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New Flood Mitigation Report Offers Insight for Houston Post-Hurricane Harvey

Study weighs in on ‘third reservoir,’ development and housing buyouts.

Harvey add3
A new level of commitment and continued funding are recommendations for future flood mitigation in Houston by a just-released report by the Greater Houston Flood Mitigation Consortium.

Following the flooding after Hurricane Harvey, local researchers focused their efforts on rethinking flood mitigation and came up with the detailed report that highlights issues including building a proposed third reservoir; regulations; regulatory oversight and buyouts of single and multi-family homes.

“I think we’ve been doing a lot of the right things,” said Christof Spieler, the consortium’s project manager. “There are successful projects that are really good and without those Harvey would have been worse, but those efforts have been in certain watersheds or certain parts of watersheds. They haven’t been comprehensive enough.”

He said the region has focused on flooding only after floods like Harvey and then tends to take its foot off the gas. The region needs a long-term strategy and focus and continued funding.

One of the proposed strategies was to build a third reservoir in northwest Harris County. The third reservoir would be built upstream of Addicks and Barker reservoirs, which couldn’t hold all the water that came with Harvey.

The proposed third reservoir would supposedly “take the pressure” off those two reservoirs, but Spieler said it may not necessarily work to provide a solution to what happened during Harvey and ended up flooding thousands of homes.

He said the specific proposal goals of the third reservoir project were to eliminate flooding in an area that is largely undeveloped. The plan would then open up that area for development. He said the development will result in water running off the area more quickly and not being absorbed by a more permeable natural environment, and that wasn’t taken into consideration.

“Even though it’s a similar area to an area we saw flooded in Harvey, it was not designed to address that flooding,” Spieler said. “This is one of the things we have to be careful about, simply funding flood mitigation projects because they have been identified.”

Spieler said regulations for development need to reflect a better understanding of potential flooding. For example, regulations for development say if you develop a property you must provide detention and that the runoff rate for post-development can’t be more than it was for pre-development.

But that only accounts for rate and not volume, meaning runoff could continue at the proper rate but for a longer period. “You’d have a larger volume of runoff, which during a multi-day rain event can make a big difference,” Spieler said. “That water is piling up downstream.”

And the development means, again, that water will be running off faster than it would in a natural landscape or over farm fields, which capture water. He said calculations for regulation don’t take this into account.

“The takeaway from that is that these watersheds that have large undeveloped areas in them, if development continues at current standards, the downstream flooding problem will continue to worsen.”

The study also highlighted the multitude of agencies or jurisdictions that may manage a single flood project, resulting in a lack of coordination. For instance, on a single site, the city of Houston could oversee mapping, but Harris County might be in charge of building requirements and the Harris County Flood Control District might oversee detention.

“From a regulatory standpoint, the idea that a single waterway can have half a dozen entities doing the management of that floodplain makes it hard to look at the big picture,” Spieler said. He said a solution might mean more local coordination or new laws or one local coordinating office.

Buyouts were another major topic in the study, which found potential problems with a mass of buyouts, which could potentially limit the affordable housing in the area. Where would the residents move in an area that is already seeing a tightening of the affordable housing market? Proper planning would need to take place before a large number of buyouts.

“If you do buyouts in conjunction with a housing plan, you could coordinate those things and make sure you provide affordable housing in places that are accessible to jobs and not in that low-lying area,” Spieler said.