Any experts here on computer simulations and floods?

[Skidmore]

We have so many talented people here.

I'm wondering if there is any simulation that has ever been done on what a 500 year flood would look like in the absence of all the dams and levees we have built. How big would the flood plain be? Is the flood plain we see referenced one that is based on the dammed rivers or on the original river?

Anyone know? Probably stupid questions all but I'd like some idea.

[Frustratedlady]

1. In 1993, we went nearly bluff to bluff.

The Mississippi tries to reclaim its original area. Since the dams control the flow, it can keep that down somewhat, but there is just so much they can do. They can't open and close the gates now and have even removed the equipment, I think.

We have a lock above us and the dam below at Keokuk. I don't think anyone in the area would want to see what would happen. I was concerned about that when all the terrorist threats were out before the 2004 election. Fortunately, the threats were bogus.

[Skidmore]

4. I just saw a report that Keokuk will be getting hit later in the week.

I grew up in Illinois just a little downstream from that lock and dam. The bottom land below Warsaw used to flood regularly in the spring. My grandfather used to farm it. Some of the richest soil you could imagine, unless it was flooded.

[Frustratedlady]

9. Yes, that is the same as Green Bay Bottoms. Fantastic farming if dry.

We have the Iowa River above us, which has flooded quite a bit of property on its way and Burlington should crest next Wednesday to Friday...depending on how this next storm acts. Then, it will hit Keokuk.

Lock and Dam 18 (just above Burlington) removed their equipment to open the locks a few days ago. The Keokuk dam is the next obstruction of flow. That dam is old, but it keeps on keepin' on.

In 1993, some nut caused a levee by Niota to be compromised and that flooded a lot of that area. I believe he ended up serving time.

[HereSince1628]

2. You don't need a simulation to get historic (or prehistoric) floodplains

Regular flooding often leaves a fingerprint in the earth, these have been mapped by geologists. I looked at these when siting the septic system for a new house out on my farm.

[Speck Tater]

3. You can always get a topo map of the area

and trace the contours for any given level of flooding.

Coastal flooding from sea level rise can also be easily determined with topo maps from the USGS: http://topomaps.usgs.gov/

[XemaSab]

5. The whole "500-year" thing is nonsense

It's all based on models anyway, and we have no idea what the real 500-year recurrence interval looks like.

Also, there are sort of two meanings of the term "floodplain," there's the geology meaning and the insurance meaning. The insurance meaning is with the presence of dams, so take that as you will...

[Skidmore]

6. Thanks. That is helpful information.

[Frustratedlady]

7. 1993 was a 500-year flood, so what do you call a 500-year flood 15 years later.

I agree, it doesn't mean a hill of beans, except as a measurement of how extensive it is...or to calm people down that they won't see another one of those in their lifetime. So much for that thought.

[XemaSab]

8. Exactly

First of all, 500 years isn't the recurrence interval, it's the odds of a flood of that magnitude happening in any given year. Secondly, um... have there been people mapping the flood stages there for the last several thousand years? Trying to decide what a big flood is when we've only been keeping records for the last two hundred years isn't going to produce accurate results.