UNIVERSITY CITY — Stormwater experts on Monday urged the city council here to adopt a list of flood-control recommendations, from the reduction of concrete and asphalt to a survey of high-risk homes to a public warning system for flash floods.
The presentation from the city’s Commission on Storm Water Issues highlighted key findings about the flooding triggered by record-shattering rain last summer, as well as the dangers that flash floods pose to people and property.
“It’s incredible how sudden these things are,” commission member Bob Criss, a professor emeritus at Washington University who studies flooding, told the council. “The consequences are severe.”
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On July 26 — when more than 9 inches of rain walloped the Ƶ area — University City was an epicenter of damage: Officials here estimated more than 300 homes or apartment units were condemned or declared unfit for human occupation due to the flash flooding, making it the worst-hit municipality in the region.
In the event’s aftermath, the city’s stormwater commission — which includes engineers and professors who examine flooding issues — put together a study of the flood, in the hope that its findings can guide management decisions by the city. Data was gleaned from a network of sensors in the stream channel of the upper River Des Peres, but also through hundreds of hours surveying areas to assess how high floodwaters climbed — even using clues like how high leafy debris reached in chain-link fences.
That kind of precision, said commission member Eric Stein, “is gold when it comes to making decisions.” It allows officials to gauge which properties are hopeless and which should be considered for flood-proofing, he said.
The commission on Monday urged officials to act: Its members called for the urgent adoption of an early warning system that could notify the public of flash flood risks, much like Amber Alerts or other emergency notifications.
The commission also asked the city to strengthen codes for impervious surfaces, like asphalt, that do not absorb rainwater and divert it, instead, into local creeks such as the upper River Des Peres — setting it up to be overwhelmed and sprawl beyond its banks. Currently, more than 43% of the watershed’s area is impervious, the commission said.
Another recommendation called for the city to require the disclosure of flood histories for homes and rental properties.
Additionally, the commission said a top priority should be for the city to budget about $35,000 to survey the height of the ground floors of all properties subject to flooding, which it said is “needed to prioritize buyouts and flood-proofing recommendations.”
Even a public information campaign about flood risks — such as a website and lecture series — could help bolster awareness in the community, commission members said.
The commission’s experts warned that other big floods are an inevitability, particularly given the sensitivity of the upper River Des Peres watershed to rain. Criss has found the small, urbanized basin to be the most flash-flood-prone stream in Missouri.
That sensitivity can bring flood problems to nearby residents, even when rainfall is far shy of record-setting volumes. For example, multiple stream gauges in University City showed that the River Des Peres’ water levels rose more than 10 feet in a single hour after the onset of the storm — before most of the rain had yet fallen.
Most of the rise of the river happened in those first two hours, Criss said. The continued rain pushed the high water incrementally higher in the hours that followed.
“There’s no engineering fix for that channel,” Stein said. “The basic problem is just overbuilding, and that’s gone on for decades.
“It’s been unwise building practices that caused this, and now the bill has come due,” he said.
Stormwater commission members said some of the recommendations have been suggested for years without adoption. Others, they said, could be enacted with no cost. And some — like the early warning system geared for flash floods — have been ready for more than a year.
“Most of those recommendations are timely — they’re needed,” said Stein. “Some of these are long-standing and we’ve been recommending all along.”
Some commission members said they are disappointed by past inaction but want to focus on solving problems instead of pointing fingers.
Still, minimizing flood risk is a challenge without cheap or easy solutions, said commissioners and city leaders, and one that will ultimately require a more unified, region-wide approach, since the issue extends far beyond University City.
“This kind of stormwater problem is area-wide,” said Stein. “It’s a hugely expensive thing to fix and it needs cooperation. ... There’s no structure for that.”