It is good news the 86th Texas Legislature authorized the first Texas statewide flood plan under Senate Bill 8 in 2019. Floods are the second deadliest weather-related hazard in the United States, after heat, and Texas leads the nation in flood fatalities. Texas’ flood fatalities are greatest in what the National Weather Service calls “Flash Flood Alley,” near the Balcones Escarpment in the Hill Country and Central Texas and encompassing much of the recharge area of the Edwards and Trinity aquifers.
Developing a statewide flood plan for Texas is a challenging process. Texas is a very large geographic area and contains a wide range of physical conditions. Flood planning in the Houston area, for example, involves issues such as sea-level rise and sinking land through subsidence. The karst landscape of the Hill Country, on the other hand, contributes to flooding in some areas but also acts as a conduit for very large amounts of stormwater to recharge our aquifers.
Changing rainfall patterns are complicating the planning, too. Flood plans based on 2004 rainfall estimates for Texas are already out of date. The latest estimate of rainfall patterns released in 2018 shows, for example, that Comal County’s average 24-hour rainfall in a 1-in-100-year storm has increased from 10 inches to 13 inches. As of this writing, the U.S. Drought Monitor rates portions of the San Antonio-Austin corridor from being abnormally dry to experiencing severe drought. Climate experts predict that it will rain less often, but, when it does, it will rain harder and in greater volumes.
Another challenge is the pace of population growth. Both Hays and Comal counties are among the top-10 fastest growing U.S. counties. Every rooftop, driveway, parking lot and road prevents rainfall from infiltrating into the ground and can increase flooding frequency and depth while contaminating creeks, rivers, aquifers and springs. Building in flood plains makes the situation worse. A 2013 study for the Federal Emergency Management Agency concluded that the increase in rainfall and land development will together expand the size of floodplains near rivers by 45 percent by 2100.
The principles of flood mitigation planning and engineering are also changing. Nature-based or “green” infrastructure, including land conservation, has proven to be less expensive and more effective than “gray” infrastructure such as concrete channels, dams, pipes and culverts. In fact, in 2020 Congress directed the Army Corps of Engineers to consider nature-based systems on equal footing with concrete infrastructure. Lt. Gen. Scott A. Spellmon, chief of engineers and commanding general of the United States Army Corps of Engineers, called the new nature-based approach “revolutionary.”
Is this not the key issue for the Texas flood planning process as well, particularly in the unique Texas Hill Country and Central Texas? With potentially less overall rainfall in the future, we should focus on nature-based systems to get rain into the soil to recharge our aquifers and manage floods. Will the flood management benefit-cost analyses correctly evaluate conserving recharge land and karst features, the planting of native vegetation, creating shallow channels called swales, incorporating organic material into soils, creating greenways with trails for recreation and wildfire mitigation, and using natural channel design for habitat enhancement in the same way that traditional infrastructure projects are?
We sure hope so. Nature-based measures are exactly what is needed for effective floodplain management and the health of the Edwards Aquifer between San Antonio and Austin, which provides clear, clean drinking water for a population of 2.3 million people and growing. In fact, nature-based infrastructure should be a priority in “Flash Flood Alley.”
Bill Barker is a fellow with the American Institute of Certified Planners, a transportation consultant and former UTSA adjunct professor.