The Cost of Fixing the Trinity River Levees Keeps Getting Cheaper and Cheaper

Categories: City Hall
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Not two years ago Dallas city officials believed, based upon information provided by HNTB, that to bring the unaccredited Trinity River levees back to that so-called 100-year flood level of protection, it would cost anywhere from $100 million to $150 million. The solution: cut-off walls sunk into the levee, around three miles' worth, give or take. Which was a far cry from the about-a-billion-dollar figure once thrown around.

But then, in October, the city council was told the price tag was much, much, much less: $20 million to $30 million. That number was based upon the U.S. Army Corps of Engineers' willingness to let the city make the needed repairs while also "integrat[ing] the Corps' new Risk Assessment process into the ongoing concurrent study of the Dallas Floodway system for flood events up to the 800-year level and beyond."

And while the city and Corps had different definitions for what that meant -- essentially: fixing the levees, making sure the sump pumps work and having and evacuation plan sitting nearby -- one thing was certain. As the Corps explained in its October 3 release, "The City and the Corps have collaborated to identify safe and cost-effective construction methods to complete the 100-year fixes at an anticipated cost savings of approximately $30 million to $50 million."

Or more: A glance at the city's inscrutable bids website shows that this week the city posted a heads-up for prospective construction companies wanting to tackle the project. Bids are due February 23 -- a mere six days after they're given a pre-bid tour of the site. And the cost has taken yet another dip: "Estimated construction cost is $18 million." I've asked City Hall how it arrived at the latest figure. Till I hear back the whole bid's after the jump. And, yes, the opening and closing dates are correct, at least according to the doc posted at present.

Update at 3:45 p.m.: Frank Librio, city spokesman, just dispatched this explanation regarding the bid estimate:
The bid packet you are looking at was for the majority of the work, but there is a second bid packet for a smaller amount. In addition, the City will have to pay HNTB for services related to overseeing the construction work and finishing the certification submittal to FEMA. The total of all of these is close to $20m
CITY OF DALLAS CONSTRUCTION ADVERTISEMENT FOR BIDS

Sealed bids will be received at the Office of Purchasing Agent of the City of Dallas, 1500 Marilla St., Room 3FN, Dallas, TX 75201, until 1:00 p.m. on Thursdays. The Bids will be publicly open at 2:00 p.m. on Thursdays in the Express Business Center, Rm L2ES at City Hall. Bid Openings can also be viewed on the City of Dallas Webcasting Website (www.dallascityhall.com, click on City Meetings). Bid titles, department and dates of public opening are listed below. Bid packets and plans and specifications may be obtained from the department. For alternative plans and specifications pick up site, please contact department.
______________________________________________________________________________________

"100-YEAR LEVEE REMEDIATION - CUTOFF WALL IMPROVEMENTS (PB98P558)" This project involves the installation of about 3 miles of cutoff walls within the floodway, improvements to the Hampton Pump Station outfall, and construction of maintenance roads. Estimated construction cost is $18 million. Pre-bid meeting for this flood control project will be held at 10:00 A.M. on Friday, February 17, 2012, at City Hall, 1500 Marilla, Auditorium Room (L1FN) by the Green elevators. It is recommended that all prospective bidders attend this meeting as a brief project presentation will be given and out of town design engineers will be present at this meeting. A site visit to the project area will be given immediately after this pre-bid meeting. Plan set are available for purchase at Oak Cliff Municipal Center, Public Works, 320 East Jefferson Boulevard, Room 307, Dallas, Texas 75203. Please contact Thomas Greene at (214) 948-4492 or fax (214) 948-4680 for information concerning the current plan holders list and availability of the plans. The nonrefundable cost for plans and specifications is $30.00 per hard copy set, $30 for the project DVD which includes the plans and specifications, or $45 for both. Sets must be purchased by check or money order only and made payable to the City of Dallas. For information concerning this project and site visit, please contact the project manager, Than Nguyen at (214) 948-4685 or than.nguyen@dallascityhall.com. Plan sets will be available for purchase by Monday, January 30, 2012.
Bid Opening Date: February 23, 2012
Bid Due Date: February 23, 2012

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26 comments
Dan in D
Dan in D

Hi there, please forgive me for I am a clueless newbie to Dallas. I honestly think this Trinity River/Levee thing has taken on a whole other meaning to where I don't know what it means! Perhaps the conversation is so far along that it bypasses me completely.

Is the majority of the levee conversation based solely on getting the levee's up to "standard"? As in they could (or are) prove to be faulty and cause flooding a la Katrina? Obviously a hurricane isn't hitting Dallas anytime soon. But is that it...they need updating?

Where does the Trinity River people-friendly initiative fit in? Is it made-up, part of the levee initiative or what?

I only ask b/c a friend told me there are "talks" about "flooding" the Trinity, so-to-speak, so it becomes a real river with size, depth and width. To create a riverfront kind of thing w/ paths, activities, etc. Like many other cities have. Though i do understand that the area is a flood plain and not necessarily a "river's river". Was it ever?

I grew up in Cincinnati and have a lot of family in Louisville. I'm not here pumping them up, b/c there's a reason why I'm not living in FUCKING OHIO anymore. But their riverfronts, while different types of rivers altogether, are nice to just be able to go down and enjoy. Dallas, if possible, could something as simple as this.

Not sure if I'll get any responses...but these articles and subsequent comments are so difficult to read!

Dan in D
Dan in D

Hi there, please forgive me for I am a clueless newbie to Dallas. I honestly think this Trinity River/Levee thing has taken on a whole other meaning to where I don't know what it means! Perhaps the conversation is so far along that it bypasses me completely.

Is the majority of the levee conversation based solely on getting the levee's up to "standard"? As in they could (or are) prove to be faulty and cause flooding a la Katrina? Obviously a hurricane isn't hitting Dallas anytime soon. But is that it...they need updating?

Where does the Trinity River people-friendly initiative fit in? Is it made-up, part of the levee initiative or what?

I only ask b/c a friend told me there are "talks" about "flooding" the Trinity, so-to-speak, so it becomes a real river with size, depth and width. To create a riverfront kind of thing w/ paths, activities, etc. Like many other cities have. Though i do understand that the area is a flood plain and not necessarily a "river's river". Was it ever?

I grew up in Cincinnati and have a lot of family in Louisville. I'm not here pumping them up, b/c there's a reason why I'm not living in FUCKING OHIO anymore. But their riverfronts, while different types of rivers altogether, are nice to just be able to go down and enjoy. Dallas, if possible, could something as simple as this.

Not sure if I'll get any responses...but these articles and subsequent comments are so difficult to read!

Oak Cliff Townie
Oak Cliff Townie

I don't think it will be a super massive back under an ocean  prehistoric flood that will get us .Who can say how many disastrous floods we have missed by a foot or two. And I don't mean water going over the top .

It will be one of the Normal rains causing the river to come out of the man made channel deals that finally finds one of the weak spots and eats its way through.Catastrophic doesn't have to start big . Any one who has watched the earth works that contain the the river has seen the  repairs done on both the in side and out side of the structure .

richard_schumacher
richard_schumacher

When do we get those updated flood maps, and when do we see our new insurance premiums?

engmofo
engmofo

Let's build big concrete ditches that double as skateparks ......Problem solved

Texaspainter
Texaspainter

All of you guys raise good,serious questions and it would be great if you can go down to the City Council meeting next Wednesday and ask those questions. I want to hear how well Mary Suhm's Engineering degree has done for her along with her librarian certificate.You have to sign up now so......... do it. If not, all I got to say is  RUN FOR THE SUBURBS. FLOOD!

RTGolden
RTGolden

Original estimate was $100-$150million, ACE identified 'safe and cost-effective measures' that save approx. $30-$50million, and Dallas comes up with a grand total of $20mill?  If the engineers are as incompetent at math as the money folks are, I don't want them anywhere near this project.

Couldn't we just build a spillway, like the Morganza in LA? Flood coming downstream, open the  'Stampede Spillway' and wash downtown Ft. Worth ..... Nevermind, it would just end up washing into downtown Dallas anyway.

NewsDog
NewsDog

And they actually have P.E. that's willing to sign off on this?      A P.E. from this country, not Elbonia where mud is currency.    

Dallas Diner
Dallas Diner

Nobody, but nobody, can do creative math like the City of Dallas.

Paul
Paul

Does it have an H1B?

Note that the repairs are only to obtain the so called "100 year" level of protection, not the "800 year" level of protection that the Corps wants us to have and maintain.

Although at the "800 year" level, dams rather than levees are needed.

An "800 year" flood is already an extreme event and cannot be accurately predicted (mostly in terms of volume and duration) based upon our existing precipitation records.

I am of the opinion that if we ever have the "800 year" event storm, we will have far, far larger problems than with just the levees.

For me, I think that we would be far, far better off controlling run off rates upstream of the narrows at Downtown Dallas for flood control rather than building up and reinforcing the levees of the current floodway.

The current floodway can handle a certain peak flowrate for a certain amount of time. how do we make sure that the flood events stay below these rate and time limitations.

JimS
JimS

Paul, are you aware that the Europeans build to 5 and 10 thousand year floods? The flood level at which there is moderate flooding in Dallas is 40 feet. We were at 38 feet-plus the other night. The level at which the levees will be overtopped, which means blown away, which mean is downtown goes, is 60 feet. So we were at 63 percent of disaster two nights ago. Then you must remember that those assumptions are based on the assumption that the levees are performing at the 800-year level. But as we now know, the levees aren't even safe to the 100 year level. So who knows how close we are to the big one? I actually know who knows. The Corps and FEMA. I invite you to try prying it out of them. They'd never get another earmark, and they'd be out of business. I'm afraid your remarks strike me as head-in-sand stuff.

Paul
Paul

Storms like the one you describe are indeed rare, though tragic events.  With reliable weather records reaching back only 100 to 120 years, it is difficult to accurately predict the occurrence of storms such as these.

The storm probability predictions are based upon a key, though unproven assumption, that the distribution of flows is a a normal distribution.  With extreme probability events, the assumption of the normal distribution may or may not hold past the 99% probability level.  In other words, any flows past the 99% exceedance level are, at best, just a really good idea.

For the floodway at the Trinity narrows at downtown Dallas, the 1% flood event is at a ~40 foot level.  With a capacity height of 60 feet, this flood event is well within the height of the levees.

The question is, for how long can the levees retain this level without being undermined.  I have not heard anything for how long this period of time is.  The recent flood crest was out of the low flow channel for 3 days.  Is this sufficient? Or do we need to plan on a week, 2 weeks, or what length of time?  The longer the time that the levees need to withstand the higher water level, the more that they will look like a dam and not a levee.

The biggest threat of flooding comes from the lack of floodwater control on the West Fork of the Trinity River upstream of downtown Ft. Worth.  This area covers all or part of Jack, Montague, Parker, Tarrant, Wise and Young counties.

The high levels seen at downtown Dallas in the 1989 to 1993 time period was due to heavy precipitation events on this portion of the upstream watershed area.  The Trinity River Authority addressed this issue in 1995 and issued a report recommending the construction of a floodwater retention basin upstream of Lake Bridgeport.  When the Wise County commissioners found out that the primary beneficiaries of this structure would be the Cities of Dallas and Ft. Worth, they rejected the proposal.  This project has the potential of reducing peak flows past downtown Dallas by more than 10%.

As far as extreme events go there is the tropical storm that stalled over an area south of Houston in 1978 that dropped 36" of rain in 36 hours before moving on.  There was widespread flooding.  TX Highway 6 between Manvel and Alvin was closed for over a year due to high water.

As far as the "storm" or "flood levels" go, they are independent events and can indeed occur not only in back to back years, but also within the same year.

hth

Marc
Marc

Paul, you may or may not be correct about your statistics and probabilities, but IF that 1% chance does happen the percentage chances will not matter at all, and nobody can ever predict when a major flood will occur.

I was in Comal County in 2002, when a storm cell blew in, stalled and dumped rain for 17 days. The Upper Guadalupe River flooded severely, rising to over 42 feet and 220,000+ cfs. The floodgates at Canyon Lake can only release a maximum of about 6,500 cfs into the Lower Guadalupe. In three days the lake grew from about 237,00 acre-feet to nearly one million acre-feet. Water flooded over the spillway by 8.5 feet and cut a canyon about 60-70 feet deep and 40 yards wide through limestone all the way from the spillway to the Guadalupe River over a mile away.

At Gonzales, the river went from about 50 feet wide to five miles wide. The flood killed about 75,000 head of cattle including about 15,000 in Guadalupe County alone. 43 people died in that flood. It was unpredictable. Even when the rains started falling there was no basis to believe that it would linger and dump rain for 17 days. It was one of those "Acts of God."

The reason to plan for the unforeseen event is because there is no time to do anything about if and when it does come unless precautions have been put in place before the fact. THAT is why the USACE wants our levees to withstand an 800-year flood, which, by the way, does NOT mean a flood of those proportions once every 800 years, as our former idiot mayor and my councilman Ron Natinsky like to say, but rather that there is a 1-in-800 chance of a flood of that magnitude EVERY year!

Paul
Paul

One other item Jim ... on the graph for the link that you posted notice that the scale on the right hand side of the graph is not linear.   For the recent flood crest the flowrate was ~33 kcfs (thousand cubic feet per second).  If the flood crest were to rise to 46 feet the flowrate would be ~75 kcfs or more than twice the flow for only a 20% increase in flood crest.

A good question to pose to the USACE and the City would be: What is the level for a 100 year storm event?

Paul
Paul

The concept of detention basins in the upstream watershed does not take very strong land use regulations.  All is requires is that when any parcel of land is developed, the runoff rate does not exceed that prior to development.  Of course developers will scream but it is time that the societal risk of flooding by development be born by those who do the developing.

We have already taken steps in this direction by the flood pools in Lakes Grapevine and Lewisville.

For a model approach to runoff rate control, look to Harris County.

NewsDog
NewsDog

Jim,You probably have better info on this... but haven't we had a few 100 year level events in just the past 10-12 years? If memory serves I thought we had two in back to back years in the '90s. The reference Caddilac Heights comes to mind.

JimS
JimS

I am sure that you are right, and that your solution in the long run is the only solution. I didn't understand what you were saying earlier. Now I do. I apologize for the sand remark. I read something published by the Corps recently quoting a guy who was kind of a flood control big picture overview expert, talking about Europe, who said that there is no flood control, in the end, except for strong kand-use regulation, which may be sort of the same thing you are saying. But he also said we're screwed here, because Americans would never accept the level of land-use regulation they have over there.

Paul
Paul

Hi JimS

I'm afraid that I don't see how my remarks are "head in sand".

My comments were that this repair is only to the "100 year" event or the 1% event, which means that 99% of all flood events are covered.

The "800 year" event or the 0.125% event is what the USACE wants the floodway built to.  This means that 99.875% of all floods are contained.  Unfortunately, this does not mean there is only 0.875% more water, but rather an amount that is described by the normal distribution, which off the top of my head may mean somewhere between 25% and 75% more water.

The design aspect of the floodway is what flowrate is it capable of carrying and for how long can it carry it without failure.

As you so aptly mention there is a limit to how high the current levee system can operate.  If I understand your numbers correctly, overtopping occurs at 62 feet, maximum is 60 feet and flood level is 40 feet.

My questions are if the floodway capacity is at 60 feet, what year event storm does this level represent and for how long can the levees contain this level?

Similarly, at what level is the "100 year" event and for how long can the levees contain this flood event?

The capacity of the floodway is dictated by two items: 1) What is the cross sectional area at capacity; and, what is the average flow velocity?

In order to increase floodway capacity, the cross sectional area needs to be increased.  This can be down by digging down (as was done originally) or by increasing the height of the levees ( or both).  The floodway is already constrained for width and slope.

The other significant item is for how long can the levees support a 60 foot water column during the capacity events?  For comparison, go look at the various dams around the area and compare their construction to that of the levees.  They may be holding back the same level of water but they are doing it for an indefinite period, whereas the levee only needs to hold the water back for a few days to a few weeks at best.

Finally, if we cannot increase the capacity of the floodway, the only then that we can then do is build upstream detention basins to reduce the flood crest.

This is because the height and duration of the flood crest at Dallas is influenced by the runoff rate upstream.  With areas being paved over and developed the runoff rate has increased which has the same effect of reducing the floodway levee protection levels.  That is the flood event protection provided 50 years ago is no longer there because of the higher runoff rates.

I believe that we need to seriously consider upstream watershed management in addition to fortifying the floodway levee system.

hth

JimS
JimS

My my my mistake mistake mistake. That means two nights ago we were only at 62 percent of tragedy, not 63. And under normal circumtances we're at 20 percent. Yeah, you're right. Fuck it.

JimS
JimS

My my mistake mistake. Overtopping at 62.

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