I live in a 500 year flood plain. In other words, not a flood zone. However, a downstream spillway backed up during Harvey and I flooded from downstream. Slowly rising water, which made it fairly easy to evacuate. My prior home, just 2 miles away and in the 100 year zone, did NOT flood. Two years later, after developers clear cut the land behind the 100 year home and didn't build proper detention, the 100 year home flooded in Imelda, and my current 500 year home did not. The point is that circumstances change, almost whimsically. If you rely on flood elevations, you can get lazy about assessing real-time conditions.
I have a second home on Bolivar. It is in the 100 year. Most neighboring homes are in the actual floodway. New construction in Harris County wouldn't be allowed in either zone, and if you elevate out of the 100 year to build in the 500 year, there has to be "zero-net fill," which means you have to dig a hole at least as big as the mountain you created. At the beach, the obvious flood hazard comes from surge. This is predictable. A tropical storm heads in, and you head out, and hope your home loan from God isn't expiring.
In the case of the Hill Country, flash flooding is the culprit. The scariest parts are the speed at which it occurs, and the fact that it can be dry where you are, but upstream rains can accumulate so quickly. Isaac Cline (the chief meteorologist in Galveston in 1900) recounted seeing a horse-pulled coach washed away in an arroyo, with the flooding occurring on a sunny day. The flood was a result of melting hailstones upstream. Wow.
The point is, flooding can occur for lots of reasons, and sometimes one can be in more danger "out" of the flood plain than "in" it. Therefore, blanket prohibitions about where people can build, and what constitutes "safe," just won't work. Those things can just cause complacency. If you work in an office, you should have a tornado assembly point. When I was a kid, my neighbor had a tornado shelter. Basements need to have a point of egress if people are sleeping in them, etc.
If you sleep in an area prone to flash flooding, you need a quick evacuation route to sheltered high ground, accessible to EVERYONE (elderly, disabled, children). This is the bottom line. It just looks like there wasn't a good plan, but there could have easily been one.
94chem,
That, sir, was the greatest post in the history of TexAgs. I salute you. -- Dough