Editor’s note: This is part one of a series exploring efforts to make Houston a flood-resilient city. Find other coverage in this series at http://communityimpact.com/topics/flood-resilient-houston
As new development regulations in Houston attempt to offset the effects of more frequent heavy storms, some advocates and researchers say targeting the area’s urban sprawl will do more to reduce those at risk than limiting the amount of development in the city’s core.
“The 610 loop is the epicenter of the city of Houston so when we’re thinking about how we can make resiliency work for all Houstonians, how can these neighborhoods play their part?” Jordan Macha, director of advocacy group Bayou City Waterkeeper said. “There are going to be people that are moving into this area … so we’re trying to think through what that will look like while maintaining the integrity of these communities.”
New regulatory changes aimed at keeping these and other areas of the city safe include adjustments to flood plain boundaries, higher elevation requirements within flood plains and more significant detention requirements outside of flood plains.
City of Houston data shows over 25 drainage permits, many of which are subject to stricter city requirements, have been approved in and around the flood plains of Buffalo and White Oak Bayous since Hurricane Harvey.
Environmental researchers and advocates are struggling to agree on whether those regulations effectively address Houston’s flood risk while development continues to expand throughout the region, beyond Houston’s jurisdiction.
“I think it’s important to keep the bigger kind of regional or watershed perspective in mind and focus on the fact that it’s all interconnected system,” said Ryan Bare, a researcher specializing in low-impact development for The Houston Advanced Research Center.
Some advocates, including Sarah Bernhardt, President of the Bayou Preservation Association, said Hurricane Harvey spurred a turning point in collaboration between the city of Houston, Harris County, the Harris County Flood Control District, which takes charge of infrastructure projects, and other stakeholders.
“They’re moving as fast as their bureaucracy will allow them and I think that absolutely has to happen,” she said.
Mapping the risk
The main regulatory tool used by government agencies at all levels is the Federal Emergency Management Agency’s flood plain maps. Within some of the map’s boundaries, homeowners are required to buy flood insurance, and developers are subject to regulations depending on jurisdiction.
These maps are being updated by FEMA using new rainfall intensity data released by the National Oceanic and Atmospheric Administration. Adjustments to the maps could take years to complete, according to the Greater Houston Flood Mitigation Consortium.
FEMA defines the 100- and 500-year flood plains as areas that are at greatest risk of flooding during rain events that have a 1% and 0.2% chance, respectively, of happening any year.
Both the Harris County Flood Control District and the city of Houston preemptively redefined their 500-year flood plains as 100-year flood plains. Now, structures within the former 500-year flood plain are subject to the regulations that applied to the 100-year flood plain, and regulations within the 100-year flood plain have tightened further, according to the HCFCD.
These changes do not account for the developments on the fringes of the current 500-year flood plain, of which several have been approved in the last two years, even though those boundaries could likely expand when FEMA releases its updated maps, said Shaun Theriot-Smith, a civil engineer with engineering consulting firm Big Red Dog.
After Harvey, a housing needs assessment from the city of Houston and the Houston Housing and Community Development Department found the 500-year flood plain had a higher percentage of households, which includes houses and individual apartment units, that flooded over 4 feet than those in the 100-year flood plain.
“We have too many people who are not in a safe location,” said Kyle Shelton, a Rice University researcher with the flood consortium. “There’s a tipping point between promoting development without impacting people’s safety, and we’re too far over.”
On top of that, mapping risk outside of traditional flood plain maps presents a challenge because there are many variables involved in any flooding event, such as blocked storm drains or heavier rainfall in some areas of the city than others, Theriot-Smith said.“There isn’t a good model out there that will show the drainage conveyance capacity. A lot of it is found out through firsthand experience or the community conveying that,” he said.
Elevation requirements are dictated within floodplains while detention regulations—which dictate how much water a site needs to store to reduce runoff speed—apply to developments outside of the flood plain as well. Under pre-Harvey regulations, developers could get a credit for the amount of detention that already existed on a site undergoing redevelopment. Under new regulations, detention requirements are determined by measuring what a site’s runoff would be if it was entirely undeveloped land, Theriot-Smith said. These changes have impacted how quickly developments get approved and how much they cost, Theriot-Smith said.
“I could say it easily increases a number of development’s detention costs by a factor of 100%,” he said. “It really depends on the existing site, before Sept. 1 some went from needing to connect to a sewer to having to add large concrete vaults. ... In some cases it’s a factor of much more than 100%.”
Within the flood plains stricter elevation and ground cover requirements are a subpar solution compared to eliminating new development in the 100-year flood plain all together, Shelton said.
“There’s a need to grapple with the form of growth and the scale of building that we allow,” Shelton said. “Availability of housing at low risk is not going to get any easier if we continue to develop in a way that increases the number of people in harm’s way.”
A wider view
Researchers, including Shelton, said approaching development regulations from a watershed level rather than a jurisdictional level would make it easier to manage stormwater runoff across Houston and its suburbs and would reduce the strain downstream on bayous and tributaries. This approach also calls for more dense development on existing property rather than converting open land into new subdivisions.
“We need to be redeveloping decrepit commercial districts [outside of flood plains] that would be suitable for multi-use residential and commercial,” said Susan Chadwick, director of nonprofit Save Buffalo Bayou. “Look at all those strip malls all the way up North Shepherd.”
Moving water through the city more effectively relies on less development upstream as well as more green space surrounding the bayous’ flood plains. This could be aided by the Houston Parks Board’s Bayou Greenways 2020 initiative, which focuses on adding parks and trails along the city’s bayous.
“We’re not against development,” Chadwick said. “It should just be intelligent development.”
Editor's note: this post has been updated for clarity.