Take Time to Study Corps of Engineers' Massive Dallas Floodway Environmental Assessment

LeveeCutoffWallSideView.jpg
Click to enlarge this cross-section of the cutoff wall -- seen in this appendix -- the city and HNTB say will bring the levees back to acceptable.
Schutze's must-read of the winter has finally arrived: the U.S. Army Corps of Engineers' Dallas Floodway Environmental Assessment, in which we finally get a good look at the city and HNTB's $30 million in proposed fixes for the Trinity River's levees. Not sure when Jim will turn in his report; there are many hundreds of pages of docs to review, including myriad appendices that document the past, present and future of the river (including this photo album). Till then, begin here: the main doc, which details the construction of "approximately 18,300 linear feet of riverside cutoff walls along selected portions of the East and West Levees of the Dallas Floodway System," the bulk of the fixes needed to get 22.7 miles' worth of the levees back to 100-year FEMA accreditation:
By implementing the Proposed Action Alternative, the City intends to correct system-wide deficiencies of the Dallas Floodway System and regain its 100-year FEMA accreditation. However, if the Proposed Action Alternative is not implemented, FEMA would finalize and reissue the final effective 100-year event FIRM. Under the latter case, the existing structures within the remapped areas that have federally-backed mortgages and loans would be required to carry flood insurance. In addition, many privately-issued mortgages would also require flood insurance security. The remapped areas would also be subject to new constraints and more stringent requirements for development.
Those wondering how this relates to the Trinity River Corridor Project or properties along the Trinity might want to begin on Page 44 of the PDF, with the section "Land Use Plans and Future Land Use;" says there's $2,437,783,612 worth of land within the "region on influence," or ROI. And further down, the report notes:
Of the 18 census tracts in the income and poverty analyses study area, 4 census tracts [Census Tract (CT) 41.00, CT 102.00, CT 104.00, CT 106.02] exhibit median household incomes below the 2011 DHHS poverty threshold of $22,350.
The master appendix, incidentally, also provides an extraordinary history lesson. With pictures, even.
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Replay
Replay

So, let me see if I have this right? The Corps of Engineers decertified the entire (22.7 miles) levee system because 15% of the Levees needed this "fix"? Something smells bad!

Ben
Ben

Back when they were digging out the Pavaho Pump Station last summer, I talked to one of the backhoe guys who said the aquiclude in that area is 18 feet. That's the Eagle Ford Shale bedrock that the concrete barrier will be built to reach. Only place you can see it without digging is at the Santa Fe Trestle Trail/Dallas Wave on the south bank. 20ish feet down. I did not realize how porous the ground was in that area until a recent visit to a perched aquifer spring in the southeast part of town. With enough time, pressure and a bedrock bottom, water can go through(or under) anything.

1822, 1844, 1858, 1866, 1871, 1890, 1908, 1913, 1922, 1935, 1942, 1949, 1989, 1991 were the big 'un floods. You'll notice up until 1942 they had a fairly regular frequency. With lakes being constructed upstream in the 1940s and 1950s, flooding became less of an issue.

Bob
Bob

Looking forward to Jim's comments about the repositioning of the Tollway as a "Boulevard."

Montemalone
Montemalone

Get yer houseboats!Get yer houseboats here!

EagleScout
EagleScout

The affected landowners were made aware of this some time ago. On the east side where it's all businesses and new residences for higher income, it's going to be interesting. On the west side, hmm never thought about that.

Negative Nanny
Negative Nanny

I already know what Jim is gonna say: "I don't like it".

Darrd2010
Darrd2010

It's my understanding that the USACE is agreeing to do the 'less expensive'(aka less safe?) version of the cutoff walls. If true, how is it that the City of Dallas can convince the USACE to go forward with this? Does Boss Suhm's reach go that far into USACE?

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