Amid Flooding and Pollution Concerns, New Ideas to Address Storm Runoff

As growth blankets San Antonio in housing developments, shopping centers, roads, and parking lots, flooding is getting worse and the city’s rivers and streams remain impaired because of bacteria that collect on hard surfaces and wash in with rainwater.

These problems aren’t new to San Antonio officials, especially after two wet years that caused frequent local flooding and the record-shattering rainfall Hurricane Harvey dropped on Houston last August.

But a recent paper by the Greater Edwards Aquifer Alliance, a Central Texas environmental group focused on water issues, proposes some specific solutions. Annalisa Peace, the alliance’s executive director, presented it to a City Council committee last week.

In the eight-page document, the alliance argues that the City of San Antonio needs to amend its building codes to require new construction projects to detain all runoff from small storms on-site and set regulations on the quality of water flowing downstream, something that’s not currently required everywhere in the city.

It also promotes low-impact development, a set of landscape and design techniques that include rain gardens and permeable pavement intended to help slow water down, filter pollution, and let water seep into the soil.

In most of San Antonio, city codes requiring low-impact development are entirely voluntary, said Nefi Garza, a stormwater engineer and assistant director with the City’s Transportation and Capital Improvements department.

“I will tell you that if we continue to do it that way, we’re really not going to get our streams off the [State’s impaired water body] list,” said Garza, who had no involvement in the paper. “We have to take some concrete steps to improve our streams.”

The long-term goal, the paper’s authors say, should be to reduce the volume of runoff to streams and rivers by 30 percent and get every stream and river segment off the impaired list within 15 years.

Stormwater runoff is the single greatest water quality issue affecting San Antonio’s waterways. The presence of bacteria, which gather on hard surfaces and run off during storms, is the only reason state and federal regulators still consider the San Antonio River and its tributaries unsafe for swimming.

Flooding has also gotten worse over the past several decades, according to a Rivard Report analysis of peak stream flow data, but there’s debate over how much of this is due to construction. Rainstorms also have gotten more intense in San Antonio, a possible effect of human-caused climate change.

To fix these issues, the paper’s authors suggest requiring all new construction to use designs that capture runoff from storms that drop up to 2.5 inches of rain over 24 hours and then slowly release it downstream.

“I think the biggest change is requiring on-site stormwater management as the rule, not the exception,” said Troy Dorman, an engineer and director of the San Antonio office of Tetra Tech. “In order for detention and stormwater management to occur on-site, it has to be required by ordinance.”

Besides Dorman and Peace, the report’s authors include Debbie Reid, the alliance’s technical director; Carol Fisher, a board member; San Antonio Planning Commission member June Kachtik; and Brian Zabcik, an advocate with Environment Texas who recently compared flooding ordinances among Texas’ major cities.

Zabcik’s report ranked San Antonio behind Austin on the strength of its ordinances but ahead of Houston, Dallas, and Fort Worth. Only Austin has a strict requirement to detain all runoff on-site for up to a 100-year storm in all parts of the city, the report states.

That’s a storm intense enough to have only a 1 percent chance of happening every year.

Currently, San Antonio’s building codes strictly require on-site detention only in so-called “mandatory detention areas.” These include parts of the upper San Antonio River, Leon Creek, and Mitchell Lake watersheds, among others.

But in most parts of the city, developers can choose to detain their runoff on-site through methods such as a detention basin. They can also participate in a mitigation project, such as raising a bridge downstream, or pay a fee in lieu of on-site detention.

If they go the fee route, they’re supposed to first prove that their project won’t make flooding worse up to 2,000 feet downstream.

The fee ranges from 15 cents to 25 cents per square foot of impervious cover. Revenue from the fees help fund the Regional Stormwater Management Program, which is then used to build large-scale catch basins, channels, and other flood control projects.

The paper’s authors clearly split with many builders, developers, and City officials on whether this fee-in-lieu-of system actually works. In the paper, they propose raising the fee, but don’t specify by how much.

“We’ve had stormwater engineers tell us that [the fee] is so attractive, there’s no incentive for doing it on-site or doing low-impact development,” Reid said. “We need to switch that so that’s the exception and the fees are high enough that [low-impact development] is attractive.”

Garza, the City’s stormwater engineer, emphasized that developers are only allowed to participate in the fee system if they can prove their projects won’t make downstream flooding worse.

“If you’re having an adverse impact, you have to do detention, you have to do mitigation,” Garza said. “I have engineers that police the engineers that are constantly monitoring that.”

Gene Dawson Jr., president of influential local engineering firm Pape-Dawson Engineers, said the current system is more effective at preventing regional flooding than putting in strict detention rules across the city.

“On-site detention on a project-by-project basis is a very inefficient way to address stormwater,” Dawson said. “In some cases, it can actually increase flooding in a watershed. … It’s not just a one-size-fits-all.”

The City last raised the fee in 2013. A 2015 overhaul of the drainage sections of the City’s Unified Development Code included incentives for developers and builders to use low-impact development in their projects, and the City now also requires the use of low-impact development techniques in some areas along the San Antonio River.

City officials open the code to changes every five years, with the next revisions scheduled for 2020.

But Mayor Ron Nirenberg, who has said in the past that managing runoff on-site is a pressing priority for City Council, said a code change should happen sooner.

“I’m confident we won’t have to wait until 2020 to have clear policy direction,” he said.

Dawson said developers fully expect more low-impact development requirements or incentives to be added to the code in 2020, along with “more rounds of drainage analysis,” another phase in the push-and-pull between environmental advocates and business interests.

“If you want to look at it from [environmental advocates’] standpoint, there’s continual progress in water quality and stormwater protection,” he said. “If you’re a developer or a landowner, there’s continued attrition of your property rights.”

Besides the code amendments and fee changes, the paper calls for a greater emphasis on low-impact development strategies, such as rain gardens, planter boxes, and bioswales to capture runoff and permeable pavement that allows water to infiltrate soil.

“We’ve got great examples of what you can do in downtown areas, especially with tree boxes,” Reid said, but she said many of the city’s construction projects don’t include it.

“It just needs to be there in every plan,” she said.

A 2015 amendment to the City’s Unified Development Code required properties adjacent to the San Antonio River on the Museum and Mission reaches and along San Pedro Creek in what are called the River Improvements Overlay districts to use low-impact development.

The San Antonio River Authority has been a strong advocate for these techniques, offering grants, rebates, and training sessions to entities interested in building them.

“It has been a game-changer,” River Authority Assistant General Manager Steve Graham said. “We’ve had all the new development coming, working through [the City] and [the River Authority], making sure they’re doing water-quality improvements.”

Dawson said such techniques should be implemented for a specific purpose, not just because they sound good.

“There’s always a balance in these codes between effectiveness, affordability, and cost,” he said. “Are we just doing things to say we did [low-impact development], and does it really have an effect?”

One issue not addressed in the paper is Texas Commission on Environmental Quality rules to protect the contributing and recharge zones of the Edwards Aquifer, which combined extend across most of northern Bexar County.

In these areas, runoff must meet certain water quality standards, and low-impact development techniques that would allow water to soak directly into the ground are not allowed.

The paper also suggests City staff develop a master plan for green infrastructure that includes low-impact development. The early phases of that are already underway, Garza said.

Under an existing contract, consultant Zephyr Environmental is developing a “visioning document,” a process that will take about three months, he said. The consultant can then develop a master plan to address certain areas of the city where water pollution is more severe.

“We will look at our entire network and say where in the city can we build these water quality improvements,” he said, “then how are we going to fund those water quality improvements, then how long will it take.”

This story was originally published on Feb. 28, 2018.