COMMENT OF THE DAY: ALL FLOODING BUCKS PASS THE SAME DIRECTION 
“Every solid thing built in a floodplain displaces water to the surrounding areas and to downstream. Houston just keeps screwing its southeast neighbors.” [movocelot, commenting on Elan Heights Shows Off Its 4 Floors of Apartment Flooding Insurance]
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You may want to re-read Chapter 19.
Mmmmm….I’m not so sure I agree, if you are including buildings. Now I agree that raised earth (such as the man-made hills that they build suburban houses on nowadays) can displace a lot of water. However, once a building gets water in it, it is not really displacing a lot of volume, since all the hollow cavities in the building will fill with water. Your real displacement is composed of only hard things below the water line, like wall studs, furniture, and bricks. Volumetrically, these are a fraction of all the volume the submerged structure will hold in its flooded out rooms and halls.
Now assuming you mean that an increase in upstream hard, impervious surfaces contribute to flooding – then you are dead on. This causes less penetration to groundwater and faster runoff through improved drainage of the surface. A pockmarked cattle pasture can hold quite a bit of water due to slow runoff times (days or weeks) and percolation to groundwater. Once it becomes a Wal-Mart parking lot, there is hardly any percolation and all the water drains off in minutes. This has nothing to do with “displacement” as a function of flooding.
All floodplain development in Harris county must mitigate for any volume removed from the floodplain. If you fill a cubic yard, you must excavate a cubic yard.
The alternative is to build on piles, piers, or other elevated structure to allow the water to pass through.
This is part of the flood plain ordinances for local cities and Harris County.
Agreed Superdave but I would also say that roofs act just as a parking lot would especially if they have downspouts connected to drain lines going out to the the curb. In Bellaire for instance since around 2007 you are not allowed to build a house on a foundation. The idea is that the space below can flood and make up for that coverage without pushing the volume downstream. Not sure if has proven correct. Just saying there has been an effort on the part of a few places.
Most of the flooding was west, northwest and north. Southeast Harris and Galveston counties did alright.
Chapter 19?
I must have been sick that day.
A bldg placed into a floodway absolutely reduces the flow volume.
For the same water to pass, the depth will incresase (water goes higher/farther into yards and streets) and/or the speed will increase, causing more destruction. Which/what depends on limitations like levees or conduits. If the water can rise it will. If it can’t rise it’ll accelerate. Water will also back up, affecting upstream areas.
There is one way to ameliorate the flooding in these big rain events: Large areas to slow the water and encourage seepage into the ground and evaporation over time. In Houston, these are reservoirs, parks and golf courses. So, as it grows, Houston needs increasingly more empty space! I
And a lot more political and stretegic will.