(This story updates and replaces a version published this morning.)
This just in: What the city has said for 20 years about flood safety and a proposed toll road along the Trinity River very possibly is not true. In a major flood that road may be underwater and threatened.
Yesterday after I filed a story about Trinity River flood levels and left my desk, the U.S. Army Corps of Engineers Fort Worth District sent me important information. It’s my fault I didn’t see it until this morning.
In his last email to me, Corps of Engineers spokesman Jim Frisinger said it’s hard to make direct comparisons between flood conditions now and conditions in 1908 when the Trinity River last reached the so-called “100-year” flood level. The 100-year flood is a technical term for a really big flood that the city should expect to happen about once every 100 years. (Yeah, right: We’re seven years overdue for it now).
But Frisinger said, given a certain number of adjustments and estimates, the 100-year flood downtown between the levees now would push the river to an elevation above sea level of between 420.6 and 422 feet. City information presented to the city council in briefings has put the toll road at an elevation of 419.06 feet.
By the way, those heights make Dallas Morning News editorial writer Rodger Jones right about one thing in a recent blog item: the recent crests of the river at 40 feet aren’t close to the 100-year flood, which Frisinger told me would be at about 52.6 feet according to data from the U.S. Geological Survey. That’s 4 feet higher than what he told Jones a week ago, reflecting, Frisinger says, better information he was able to get yesterday from engineers and scientists at the Corps.
Jones’s piece meandered a bit in what he seemed to be arguing (hey, it was a blog item, not a dissertation). If he was asserting that the proposed toll road would be safe from a 100-year flood event, then he may be quite wrong. According to the numbers Frisinger gave me, that flood event would be over the road. I think being over the road even by an inch means enormous volumes of rushing water would also be ripping away at the road’s base and drainage system. Flood water is not nice water.
I promised in my original piece not to make this an agonizing head-bender. If I could help it. I said I would tell you the punch-line first: everything everybody tells you about whether this week’s flood would have covered up the proposed Trinity toll road is gobbledygook. I would amend that this morning to half-gobbledygook, which I think is the same as gobbledygook.
A week ago Jones published a blog item under the headline: “Swollen Trinity Would Not Be Close to Threatening Either Toll Road or Beasely Road.”
What is a “Beasely road?” Please don’t worry about that right now. The point is, we have been having big floods down there in recent weeks. So the question is: If they had already built the big honking freeway between the levees where it floods, would this week’s flood have flooded it? And here comes the minor head-bending alert:
Jones told readers the river, “crested at nearly 39 feet on Sunday.” (It did, and 40 feet a week later. Right now it’s over 40 feet again.) Then he quoted Frisinger as giving him the following facts (hold on to your head a little bit):
Frisinger told Jones that a big flood that might happen once in 100 years would hit the 48-foot mark on the levees. (He told me 52 feet yesterday after conferring with more experts.) Frisinger said the tops of the levees are just over 61 feet at their lowest point. Jones said Frisinger told him the 100-year flood only goes halfway up the levees. I guess now we know the flood event goes four feet higher on the levees than what Frisinger told Jones a week ago.
Just stop. Something is missing. Rodgers said confidently — I would even say buoyantly — that the end result was that the recent floods would have left the toll road “high and dry.” But, wait. Rodgers didn’t tell you how high the toll road is.
Isn’t that what this is about? How do you know the toll road is safe from the flood if you don’t know how high the toll road is?
Now it gets way worse, and, frankly, you shouldn’t even try to read this unless you’re already in a bad mood. I looked at some material the city published about four years ago (copy below) and it showed the toll road at only 2 feet above the 100-year flood level.
In the last two weeks the river has gone up and down – fluctuating — as much as 6 feet in a two-day period. It just went up by 5 feet last night and is still rising. It was at 40.17 when I looked at this morning.
A 40-foot gage height is 40 feet above what is called “the datum” or normal flow of the river. So where is 40 feet on the levee wall? And what elevation above sea level is that?
Where is the damn toll road? The city’s graphics show the height of the road only in elevation above sea level (419.06 feet), which is not the same thing at all as the “gage height” used to measure the recent flooding (40 feet). Different scales.
Serious serious head-bending ahead.
I asked Frisinger how to translate elevation into gage height? How high would the toll road be in gage height compared with the height of the 100-year flood? I told him the height I had for the 100-year flood, from city documents, was 417.06 elevation.
He wrote me back three times (the last of which I missed at the end of the day). Part of what he said is that a gage height today is hard to compare directly with gage records taken in 1908. The terrain has changed. The amount of flow in the river is now twice what it was then in a major flood. And the equipment has changed.
But in response to my questions he consulted with experts at the Corps who did their best to generate useful comparisons. He said the Corps’ hydrology experts estimate the 100-year flood event “from the CURRENT hydraulic model for the floodway to be about elevation 422.0 ft.”
I did say at the top here that this flood level “very possibly” would put the toll road underwater, and here is my own caveat on that. If the city’s numbers for a major flood event are off, then its numbers for the elevation of the road probably are off, too.
Could be off as in too high. Could be off as in too low.
We still don’t have even a good estimate for the height of the toll road. Frisinger gave me heights only for the 100-year flood, not for the road. The only real bottom line we have so far, according to the numbers the Corps just gave me, is that the city doesn’t know where the levels for either the flood or the road really are. That alone is scary.
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I spoke with Dallas City Council member Scott Griggs about this yesterday, because I knew he had devoted some time to pursuing this very question. He told me he never did get a definitive answer from the Corps or from city staff about the height of the toll road vis a vis the 100-year flood. He wrote again yesterday to city staff in charge of the toll road project asking them to prepare simple graphics to illustrate what they know about these levels.
Griggs also pointed out what everybody and his uncle noticed last weekend in looking at the flooded river: when the river is that high, it doesn’t look like there’s that much headroom left where the toll road would have to pass underneath existing bridges and viaducts. So hopefully when the staff prepares the drawings he’s looking for, those drawings will also include the overhead clearances for the bridges.
But don’t hold your breath. Griggs and council members Sandy Greyson, Philip Kingston and Adam Medrano have been pushing for just this kind of information for years now. It’s crazy and absolutely incomprehensible that these questions have not been settled definitively by now. Do you think there could be a reason?