After the dams were built:
1981 - May 24, 1981 - Shoal Creek Flood
An intense thunderstorm formed just west of Barton Springs near 8 PM, and moved slowly north-northeast across the Colorado River and up Shoal Creek into the upper Walnut Creek drainage by 11 PM. Torrential rain fell between 8 and 11:30 PM in these drainages.
The Shoal Creek drainage received 4 to 6 in. on the lower half below Anderson Lane - and 6 to 10 in. on the upper half above Anderson Lane between 8 and 11:30 PM. The Balcones Research Center in the headwaters of Shoal Creek recorded a 1-hr intensity of 4.44 in., a 1-1/2 hr total of 5.59 in., and a storm total of 7.55 in. The headwaters of Walnut and Little Walnut Creeks received 6 to 10 in.
Five-hundred fifty cars washed from six auto dealerships along Lamar Boulevard near and below W. 6th Street. These autos formed a damming effect on Shoal Creek above the Colorado River and greatly increased flooding in the Shoal Creek drainage below W. 12th Street. Over 5,000 cars were stranded around Austin during the night. Many were washed down creeks, some into Lake Austin in the West Lake Hills area from the south side.
A dozen businesses were destroyed and hundreds of homes severely flooded the length of Shoal Creek and much of Walnut Creek. A few homes along Shoal Creek were knocked from their foundations by the raging flow. Thirteen persons drowned, all in autos except two persons along Shoal Creek who drowned trying to escape their home as the flood wave slammed through.
Yes, I was in the area in 1981 and I know about that flood. That's small stream flooding, not the same as catastrophic river flooding you were quoting earlier. Incidentally, changes to building codes and management of Shoal Creek after that flood prevented similar damage in a similar incident of intense rainfall a decade and a half later. Small stream flooding in cities need cause no damage IF you can get the cities to give up property tax income to move structures off the floodplain (expanded, because development increases surface runoff and thus flooding.
The majority of damaging floods in cities in Central Texas is directly due to the greed of cities who want the property tax income from river/streamside property and developers who want the money from selling/renting the property. There's money in allowing people to build in the floodplains--tax money, construction money when the development is first done, sales money when the structures sell, and then more construction money when the structures are flooded and someone has to repair/rebuild them. With halfway sensible land management, there wouldn't be anyone there to be hurt.
Yes, Central Texas is at risk for high intensity rainfall--I do know that, I've lived in Texas all my life. Flash floods are normal for this area because that's the climate we have--even without hurricanes. High intensity rainfall will come, and streams will produce flash floods, especially where the ground is not permeable either because it is rock or because it's been paved and covered with housing/commercial building. It's not a disaster; it's a normal hazard of this area. It should be planned for (and avoided--most of the people who are killed in them *drive into rushing water*.
Small stream flooding is not the same order of magnitude as the big river floods--and I've seen those, too. I've seen the Rio Grande go from a muddy trickle you could walk over without wetting the tops of your shoes to bankful and filling two floodways even wider to the tops of the levees and spilling over in places. The airport in our town was under so deep that an Army DUKW drove over the tops of cars (crushing them); only the tops of the hangers stuck out. I've seen an oil rig in one of the floodways tilt over.
It's different off east, where a flood that started up at the fault line can come out of nowhere, and the land is flatter...and where, thanks to the idiocy (once again) of penny-pinching by certain politicians we now have fewer automatic reporting flood gauges than we used to. In the Hill Country, including Austin, it's known exactly where small-stream flash floods occur and the only reason structures and people get hurt is they don't stay out of those danger zones in a hard rain. Don't build your house by the creek. Don't drive through moving water. Expect a flood higher than any flood before, with the same rainfall, because there's more impervious surface to shed water.
And I realize I'm sounding very harsh and maybe I am. The land was here first. Flash floods were here first. In the original landscape, that's how the rain came--high intensity, low frequency--and that's why there were springs of water, because those rains dumped enough to get through the grass, and down into the crevices of the rocky soil, and fill those aquifers for the long dry times. The frogs love flash floods; turtles and crayfish move upstream, in the floods, against the floods, heading for their favorite spawning grounds. Fish, too--after a flash flood, as the water clears, you find the tiny translucent fish fry hatching in the shallowest water. It seems as ridiculous to me to lament flash floods here, where they've been since the last Ice Age, as to lament blizzards in the northern plains or Noreasters on the New England coast. Flash floods are natural. Stores and roads in creek bottoms aren't.
And because the land here is up and down a lot, it's easy to avoid flash floods if you just use your head and don't panic. Don't be in the creek bottom in a downpour. Don't try to drive up a street that water is pouring down six inches deep (nearly lost a man in our choir that way.) People in flat land have no real recourse if their river floods--there is no higher ground to go to, but here, there is.
Anyway--if the only way to get rain is in lumps--I'll take it happily. I don't want anyone to get hurt--but we need the rain.
I actually like the torrential downpours we get here. They are one of the reasons I moved to Texas. But sometimes it gets extreme. I've seen water 5 inches deep flowing down a hill at Kerrville. I know it can be even worse than that. I feel bad that people get drowned in those big storms. It must be awful.
I agree that people shouldn't build in the 100 year floodplain. The house I'm going to build on my land will be in the lowest part of the 500 year floodplain. I want the house to be built above the height of the highest water that I know has been there. People seem to think I'm being silly. But I'm not.
Not silly at all. Put in the best (deepest, most resistant) foundations you can afford, and put the house up above ground a few feet. Underneath, the tornado shelter in a half-basement.
I look at vegetation, not floodplain maps, which are drawn and redrawn as the economy and developers fight over land. Development affects floodplains but they're rarely redesignated to take that into account.
May the market rebound and give you the resources to do what you want.
"May the market rebound and give you the resources to do what you want."
From your keystrokes to G-d's CPU.
Didn't work with K's dog. Didn't work with several other things...I think G-d wants me to hit different keystrokes. Sigh.