Best Approach for Calibrating 2D Flow Area Roughness

[Anonymous]

Hello!

Thanks for your blog/forum, I have found many useful pieces of information on this website (and your book).

I have a question regarding the calibration of a 2D HECRAS model.

Currently I have a 1D river model linked/flowing into to a 2D delta model and want to calibrate the model to match observed conditions. All of the gages I am using for calibration are in the 1D portion.

Currently, I generated the 2D mesh at the delta with a constant manning coefficient, then used an override region to define a different roughness within the actual channels in the delta.

I am going to start the calibration process by simulating a number of steady flow conditions (unsteady simulations with constant inflows until model stabilizes).

I have two main questions:

1) How to best approach the calibration of the roughness parameters in the 2D? My current thoughts are just leaving the entire area as a constant value based on land conditions/usage then iterating the override region value as the calibration parameter? Could probably take a while to do this manually.

2) Might not be able to answer this but…given that all the calibration gages are in the 1D portion, is there really anyway to choose an “optimal” calibration in the 2D portion? I.e. I could just leave the 2D portion and calibrate the 1D portion and get the same results.

Looking forward to your response,

Derek

[Anonymous]

Also, forgot to add, is there anyway to possibly add flow roughness factors to the 2D mesh like you can for the 1D roughness?

[Anonymous]

First off i do not believe the mannings override works unless you have an initial shapefile defining the mannings value first. In RAS mapper you can view the “Final” Mannings values.

I may be wrong on this, but i know initially, this feature followed the rules stated above in previous versions of HEC-RAS 5; make sure before you begin calibration

[Author]

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