Topic starter
09/10/2009 1:46 pm
Just had an email from Capt. Steve Huffman that he was dealing with a 9 foot rise in the river in 12 hours. They have had 3.8 inches of rain. In addition to wishing him the best today, I have a question from my non-scientific mind:
The Ohio River rises and falls several feet very rapidly, yet over here on the UMR we never see that. A 3.8 rainfall here might move the gauges up a foot, at most. What doesn't seem logical to me is that there is a greater volume of water in the Ohio to begin with (2/3 of New Orleans' water comes from the Ohio and her tributaries), so shouldn't an equal amount of rainfall raise the smaller river more rapidly? I've seen firsthand the rapid rise of the Cumberland, for example, on our DQ trip which ended in Clarksville...Does it have to do with a greater input from tributaries that the Ohio would have? Or would the closeness of our dams and the regulation thereof keep the Upper Miss from fluctuating less?
09/10/2009 2:15 pm
Judy, I think that the tributaries on the Ohio have something to do with it (larger tribs), but that it is principally due to the width of the Ohio vs the Upper. As you know, the Upper is quite wide in places above you, and that water has much more room to spread out. The Ohio, especially on the upper end, is relatively narrow, so all the rain that falls must channel into that smaller space.
As far as regulation through low dams, there isn't very much. On both the Upper and the Ohio, they maintain the upper pool gage at a relative constant...if the river starts to rise, they do not let it build up above the dam, but run water to keep the upper pool gage constant. The result is that the lower gage comes up. This is the case on all rivers that do not have any flood storage capacity on the main stem - that is, just about all our regulated rivers except the Tennessee and to a lesser extent, the Cumberland.
Topic starter
09/10/2009 2:26 pm
Wide spots upriver
Ok, that makes sense... just as some people wonder why we have so much more flooding now than in earlier days - because we've built so many floodwalls that the river doesn't have much room to spread out, and when it finds a wall-less area(like Davenport vs. the RI floodwall), it has a lot more to spread out. Similar concept, right?
09/10/2009 2:29 pm
Forecast 10 foot rise at St. Louis in 48 hours and it is still raining.
Topic starter
09/10/2009 2:31 pm
Rise at St. Louis
Is most of that coming from the Missouri? We've had rain, but nothing major up here.
09/10/2009 3:01 pm
Yes, it does appear that most of the water is out of the Muddy Mo.
10/10/2009 12:54 pm
In the end, the highest 24-hour rise we got on yesterday's river gage readings was 10.1' in 24 hours. The fastest portion of that rise was 5' in just 4 hours, from 4 AM to 8 AM. I've got 4.1" of rain in my rain gage.
I had left my jonboat tied to the fleet for the past few weeks, because we've been at pool level, and half of my 74' gangway to the boats has been hard aground. So Friday morning I was very surprised to find 35' of water between the shore and the very end of my 74' of docks. Thanks to thieves in 2007, I had no spare jonboat to get me over to the boats. I had to lash two 55-gallon barrels together with ratchet straps, and use a broom to get across to the end of the docks. That was a tricky balancing act!