Mike,

You are definitely between a rock and a hard place. You are also correct in your argument against a "one size fits all" approach. The more "generic" you make your investigation, the larger the probability for error in your calculations.

However, assuming that your arguments against such an approach will continue to be debated, you might take a look at the USGS Regional Regression equations to get an estimate of your flows. These divide WV into three areas and give equations for small and large watersheds. The breakpoints for small and large are contained in the text. While this is a "broad brush" view, it will at least give you an order of magnitude. However, the text itself states that "The standard errors of estimate of the regression equations range from 37 to 54 percent". There are additional stipulations as to the validity of the results, so I would recommend viewing the entire report before using any of the results. Again, this will only give you a broad brush view of the flow quantity and will not give you a flow depth. Flow depth will be based on channel geometry, slope, roughness, et. al. There are several reasonably simple equations to use (you can probably locate one in a hydraulics book). I can think of no-way to estimate flood depths without doing any analysis on the channel; you will have to do some cursory analysis even at a 50,000 foot view.

The report and computer program (National Flood Frequency program) is available from the USGS at the following URL:
http://water.usgs.gov/software/nff.html

There are several sections of the report, including state specifics, so be sure and review everything carefully before using your results.

Good Luck!
Jeff Brizendine, P.E.
jbrizendine@burnsmcd.com