Watershed Texas

New York Times map of flood damage, Hurricane Harvey, Harris County

also at  Gray Matters

Flooding during Harvey was not a random occurrence.  Heavy rainfall—averaging 35 inches in Harris County –was widespread, but the flooding was not.  The deepest flooding, the kind where rescue boats were needed, was where the bayous and creeks overflowed their banks, flooding low-lying zones along our bayous and creeks.  There were also many areas that flooded as a result of poorly maintained or designed urban drainage systems. But these were a small fraction of the overall flooding.

The low-lying areas along our waterways are the natural floodplains excavated by bayous and creeks over many thousands of years. It flooded here long before we, or even the Karankawa, ever showed up. Over the millennia, the bayous naturally widened their valleys, or floodplains, to where the system could easily absorb a storm like Harvey.

That system is still here—and it handled Harvey very well.  We were the ones who didn’t handle it well. If we had not given over most of our floodplains to development, Harvey would still have caused us grief—but it would not have much more than a nuisance.  We would have had to stay home for 2-3 days, but we would have avoided a great deal of trauma.

It seems we have never been content to let this natural system work for us. For some, those wide, natural floodplains were just too much land to allow to just sit there without making any money. So when we widened channels, or put substantial retention basins upstream, we didn’t leave a buffer of unoccupied land beyond what we considered to be the reduced floodplains. We built right up to the edge of our “new and improved floodplains.” We didn’t think we would ever get more than a 100-year event. Now we know different!

Harvey was an unimaginable storm. Now we know we were sorely lacking in imagination.  Now that we’ve experienced a Harvey, it is not so hard to imagine another one.  If we imagine another Harvey, can we imagine that the infrastructure we have built, and continue to build, to handle 100-year storms will handle a Harvey? We are not even sure how to label Harvey—was it a 1000-year storm? Or perhaps a 50,000-year storm? Maybe we should just call it a Big Freaking Storm (BFS). If we are going to be prudent, we should plan as if one or more BFSs will occur within our lifetimes.  We should be planning a city well beyond our own lifetimes –perhaps even to 7 generations as the First Peoples of this continent taught. They with so much less impact than us, but apparently so much more wisdom.

It is my contention that our natural floodplains—not necessarily the floodplains delineated on FEMA maps, but the floodplains carved out by nature – have more than enough capacity to handle a BF storm. I base this strictly on observation. I call on modelers in the area to verify and quantify this assertion, but without regard to existing development currently in the floodplain nor to lost economic opportunities for future development in low-lying areas.

If it is true that our natural conveyance system could indeed handle the next BFS, then we need to prioritize restoring the integrity of this system. We can never hope to build an engineered  system to BFS levels, particularly if we don’t make maximum use of what nature has provided us. We will always need to engineer surface or street drainage. Without that, even a 2-inch storm would be a tremendous nuisance in this very flat area. The issue is how to accommodate all that runoff in the bayous.

Reclaiming our natural floodplains will not be easy. This is not something that could be accomplished in a year or two. This is a 50-year effort, a period well beyond the scope of any elected official. But Houston has undertaken long-term projects like this. Witness the massive public works effort to convert from groundwater to surface water as our main drinking water source. This is a multi-billion dollar process playing out over a decade or two.

Reclaiming the floodplains will be painful. This will hurt some neighborhoods. How many homes overall might need to be bought out?  Some estimates suggest 100,000 homes damaged by Harvey, but let’s say 50,000 as a minimum. At $200,000 each, that would be $10 billion dollars. A sizeable amount, but an amount that could be easily amortized over 50 years.

We can start where the pain was the greatest—places deep in the floodplains, where over 4-6 feet of water got in the houses.  Buyouts would no doubt be welcomed by many in these areas.

Buyouts will be very expensive—a public works project as big as any ever undertaken in Houston, which is saying a lot. But there will be a payoff, a payoff well beyond the avoided costs of flooded structures in future storms.  The larger payoff would be the interlacing of vibrant green and urban corridors across all sectors of our metropolis. All of us would thus live close to wide open green spaces. Green spaces that would include vast natural areas with trails and woods and prairies, athletic fields, picnic areas, and just simple but essential civic gathering spaces.

It is no longer so hard for us to imagine another Harvey. But it is going to be harder to imagine a Houston that could take another Harvey with little or no trauma. I cannot imagine a resilient Houston that does not include both vibrant greenspace and walkable urban space. Vibrant green space that is available for the next flood.  Walkable urbanism that is built on higher ground far from the floodplains. Is that possible? Maybe if we try to imagine it together the vision will become clearer.