Results are starting to come in!

HEC-GEORAS processing was impressive. Bank elevations seem pretty consistent.

Next stage is estimating Manning's n. Now the fun starts. As far as I can tell, HEC-RAS wants you to already know Manning's n. But I don't know it, I'm trying to estimate it, in fact.

So WINXSPRO to the rescue. WINXSPRO will take a cross-section profile output from HEC-GEORAS, and if you give it a water level (or a range of water levels chosen to lie over the range of bankfull) will give you back, both Manning's n, and estimates of Q. Seems like exactly what I need, right?

The only catch is that you have to do it one X-section at a time. That's going to be about 400 cross-sections x 15 minutes each (estimate) = 100 hours of work.

Here I go, watch me grind.

In the sample image above the apparent drop in discharge with increased stage results from the bank discontinuity being hit - indicating increased wetter perimeter with minimal increased area as flows go overbank, thus decreasing hydraulic radius R (A/p) and increasing effective n, so resulting in the dip in apparent discharge. That's my bankfull stage right there.