re: #112 teleskiguy

austin_blue, how are things in the [Stevie Ray Vaughan’s debut album]?

Outside of the slow count of bodies piling up because of the flooding? Peachy.

Twelve still missing on the Blanco River flood (including three young children).

If you are not familiar with Balcones Fault Complex flood events, ahem (puts on hydrogeologist hat):

The Balcones Fault Complex consists of a down-thrown collapse feature in surficial Cretaceous limestones that runs from SW of San Antonio to N of Georgetown, Texas, a curving outcropping complex about 150 miles long. The up-block is anywhere from 50 to 400 feet higher than the collapse block, highest from New Braunfels to Austin, with some of the highest relief differential in the Blanco River basin. The result is that the Blanco has cut a relatively long, thin canyon from west of Wimberley to San Marcos, a distance of +/-15 miles. Wimberley is closer to the top of the complex and the Blanco River valley is wider, because the limestone is much harder. They took some major damage, but the flood wasn’t focused yet. Here’s the USGS gauge in Wimberley:

waterdata.usgs.gov

You will note that the graph is logarithmic and that in a matter of an hour and a half or so, the flow in the Blanco went from 400 cubic ft/sec to over 70,000 cu ft/sec and was still rising vertically. And it was near midnight. As the flood surge travelled east, the height of the surge built up vertically. The valley pinched in because the softer rock resulted in a steeper water course, decreasing the width of the flood plain.

Long story short, the Blanco exits the Balcones Fault Complex south of Kyle, a few miles north of San Marcos. When it did, it exited as a 45’ foot tall wall of water that overtopped the Interstate 35 bridge.

That, my friends, is a Texas flood. It is a stone cold killer.