“Flood zones” cannot all be known or accurately mapped

“We’ve had heavy back-to-back rainfalls before. So I don’t think it’s the new normal. When you talk about a 1 percent chance of happening [in a given year], it can happen. You can flip a coin and have it come up heads 10 times in a row. It’s just, statistically, it shouldn’t happen, but it can.” — Mike Talbot, then Executive Director of the Harris County Flood Control District (2016)

In the months after Allison (which was called a 500-year flood) brought massive flooding to Houston in 2001, the Harris County Flood Control District released a booklet of more than 30 pages, Off the Charts, to explain to stunned Harris County citizens why their taxes had bought them so little flood protection. It is actually an excellent primer.

On the penultimate page, we find this statement: “It’s impossible to control the extraordinary forces of nature.”

Since then the county has spent hundreds of millions of dollars more trying to control flooding, or at least reduce the risks of it. But big flood events continue. Some are calling Harvey a thousand-year event. The District is very much under scrutiny.

Mike Talbot, quoted above (interview) made several enlightening statements. Since it was published, Talbot has retired from the Harris County Flood Control District. He spoke twice to my group, the Houston Property Rights Association. He seems to be a straight-shooter. The flood protection system he is defending is based on the so-called 100-year flood event, which can happen often. He tells us that. And he speaks of “extreme rainfall events” that we get occasionally. So flooding is a given. What Talbot does not make clear is that the risk will vary depending on where you live on the landscape (which is not flat), how close you live to a bayou, and the particular characteristics of an individual storm, which are never predictable.

Note that Talbot points out that developers have to comply with “two inch thick” criteria manuals. So development is not “unchecked”. Of course, sometimes the manuals are not followed. But, in any event, the system is not designed to stop all flooding.

This is an important statement from Talbot that needs to be investigated. He implies that the prairies cannot absorb much water. Elsewhere, I have seen him refer to a report by his agency that concluded the clay and sand mixture in our prairie soil does not allow for much absorption:

A lot of the ink that has gone down after [the Tax Day flood] has been given to critics with an agenda. When somebody wants to claim that, “well, it’s because we’re paving over all the wetlands and these magic sponges out in the prairie would have absorbed all that water,” [that’s] absurd.

[During the recent floods], the heaviest rain fell on the prairie, and the prairie did some good, but then it flowed off of the prairie, and all the runoff from the prairie is what flooded that development.

Some people assert that the prairie, once covered with high grass with 10-foot-long roots, would be absorbing the storm waters if it had not replaced by impervious development. But we have clayey soils in our area. At least one report by settlers traveling inland spoke of walking for days through west Harris County with water to their knees after major rains. So, the absorbent qualities of the Gulf Coast prairie is probably exaggerated.

Many people, such as the editorial board at the Houston Chronicle, are pointing to global warming and climate change to argue that higher taxes are needed for expanded infrastructure to accelerate drainage, and that we should not look just at past flooding to determine flood zones. They argue that local governments need to draw bigger flood zones, in which development would be banned to accommodate the projected bigger, wetter storms.

I personally am dubious that wider, deeper bayous, combined with flood zones designed to accommodate the yet unseen 2,000- or 5,000-year flood (how big are we talking here?), will protect us from flooding. It would all be based on computer modeling, which is subjective and should never be trusted. The “spaghetti models” shown on TV during the run-ups to Harvey and Irma are evidence of that. Each piece of spaghetti is the product of a team of modelers making hundreds of assumptions which result in different scenarios.

In recent months, I have decided that floodproofing needs to be routine for Houston area property owners, based on their individual perception of risk. Homeowners would consider their elevation in the landscape, distance from nearby bayous and channels that can overflow, and whether their homes are on concrete pads or pier-and-beam foundations. They can use flood bags and flood gates that can protect from moderate flooding, and some structures to deal with hydrostatic pressure on windows and exterior walls.

This firm is in the business of making flood proofing products:

A few county buildings downtown were flooded by Harvey. Why did the county not use its superior knowledge of the risks of flooding to take extra precautions, such as having more “submarine doors” in the tunnel system to contain the flooding? I recently walked several of those tunnels and found only one such door, which surprised me. The Med Center has them, as well as other kinds of flood barriers now, and so do many commercial buildings in the downtown.