Matthijs: You live in Houston, which is an interesting city from a flood risk perspective. Can you tell us something about flood safety in Houston and its surroundings?
Charlie: On the one side, Houston is a pretty unique city, in that it’s a very sprawling city, and instead of maturing slowly, it’s grown rapidly. You also have the suburban cities around Houston, and then you have a very large urban area. It’s also very flat. It’s an old coastal plain, and there’s not much elevation change. The southern half of the city is made up of expansive clays that limit the absorption of rainfall. On the north side, the soil is a little more sandy and contains silt, but it is generally more silt than sand, limiting rainfall absorption. The drainage pipes are designed for a two-year rainfall event. Because the drainage pipes have a limited capacity, the streets take care of the runoff, moreover, when a hurricane occurs as of August 2017.
The downtown Houston skyline and concrete expanses according to a Nature study exacerbated floods by altering the storm itself and making it rain harder. On the photo, the highway 288 flooded in August 27, 2017. Image source: Thomas B. Shea Getty Images
On the other side, the rainfall design criteria used in the last 30 years are based on a study completed in 1963 that used a precipitation series to develop likely rainfall frequencies. This is not an accurate representation of what is happening today with climate change and increasing development. Recently, in 2018, new rainfall design criteria were developed. In Houston, precipitation totals for the 24-hour precipitation volume increased by as much as 50%, from about 300 mm in 24 hours to about 450 mm in 24 hours, so it’s a very, very large increase in total rainfall that will now be used in the design. The necessary storage volumes then increased almost 100% within the City of Houston.
Photo picturing the emergency response during the hurricane Harvey. Image source: Delft Harvey Texas Research Team.
Matthijs: And what about hurricanes?
Charlie: A lot of money has been funneled into the area because of Hurricane Harvey to recover from the impact that the region had. And so there are quite a few projects that we’re looking at by also considering never implemented initiatives dated back to the 1930s as they were seen as a “pie in the sky”. These measures might have cost us millions of dollars at the time, and now they are going to be billions of dollars, but the benefits are much greater. So that comes down to the question: what are you willing to live with? We are facing more and more extreme storms, and we have yet to figure out how to deal with them.
Matthijs: So money seems to be the biggest bottleneck.
Charlie: It’s always a sticking point. Nobody wants to pay extra taxes.
Matthijs: What also interests me is the role of research and the role of universities. It might also be useful for us in the Netherlands to know that you are interested in special research questions, and maybe we can work together on these questions.
Charlie: In Galveston (the area that was first affected by the high water levels and waves during a hurricane), we have been interested since the tropical storm Allison, in 2001, in developing a flood warning system, something that would have also been good in Germany this year. Again, we need to set up systems to give good warnings so that you can actually do something to protect yourself. Also, the city of Galveston is very interested in pumps and pumping stations, similar to what New Orleans has done, rather than relying entirely on gravity. I think this is a great place where the Dutch knowledge could be very useful. So I’m going to contact the city engineer in Galveston and suggest that he contact Baukje Kothuis of the Dutch consulate in Houston to make contact with some Dutch experts to help Galveston implement that system, possibly.
This morning, we had a presentation about a major project: a deep drainage tunnel that would bypass the city, similar to what they have in San Antonio and Dallas. I know you’re well aware of all the coastal defences we’ve been looking at, both with a robust watershed “Ike Dike” and the “Galveston Bay Park” plan. We also have huge petrochemical plants that are out there on the water, and it would be a major disaster if something happened as a result of the hurricane, so obviously, that is a major concern.
Matthijs: We’ve been talking about climate change for a while now. Putting aside the political discussion, is there much technical discussion about it with you?
Charlie: The problem here is that everything that can be done by the government is politicized because that’s how politics works here to get elected. So if a politician can somehow catch a fever about anything, everyone has to take sides. So I think it’s a big problem for us. But I don’t think there’s any doubt about climate change among those who are responsible for getting moving. They know what climate change means, and they want to address it in the right way. There are plenty of initiatives in the works that take climate change into account in this area.
Matthijs: So take it at the technical level and not the political level.
Charlie: Indeed, I also see a lot in what we call ‘Low Impact Development’, where we try to take advantage of green roofs and rain gardens to dampen the runoff. The challenge is to talk to the people involved about these possibilities and so that they understand that this is good, and can actually be done in a way that will be beneficial to them both the cost now and in future maintenance. If it’s done right, it also makes the city much more aesthetically pleasing. So that challenge is always there. But I think some people who haven’t really embraced “Low Impact Design” in the past are starting to think about it a bit more.
Last modified: 17/10/2021