Watershed Texas

An example of floodplain tailgating?

As I drove into work this morning I found myself behind an 18-wheeler. I was keeping the required distance—one car length for every 10mph, more or less, when the truck swerved just a wee bit, getting pretty close to the concrete divider of the inside lane we were traveling in.
Nothing happened, but I wondered if I really had enough room to avoid a collision had the driver overreacted and jackknifed or swerved the other way into traffic.  I probably should have had a longer buffer if I really wanted to reduce the odds of a collision.  But many folks are wont to push the buffer the other way. We’ve all ridden with them, squirming all the way. If you habitually tailgate, the odds are very high that you will find yourself without a margin of safety and you might just buy the big one.

So, have we in Houston maybe been playing the tailgating game with respect to where we develop in relation to floodplains?  The Memorial Day flood of 2015 and the Tax Day flood of 2016 strongly suggest many developers and city permit writers pushed the limits of safety. All those people deep in the floodplain, walking out of their houses or apartments in chest-high water. How did that happen?  Did we get the equivalent of a freak accident happening in front of us?  Was somebody following traffic at little too closely and they didn’t have enough of a safety margin? Or in other words, were  some developers pushing just a bit too closely into the floodplain?

I think that is exactly what has been happening in the Houston region. Granted, it was much worse in the past. But it is still happening today. Wimbledon Champion Estates—fresh construction, under water on Tax Day.  The houses there did not appear to have been in the 100-year floodplain. Many, perhaps most were in the 500-year floodplain.  What happened here?  I am guessing that the area was originally in the 100 year floodplain, and the developer raised the streets a bit and got the county or FEMA to agree to a change.  A change that was the equivalent of driving one car length behind an 18-wheeler at 70 miles per hour!

We need a new way of looking at the landscape. We need prudence. We need caution. We need to respect Mother Nature. It is going to flood again. Lets add to the margin of safety—not take away from it.  We should consider the 500-year floodplain, not the 100-year floodplain, as the zone we need to stay out of. Adding a margin of safety above that would not be a bad idea. FEMA calls that margin “freeboard”.

The graphic above shows Wimbledon Champions Estate—a development deeply flooded this past Tax Day. The FEMA floodplain map is overlain on a recent  aerial photo (photo courtesy of Google Earth).  I don’t way to pick just on this development—but it was in the news, it was flooded, and it is new development. But it is far from the only place like this in Houston.  The blue 100-year floodplain has a 1% chance of flooding in a given year. But it is well to remember that that probability is strictly an estimate. The brown 500 year floodplain has an estimated  0.2% chance of flooding in a given year.  The area of development south of Cypress Creek Parkway is “tailgating” the floodplain. Way too close for comfort.  That brown area of 0.2% floodplain in an area that likely should have been 1% floodplain looks suspicious. How did that happen? No mortgage insurance is required for houses in the 500-year or 0.2% floodplain. That couldn’t have influenced anything, right??

In my opinion, no building should be permitted within the 500-year floodplain, and incentives should be given for development 2-3 feet higher in the landscape than the 500-yr floodplain. That’s called keeping your distance.  I call it prudence and caution. Good bedrock conservative values. That’s not how the roll the dice in  Vegas, but it is how we should do things here.