case? The messages are something like below. Just to say, "barrag3" is the name of my Dam. Thank you! Arthur Tschiedel

    "29OCT2016 00:28:46 1D/2D Flow error -10. barrag3
    29OCT2016 00:28:47 SA 7 538.37 0.410
    29OCT2016 00:28:47 SA 7 538.05 0.107
    29OCT2016 00:28:47 1D/2D Flow error 123. barrag3
    29OCT2016 00:28:47 1D/2D Flow error -10. barrag3
    29OCT2016 00:28:48 SA 7 538.36 0.409
    29OCT2016 00:28:48 SA 7 538.05 0.106
    29OCT2016 00:28:48 1D/2D Flow error 123. barrag3
    29OCT2016 00:28:48 1D/2D Flow error -10. barrag3
    29OCT2016 00:28:49 SA 7 538.36 0.407
    29OCT2016 00:28:49 SA 7 538.05 0.106

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  38. Hi Arthur. The flow error messages are where HEC-RAS is trying to balance the flow computed through the SA/2D area connection with the flow computed in the cells adjacent to the SA/2D area connection. It's in units of discharge (m^3/s). The fact that it says 1D/2D flow error is a mistype in the software, it should say SA/2D Connection to 2D area flow error instead. Anyway, increasing the number of 1D/2D Maximum Iterations should help to reduce or eliminate these errors (from the unsteady flow analysis window, Options, Calculation Options and Tolerances, 1D/2D Options tab).

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  39. Hello . Please I have a concern regarding the calibration and validation of the 2D model with hec-ras. How do I know that my model reflects reality? think to answer me

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    1. The more calibration you do, the more confidence you have that it reflects reality. But remember the famous quote by Dr. George Box: "All models are wrong. Some are useful." Doing sensitivity analyses can help you to understand the uncertainty in your results. Doing a probabilistic analysis can help you to quantify the uncertainty in the results.

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  40. Hi Cris

    Is the modelation with only a mesh as accurate as with a mesh and sections? If I decide to do it with both mesh and sections, will I have to asing the hydrograph and the normal depth to both downstream-upstream BC lines and downstream-upstream sections?

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    1. The accuracy of the model is dependent on how you set it up, what input parameters you use, and if whether or not you've calibrated your model. If you have inline connections to 2D areas, you only need to assign boundary conditions to the upstream and downstream extents of your model.

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  41. Hello Chris. Please see how the simulated flow can be visualized by a model in ras mapper.thank to answer me.

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  42. Hi Chris,

    first of all, thank you so much for your hints. I would like to ask you if I can use a break line to model the river channel. Thanks a lot.

    Antonio.

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    1. While it is not required, yes you can do that. It's helpful to do this to make sure you have enough cells across a major conveyance, like the river channel.

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  43. Hi Chris,

    I am currently working on a project combining 1D and 2D simulation and I'm facing an issue I can't solve...
    When I'm done drawing my 2D Flow Area, I then specify the size of the cells (40m x 40m for now) and then I have this message popping in the lower left corner of the screen saying : "Mesh 'name of my mesh' : FATAL ERROR : 1 face errors detected on the perimeter of the mesh."

    I tried to delete the area and draw it again but still... Also I tried to identify the corrupted cell and erase it but it seems that as soon as I delete it, the problem then spreads to the surrounding cells...

    I'd like to know what you think about it,
    Thanks a lot in advance
    Victor

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    1. Try making the perimeter of your 2D area (especially around the corrupted cell) smooth, avoiding sharp angles and narrow protrusions. You may also experiment with slightly different cells sizes and see if that helps.

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    2. Thanks for your help, everything seems to work now !

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  44. Hi Chris, Is it possible to run a steady flow model with Mesh only without cross section of the channel? If, possible then how can i put the boundary condition. This is for a small seasonal river with flow of 6 cumec only! Thanks in advance!

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    1. Yes. You still have to do it with unsteady flow, but to simulate steady flow conditions, just put in a time series of constant flows.

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    2. Thank you very much Chris for your kind reply. Now I am trying to create smaller mesh of 1mx1m but giving an error " 1 facepoint error" fatal error. Could you please tell me, how can I solve this error? And also, can I create different cell size for channel and floodplain? Thanks in advance. Regards

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    3. Sounds like a cell violation. First, scan your mesh for a "red dot". This is an indication of a cell violation. If you see this, you can either 1) add some cell center points around the affected cell to try to get rid of the violation, 2)smooth out the mesh boundary to remove any sharp angles or narrow protrusions (these things tend to cause cell violations on the boundaries) or 3) try a difference cell center spacing (try 2 meters, or 1.5 meters...just something different).

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  45. Hello Chris,

    I am using two different mesh size (4 feet for main stream and 10 feet for floodplain). In this condition, how should I decide to select the time steps for simulation considering courant number?
    Thank you.

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    1. Use the 4 feet main channel mesh. Whenever I have varying mesh sizes and velocities, I try to hedge towards the more restrictive conditions (i.e. the one that will give the smallest time step, within reason), then I further fine tune from there.

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  46. Thank you. And I have same problem like other. I got "Error with program: RasUnsteady64.exe Exit Code = -1073740940" when I used full momentum equation for the same mesh which I used for Diffusion wave equation. There was not any error for Diffusion wave equation. Do you think this error is due to error in mesh? I have no idea what parameters to check to eliminate this error.

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  47. Thank you very much Chris. Problem solved as i was able to create the mesh for 1mx1m cell size avoiding sharp angle and following your instruction. Now about creating hots start file, is there any recommendate time frame for the length of " hot start run"?

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    1. As long as it takes to get to the desired starting condition. It's different for every project. For smaller projects, I usually start with an hour and then adjust as necessary (based on results). For big projects I might start with a day. Really big projects, maybe a 2 or 3 days.

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  48. Hello -

    I downloaded USGS NED 1/3 arc data. When I unzipped, I do not see a .prj file? How should I proceed with using USGS elevation data into HEC_RAS. Thanks.

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    1. I would go back to the USGS site and see if it provides information on the projection file to use. You may also have luck brownsing www.spatialreference.org.

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