mannings and OB distances

[ausland]

I have been working on several step-backwater models for 'no-rise' analyses and have a couple of questions:

1. Manning's n: I encountered a counter-intuitive result in one model - Decreasing "n" on one bank resulted in an increase in the W.S. Elev upstream.

2. Is there an accepted way to 'calibrate' my existing model to match the FEMA FIS W.S. Elevs, Top widths, velocities, etc.?

Thank you,

Kelsy Ausland, EIT
Oregon

Kelsy in Oregon,

If you contact FEMA, you can get the geometric data from them, and model I/O files. It may even be in the machine readable format you can use. That is the most helpful thing in duplicating the FEMA analysis so you can spring off to where you want to go.

As far as an "accepted" way...... adjust only what is necessary, and make reasonable adjustments, and probably most of all have someone who is qualified, but not directly related to the project, look everything over before you present it.

gook luck
Josh Gilbert
jgilbert@usgs.gov