[ethagknight]

Civil engineering has pretty well quantified the rate at which water is absorbed by certain soils, accounting for groundcover, trees, pavement, local detainment, etc. Berlin's sponge mission is baiscially distributed detainment, working to offset hardscaping (driveways and roofing). In other words, it's a well known and very predictable science, but we (we being US land development industry) has not cared. HOWEVER rain at the scale of Harvey cannot practically be planned for beyond "don't build on land that's lower than average"

[Declanomous]

Well, that's partly true. A lot of the flooding is due to the fact that the entirety of Texas doesn't care about hydrology, and all that water is ending up downstream, in Houston.

There'd still be flooding, and it would still be bad, but a certain degree of flooding was avoidable.

[microcolonel]

The other thought, I imagine, is that they felt the probability was low that they would see a flood of this scale even within their lifetime; that ended up being a poor bet. Even so, flood insurance is also cheaper when the perceived likelihood of a flood is low.

[robotresearcher]

Since cities usually survive much more than one human lifetime, this is not good reasoning.

[microcolonel]

People build houses, cities don't.

[robotresearcher]

As you almost certainly know, the city controls permissions for every building.

A city that gives planning permission for a development that is probably going to be destroyed with loss of life in the next hundred years is not serving people well.

[ethagknight]

Eh it is wholly true. Distributed detention schemes still have a finite volume of containment, and once the detention zones are saturated, those areas behave equally to pavement for each additional unit of water. 50 inches of water across the majority of Texas with severe storm surge cannot be practically prepared for beyond insurance, evacuation, and/or a boat. To say “it was avoidable” is a strong and expensive assertion requires some hard backup. Heres an introduction to runoff coefficient (disclaimer! exciting stuff!). Everything is based on a “design storm” with a specified duration and intensity, where those two variables lead to a sigmoid curve (as i recall) for runoff, or the greater the intensity and longer the duration, the less water that gets detained. http://www.brighthubengineering.com/hydraulics-civil-enginee...

[downrightmike]

Deregulation at work