A Preview of RAS2D, two-dimensional modeling in HEC-RAS

Written by Aaron A. Lee | WEST Consultants
Copyright © RASModel.com. 2013.  All rights reserved.

UPDATE.  HEC has asked that I no longer distribute HEC-RAS 4.2 with 2D Alpha.  Their purpose for releasing this alpha version is to get constructive feedback so that they can improve its functionality and efficiency; and to minimize bugs before the offical beta release-not to be critically compared to other established 2D software packages...yet.  So far, they have received no comments from anyone I have distributed the software to, which is very disappointing.  Please keep your eye out for the official beta release, which is due out early next calendar year some time.  You will be very impressed with its capabilities!  In the meantime, if you have been given a copy of the alpha version of RAS2D, please take a brief moment and provide some comments and/or suggestions to HEC.  User feedback is very important to their product development. 
Sorry for any inconvenience.  Chris    @RASModel

ANOTHER UPDATE.  The release of RAS2D beta is now projected to be end of February, 2014.  I'll post updates as I get them.   Chris    @RASModel

UPDATE #3.  RAS2D will now be released as a new feature in HEC-RAS Version 5.0.  There will be no official release of RAS2D under version 4.2.  The Beta version of HEC-RAS 5.0 is due to be released in the March/April 2014 timeframe. 
UPDATE #4.  Latest indications are Version 5.0 beta will be released at the end of April, and the full version will  be released at the end of the summer.
UPDATE #5 (as of May 11, 2014).  Latest indications are Version 5.0 beta will be released in 2 to 3 weeks, putting it at the end of May, early June time frame.  
UPDATE #6 (as of May 23, 2014).  Version 5.0 beta is out!!! Go get it at http://hecrasmodel.blogspot.com/2014/06/update-to-hec-ras-50-beta.html




I’ve gotten a chance to play around with the alpha version of HEC-RAS 4.2 and check out the program’s new two-dimensional (2D) modeling capabilities. From what I’ve seen this will be a really useful feature! Being the alpha version of RAS2D there are still features in development, and is bound to be a bit “buggy”, but it is definitely worth looking forward to. What is it?
The new build of RAS will allow users to connect 2D flow elements to a 1D river system. You will now be able to model overland areas as dynamic, 2 dimensional grids, rather than level pool storage areas. The figure below shows the 1D and 2D features together in the geometry window.

• The 2D area can be drawn in as a polygon (much like a storage area)
• The grid cells are automatically generated at a user-specified size within the 2D area
• Cells can be added, removed, or edited manually

How does it work? The 2D mesh and the 1D system are tightly coupled during an unsteady simulation. This means that water surface elevation is calculated at each XS and each grid cell for every timestep, allowing direct feedback at the connections. 2D flow areas can be linked to the 1D system the same way storage areas are. The Figure shown below is a schematic of how the 2D mesh is built, and how RAS routes flow from cell to cell. Upon creating the 2D mesh, you need to load a digital terrain file (.flt format). Both the pre- and post-processing steps for the 2D flow area are done through RAS Mapper.

• RAS pre-processes the 2D mesh separately from the 1D system. During this process RAS creates an elevation-storage curve for each cell, and calculates hydraulic properties for each cell face. These hydraulic properties are similar to the cross section hydraulic properties (HTAB curves).
• The Cell Center is where water surface elevation is computed for the whole cell.
• Cell Faces control flow between cells by acting as a detailed XS. Station/elevation data is captured directly from the underlying terrain file.
• Cell Face Points are used for stationing to connect to a lateral structure. They also represent the ends of cell faces.
• Manning’s n-values for each cell will be assigned by a spatially varied polygon or manually entered.

Computationally, RAS will allow the user to choose between using 2D Diffusion Wave equations (default), or the full 2D Dynamic Wave equations. Most flood applications should be adequately modeled using the Diffusion Wave equations. What are the advantages?Besides computing in 2-dimensions, the main advantage is the program’s ability to maintain computational robustness while preserving the details of the underlying terrain. Smaller features (i.e. drainage ditches) that run through large cells will be captured in the hydraulic properties of the cell faces. Therefore, these features will be preserved and accounted for both computationally and visually, even though they are smaller than the grid cell size, as demonstrated in the RAS2D output displayed in the figure below. Traditionally, many 2D models require cell size to be consistent with the size of the features to be included. Not the case with RAS2D. Additional advantages include:

• Cells can be any size and shape. This allows the user to model odd-shaped features within the 2D flow area as well as provide more computational detail around areas of interest.
• Faster computation times. RAS uses an implicit scheme to calculate water surface and flow at each XS and cell simultaneously. The implicit scheme is also more stable, which allows for larger cell sizes.
• Detailed mapping. RAS Mapper will be able to post-process results to map depth and velocity grids on detailed terrain.
• RAS2D will be able to utilize multiple processors (if available).

New Forum Up!

First, let me apologize for the downtime with the previous HEC-RAS Bloggery Forum.  There were some issues with the forum hosting service.  Unfortunately, I lost all of the previous posts and comments.  The upside is that now I have much more control over content/storage. 

Please have a look at the new forum and post comments/questions/replies.  I encourage you all to register to the forum and don't worry, no spam!  You can get to the forum by clicking on the page link above titled "Forum" or by pasting this web address in your internet browser:  http://hecrasmodel.blogspot.com/p/hec-ras-bloggery-forum.html.  There is also a link to the right in the "Welcome" section. 

Since undoubtedly, many of the previous forum commentors will be wondering where the old forum went, please help me spread the word about this new forum.

Thanks-
Chris

 

Dam Breach Class Boston, MA May 1-3, 2013

Written by Chris Goodell | WEST Consultants

Hi everyone. For those of you who are HEC-RAS dam breach enthusiasts, I will be teaching a 3-day course on dam breach modeling with HEC-RAS in Boston in a few weeks. The course will be held next to the historic MIT campus overlooking the Charles River and downtown Boston, May 1-3. In this course you'll learn all the standard and some of the not-so-well-known techniques for stabilizing and improving the accuracy of very dynamic and stubborn unsteady flow HEC-RAS models (dam breach models are notorious for this). You'll also learn state-of-the-art approaches to dam breach modeling, including level-pool versus dynamic reservoir drawdown and probabilistic techniques for dam breach modeling. Hope to see you there.

Check here for more information:
http://mylearning.asce.org/diweb/catalog/item/id/78019/q/c=79&t=2116&t=2122

If you can't make this one, the next one is in Denver September 11 - 13, 2013. 

Chris

HEC-RAS File Types

Written by Aaron A. Lee 
Copyright © RASModel.com. 2013.  All rights reserved.

Behind the scenes, HEC-RAS automatically creates a series of input and output files when working with a model. It is important to know what each of these files does and how they fit into the overall scheme of your project. Keeping track of these files in an organized manner is good practice, especially as your models grow in size and complexity. This post will feature a steady flow example project, and will list common HEC-RAS files that you’ll see for Unsteady flow, Sediment Analysis, Water Quality, and Hydraulic Design projects.  Although these examples all use the number "01" in the extension, RAS can have multiple instances of each of these files for a given project (except the .prj-only one of those).  Numbers can go as high as "99" and are assigned in the order in which the files were created.   This screenshot is a folder containing the input files generated by RAS after opening and saving one of the installed example projects. At the very least, you need these input files to run the model. If someone asks you to send them your model, these files must be sent, at a minimum. Differences between Steady and Unsteady files are listed when relevant.

• .prj is the Project file. Contains current plan files, units and project description.
• .g01 is the Geometry file. Cross-sectional data, hydraulic structures and modeling approach data are stored here.
• .f01 is the Steady Flow file. Profile information, flow data and boundary conditions written in this file.
• For Unsteady Flow, .u01 is the flow file extension. This is where hydrographs and initial conditions are stored, as well as any user-defined flow options.
• For Quasi-Unsteady Flow (for a sediment analysis), .q01 is the flow file extension.
• .p01 is the Plan file. Contains a list of the associated input files, and all simulation options.

These are all text files and can be directly read and edited in a text editor. The following screenshot shows the input and output files after the steady flow model has been run. Note that some of these are only used by RAS as intermediate files during computations.

• .O01 is the Output file. Contains all of the computed results from the associated plan. This file is written in binary format and can only be read from the user interface.
• For Unsteady Flow, a .dss file is automatically generated as an output. This file contains time series data that is viewable by any program that can read dss files (typically HEC software).
• If your model links to a dss file for use as input data (e.g. inflow hydrographs, stage hydrographs, observed data, etc.), then that .dss file will be necessary to run the model and should be included in your group of files you send to a reviewer.
• .r01 is the Run file for steady flow analysis. Contains all of the necessary input data required for the RAS computational engine. The run file is created during the model simulation, and is not required to view final results.
• For Unsteady Flow, .x01 is the extension.
• .comp_msgs.txt is the Computational Message text file. Records the computational messages that pop up in the computation window. The messages file is not required to view final results, but can be useful in troubleshooting errors identified by RAS.
• .hyd01 is the Detailed Computational Level output file. This can be switched on in the Unsteady Flow Analysis window.
• .p01.rst is a Restart File (also called a Hot Start File, or Initial Conditions File). This option can be switched on by the user in the Output Control Options window. See the Hot Start post for more guidance.

For Unsteady Flow analysis, these files are categorized as “intermediate,” which means that they are not essential for running a model or viewing results, since they are recreated by RAS during run-time.

• .c01 is the Geometric Pre-Processor output file. Contains the hydraulic properties tables, rating curves, and family of rating curves for each cross-section, bridge, culvert, storage area, inline and lateral structure. This file is rewritten each time you change your geometry file.
• .b01 is the Boundary Condition file.
• .bco01 is the Unsteady Flow Log output file.
• .p01.blf is the Binary Log file.
• .IC.O01 is the Initial Conditions file.

If submitting your final model to a client or a reviewer, you will likely only send the necessary input files. Sending output files are optional, but will allow the reviewer to avoid rerunning the model on their end. Including the .c## files might be a good idea for larger models so that RAS can skip the pre-processing step. SEDIMENT ANALYSIS

• .S01 is the file extension for Sediment Data. This file contains flow data, boundary conditions, and sediment data.
• .SedCap01 is the extension for Sediment Transport Capacity data. When sediment transport computations are performed, RAS creates a set of intermediate files:
• .sed is the detailed sediment output file.
• .SedHeadXS01 is the header file for the cross section output.
• .SedXS01 is the cross section output file.
• .H01 is the Hydraulic Design data file.
• .H01.SiamInput is the SIAM Input Data file.
• .H01.SiamOutput is the SIAM Output Data file.

WATER QUALITY ANALYSIS

• .W01 is the file extension for Water Quality data. This file contains temperature boundary conditions, initial conditions, advection dispersion parameters and meteorological data. When water quality computations are performed, RAS creates a set of intermediate files;
• .bco is the water quality log file.
• .p01.wqrst01 is the water quality restart file.
• .color_scales is the file that contains the water quality color scale.

Remember that file extensions can be numbered from 01 to 99, and are assigned in the order that they are created.

Two-Dimensional modeling in HEC-RAS

Here's a quick sneak preview of what's coming in 2-D HEC-RAS.  Click either figure below to see an animation of the levee breach simulation.  More to come soon...