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Cool hurricane hydrology

From my dry vantage point 4 states away, I stop to point out a very interesting consequence of Hurricane Ike's move onshore in southeast Texas:
On this stream gage in Beaumont, the storm surge is strong enough to reverse the flow in the river. The gage height graph at the top shows the typical water-level rise of a flood, but the bottom graph shows streamflow (discharge) that went negative when the storm hit. Positive values are flow downstream, negative means the river is flowing upstream. (The negative values will show up on the default graph for 7 days, then you can adjust the plotting period to see them for 60 days before they age off.)

Cool. I didn't know our gages could even record that. (OK, I'm a ground-water hydrologist, not a surface-water one, so I never thought about the problem before). Must be the relatively new equipment that measures velocity as well as gage height. The old-fashioned method of stream gaging was/is that you install a continuous monitor for the gage height, and then you go measure the streamflow over the range of gage heights and construct a stage-discharge curve so you can translate any gage height to a streamflow. Well, any height that's in the range of your curve...thus the desire to go measure the stream anytime the river gets higher or lower than you've measured before, and the reason that field technicians go out to try to measure streams at the peak of a flood. But a gage height monitor wouldn't let you know that the river was running backwards.

I note that this is a gage right at the coast, and it shows flows that are just barely negative regularly (tides). Under Ike's influence, it's flowing at quantities well above the daily maximum recorded there, and upstream. However, it looks like the flow has already reversed and that water will all now go the other way--and the daily average may well come out close to zero. I'll be interested to see...



Sep. 13th, 2008 07:58 pm (UTC)
Fascinating! With an oddity like that, will there be some sort of asterisk or footnote in the records denoting what the circumstances were?

I keep watching the radars of the SE (because of Emily being located in Charlotte now), and thinking of y'all, and hoping to see rain to ease your drought. Sadly, it doesn't look like the remnants of Ike will help you much.
Sep. 13th, 2008 08:44 pm (UTC)
Not on the actual gage record, I don't think. The format has a place for the highest values ever recorded--look here (the 2007 published record for this gage) at the heading "Extremes for period of record":
I note that this gage has only been around since 2003, which probably is also because it's tidal, and without those velocity gages tidal gages were of limited use.

Before the "published records" went to a Web product, there was a book for each State and it had introductory material that would discuss things like droughts and floods that affected the State. This is the national summary that's the equivalent, but it doesn't look like they plan to include things like individual flood events:

And yeah, we still hope for a nice gently hurricane to move slowly across the southeast, raining steadily as it goes. Atlanta's major reservoir got a 2-ft. boost from Fay, but we need a lot more than that.


Nancy Barber

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