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UT’s Jon Hathaway, an assistant professor of civil and environmental engineering, is an expert in flooding, water runoff, and urban water issues. He provides some information about the issues facing Texas and Louisiana when floodwaters from Hurricane Harvey begin to recede.

Question: What measures can be taken to control or mitigate such flooding?

Hathaway: It is very difficult to manage flooding from this magnitude of rainfall. There are strategies for more frequent nuisance flooding and for urban flash flooding, but controlling runoff from this type of rainfall is difficult. 

Q: Why is flooding such a risk and a problem in these states?

Hathaway: There are numerous things at play here, Houston is in a relatively low-lying area that historically had a lot of wetlands. This means that this land would typically have some buffering capacity, or ability to store water, that it no longer has as we remove wetlands and replace them with urban development. Exacerbating this is that urbanization causes much more runoff. There is just less ability to soak up excess rainfall. As if this isn’t enough, you also have storm surge that acts to hold that water in place by reducing the amount of water that can leave the landscape through local rivers.

Q: How can modern urban design actually worsen flooding?

Hathaway: When we replace natural areas that have some capacity to store rainfall with impervious surfaces, we generate a lot more runoff that moves much faster through the landscape. We need to plan our development around the places that are the most prone to flooding during large rainfalls.

Q: What are the main health concerns that might arise?

Hathaway: Flooding is a huge concern for urban systems. Wastewater from inundated and compromised pipes will mix with floodwaters, creating major health issues. Floodwater will carry large debris that can strike individuals. And perhaps most concerning is just the velocity and power of the water. Water doesn’t have to be very deep to float a vehicle and send it downstream. Also, water supply is sometimes interrupted when cities can no longer guarantee that tap water is safe to drink because flooding has caused it to come into contact with nonpotable water.

Q: What destruction is likely in the aftermath of flooding?

Hathaway: Water is powerful. It can cause erosion around bridge abutments, inundation of critical power stations, and compromising of roads. This level of flooding is going to result in a lot of work to ensure that Houston’s infrastructure is stable and functional. 

Q: Why do dams release water in the midst of flooding?

Hathaway: Dam operators are faced with extremely difficult choices during catastrophic rainfall. As lakes fill with runoff, dams are typically equipped to deal with some amount of excessive flow through emergency spillways. However, if that effort doesn’t alleviate the rise of lake waters, the safety of a dam becomes a concern. You do not want a dam to be overtopped and risk failure. In cases like this, it’s sometimes necessary to release water from a lake to try and keep the rising water from reaching a critical elevation. 

Q: What determined current plans and models, and are those plans changing?

Hathaway: A lot of our water infrastructure design is based on historical rainfall data. As rainfall patterns change over time, we need to consider what things will look like in the future under various climate change scenarios

Q: How can cities rebuild with future concerns in mind?

Hathaway: Obviously, the more water you can store in the urban setting through interventions such as green infrastructure, the better for more frequent nuisance and/or flash floods. However, the amount of rainfall Houston is experiencing will likely overwhelm even these efforts. Cities can be better prepared for these large events by understanding how and when floodplains will be accessed by streams and rivers, and also restricting development in flood-prone areas. It sounds cliché, but when you have 30 to 50 inches of rain, you really want to have as many people as possible out of harm’s way.

Hathaway has worked with national, state, and local government agencies in flood-related projects, and has been honored by the National Science Foundation for his work.