Tuesday, July 21, 2009

Other New Features in version 4.0.1

Written by Chris Goodell, P.E., D. WRE | WEST Consultants
Copyright © 2009. All rights reserved.

Here's a brief summary of some of the other new features that will be debuted in the new 4.0.1 release:

1. Geometry Window...Options...Main Channel Manning's n Value Compositing. I believe this was available elsewhere to a limited degree before. Now you can change the Compositing Slope Criteria or choose to not autmatically composite.

2. Geometry Window...Tables...Contraction/Expansion Coefficients for Unsteady Flow. Not sure what this is about. My understanding is that the C&E losses were built into the unsteady flow equations. I'll have to check into this.
3. Geometry Window...Tables...Minor Losses. Apparently you can add additional losses to a specific cross section. This is set up to take a Minor Loss Coefficient that I'm guessing is muliplied by the velocity head at every time step for the additional loss. Maybe to be used for tunnels or pipe networks (using cross sections with lids, or priessman slot...).
4. Unsteady Flow Analysis...Options...View Runtime messages file. Awesome! Gone are the days where you have to rerun your 10 minute-long simulation just to find out where it crashed because you inadvertantly closed the computation message window. RAS now stores this info in a log file. By selecting this option, you can view that log file. Great add!

5. Unsteady Flow Analysis...Options...Automated Roughness Calibration. This is HUGE if it is what I think it is. I haven't had a chance to try it out, but is appears you set up flow roughness factors and add in some observed stage gage data (unsteady flow editor options), then in this window, you can specify some calibration parameters. RAS will then automatically adjust your Manning's n flow roughness factors to match the gage records. Very cool.

Not sure when this new version will be officially out for the public to download, but hopefully soon. Keep checking back at the HEC website.


  1. There's alot of new addition on the next release...
    Almost too many.
    I fear that some of them will not be working!
    (i'll keep looking at this blog which is a great addition btw).

  2. Were you ever able to figure out #2? My understanding also was that the C&E coefficients were taken care of in the unsteady flow equations.

    1. Yes. Losses due to contraction and expansion are built into the unsteady flow equations (the conservation of momentum equation to be precise). However, this table allows for added energy loss due to effects of contraction and expansion that aren't accounted for in the momentum equation. For example, flow separation turbulence. General advice is if you need to lose some energy to hit a calibration high water mark and you think there is significant loss due to contraction or expansion, then go ahead and use this feature. Otherwise don't use it.

  3. how to Calibrated n manning in steady flow

    1. Get some observed data (water surface elevations) for a past flood event. Replicate the past event in your RAS model. Adjust Manning's n values until the computed water surface elevations match the observed water surface elevations.


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