Creating Static Results Maps (Shapefiles or Rasters) using RAS Mapper

Written by Mikell Warms  |  WEST Consultants
Copyright © The RAS Solution.  2016.  All rights reserved.

Many readers have been asking how to create shapefiles and other static maps in RAS Mapper. One of the main differences between RAS Mapper in RAS 4.1 and RAS 5.0 is the existence of Dynamic Maps. What makes these maps dynamic is that when you have that Results Layer selected in RAS Mapper, you can use the slider bar (top right) to animate through the simulation and see the results of that layer at each mapping output interval (or each profile for steady flow models). These maps are not saved to the disk, they are temporarily stored in memory.

With this change, you can no longer “Export Layer to Shapefile” as you could previously, due to the fact that these dynamic layers are not one map, they are many maps.

To create static maps, such as shapefiles or rasters, we must first tell RAS Mapper what type of static map we want (Inundation Boundary, Velocity, Shear Stress, etc.) and whether we want the data from a specific timestep, or max/min. To do this, right click on the bold “Results” heading in the Layer Manager in RAS Mapper, then choose “Manage Results Maps”.  All of your plans and default layers will load (like below):

Choose the plan you are interested in, and click on “Add New Map.”

If you’re running a Steady model, the window that pops up will look like this: 

If you’re running an Unsteady model, the window that pops up will look like this: 

Choose the Map Type you are interested in creating; in this case we are creating a maximum Inundation Boundary. Notice we have chosen “Maximum” under the Unsteady Profile options, but we could have chosen “Minimum” or a specific point in time. On the right hand side of the window, make sure to change the Map Output Mode to one of the “Stored (saved to disk)” options, depending on your needs. In this case, we are creating a shapefile polygon. Then click Add Map.

One last step. The Manage Results Maps layer should now look like below:

Notice the static map we have added has appeared. However, the Inundation Boundary map status says “Map Not Created”. You will need to select that map, and click on “Compute/Update Stored Maps” at the top right. If you have multiple static maps, you can select them all by holding the CTRL key and selecting multiple maps prior to computing them.

Once the computations have completed, the status will change to “Map files up to date” and RAS will save your shapefile in your HEC-RAS project folder, in a subfolder that has the same name as the plan from which the shapefiles were created.

“Using HEC-RAS for Dam Break Studies”

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

HEC recently published a new training document called “Using HEC-RAS for Dam Break Studies”.  Written by Gary Brunner, P.E., D.WRE, it is an easy to follow guide for performing Dam Break simulations in HEC-RAS.
 
It covers topics like:

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

Dynamic versus Level Pool Reservoir Drawdown for Dam Breach Modeling

Written by Chris Goodell, P.E., D. WRE | WEST Consultants
Copyright © RASModel.com. 2010. All rights reserved.
This is a summary from a paper (Goodell,Christopher;Wahlin, Brian. “Dynamic and Level Pool Reservoir Drawdown: A Practical Comparison for Dam Breach Modeling.” 33rd IAHR Congress Proceedings, Vancouver Canada, 2009) on level pool versus dynamic reservoir drawdown for dam breach modeling. In RAS you can define your reservoir with a series of cross sections (which uses dynamic routing) or a storage area (which uses level pool routing). Dynamic routing is generally assumed to be more accurate, but the size and shape of a reservoir can sometimes make level pool reservoir adequate.

A key component to dam breach modeling is the reservoir drawdown. This has a significant impact on the magnitude and shape of the breach outflow hydrograph, and ultimately the extent of flood inundation in the downstream reach. Drawdown of the reservoir can be modeled with the precise and physically correct dynamic routing method, which uses the full St. Venant equations of Conservation of Mass and Conservation of Momentum. However, this requires detailed bathymetric data for the reservoir, which is frequently very difficult and expensive to obtain for existing reservoirs. Furthermore, dynamic routing is complex and prone to numeric instabilities. A level pool drawdown is a more simplistic, numerically stable approach that can be used successfully under certain circumstances and requires only a simple stage-storage curve for the reservoir.

Two primary characteristics emerge as indicators of a given reservoir’s ability to be described by a level pool analysis. The Compactness Factor, F_c, is simply the ratio of the dam height (H) to the reservoir length (L). The longer and shallower the reservoir, the lower the Compactness Factor and the more the reservoir acts like a river during its drawdown. Thus dynamic routing would be more appropriate in this situation. Short, relatively deep reservoirs are more compact, have a larger F_c value, and can be adequately described using a level pool analysis.

The Translation Factor, F_t, describes the relationship between the speed of the breach development and the ability of the reservoir to supply water to replace the water leaving through the breach. The easier the reservoir can deliver water to the breach, the more it can be described by a level pool analysis. Fast breach developments and long reservoirs are more appropriate to be modeled by dynamic routing. The Translation Factor is computed as:

F_t = ct/L

Where: c = shallow water wave celerity =.

d = representative reservoir depth.

and t = time.

A third parameter can be used to help graphically display the results of the various simulations. The Drawdown Number, D_n, is defined as the product of the Translation Factor and the Compactness Factor.






It becomes apparent that for high Drawdown Numbers, the level pool analysis produces results very close to dynamic routing. By enveloping the data points, a 5% threshold Drawdown Number is shown to be 0.41. That means that a reservoir with a Drawdown Number of 0.41 or greater will produce peak outflow results within 5% of a dynamic routing simulation. The 10% threshold Drawdown Number of 0.24 is also indicated on the plot.

You can see the full paper in the referenced proceedings. Also, the Hbox software has an automated utility for determining the appropriateness of level pool reservoir drawdown based on thd Drawdown Number analysis.