You Think Flooding Was Bad Last Weekend? Better Grab a Bible.
The Trojans all jeered at Cassandra, too, right before they DIED. Just sayin'.
"Cassandra" by Evelyn De Morgan - Flickr
Ten weeks ago I had my hair shirt on with my sandwich-board sign hanging from my shoulders, predicting a possible biblical-scale flooding catastrophe as we entered the season of the fall rains. Might be time to grab those Bibles soon.
All those stories you saw on TV last weekend of people dying in spot flooding in North Texas, stories of sewage eruptions and threatened levees: Those things are not strictly speaking the direct result of rainfall, per se, but of a man-made phenomenon called runoff — the amount of rainwater that can’t get through pavement and rooftops to soak into the ground.
Our flood control or flood safety system is all about managing runoff. And it’s a fraud.
The flood safety system for Dallas is based on lakes, or, as the U.S. Army Corps of Engineers likes to call them, flood risk management reservoirs. The idea is that all of the rainwater runoff caused by development will be impounded or temporarily stored in the lakes until the danger of flooding passes.
That works when the glass is part empty, but we can’t pour any more water into the glass if the glass is already full. As of yesterday, all of the big lakes directly connected to the Trinity River in Dallas were well over their full level.
To be fair, to be fair, before the Corps of Engineers guys start banging off emails at me, in the engineering of reservoirs there is full and then there is really full. None of the Dallas area lakes is at really full yet, a level they call the “flood pool” elevation, which I call Bible times.
Lake Ray Roberts above "flood pool" level last spring.
But we’re barely a third of the way into what is predicted to be a very wet fall rainy season, and those lakes are lapping right up close to the Bible already. Yesterday Lake Lewisville, for example, was at an elevation above sea level of 530 feet, which is 8 feet above its normal full level and only 2 feet below the really full level where it starts pouring over the spillway.
Who cares if it spills over the spillway? Everybody downriver but especially you and me. If they ever let the lakes loose, we will catch hell along the Trinity River downtown.
During this last weekend’s heavy rains, the Corps was allowing no water or barely a trickle to escape past the dams from the lakes upstream from downtown Dallas, because the Trinity River was already at major flood stage. They couldn’t release more water, because the river couldn’t take more water.
Does that mean we had a major flood downtown? No. But it means that areas below downtown along the Trinity were beginning to flood last weekend. The river was at a height of 42 feet above its normal “stage” or moderate flow level at one point over the weekend, way up high on the levees.
I know, I know: I’m using two different heights — elevation above sea level for the lakes and height "above stage" for the river. They’re harder to relate accurately than you might think. I have to work with what I’ve got. The height above stage is a height in feet above where you normally see the river.
The levees are supposed to be 61 feet high at their lowest point. The biblical floods will occur if flood waters ever get over the top of the levees, as happened in Hurricane Katrina in New Orleans in 2005. Flood water, once over the top of an earthen levee, begins to tear the levee down. Sometimes flood water can tear a levee down without overtopping it by scouring against the side of the levee and causing dirt to slough off and erode.
That’s why so little water was released last weekend from the five main reservoirs above us even though they were filling up quickly (Grapevine rose more than 5 feet in a 24-hour period at the end of last week). Big water releases to get those lakes back down quickly might have spelled disaster in downtown Dallas by filling the levee system too high and threatening the stability of the levees.
Now, so far this has been all me, the hair shirt and the sandwich board. Only fair now that I let you hear what the Corps of Engineers people have to say about this rain event just behind us.
Clay Church, spokesman for the Fort Worth District of the U.S. Army Corps of Engineers, told me: “The fact is that the Fort Worth and Dallas flood risk damage systems were functioning as designed. That includes both the Dallas and Fort Worth floodway systems and then the six Metroplex flood risk management reservoirs that the Army Corps of Engineers operates.
“Those lakes are doing their jobs,” Church said. “They do their jobs by holding flood waters above the conservation pools in what we call the flood pool.”
The Trinity River downtown last spring.
Note from Hair Shirt: “Conservation pool” is a Corps of Engineers term for the normal full level. The “flood pool” is the additional amount of water the lake can hold above the normal full level, before it goes biblical.
So here is where the Corps people and I diverge, and here is where I come to my view that this whole “flood risk management system” is based on a fundamental deception.
They say the picture they have painted is of a system that works. I say it is a system that barely works and will fail fairly soon unless we stop having intensive spring and fall rainfall.
Last spring at the beginning of a record wet season, the lakes above Dallas were at all-time low levels, an average of one-third below the normal full level, some of them at half of normal full. And yet last spring’s rains filled them all the way up beyond biblical, until they were literally overflowing. At that time Church told me not to worry (fat chance). He said the lakes would be brought down over the summer. And they were. But only back to the normal full level.
So that means we are entering this fall season without the extra cushion of safety we had last spring when the lakes were low. All we have now is that margin between full and biblical, and we’re already lapping up toward that upper limit.
Church said this week that even if the lakes get above the flood pool level, it’s not hair-shirt/sandwich-board time in his view, because the lakes can handle it:
“You design a flood risk management reservoir to hold what you believe is going to be your standard project storm that creates your probable maximum flood. That’s why the flood risk management reservoirs are so large and why you have 10 feet of area you can hold flood waters in. That’s a lot of water.”
I told him I just didn’t buy that assurance, because from everything I have ever been able to read or get anybody to tell me, the single biggest contributing factor to urban/suburban flooding is runoff. And in the last third of a century since the Corps came up with its “standard project flood” predictions, neither the Corps nor any other unit of government has even tried to measure the increased amount of runoff we have created by paving and roof-topping this entire corner of the globe.
This, by the way, is an old argument I have had with the Corps over a long period of time, so that when I bring it up on the phone now I can hear people groaning in the background and muttering that he should tell me they’ve already answered this question.
Right. They have. And right. I’m right. They haven’t measured runoff in North Texas watersheds in decades.
They always remind me that they are in charge of lakes and the river, not creeks and storm sewers in developed areas. They’re right again. Those are the responsibility of local governments.
But here is the grand unifying theme: Thirty years ago the Corps recognized that runoff was the big flood risk factor, mainly because everybody on earth recognized it by then, beginning with the Dutch. The Dutch dealt with runoff by creating a tough national land-use policy they called “Living with Water,” which told people whether and how they could develop their land according to the impact on runoff.
In the early 1980s the Corps took Dallas and some surrounding suburbs to court, as it did similar cities around the country, and got them to sign out-of-court settlements agreeing not to increase runoff. Oh, sure.
So Dallas and its hungrily competitive suburbs, all at the receiving end of one of the biggest demographic shifts in the history of North America, were going to adopt something called “Living with Water” and tell people they couldn’t develop their land? That never happened, and the promises were never even faintly enforced.
Instead we got Plan B — flood risk management impoundments, or, as they are called by suburban mayors, good old reservoirs — more drinking and more lawn water for more sprawl.
Even at that, Plan B might have been sort of marginally viable if anyone had kept track of runoff. With that factor in hand we could know now if the lakes we have in place are big enough to hold back the new amounts of runoff.
But inevitably that factor would also operate as an effective limit on sprawl — the one thing we were never going to accept, discuss or countenance in any way.
What we have instead is what we see beginning to form out there now — a kind of urban entropy, where major man-made disruption of the basic plumbing of the planet is coming back to bite us. We will never channel that reality through any medium short of catastrophe. Hence, hair shirt. Hence, sandwich board.
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