Welcome, Instapundit readers! Thanks for stopping by, and please be sure to read the comments. There are some excellent updates and additional information and observations from readers.
A lot of hand-wringing and second-guessing now and for the foreseeable future focuses on how a city as big as Houston (and the surrounding areas) could “be allowed” to flood. Setting aside the little problem of humans’ inability to steer storms and rain to or from desired locations, what we’re seeing is a combination of hydrology, urban development, and “excess” precipitation. And it is rather predictable that when you have certain combinations of the above, you get “flooding.” Flooding in this case means water in places where it is not desired, in sufficient quantities to cause damage and to endanger human and animal life. You see, Texas drains into Houston and Brownsville.
Texas can be divided into roughly three major drainage areas. Those places that eventually flow into the Rio Grande, those that feed into the Brazos and Trinity, and those that supply the Red. Many of those streams drain south and east into the plains around what is now Houston – Port Arthur.
The geology of the state explains why: Houston more or less sits on the silt and gravel that has washed off the rest of the state, aside from the Panhandle and Edwards Plateau west.
So Houston was developed on wetlands, or specifically on higher areas within wetlands and streams called bayous. Buffalo Bayou is one of the best known, but there are scads of them, or were. Houston also sits on sediment that is slowly sliding down into the Gulf of Mexico and has been since the end of the last ice age. To compound the problem, in the ’50s and ’60s, groundwater pumping was tried to augment Houston and some of the surrounding towns’ water supplies, and that lowered a few areas almost below sea level before pumping stopped.
So the area under Houston has always been low and moist, with water coming up from below and down from “above,” above meaning north and the clouds together.
However, ground absorbs rain. Trees, grasses, and brush all slow down rain and absorb some of the water, keeping less of what falls from overloading the soil. Even bare ground can absorb some rain, but not as much as soft, grassy soil or pure sand. When the air spaces between bits or soil fill with water, the ground is saturated. Saturated ground turns from a sponge into a watercourse, and you have what is called “Hortonian Overland Flow.” That’s a fancy word for water on the surface that can’t soak in so it flows off.
Buildings, parking lots, and streets do not absorb rain. So the water must be directed somewhere, through storm sewers usually, and sent away. To make a long story really short and simple, a lot of urban areas have so much pavement (impermeable surface) as compared to absorbent ground that hard, fast rainfall causes street flooding. Denver, Amarillo, Garden City in KS, LA, anywhere you get a lot of rain in a short period of time can have minor flooding.
The problem with Houston and the surrounding area is that over the past 150 years or so, more and more has been built on the bayous and wetlands along the Texas Gulf Coast, and upstream. So not only has there been far too much rainfall for the ground to absorb (30″ in 36 hours is too much even on absorbent ground), but it is falling upstream and filling the rivers that drain into the lower areas. And the development in that part of the state has covered over the soil and streams, reducing the amount of vegetation, and so it flooded. Houston always floods. Mom Red waded to her college graduation because part of her campus always went under water. There’s a reason the Heights district in Houston is called The Heights. It sits on a relatively high area. Low, flood-prone patches was true of my Alma Mater in GA as well, and you learned to avoid the low areas (unless in my case you really wanted to see just how sticky Georgia red clay is. And yes, it stains everything.)
However, the truly awe-full amount of rain in a short time, plus lots of impermeable surfaces, plus reduced drainage, plus more water rushing in from upstream has put Harris County and a lot of the surrounding area under water. From a hydrologic point of view, sitting 800 miles uphill, it is not the least bit surprising. For the people dealing with the disaster, it is horrible and the scale is unexpected. Everything that could go hydrologically wrong, with the exception of an earthquake or sustained Cat V hurricane winds, did.
Eventually, the water will flow into the Gulf, the bayous will return to their usual contained courses, and the interstates will emerge from the waters. New flood maps will be drawn up, and people will be assured that this was a “one in [X] hundred years” event. Which means hydrology people will groan, because “A one hundred year flood” only means your odds of having it happen are 1:100, not because you can mark your calendar that there won’t be another flood of this size for a hundred years. So, [DEITY] forbid, something like this could happen next year if everything goes wrong in the same way again. It is not likely, but certainly possible.
How do you prevent this kind of flooding? You can’t. You can modify building and construction codes to maximize water absorption by requiring permeable paving where possible and by insisting on certain amounts of water-absorbant green-space to counter the hard-space. You can install pumps a la New Orleans and try to bail out low areas, preemptively draining the bayous so they could take more rainfall before they overflow. You can install upstream dams to slow the flood crest, although they have the dams open right now (Tuesday afternoon) so the dams don’t overload and fail.You can insist that all new construction be on stilts. It’s a little too late to, oh, dig canals to re-direct all the rivers aimed at Harris County so they drain into the Red River. You can’t move Houston, Katy, and all the adjacent towns. In some cases, the geology will work against you. In others, the cost is so high, and retroactively changing building codes? Not popular, and not cheap. Heck, trying to get zoning in Houston is enough of a challenge.
Hydrology and geology, with a large slug of meteorology are why Southeastern Texas is a lake at the moment. It’s not the time to blame any one person, unless you want to find the grave of the man who developed the area in the first place, back in the early 1900s, and curse his bones. Now is the time to take care of people and animals, and then see to property. And one hopes, to start looking at the landscape and considering what to do the next time the water is “nine foot high and risin’.”