Thursday, September 18, 2014

HEC-RAS 2D Updates Coming!

Written by Christopher Goodell, P.E., D.WRE  |  WEST Consultants
Copyright © The RAS Solution 2014.  All rights reserved.

(Update:  New release is now available here)

Just heard from HEC that a new, updated beta version of HEC-RAS 5.0 will be coming out soon (later this month or early next).  The full release of HEC-RAS Version 5.0 is still scheduled for the end of the calendar year. 

New features in the next beta release are:
  1. Multiple Manning's n value definition in 2D areas
  2. Velocity Vectors in RAS Mapper
  3. Particle Tracking Visualization Tool in RAS Mapper
Plus most (if not all) of the bugs found to date will be fixed.

Here’s a sneak peak of a new velocity visualization feature in HEC-RAS used in an “instantaneous” dam break example, courtesy of Gary Brunner.

(The YouTube Link will offer a better quality video)

https://www.youtube.com/watch?v=-lZkE0IPj0c&index=1&list=UUgkWjGRSy2Vc_wqdX-sC5rA




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Tuesday, September 16, 2014

Creating your mesh in RAS 2D

Written by Christopher Goodell, P.E., D.WRE  |  WEST Consultants Copyright © The RAS Solution 2014.  All rights reserved.

Your computational mesh is what will allow you to do 2D modeling in HEC-RAS.  Think of a mesh as a net that you drape over your terrain.  The continuous properties of the “infinite” terrain are then discretized onto the mesh so that computations can be made over a finite domain.  Here in the geometry editor, we can see the computational mesh “draped” over the terrain.  Notice that the mesh remains within the perimeter of the terrain.  This is required for HEC-RAS.  RAS is able to work with structured or unstructured meshes with cells that have up to eight sides.  Typically you’ll begin with a Cartesian or rectilinear structured mesh and where you add more detail and resolution, you’ll have unstructured (irregular) zones within your mesh.  Boundary cells will also exhibit unstructured characteristics where RAS works to fit the mesh to the mesh perimeter.


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Before building your mesh, it can be useful to include a background image of your terrain so that you can make sure you draw your grid within the bounds of your terrain. The background image will also give you a clue about areas in your 2D grid that might need more or less detail. The background image has to be created external to HEC-RAS and must be accompanied by a world file. More information about world files can be found here: http://webhelp.esri.com/arcims/9.2/general/topics/author_world_files.htm


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Use the 2D Flow Area button at the top of the geometry schematic to draw a new 2D area. This is drawn exactly the same way storage areas are drawn. Single click the points to define a polygon shape, staying within the bounds of the terrain (very important), and to complete the area, double click.
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Once a 2D area has been defined, click on the 2D Flow Area editor button to set up the mesh. The first windows provides the user options for Manning’s n value for the 2D Area. Only 1 n value can be used for now in the 5.0 beta version of HEC-RAS for a 2D Area, but future versions will allow multiple n value definition for a single 2D Flow area. The tolerance input boxes allows the user to have some control on how much data goes into each of the cells on the soon-to-be-created 2D grid. The defaults usually work very well for the tolerance inputs. Typically you’ll enter the Manning’s n value and then click the “Generate Computation points on regular interval. Then go ahead and define the grid cell size (both width, DX, and height, DY). The starting offset point is optional. Default is to leave it at 0,0. Then click “Generate Points in 2D Flow Area, and HEC-RAS will build a structured mesh of constant cell size (this can be adjusted later).
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Here we can see the mesh that was created with 500 ft X 500 ft spacing. Notice that the majority of the mesh was created with 500-ft by 500-ft square cells, but around the perimeter of the 2D area, RAS automatically creates irregularly shaped cells to fit the edges. These should always be checked after the mesh is created to make sure the edge cells are suitable. Look for cells with multiple centers, or cells that are not generally the same size and aspect ratio as the others (like the example highlighted above).
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You can fine tune your mesh (either correcting unsuitable boundary cells or adding more detail/resolution) by using the “Move”, “Add”, and “Remove” tools in the Edit menu of the Geometry Schematic.  After you select Edit…Move Points/Objects, you can click and drag any of the cell center points.  Once you “de-select” Move Points/Objects, HEC-RAS will redraw the grid based on the new, manual placement of centers.


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In addition to moving cell centers, you can add more cell centers to your mesh where you need more detail, and remove cell centers where you need less detail. For example, in this narrow connection between two flooded areas, we want more definition to better simulate the flow through here. Manually click some points where more definition is needed. Once “Add Points” is unchecked, HEC-RAS will automatically redraw the grid. Where you move points or add more points, the mesh will look a lot less structured.   image

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Look closely at this last figure.  We have a nice structured grid in the large floodplains to the northwest and southeast.  The narrow connection between the two exhibits a very unstructured mesh with more detail.  There are (at least) two things wrong with the grid.  In fact, these two things will prevent RAS from running until they are resolved.  Post a comment below and let me know what you think the errors are. 


More information on 2D modeling in HEC-RAS can be found here:  https://drive.google.com/file/d/0B_s8OLJOgOi0Nm5sdHFhSzFUYkk/edit?usp=sharing

Images in this post are from the Bald Eagle Creek Example Dam Break Study example data set.  The Bald Eagle Creek Example Dam Break Study HEC-RAS model is provided courtesy of the Hydrologic Engineering Center and can be downloaded along with HEC-RAS Version 5.0 beta here: http://hecrasmodel.blogspot.com/2014/10/updated-hec-ras-version-50-beta-now.html





Friday, September 5, 2014

Web Imagery for RAS Mapper in Version 5.0

Written by Christopher Goodell, P.E., D.WRE  |  WEST Consultants
Copyright © The RAS Solution 2014.  All rights reserved.

There are a lot of new features in Version 5.0.  We’ve discussed quite a bit the new two-dimensional capabilities.  But a real pleasant surprise for me was how great the new RAS Mapper is.  I’m going to try to highlight some of these new Mapper features over the next few months, but in this post I’ll share perhaps my favorite added tool:  Web Imagery. 
RAS has had the ability to add background images for quite a while now.  And when RAS Mapper was introduced in Version 4.1, it too had that feature.  But if you wanted to add aerial photographs behind your project, you had to go and find them.  There are many sources on-line for that:  some good, some not-so-good.  But, once you found the aerial photos, it was common to have to spend some time re-projecting them into the geographic projection and coordinate system you are using.  That all took time working in a GIS program, and frankly, some skill that I don’t have a lot of. 
In RAS Mapper in 5.0 a new feature called Web Imagery is added.  Web Imagery allows you to choose from 21 different web-based map types: Imagery, street maps, physical maps, topo maps, even infrared maps.  You can select these background images right from the RAS Mapper and they are re-projected on the fly. These come from a variety of hosts like ArcGIS, Bing, Google, NASA, and the USGS.  And each have worldwide coverage.  Some of these maps/images will work well for you, some won’t, depending on the scale and location of your project.  I have found that Google and Bing have excellent worldwide satellite coverage. 
And here’s where it gets really cool:  All of these maps and images are on the web, not your computer.  Just like in Google Earth as you zoom out, different, and less detailed images are used, so that you are not unnecessarily downloading more detail than you need.  As you zoom in, more detailed images are used so that you always have a nice crisp view.  This is all done seamlessly and very quickly.  And RAS only downloads what you need from the web for the current view extents you are at.  Take the Muncie demonstration dataset that comes with HEC-RAS 5.0.  I can zoom out to the full extent of the project and with Bing Satellite activated as my background image I have very nice coverage:
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Now, I can also zoom in to a city block and have all the detail and precision I need. 
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By the way, the time it took RAS to redraw the inundation, download and clip the more detailed image, and reproject the new image was only 2.5 seconds on my computer. 

To access the web imagery in RAS Mapper, first make sure your model is projected to a recognized projection system.  At the top of RAS Mapper, select Tools…Set Projection for Project…Here you’ll select a projection file (*.prj – NOT to be confused with a RAS project file!).  If it’s a proper projection file, you’ll see the Metadata show up in the window below.
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Once your model has a defined projection, you can add web imagery by right-clicking on Map Layers in the Layer Manager and selecting “Add Web Imagery layer…” or by selecting “Web Imagery…” from the Tools menu item.  Once selected the following window will appear and you can choose any or all of the 21 available maps/images (you can only add one at a time though).
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For most projects, you’ll probably be using Bing Satellite, ArcGIS World Imagery, Google Satellite, and perhaps some of the topo maps.  The quality and usability of these different maps will depend on your location and viewing scale (as you zoom in closer and closer, some of the maps will no longer load). 
Requirements for using Web Imagery in HEC-RAS 5.0:
1.  Your RAS model must be set to a known projection. 
2.  You have to have internet access (high speed is obviously better).

For more information about Web Imagery in HEC-RAS Version 5.0, check out the document “Combined 1D and 2D Modeling with HEC-RAS”

Get the lastest beta release of HEC-RAS Version 5.0 here.

Tuesday, September 2, 2014

Floodplain Management Association Quarterly News and Analysis

See link below for the latest newsletter.  Check the last page especially for an editor’s note about HEC-RAS 5.0.


FMA Header Logo New
FLOODPLAIN MANAGEMENT QUARTERLY NEWS AND ANALYSIS
for FMA Members

We are pleased to announce the Summer 2014 FMA Quarterly Newsletter.  Highlights include:
  • 2014 FMA Annual Conference - "Keeping Our Heads Above Water"
  • FloodSmart Tools and Resources