Transect for Extracting Flow in a 2D Area

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

*Update:  Version 5.0.2 now does flow transects in RAS Mapper with profile lines.  No longer necessary to use a 2D Area Connection to do this.

A very common output request in 2D modeling is for flow over (through) a transect line.  HEC-RAS 5.0 does not have a specific tool for extracting flow data along a line in a 2D area, however it CAN be done.  Here’s how you do it.
Inside your 2D area, draw a 2D Area Connection where you would like to extract flow.  In the figure below, I’ve drawn my 2D Area Connection line from bottom to top, which represents left to right, looking in the downstream direction. 

Notice that with the completely orthogonal cell orientation, but with a skewed 2D Area Connection line, the black and red striped connection line is “jagged”, following cell faces between the connecting cells.   To fix this, we need to use a breakline.  You could draw a break line on top of the 2D Area Connection (click the 2D Area Break Lines button on the top of the Geometric Data window), however, HEC-RAS also has a short cut for putting breaklines on 2D Area Connections.  If you right click on the 2D Area Connection (I’ve named if “Flow Line”), you’ll see an option to “Create 2D Flow Area Breakline”.  Select this for quick cell re-orientation around the 2D Area Connection Line.


Now you’re ready to enter data to the 2D Area Connection that you’ll use for extracting flow.  Click the SA/2D Area Conn button on the left side of the Geometric Data window. 
Make sure you connect “From” and “To” to the same 2D flow area.  Then choose “Normal 2D Equation Domain”.  This will force RAS to use the same 2D St. Venant equations over the terrain under the 2D Connection line as if the connection line wasn’t there.  BUT…you still have to define the Structure Type as a Weir and provide station-elevation data to define the crest of the weir, even though RAS will not use it.  Maybe this gets fixed in a later version.  HEC makes this easy though as you can extract the terrain profile from the 2D Connection cutline by clicking the button “Terrain Profile” as shown below.  Just copy and paste the terrain profile into your station-elevation table and you will  have defined a “zero-height” weir.  I guess it’s possible to use any crest definition, since RAS shouldn’t use the weir equation-it will use the normal 2D equation domain, but I haven’t tried it. 

Now you are ready to compute.  After computing, go to the Stage and Flow Hydrographs output window.

Make sure you select Type…Storage Area Connections (yes, it is technically an SA/2D Area Connection, but HEC hasn’t gotten around to renaming this yet in this window).  Now you can see the flow hydrograph for the flow line you’ve drawn.  You can check, but you’ll see the results are exactly the same as before including the flow line.

New Beta Version of HEC-RAS 5.0

Fellow HEC-RAS users:

A new beta version of HEC-RAS (August 21, 2015 build-"Release Candidate 2") is now available to download and install.  I have no new information about  when the final release will be made available, but for now this new beta version has a lot of bugs fixed and many new features, including breaklines, Manning’s n value regions, and mapping of sloped water surfaces in RAS Mapper for 2D areas.  Please follow the directions from HEC below for downloading and installing.

Enclosed is a link to a new HEC-RAS 5.0 version, Release Candidate 2, August 2015.  We have fixed several Bugs since the Release Candidate 1 version.  This version has all the features we have planned for the final release.  We are in a No New Features mode, and performing the final testing and documentation updates.

     Here is the link:

https://drive.google.com/file/d/0B0bpiyLiUeRXVEZyVWJVd0FNNUk/view?usp=sharing

     This self extracting exe should be run in a separate directory.  Once it is run, there will be a new Setup package for the HEC-RAS 5.0 beta software; a new 2D User’s Manual in PDF format; and a new set of 2D example data sets in a zip file.  You must have admin privileges to run and install the software using the setup package.  Please Uninstall the previous HEC-RAS 5.0 beta first!!!!

     Thank you for installing and testing this final Beta version of the software.

Some of the New Stuff:

1. Lateral Structures can now be Georeferenced.  So it will be easier to lay them out, and get them connected to 1D river reaches and 2D Flow Areas.
2. HEC-RAS Mapper, now uses a TIN based sloping water surface technique to show spatial results inside of RAS Mapper. Previous versions, in 2D area the depth, velocity, etc.. was plotted as a single value for the entire cell, which produced some blocky looking plots in steep terrain.
3. More flexible internal hydraulic structures.
4. Improvements to the stability of connecting 1D reaches into and out of 2D flow areas.
5. Several New output capabilities in RAS Mapper – please see the 2D user’s manual.
6. Many Bug fixes, especially in RAS Mapper.

Combining Two Reaches or Splitting One

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

Suppose you have two separate HEC-RAS rivers and wish to combine them.  There is no “combine two rivers” option in HEC-RAS, but it can be done using the Move Points/Objects option.  Take the very simple reach presented below:



I wish to combine the Upper Tualatin with the Clackamas reach of the Willamette River.  In the figure above, they are disconnected-two separate rivers.  Select Edit…Move Points/Objects and