You spent Memorial Day weekend doing your holiday thing, whatever. I spent it doing mine – watching the flood levels on the Trinity River downtown. Takes all kinds, right?
Most of my flood watching – the more gripping part, in fact – was online, although I did spend some time actually going down there and walking around (see video).
If you know where to look and what to watch for, the online part is exciting because you can see this loose regional confederation of civil engineers and water managers at work, opening water gates, screwing them down shut again, letting water out of lakes, holding it in, trying to cooperatively manage the storms and stave off disastrous flooding.
I only get what they’re doing in the most simplistic way, I’m sure, but I have talked to some of these people over the years, and I think I get the larger principle. Mainly it’s this: Rainfall directly over the Trinity River as it enters the city is the least important factor in determining the level of the river where it passes through downtown.
The river between the levees downtown is a pipe that drains a system of reservoirs upstream. Water can be traded around between all of the reservoirs in the watershed, which is something I profoundly do not get, but there’s a reason I chose journalism instead of civil engineering.
What I do get is this: Water pours into the levee system from multiple sources. The three most direct are Lake Ray Roberts , 42 miles northwest of downtown, Lake Lewisville, 23 miles northwest, and Lake Grapevine, 20 miles northwest. If you go here, you can see how high the river is downtown. If you go here and scroll down to the bottom of the page, it will tell you exactly what’s going to flood at each level of the river.
If you go here, you can see how fast they are letting the water out of Roberts, Lewisville and Grapevine. All weekend as I watched it, this was like the Mad Hatter juggling over-filled teacups in Alice-in-Wonderland. Roberts and Lewisville were almost brimming, and Grapevine was brimming to the rim. You could see them sluicing significant amounts of water out of Roberts, while they were just tweaking Lewisville and Grapevine up and down, trying to take the pressure off Roberts.
All weekend, every time I went back to this page, the volumes being released from Grapevine were changing. Sometimes they shut it off entirely. Sometimes they opened it up a lot. More often they let it trickle. But Roberts just gushed all weekend.
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I assume that’s because Roberts is so much bigger. If they ever allow Roberts to get all the way filled up to the brim, then the volume of water required to bring that level back down will be huge, compared with Grapevine. So they have to keep draining Roberts as much a possible while they adjust the flows from Lewisville and Grapevine.
You know what? It’s sort of like watching the Mad Hatter pour from Robert’s, which is the teapot, into Lewisville and Grapevine, which are the teacups, into the levee system downtown, which is the saucers. And we hope he doesn’t spill into on the tablecloth, which is us.
If you really want to wonk out, you can go here and see how the watersheds in the area work. You can go here and see which streets and roads have been closed due to flooding. You have to click on the red underlined intersections, and the list on the next page shows you what’s closed and what’s open.
I made a little video for you. Some of you will be happy to hear I did not make it with my hatcam. The hatcam videos all suffered from some kind of bobble effect I was never able to track down. Let's hope this interesting chapter in the history of the Trinity remains only that and nothing more serious. Fingers seriously crossed here.