URGENT - VIRGINIA - OCCOQUAN RIVER DAM AT OCCOQUAN IN DANGER OF FAILURE

National Weather Service Forecast Office - Sterling, VA ^ | February 23, 2003 | National Weather Service

[leadpenny]

I read somewhere that Occoquan is Native American for River's End. I'll think of the tribe after I hit the post button. BTW, that 11' of water happened before they put a 4' cap on the dam about 15-20 years ago. What was it, 72, when the town was wiped out by a flood from Hurricane rains? Agnes?

[leadpenny]

Dogue! That's it. Thanks for the post. I think of it as traffic down there.

[LBGA]

Woops, I meant the Jamestown... which was it, and was it in the 70's? I can't find it because I am not sure of the name, but a lot of people lost their lives.

[muggs]

leadpenny, if you don't watch TV but get your info from the computer, you think about installing the Weatherbug.http://www.weatherbug.com/aws/index.asp

It will alert you with a chirpping cricket sound whenever there is a weather advisory. Mine has been chirpping alot lately.

[Chairman_December_19th_Society]

What was it, 72, when the town was wiped out by a flood from Hurricane rains? Agnes?

1972 would have been Agnes, yes.

[ErnBatavia]

Now THIS is a "dam failure" = the St. Francis dam that blew out in the 1920's I believe.....hundreds killed as the water flooded all the way to the coast at Ventura, California (about 40 miles away).

[AnAmericanMother]

Correction. I found it on the web - Kelley Barnes Dam in Toccoa, GA. 1977. 39 people were killed. The USACOE investigation found that the dam was in poor condition, but that overtopping was not a factor (they were undecided between a landslip adjoining the dam and "piping" or low level breach of the dam due to tree root infiltration and old abandoned structures in the body of the dam.)

Living downstream of a dam in the flood plain is in any event not a good idea. I live about 9 river miles downstream of Morgan Falls Dam on the Chattahoochee, but we're on the first ridge above the river and it's got room to spread below. Unfortunately, Cobb County gave some fool developer permission to build these huge mansions down in the flood plain. In the spring floods, water covers the river road along there, and the mansions sit on their little man-made islands (called the Vinings Indian Mounds locally) completely surrounded by water. If Morgan Falls ever goes, they will simply be washed away.

[LBGA]

You are welcome. After reading the warning, I went searching for info on the town. I sure hope that dam holds!

I think a dam can be considered to have failed if great amounts of water go over the top. It doesn't have to collapse to not do the job it was designed to do, which is to manage water flow.

It would seem to me, though, that if great amounts of water go over the top, the dam might be in danger of collapsing. There would be more pressure on the structure from a greatly increased amount of water flowing up to the top and over it. I am no scientist, but this doesn't seem like a good situation to me.

[Chairman_December_19th_Society]

leadpenny, if you don't watch TV but get your info from the computer, you think about installing the Weatherbug.http://www.weatherbug.com/aws/index.asp

I have heard about many folks having problems with WeatherBug when they've wanted to uninstall the program.

I use Weather Message. Pulls in the whole Emergency Manager's Weather Information Network, and sorts out the information you need. Really need a permanent Internet connection for that, however - if you don't, it doesn't work so well. You also need to know the code for the Sterling forecast office is "LWX", but after that, it's real easy. It will also e-mail or page you remotely with the weather message. And the guy who wrote it wrote the book on customer service. Incredibly flexible program.

[He didn't pay me to say that - I really like the software!]

Weather Message

[leadpenny]

Thanks. I do check Intellicast all the time when things are happening. I live up stream near Hoos Run and can see the water level through the trees. If it drops like someone pulled the plug, I'm gonna hit Breaking News.

[Chairman_December_19th_Society]

I took a tour of the Flaming Gorge Dam this last summer - in Utah. One of the things they stressed on several occassions was resevoir control and how it is a very bad thing to have the water top the dam, saying it would lead to failure.

[LBGA]

Thanks for that confirmation. I thought it didn't sound good.

Praying for the little town of Occuquan and the other people living below the dam.

[AnAmericanMother]

That IS a heck of a dam failure.

Of course, this is the granddaddy of them all:

Johnstown, May 31, 1889. Over 2,000 people dead.

What was left of the dam:

Recent repairs had changed the configuration of the dam and narrowed the spillway. That and very heavy rains in the narrow valley sealed Johnstown's doom.

[muggs]

I witnessed a flashflood in the summer of 2001. It was the worst natural disaster I ever saw. I don't even want to think about how much worse it would have been if it had been in winter when it is cold. I hope everyone is taking whatever precautions they can.

[commish]

Exactly. Once water tops the dam the forces change from pressing against the dam, to puching down on the top of the dam.

Once the cap of the dam gives way to these pressures it is a domino effect downward.

Most modern dams have been built with the possibility of pressures from the top, but most older dams will crumble once water starts overtopping them.

The second danger is that the water will erode sownward from the edges of dam, in essence breaching not just the tops but the sides. Once that begins a blowout is inevitable.

[Chairman_December_19th_Society]

Rank speculation here, but I think about 8:30, the Occuquan dam operator was talking to the NWS forecast office in Sterling, and mentioned that water would top the dam and he/she couldn't control it. NWSFO Sterling probably drew the initial conclusion the dam could fail. There was probably another phone conversation about 8:45, after the alert hit the wires, leading to the second, revised issuance of the flood advisory.

[commish]

A third danger is that the poster will not proofread and will post words such as puching (pushing) and sownward (downward)

[Chairman_December_19th_Society]

The last week in these parts (Northern Virginia) has really been the weather week from he[~~]!

[cajungirl]

This is what I love about FR,,there is always someone who knows alot,,we even have dam experts,,years ago, maybe 1993 or was it 1996 the Mississippi River came up to the very top of the levee in areas south of Baton rouge. We drove up on the levee and it was positively unnerviing to see that water up that high. There was worry about the levee as everyone knows New Orleans would be protected rather than Baton Rouge. Scary scary scenario but predictable at some poiint.

[Chairman_December_19th_Society]

I already crossed that threashold - ;^ - when I didn't notice that NWS had slightly changed their alert twx from the time I first saw it...

High Wind Warning - yep, ok
Flood Warning for rivers - yep, ok
Small Stream Advisory - yep
Dam Alert for Occuquan - all right
Colder weather on ...

DAM ALERT ---- ??

Oh, wow - just what we need. (Is it posted on FR? Nope, better do the deed. And in haste, didn't notice the subtle, but important, change.)