HEC-RAS 5.0 beta with 2D modeling is out!

***Note-this post was for the old 5.0 beta version.  Please get the latest version here:  http://hecrasmodel.blogspot.com/2014/10/updated-hec-ras-version-50-beta-now.html


Hey RAS Modelers-The long awaited HEC-RAS Version 5.0 with 2D Modeling is finally out in beta form!  Please read the message below from Gary Brunner that provides instructions for downloading and installing HEC-RAS 5.0 beta.   Please note that there is a required password to install, "ras4you!"  Have fun with it and please provide constructive comments/suggestions to HEC.  As you'll read below, there will be an aggressive testing period of only 4 months, so give this version a try as soon as possible and let HEC know if you run into any bugs. 


I've also uploaded the "What's New" document and the updated "Combined 1D and 2D Modeling" document to my The RAS Solution Google Drive Site:


https://drive.google.com/file/d/0B_s8OLJOgOi0OTlwbjNYSGd4SFE/edit?usp=sharing
https://drive.google.com/file/d/0B_s8OLJOgOi0Nm5sdHFhSzFUYkk/edit?usp=sharing




Chris G.

Dear HEC-RAS 5.0 Beta (with 2D) tester,

     You are receiving the this email, and a link to an updated version of "HEC-RAS 5.0.0 May 2014 Beta (with 2D Flow Areas)", because you are either a previous Beta tester, or you have expressed interest in the new 2-Dimensional modeling capabilities being added to HEC-RAS.  Here is the link to the latest version:

      http://www.hec.usace.army.mil/misc/files/ras/HEC-RAS_5.0_Beta_2014-05-23.exe

      This link lets you download a self extracting Archive file called "HEC-RAS_5.0_Beta_2014-05-23.exe" 

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

            1). The installation setup package called: " HEC-RAS_5.0_Beta_2014-05-23_Setup.exe"

            2). A updated PDF version of the User's Manual called "Combine 1D and 2D Modeling with HEC-RAS.pdf"

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

      This installation setup package is password protected.  The password to run the setup package is: "ras4you!"

      This version of HEC-RAS has many new features.  I have enclosed a Word Document called "Whats New in HEC-RAS 50 Beta.docx", that describes most of the new features.

Here is a link to the User’s manual:

            http://www.hec.usace.army.mil/misc/files/ras/Combined_1D_and_2D_Modeling_with_HEC-RAS.pdf

The main new features are the following:

            1.         2D Only Computations (no 1D elements) and Multiple 2D areas in the same model

            2.         Several New Ways to Link 2D Flow Areas to 1D Elements

            3.         Hydraulic Structures Inside of 2D Flow Areas

            4.         Improved Computational Speed for 2D and 1D

            5.         New HEC-RAS Mapper Features and Output Capabilities

            6.         New Computational Options for 2D and 1D

            7.         Improved Speed and Memory Usage of the 2D Pre-Processor

            8.         Additional 2D Flow Area Initial Conditions Options

     9.   New Sediment bank erosion capabilities (USDA-ARS Bank Stability and Toe Erosion Model (BSTEM))

10.       Unsteady Flow Sediment Transport Modeling (please Contact Stanford Gibson at HEC for updated Sediment documentation)

            IMPORTANT NOTE:  We have changed the file format for how we store Terrain data in HEC-RAS.  To use this version of HEC-RAS, you will need to redo the development of your Terrain model for use in RAS Mapper and 2D modeling.  You will also have to rerun your model to see mapping output.  Please See Section II of the enclosed User’s Manual for building Terrain models in HEC-RAS.  Previously we were using our own file format called the “Tiled Mapping System” (*tms).  We have switched to using the GeoTiff file format (*.tif).  The GeoTiff files are tiled, pyramided, and compressed, just like our own format was.  So it has all the same benefits of the TMS files.  However, GeoTiff is a standard file format, which you can drag and drop into ArcGIS, or other software.  So for compatibility with other industry standard software, we have changed how we make and store terrain data.  We have also switched all of our output grids to the GeoTiff format to make it easier for user’s to get the results into a GIS or other piece of software.

      I have enclosed an updated version of the User's Manual on how to use the 2D modeling capabilities within HEC-RAS 5.0 Beta ("Combine 1D and 2D Modeling with HEC-RAS.pdf".  This document has been dramatically expanded.  If you really want to learn how to use the 2D modeling capabilities in HEC-RAS, Please Read This Manual.  I have spent a lot of time working on this document, and I think anyone who currently knows how to use HEC-RAS for 1D unsteady flow modeling will be able to learn how to use the new 2D unsteady flow modeling capabilities with just the software and this document.  Please give me some feedback on this User’s manual if you find mistakes or there is information you feel is missing, or could be explained better.

            There are two example data sets that come with the self extracting zip file: “Muncie.prj” and “BaldEagleDamBrk.prj”.  The Muncie data set is a 1D river with a 2D Flow Area inside of a Levee system.  The levee system is breached and flow goes into the protected area.  The BaldEagleDamBrk data set has seven different Plans in it.  This data set has examples of all the different ways to use 2D areas.  The purpose of this data set is just to demonstrate all the different Ways 2D areas can be linked to 1D elements, as well as modified computational mesh examples, and hydraulic structures inside of a 2D Flow Area.

            Our Plan is to have approximately a four month Beta test period, then release the Final HEC-RAS 5.0 version this fall.  During this time we hope to get feedback from Users on bugs, interface issues, usability, missing features, documentation, etc…  So, we need you to test this version of the software and provide us feedback.  Please send all comments on this version to me through hec.ras@usace.army.mil.

      Thank you for testing HEC-RAS, we look forward to your comments and feedback. 

Gary W. Brunner, P.E., D.WRE, M.ASCE

Senior Technical Hydraulic Engineer

Hydrologic Engineering Center. USACE

www.hec.usace.army.mil

Lateral Structure Coefficients

Written by Chris Goodell, P.E., D.WRE  |  WEST Consultants

Copyright © RASModel.com.  2013.  All rights reserved.

Lateral structures can be used in HEC-RAS to transfer flow from a river/reach to a storage area, or to another river/reach.  With the coming release of HEC-RAS with 2D capabilities (estimated beta release January/February 2014), you’ll be able to hook a river/reach to a 2-D area using a lateral structure. 
Although its primary function in HEC-RAS is to transfer flow out of one river/reach into another component (river/reach, storage area, 2D area), a lateral structure can physically represent a wide range of geometric features, including a levee, a flow diversion structure, a morning glory spillway, or even a natural ground or bathymetric profile.  Including a lateral structure in your model to represent a levee is important if the levee is ever overtopped or breached during the simulation.  Flow diversion structures can have multiple outlet features, including culverts, gates, and spillways.  These features are all available in the lateral structure editor in HEC-RAS. 
Another common use of lateral structures is to simulate flow transfer from the river to a tributary during a flood event.  This is especially convenient if you don’t want to model the tributary as an individual reach, but still want to account for it’s available storage, for a proper accounting of flood wave attenuation in the main stem river/reach.  As an example, the following figure shows a storage area representing a tributary to the main stem river.  This storage area is connected to the main stem by a lateral structure (highlighted in red). 

Because a lateral structure can represent a variety of different flow transferring structures (or non-structures), the hydraulics in and around the lateral structure can be quite different, depending upon the case.  Every lateral structure in HEC-RAS requires a lateral weir coefficient, and different hydraulics mean different lateral weir coefficients.  Any hydraulics textbook will have a multitude of weir coefficients for “inline” conditions, but it’s rare to find something similar for lateral flows, or diversion flows.  But it is generally agreed that lateral structure weir coefficients should be much lower than a similar inline configuration.  For example, an inline, hydraulically efficient broad-crested weir might have a weir coefficient around 3.0 (US units) or 1.7 (SI Units).  Turn that structure sideways (a lateral structure), and it will have a coefficient closer to 2.0 (US Units) or 1.1 (SI Units).  The difference is due to the energy/momentum loss associated with turning flow lines from their downstream orientation to a lateral direction out of the river/reach.    Unfortunately, there has simply not been a lot of research done on quantifying this energy/momentum loss and what that does to lateral weir coefficients.
The research that is available could be useful and might be worth checking out.  Hagar’s equation is one reference and is actually built into the HEC-RAS lateral structure editor, under Lateral Weir Embankment…Weir Computations.  It will compute an equivalent lateral weir coefficient based on an inline value (the Default Weir Coefficient) and some physical and hydraulic properties of the weir and  the adjacent river/reach. 

You can read more about Hagar’s equation in the HEC-RAS Hydraulic Reference Manual on page 8-17. 
Useful references for lateral structure weir coefficients (including Hager’s):

• Hager, W.H. (1987). “Lateral Outflow over Side Weirs.” Journal of Hydraulic Engineering, ASCE, 113(4).
• Borghei, S.M.; Malili, M.R.; Ghodsian, M. (1999). “Discharge Coefficient for Sharp-Crested Side Weir in Subcritical Flow.” Journal of Hydraulic Engineering, ASCE, October, 1999.
• Ranga Raju, K.G.; Prasad, B.; Gupta, S.K. (1979). “Side Weir in Rectangular Channel.” Journal of Hydraulic Engineering, ASCE, 105(5).
• Subramanya, K.; Awasthy, S.C. (1972). “Spatially Varied Flow over Side Weirs.” J. Hydr. Div., ASCE, 98(1).
• Singh, R.; Manivannan, D.; Satyanarayana T. (1994). “Discharge Coefficient of Rectangular Side Weirs.” Journal of Irrigation and Drainage Engineering, ASCE, 120(4).

However, none of these references discuss lateral weir coefficients for lateral flow transfers over natural ground, or surface flow (i.e. non-elevation overbank terrain).  HEC has a reference table for lateral structure coefficients that I like to use-it’s also included in the new “Combined 1D and 2D Modeling with HEC-RAS” document that was released in August 2013, in anticipation of the new 2D feature in HEC-RAS expected to be released as a beta version in the January/February 2014 time frame.   Note how low the suggested range of coefficients is for “non-elevated overbank terrain.”  Because they are not dimensionless, be aware that weir coefficients in SI Units are different from US units by a factor of the square root of the ratio of the SI gravitational constant to the US gravitational constant,

What is being modeled with the Lateral Structure	Description	Range of Weir Coefficients
Levee/Roadway – 3 ft (1 meter) or higher above natural ground	Broad crested weir shape, flow over Levee/road acts like weir flow	US Units: 1.5 to 2.2 (2.0 default) SI Units:  0.83 to 1.2 (1.1 default)
Levee/Roadway – 1 to 3 ft (0.3 to 1.0 meter) elevated above ground	Broad crested weir shape, flow over levee/road acts like weir flow, but becomes submerged easily.	US Units:  1.0 to 2.0 SI Units:  0.55 to 1.1
Natural high ground barrier – 1 to 3 ft (0.3 to 1.0 meter) high.	Does not really act like a weir, but must flow over high ground to get into 2D (or storage) area.	US Units: 0.5 to 1.0 SI Units: 0.28 to 0.55
Non-elevated overbank terrain. Lateral Structure not elevated above ground	Overland flow escaping the main river.	US Units: 0.1 to 0.5 SI Units:  0.06 to 0.28

*Hydrologic Engineering Center, August 2013.  “Combined 1D and 2D Modeling with HEC-RAS”

Although this table is presented within the context of 1-D to 2-D flow transfers, these values will work with river/reach to storage area or river/reach to river/reach flow transfers as well.  As noted in the referenced document (HEC 2013), “In general, Lateral Structure weir coefficients should be lower than typical values used for inline weirs.  Additionally, when a lateral structure (i.e. weir equation) is being used to transfer flow from the river (1D region) to the floodplain (2D Flow Area), and then [sic] the weir coefficients that are used need to be very low, or too much flow will be transferred.”  Also, “The number 1 problem people have been having with interfacing 1D river reaches with 2D areas, is user’s [sic] have been using way to [sic] high of weir coefficients for the situation being modeled.  If the lateral structure is really just an overland flow interface between the 1D river and the 2D floodplain, then weir coefficients in the range of 0.1 to 0.5 must be used to get the right flow transfer and keep the model stable.” 

The HEC 2013 document ("Combined 1D and 2D Modeling with HEC-RAS") with the Table of lateral weir coefficients can be downloaded from my Google Drive site here:  https://drive.google.com/file/d/0B_s8OLJOgOi0Nm5sdHFhSzFUYkk/edit?usp=sharing.  The lateral weir coefficient table is on page 35.

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...

 

Quasi Two-Dimensional Modeling in HEC-RAS

Written by Chris Goodell, P.E., D. WRE | WEST Consultants
Copyright © RASModel.com. 2013.  All rights reserved.

One of the limitations of HEC-RAS is that it is a one-dimensional model. Simply put, RAS assumes all flow moves along a singular dimension. For a given cross section, all of the flow is assumed to move either downstream, or all of it moves upstream, along the singular dimension (which can be defined as a polyline-does not have to be a straight line). The consequence of this is that there is only one water surface elevation (stage), and one total flow for a given time step at a given cross section. All of the other variables for a given cross section that you see in the profile output table, detailed output table, DSS, etc. are derived from the stage and flow values. This includes the velocity and shear stress distributions over a cross section, which can provide the appearance of a 2-dimensional analysis. But that is all based on a conveyance distribution over geometric segments of the cross section using that single water surface elevation and single total flow.

So why do I bring this up? First, it's always good to know ALL of the limitations of whatever model you're using to predict future outcomes. But I also want to demonstrate the "quasi-2-dimensional" capabilities of HEC-RAS. While planning a hydraulic study in an estuarine environment, you may immediately start thinking about which 2-dimensional model you want to use. But I've seen many great (and creative) applications of HEC-RAS in these 2-dimensional environments that produce very reasonable, if not accurate results.  In short, a quasi-2-d analysis in RAS requires you, the user, to understand up front the likely flow patterns in your study area. This is best accomplished by going out to the field and looking at your site, studying topographic and bathymetric maps, looking at aerial photographs, and simple common sense and experience. Once you've determined your perceived flow paths, all water outside of these flow paths should either be ineffective flow areas, storage areas, or even separate reaches.
  

Here’s an example of an estuarine environment on the Oregon Coast (Yaquina Bay). I haven’t modeled this yet, but if I were, here’s how I would approach my model setup:










1. Draw a stream centerline (blue in the figure) that represents the singular dimension of flow movement-i.e. flow will either move downstream or upstream along in the direction of this line. Cut cross sections at an appropriate spacing, making sure to cover all areas that could get wet during the simulation. Yes, the trib channel south of the main reach is not covered, but I’ll get to that in a second.

2. Define ineffective flow areas. These are areas that you will expect WON’T have flow actively moving along the singular dimension. Be sure to appropriately define expansion and contraction of flow as you draw in the ineffective polygons. All portions of your cross sections that fall within these areas should be set to be ineffective in your RAS model.  


3. Areas that could possibly have a different water surface elevation than the nearest cross section should be split out and modeled as an off-line storage area. Connect that Storage Area to the main reach using a Lateral Structure. You’ll have to come up with a stage-storage curve for the storage area, to be able to model it in RAS. This is a very easy and straight-forward exercise in GIS, as long as you have sufficient topographic coverage. Keep in mind, RAS uses the simplified level pool routing method for Storage Areas. Lateral Structures used for this application will not have an actual “structure” associated with it, so the discharge coefficient you use is very subjective. Typically values on the order of 0.5 to 1.5 are used. Calibrate this if you can.


4. Alternatively, you can model the tributary as its own reach, connected to the main channel with a junction. This will allow you to model it using the full dynamic St. Venant equations, giving a more physically representative answer in the trib. However, if movement of water through this reach is relatively slow (i.e. typical ebb and flood tides), a storage area will be fine-and easier!  You can get as complex as you want. There are no limitations within RAS to the number of storage areas, ineffective flow areas, lateral structures, and tributary reaches you use. Just keep in mind, the more complex you make it, the more difficult it will be to troubleshoot any instabilities.


The following video is a great example of a quasi-2-d application of HEC-RAS. This very complex model and the video were created by Gary Brunner at the Hydrologic Engineering Center.

HEC-RAS model of the Lower Columbia River Estuary-Courtesy Gary Brunner